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Control and stability of self-assembled monolayers under biosensing conditions
Abstract
The ability to stabilize and control the attachment of cells on the surfaces of a variety of inorganic materials is important for the development of biomedical devices and sensors. An important intermediate step is the functionalization of semiconducting surfaces with a self-assembled monolayer (SAM) with an appropriate surface termination to interact with proteins. The stability of such SAMs is critical to withstanding subsequent processing and measurement conditions (e.g. long exposure to a buffer solution) to avoid artifacts resulting from such deterioration during electrical measurements. This work highlights the importance of surface cleaning and SAM chain length by comparing two commonly used short alkyl chains, aminopropyltriethoxysilane (APTES) or 3-(trimethoxysilyl)propyl aldehyde (C4-ald) molecules, with their long-chain counterparts, amino-undecilenyltriethoxysilane (AUTES) and 11-(triethoxysilyl)undecanal (C11-ald). Using IR spectroscopy, spectroscopic ellipsometry, and electrical measurements, a cleaning method is developed, based on a short room temperature (RT) SC-1 treatment, to remove photoresist without degrading device performance as is the case with currently used oxygen plasma methods. The spectroscopic and electrical measurements also show that short-chain SAMs, typically used for pH- or bio-sensing, do not have the stability suitable for biosensor environments. In contrast, long-chain SAMs display much higher stability and can be reproducibly grafted. These findings are the basis for a reliable preparation and robust operation of biosensors.
... The PC surface was preliminarily treated with plasma and APTES was applied to introduce amino groups on the PC sensitive surface. As a result, APTES bond to activated silanol groups through ethoxy groups in the form of a monolayer with high physicochemical stability [47][48][49], while the amino group remained reactive and available for further silanol groups through ethoxy groups in the form of a monolayer with high physicochemical stability [47][48][49], while the amino group remained reactive and available for further modification. A schematic view of the PC surface modification with APTES and GAA-HA is shown in Figure 4. ED was deposited on the APTES-treated PC surface for 20 min. ...
... The PC surface was preliminarily treated with plasma and APTES was applied to introduce amino groups on the PC sensitive surface. As a result, APTES bond to activated silanol groups through ethoxy groups in the form of a monolayer with high physicochemical stability [47][48][49], while the amino group remained reactive and available for further silanol groups through ethoxy groups in the form of a monolayer with high physicochemical stability [47][48][49], while the amino group remained reactive and available for further modification. A schematic view of the PC surface modification with APTES and GAA-HA is shown in Figure 4. ED was deposited on the APTES-treated PC surface for 20 min. ...
... Polymers 2022, 13, x FOR PEER REVIEW 8 of 1 silanol groups through ethoxy groups in the form of a monolayer with high physicochem ical stability [47][48][49], while the amino group remained reactive and available for furthe modification. A schematic view of the PC surface modification with APTES and GAA-HA is shown in Figure 4. ED was deposited on the APTES-treated PC surface for 20 min. ...
Here, we propose and study several types of quartz surface coatings designed for the high-performance sorption of biomolecules and their subsequent detection by a photonic crystal surface mode (PC SM) biosensor. The deposition and sorption of biomolecules are revealed by analyzing changes in the propagation parameters of optical modes on the surface of a photonic crystal (PC). The method makes it possible to measure molecular and cellular affinity interactions in real time by independently recording the values of the angle of total internal reflection and the angle of excitation of the surface wave on the surface of the PC. A series of dextrans with various anchor groups (aldehyde, carboxy, epoxy) suitable for binding with bioligands have been studied. We have carried out comparative experiments with dextrans with other molecular weights. The results confirmed that dextran with a Mw of 500 kDa and anchor epoxy groups have a promising potential as a matrix for the detection of proteins in optical biosensors. The proposed approach would make it possible to enhance the sensitivity of the PC SM biosensor and also permit studying the binding process of low molecular weight molecules in real time.
... Although silanization is a very well-known method of producing a silane layer on silicon surface, it suffers from the demerit that most of the silanization approaches produce a thick and non-uniform silane layer, which negatively impacts the sensitivity of any biosensor [7]. There are various other factors that affect the silanization process such as the concentration of the silane, silanization time, moisture (humidity), and temperature of the solution [12][13][14][15]. ...
... A thin and stable layer of silane can be formed with silane solutions prepared in organic solvents. Silane coupling reagents with different functional groups are available in the literature and among them (3-aminopropyl)triethoxysilane (APTES) is extensively employed for biomolecule immobilization to develop biosensors [1,3,8,[14][15][16][17][18][19][20][21][22][23]. ...
... From the existing literature [3,8,14,15,[18][19][20][21][22][23], it has been observed that although silanization is a well-known process for immobilization of proteins, optimization of which has not yet been well developed with a well characterized protocol for producing a silane layer on a silicon surface. In the present study, optimized conditions required to produce a thin, stable silane layer for immobilization of biomolecules are investigated. ...
In the present work, we developed and optimized a technique to produce a thin, stable silane layer on silicon substrate in a controlled environment using (3-aminopropyl)triethoxysilane (APTES). The effect of APTES concentration and silanization time on the formation of silane layer is studied using spectroscopic ellipsometry and Fourier transform infrared spectroscopy (FTIR). Biomolecules of interest are immobilized on optimized silane layer formed silicon substrates using glutaraldehyde linker. Surface analytical techniques such as ellipsometry, FTIR, contact angle measurement system, and atomic force microscopy are employed to characterize the bio-chemically modified silicon surfaces at each step of the biomolecule immobilization process. It is observed that a uniform, homogenous and highly dense layer of biomolecules are immobilized with optimized silane layer on the silicon substrate. The developed immobilization method is successfully implemented on different silicon substrates (flat and pillar). Also, different types of biomolecules such as anti-human IgG (rabbit monoclonal to human IgG), Listeria monocytogenes, myoglobin and dengue capture antibodies were successfully immobilized. Further, standard sandwich immunoassay (antibody-antigen-antibody) is employed on respective capture antibody coated silicon substrates. Fluorescence microscopy is used to detect the respective FITC tagged detection antibodies bound to the surface after immunoassay. C) 2014 Elsevier B.V. All rights reserved.
... Data was collected from N=75 individual resonators or chains of silicon blocks, and we note that the high density of sensing elements on our chips can enable significant increases in measurement throughput compared to typical photonic sensors where signals are averaged over larger 2-D arrays. The deviation between experimental and simulated wavelength shifts for the AUTES and MBS layers is likely due to the tendency for aminosilane molecules to form multilayer structures; differences in the attachment of DNA probes and subsequent target hybridization are likely due to a strong influence of steric hindrance and electrostatic repulsion effects on the packing density and hybridization efficiency of the DNA strands [37,38,39,40]. ...
... The large variability in resonant wavelength shifts at each concentration are likely due to the stochastic nature of surface binding; notably, the signal from any particular resonator will depend on the local concentration and spatial position of bound targets (and hence binding at sites with the greatest electric field concentration will produce larger resonant shifts). Additionally, signal variation is also likely introduced through the hydrolytic degradation of silane layers in aqueous solutions during functionalization and hybridization experiments [37,38] (as seen in blue-shifted data points in Fig. 4b). We expect optimization of the surface functionalization homogeneity and stability to dramatically improve the performance of our sensors. ...
Genetic analysis methods are foundational to advancing personalized and preventative medicine, accelerating disease diagnostics, and monitoring the health of organisms and ecosystems. Current nucleic acid technologies such as polymerase chain reaction (PCR), next-generation sequencing (NGS), and DNA microarrays rely on fluorescence and absorbance, necessitating sample amplification or replication and leading to increased processing time and cost. Here, we introduce a label-free genetic screening platform based on high quality (high-Q) factor silicon nanoantennas functionalized with monolayers of nucleic acid fragments. Each nanoantenna exhibits substantial electromagnetic field enhancements with sufficiently localized fields to ensure isolation from neighboring resonators, enabling dense biosensor integration. Quantitative detection of complementary target sequences via hybridization occurs simultaneously for arrays of sensing elements patterned at densities of 160,000 pixels per cm$^2$. In physiological buffer, our nanoantennas exhibit average resonant quality factors of 2,200, allowing detection of purified SARS-CoV-2 envelope (E) and open reading frame 1b (ORF1b) gene fragments with high sensitivity and specificity (up to 94$\%$ and 96$\%$) within 5 minutes of nucleic acid introduction. Combined with advances in nucleic acid extraction from complex samples (eg, mucus, blood, or wastewater), our work provides a foundation for rapid, compact, and high throughput multiplexed genetic screening assays spanning medical diagnostics to environmental monitoring.
... Data was collected from N=75 individual resonators or chains of silicon blocks, and we note that the high density of sensing elements on our chips can enable significant increases in measurement throughput compared to typical photonic sensors where signals are averaged over larger 2-D arrays. The deviation between experimental and simulated wavelength shifts for the AUTES and MBS layers is likely due to the tendency for aminosilane molecules to form multilayer structures; differences in the attachment of DNA probes and subsequent target hybridization are likely due to a strong influence of steric hindrance and electrostatic repulsion effects on the packing density and hybridization efficiency of the DNA strands [37,38,39,40]. ...
... The large variability in resonant wavelength shifts at each concentration are likely due to the stochastic nature of surface binding; notably, the signal from any particular resonator will depend on the local concentration and spatial position of bound targets (and hence binding at sites with the greatest electric field concentration will produce larger resonant shifts). Additionally, signal variation is also likely introduced through the hydrolytic degradation of silane layers in aqueous solutions during functionalization and hybridization experiments [37,38] (as seen in blue-shifted data points in Fig. 4b). We expect optimization of the surface functionalization homogeneity and stability to dramatically improve the performance of our sensors. ...
Genetic analysis methods are foundational to advancing personalized and preventative medicine, accelerating disease diagnostics, and monitoring the health of organisms and ecosystems. Current nucleic acid technologies such as polymerase chain reaction (PCR), next-generation sequencing (NGS), and DNA microarrays rely on fluorescence and absorbance, necessitating sample amplification or replication and leading to increased processing time and cost. Here, we introduce a label-free genetic screening platform based on high quality (high-Q) factor silicon nanoantennas functionalized with monolayers of nucleic acid fragments. Each nanoantenna exhibits substantial electromagnetic field enhancements with sufficiently localized fields to ensure isolation from neighboring resonators, enabling dense biosensor integration. Quantitative detection of complementary target sequences via hybridization occurs simultaneously for arrays of sensing elements patterned at densities of 160,000 pixels per cm$^2$. In physiological buffer, our nanoantennas exhibit average resonant quality factors of 2,200, allowing detection of purified SARS-CoV-2 envelope (E) and open reading frame 1b (ORF1b) gene fragments with high sensitivity and specificity (up to 94$\%$ and 96$\%$) within 5 minutes of nucleic acid introduction. Combined with advances in nucleic acid extraction from complex samples (eg, mucus, blood, or wastewater), our work provides a foundation for rapid, compact, and high throughput multiplexed genetic screening assays spanning medical diagnostics to environmental monitoring.
... [1][2][3] SAMs are twodimensional nanomaterials that form spontaneously on a variety of solid surfaces in a highly ordered fashion, through the process of self-assembly of their molecular components. [4][5][6][7] In particular SAM formation is one of the simplest approaches in achieving thermodynamically stable monolayers through strong chemisorption that is in contrast to Langmuir-Blodgett and other techniques that lead to physisorption and unstable mono or multilayer films. [8] Specifically, in SAMs the adsorption of a surfactant with a specific affinity leads to the chemisorption of head groups onto a substrate from either the vapor or liquid phase, followed by the slow organization of tail groups. ...
... Chem. Acta 2020, 93(1), [1][2][3][4][5][6][7][8][9][10][11][12][13][14] In Figure 21 the IRAS spectrum of the film is depicted showing the biotin-thiol bond on an Au surface. In particular the peak at 1705.81 cm -1 corresponds to the amide vibration (amide I) of the urea group (predominantly the C=O stretching mode) while the peak at 1556.24 cm -1 corresponds to the amide II mode representing the out of phase combination of N-H in plane bending as well as C-N stretching vibrations. ...
... Later, organic amines have attracted interest in the fields of biochemistry and nanotechnology for their ability to functionalize surfaces. For instance, amines such as aminosilanes 1,5,6,8 and diamines 7,9,10 can act as linkers to attach nanoparticles, quantum dots, or biomolecules, enabling the development of advanced biosensors and solar cells. [1][2][3]6,9,10 Among organic amines, diamines are particularly interesting, in part because they enable reactions only possible with this bifunctionality. ...
... The atomically flat Si(111)-H surface has been used and studied for decades 39−41 and shown to be an ideal substrate to graft alkene-terminated molecules by hydrosilylation. 5,6 Fluorination of Si is more difficult as fluorine tends to etch silicon very easily. However, starting from an atomically flat Hterminated Si(111) surface, Michalak et al. 42 have developed a method to produce a mixed surface with 1/3 ML F-and 2/3 ML H-termination (where ML stands for monolayer), remaining atomically flat and stable through numbers of wet chemical steps. ...
Amine termination of surfaces constitutes a core platform for fields as diverse as microelectronics and bioengineering, and for nanotechnology in general. Diamines are particularly attractive for surface amination because unlike ammonia or simple amine molecules, they have a metal chelating capability useful in fabricating heterostructures. They can act as a linker molecule between inorganic electronic materials and biomolecules or photoactive quantum dots for applications in microelectronic, photonics, and biosensing. In contrast to ammonia modification of silicon surfaces, the direct grafting of diamine on silicon surfaces has been less explored. In this work, the attachment of liquid and vapor-phase ethylenediamine (EDA) on three types of oxide-free (H-, 1/3 ML F-, and Cl-terminated) Si(111) surfaces is therefore examined by infrared absorption spectroscopy and X-ray photoelectron spectroscopy in conjunction with first-principle calculations. We find that EDA chemisorption is only possible on 1/3 ML F- and Cl-terminated Si(111) surfaces: EDA only physisorbs on H-terminated Si(111) surfaces. On Cl-terminated Si(111) surfaces, EDA molecules adsorb in a mixture of monodentate and bridging configurations (chemical reaction of both EDA end groups), while on 1/3 ML F-terminated Si(111) surfaces the adsorption occurs primarily at one end of the molecule. EDA reaction with Cl-terminated Si(111) surfaces is also characterized by complete removal of Cl and partial Si–H (∼25% ML) formation on the surface. This unexpected Si–H product suggests that a proton–chlorine exchange may take place, with the endothermic barrier possibly reduced via concerted chemical reactions after an initial attachment of EDA to the surface.
... Surface amination has become more important for applications in microelectronics, [1][2][3][4] biotechnology, [5][6][7][8] and nanotechnology. [1,6,9,10] Ammonia has been widely used to achieve surface nitridation and amination, particularly on silicon surfaces. ...
... In the case of silicon, it has been shown atomically flat H-terminated Si(111) surfaces can be prepared [28][29][30] and used to graft alkeneterminated molecules by hydrosilylation. [5,6] Starting from this H-terminated surface, complete chlorination can be achieved, using either wet chemistry (PCl 5 ) or gas phase chlorination, without roughening the surface. [24,32,33] Fluorination of silicon is more difficult as fluorine easily etches silicon surfaces. ...
Amination of surfaces is useful in a variety of fields, ranging from device manufacturing to biological applications. Previous studies of ammonia reaction on silicon surfaces have concentrated on vapor phase rather than wet chemical processes, and mostly on clean Si surfaces. In this work, the interaction of liquid and vapor-phase ammonia is examined on three types of oxide-free surfaces– passivated by hydrogen, fluorine (1/3 monolayer) or chlorine – combining infrared absorption spectroscopy, X-ray photoelectron spectroscopy and first-principles calculations. The resulting chemical composition highly depends on the starting surface; there is a stronger reaction on both F- and Cl-terminated than on the H-terminated Si surfaces, as evidenced by the formation of Si-NH2. Side reactions can also occur, such as solvent reaction with surfaces, formation of ammonium salt by-products (in the case of 0.2 M ammonia in dioxane solution), and nitridation of silicon (in the case of neat and gas phase ammonia reactions for instance). Unexpectedly, there is formation of Si-H bonds on hydrogen-free Cl-terminated Si(111) surfaces in all cases, whether vapor phase of neat liquid ammonia is used. First principles modeling of this complex system suggests that step edge surface defects may play a key role in enabling the reaction under certain circumstances, despite the endothermic nature for Si-H bond formation.
... Later, organic amines have attracted interest in the fields of biochemistry and nanotechnology for their ability to functionalize surfaces. For instance, amines such as aminosilanes 1,5,6,8 and diamines 7,9,10 can act as linkers to attach nanoparticles, quantum dots, or biomolecules, enabling the development of advanced biosensors and solar cells. [1][2][3]6,9,10 Among organic amines, diamines are particularly interesting, in part because they enable reactions only possible with this bifunctionality. ...
... The atomically flat Si(111)-H surface has been used and studied for decades 39−41 and shown to be an ideal substrate to graft alkene-terminated molecules by hydrosilylation. 5,6 Fluorination of Si is more difficult as fluorine tends to etch silicon very easily. However, starting from an atomically flat Hterminated Si(111) surface, Michalak et al. 42 have developed a method to produce a mixed surface with 1/3 ML F-and 2/3 ML H-termination (where ML stands for monolayer), remaining atomically flat and stable through numbers of wet chemical steps. ...
Amine termination of surfaces constitutes a core platform for fields as diverse as microelectronics and bioengineering, and for nanotechnology in general. Diamines are particularly attractive for surface amination because unlike ammonia or simple amine molecules, they have a metal chelating capability useful in fabricating heterostructures. They can act as a linker molecule between inorganic electronic materials and biomolecules or photoactive quantum dots for applications in microelectronic, photonics, and biosensing. In contrast to ammonia modification of silicon surfaces, the direct grafting of diamine on silicon surfaces has been less explored. In this work, the attachment of liquid and vapor-phase ethylenediamine (EDA) on three types of oxide-free (H-, 1/3 ML F-, and Cl-terminated) Si(111) surfaces is therefore examined by infrared absorption spectroscopy and X-ray photoelectron spectroscopy in conjunction with first-principle calculations. We find that EDA chemisorption is only possible on 1/3 ML F- and Cl-terminated Si(111) surfaces: EDA only physisorbs on H-terminated Si(111) surfaces. On Cl-terminated Si(111) surfaces, EDA molecules adsorb in a mixture of monodentate and bridging configurations (chemical reaction of both EDA end groups), while on 1/3 ML F-terminated Si(111) surfaces the adsorption occurs primarily at one end of the molecule. EDA reaction with Cl-terminated Si(111) surfaces is also characterized by complete removal of Cl and partial Si-H (∼25% ML) formation on the surface. This unexpected Si-H product suggests that a proton-chlorine exchange may take place, with the endothermic barrier possibly reduced via concerted chemical reactions after an initial attachment of EDA to the surface.
... Functionalized Electrolyte/Insulator/Silicon (EIS) field effect devices for health science and biomedical research are under intense investigation in recent years [1][2][3][4]. Direct deposition of biological elements to the surface of silicon is a challenging process. ...
... Hence, they can be used for disposable applications by manufacturing on silicon substrates that can be mass-produced at very low cost and integrated with simple interface electronics making them suitable for portable system point-of-care applications. Structured protocols have been published for the SAM/Si devices processing step [4]; however, the stability and reproducibility of those devices in real-life biological solutions have yet to be established [8]. ...
... In general, 3-aminopropyltriethoxysilzne (APTES) is widely used in bioelectronics for self-assembly monolayer (SAM), which has a functional group at terminal end to coupling biomolecule [13,14]. However, silanization process of selfassembly monolayer is time-consuming and complicated, which makes reproducibility issue of sensor performance attributed to specific reaction condition [15]. ...
... Compared with APTES slianization and NH 3 plasma treatment, the sample with NH 3 plasma treatment which surface charge is larger than the sample with APTES silanization. It could result from APTES molecules formed a three dimensional attachment due to 3D polymerization [15] and the amount of terminal groups is less than the sample with NH 3 plasma treatment. In contrast, the NH 3 plasma treatment could be produce dense amine groups ( NH, NH 2 ) on the surface effectively for following molecular immobilization [17]. ...
A capacitive electrolyte-insulator-semiconductor structure was introduced to quantify and distinguish point mutation from the corresponding PCR product of KRAS gene. Si3N4 surface with remote NH3 plasma is proposed to form amino group for DNA probe immobilization. The sensing response was investigated by capacitance-voltage measurement. A linear relationship was found between the reference voltage and DNA concentration from 10(-6) to 10(-9) M. Non-complementary DNA was used for specificity testing, no DNA hybridized with DNA probes and the specificity of EIS structure with NH3 treatment was confirmed. Compared with APTES silanization and NH3 plasma treatment, the sample with NH3 plasma treatment reveal excellent selectivity and specificity, even in the presence of non-complementary DNA. The NH3 plasma treatment provided suitable method which compatible CMOS technology and could be improved accuracy of bio-sensing in clinical diagnosis.
... We consider that this is because the reaction time for APTMS is much longer than that for GPTMS (overnight compared to 2), which led to an increase in the vertical polymerization of APTMS leading to the formation of 3D "islands" compared with mostly horizontal polymerization for GPTMS. (39,40) APTMS also has a short carbon chain, which meant that it is more prone to 3D polymerization as reaction time is increased Therefore, GPTMS is more successful in forming a thin silane layer than APTMS, which is also effective in lowering pH sensitivity as explained in the next section. P and N data for both APTMS and GTPMS are also shown. ...
... The nature of the linker and terminal group also influences SAM stability. Longer-chain linkers have been shown to be more stable over time under physiological conditions, likely because the increased van der Waals packing between chains limits the ability of water and other chemical species to diffuse across the SAM and react with the anchor group [99,100]. Additionally, under ambient conditions, terminal amine groups can be oxidized to amides, thus changing the nature of the surface chemistry [101], and similar processes likely occur in other functionalized SAMs. ...
Bacterial infections due to biofilms account for up to 80% of bacterial infections in humans. With the increased use of antibiotic treatments, indwelling medical devices, disinfectants, and longer hospital stays, antibiotic resistant infections are sharply increasing. Annual deaths are predicted to outpace cancer and diabetes combined by 2050. In the past two decades, both chemical and physical strategies have arisen to combat biofilm formation on surfaces. One such promising chemical strategy is the formation of a self-assembled monolayer (SAM), due to its small layer thickness, strong covalent bonds, typically facile synthesis, and versatility. With the goal of combating biofilm formation, the SAM could be used to tether an antibacterial agent such as a small-molecule antibiotic, nanoparticle, peptide, or polymer to the surface, and limit the agent’s release into its environment. This review focuses on the use of SAMs to inhibit biofilm formation, both on their own and by covalent grafting of a biocidal agent, with the potential to be used in indwelling medical devices. We conclude with our perspectives on ongoing challenges and future directions for this field.
... These ethoxy groups can polymerize in the presence of water, which can give rise to different surface coverages: covalent attachment, two-dimensional self-assembly (horizontal polymerization), and multilayers (vertical polymerization). The resulting structure and coverage of the layers are highly dependent on several experimental parameters, including temperature [35] and humidity [33,36]. The simplest route yields a single aminopropylsilane layer having amine-terminal groups on the modified surface. ...
Human chorionic gonadotropin (hCG) is a key diagnostic marker of pregnancy. A sensor device for detection of hCG has been fabricated using a CNT (carbon nanotube) screen printed electrode (SPE). The CNT working electrode was first electrochemically oxidised to yield a hydroxyl terminated surface, which was subsequently silanized to produce an amine terminated CNT. The aminated surface allowed oriented binding of an antibody (Ab) bioreceptor, targeted against hCG (anti-hCG), to the CNT-SPE. This was achieved by activating the-COOH group at the F c terminal of the antibody and incubating the SPE-CNT-NH 2 electrode in the activated Ab solution. Electrochemical Impedance Spectroscopy (EIS) and Raman Spectrometry with Confocal Microscopy studies were performed at each stage of the chemical modification process in order to confirm the resulting surface changes associated with each functionalization process. The SPE-CNT-NH 2-Ab devices displayed linear responses to hCG in EIS assays in the concentration range from 0.01 × 10 −9 g cm −3 to 100 × 10 −9 g cm −3. High specificity was observed with respect to hCG detected in solutions containing urine components-these components producing a negligible change in the sensor readout relative to changes induced by hCG. Successful hCG detection was also achieved using real urine samples from pregnant woman. Overall, the immunosensor developed is a promising tool for detecting hCG in a point-of-care diagnostic (POC), due to the excellent detection capability, simplicity of fabrication, low cost, high sensitivity and selectivity.
... Silanization is a recognized and efficient process to activate the surfaces of cellulose for biomolecular immobilization in the development of biological platforms or microfluidic devices for cell and tissue engineering applications. The process provides simplicity and efficiency of establishing covalent connections between electrode surfaces and the biomolecules [42][43][44]. Herein, the functionalization of Cel NFMs with APTES works as an active spacer arm to afford the desired amine functional groups for immobilization of the MBlabeled aptamer by reacting with its 5′-terminus end carboxylic group. Furthermore, it is necessary to keep the redox probe in a long distance from the surface of the electrode to reduce the background current generated from the unfolded aptamer in absence of the target, and consequently, improving the sensitivity of the assembled sensing system. ...
An innovative ultrasensitive electrochemical aptamer-based sensor was developed for ochratoxin A (OTA) detection in cold brew coffee through revolutionary combination of nanofibers, electrochemical method, and aptamer technologies. The assembly of the aptasensor was based on the activation of silanized cellulose nanofibrous membranes as a supporting matrix for methylene blue (MB) redox probe-labeled aptamer tethering. Cellulose nanofibrous membranes were regenerated by deacetylating electrospun cellulose acetate nanofibrous membranes with deacetylation efficacy of 97%, followed by silanization of the nanofiber surfaces by using (3-aminopropyl)triethoxysilane (APTES). A replacement of conventionally casted membranes by the nanofibrous membranes increased the active surface area on the working electrode of a screen-printed three-electrode sensor by more than two times, consequently enhancing the fabricated aptasensor performance. The developed aptasensor demonstrated high sensitivity and specificity toward OTA in a range 0.002–2 ng mL−1, with a detection limit of 0.81 pg mL−1. Moreover, the assembled aptamer-based sensor successfully detected OTA in cold brew coffee samples without any pretreatment. The aptasensor exhibited good reusability and stability over long storage time.
Graphical abstract
... La silanisation avec l'APTES est généralement réalisée en phase liquide dans un solvant tel que l'éthanol (typiquement en présence de 5 %vol d'eau) Nuzaihan 2016] ou le toluène [Razumovitch 2009;Seitz 2011;Taylor 2003;Singh 2015]. Elle peut également être effectuée en phase vapeur sous atmosphère sèche (taux d'humidité contrôlé, en général inférieur à 5 %), c'està-dire sous vide Karakoy 2014] ou sous gaz neutre (N 2 , Ar…) Steinbach 2016;Heim 2002], l'évaporation de l'organosilane étant provoquée par une augmentation de température ou une diminution de pression. ...
Les réseaux bidimensionnels de nanofils (NFs) d’oxyde de zinc (ZnO) aléatoirement orientés, ou nanonets (pour « nanowire networks »), constituent des nanostructures innovantes et prometteuses pour de nombreuses applications. L’objectif de cette thèse est de développer des nanonets de ZnO en vue d’applications à la détection de molécules biologiques ou gazeuses, en particulier de l’ADN, ceci selon une procédure bas coût et industrialisable. Dans ce but, il est essentiel de bien maitriser les différentes étapes d’élaboration qui sont : (i) le dépôt de couches minces de germination de ZnO sur des substrats de silicium par voie sol-gel, (ii) la croissance de NFs de ZnO sur ces couches de germination par synthèse hydrothermale, et (iii) l’assemblage par filtration sous vide de ces NFs en nanonets de ZnO. Des études approfondies de chacun de ces procédés ont donc été menées. Ces travaux ont permis d’élaborer des couches minces, des NFs et des nanonets de ZnO reproductibles et homogènes dont les propriétés morphologiques sont précisément contrôlées sur une large gamme. Deux protocoles de biofonctionnalisation des nanonets avec de l’ADN ont ensuite été développés et ont abouti à des résultats encourageants mais restant à optimiser. Les nanonets ont également été intégrés au sein de dispositifs fonctionnels et les premières caractérisations électriques ont fourni des résultats prometteurs. A terme, ce travail ouvre la voie à l’intégration collective de NFs de ZnO qui permettrait la réalisation d’une nouvelle génération de capteurs (de biomolécules, de gaz…) à la fois portables, rapides et très sensibles.
... Thus, it is essential to develop a new method for MAU detection with sensitivity, simple operations, economic, and safe reagents. Biosensors based on field-effect transistor (FET) provides high sensitivity, real-time, and label-free detection of a wide range application in chemical and medical field (Han et al., 2010;Kim et al., 2010;Seitz et al., 2011;Hideshima et al., 2011). In 1970 Bergveld presented the first ion-sensitive field effect transistor (ISFET) based biosensor (Bergveld, 1970). ...
The main objective of this study is to develop biosensor system based on antibody-modified ion-sensitive field effect transistor (ISFET) for detection of albumin in microgram range. The surface of ISFET was modified by coating with different concentration of protein A (PA) in 10 mM PBS, pH 7.4 with various incubation times to obtain suitable surface for antibody immobilization. Then, this modified anti-human serum albumin (Ab-HSA) layer was treated with 1% casein solution to prevent nonspecific bindings. The target concentrations of human serum albumin (HSA) in 10 mM PBS, pH 7.4 were applied to this Ab-modified ISFET to present the availability of functional antibody. All the measuring data was carried out by monitoring the gate potential by controlling the source-drain current at 25 µA. The suitable amount of protein A coating on ISFET is 1 mg/mL for 1 hour at room temperature with 12.50±3.42 mV change. This PA layer on ISFET has ability to immobilize Ab-HSA at the concentration of 0.5 mg/mL with 16.63±2.82 mV change. The binding ability to albumin of this immunosensor showed the response range between 10-500 µg/mL. This immunosensor device is suitable to apply in the measurement of microalbumin in urine sample.
... Therefore, a controlled and adaptative chemical preparation of the sensing surfaces is important for the biofunctionalization step. Modification of solid substrates by deposition of organic monolayers with controlled architecture, 3,4 such as thiols on gold, carboxylic acids on alumina, or alkanes on silicon and silica, are a subject of growing interest. Moreover, several approaches exist to supply high yield grafting organosilane on solid surfaces: using for instance trifunctional silanes (APTES, GPTS) or trichloroalkylsilanes. ...
The aim of this work is to develop a sensitive and specific immune-sensing platform dedicated to the detection of potential biomarkers of Alzheimer disease (AD) in biological fluids. Accordingly, a controlled and adaptive surface functionalization of a silicon wafer with 7-octenyltrichlorosilane has been performed. The surface has extensively been characterized by AFM (morphology) and XPS (chemical composition) and contact angle measurements. The wettability of the grafted chemical groups demonstrated the gradual trend from hydrophilic to hydrophobic surface during functionalization. XPS evidenced the presence of silanes on the surface after silanization, and even carboxylic groups as products from the oxidation step of the functionalization process. The characterization results permitted us to define an optimal protocol to reach a high-quality grafting yield. The issue of the quality of controlled chemical preparation on bio-receiving surfaces was also investigated by the recognition of one Alzheimer disease (AD) biomarker, the Amyloïd peptide Aβ 1-42. We have therefore evaluated the biological activity of the grafted anti Aβ antibodies onto this silanized surface by fluorescent microscopy. In conclusion, we have shown, both qualitatively and quantitatively, the uniformity of the optimized functionalization on slightly oxidized silicon surfaces, providing reliable and chemically stable procedure to determine specific biomarkers of Alzheimer disease. This work opens the route to the integration of controlled immune-sensing applications on lab-on-chip systems.
Genetic analysis methods are foundational to advancing personalized medicine, accelerating disease diagnostics, and monitoring the health of organisms and ecosystems. Current nucleic acid technologies such as polymerase chain reaction (PCR) and next-generation sequencing (NGS) rely on sample amplification and can suffer from inhibition. Here, we introduce a label-free genetic screening platform based on high quality (high-Q) factor silicon nanoantennas functionalized with nucleic acid fragments. Each high-Q nanoantenna exhibits average resonant quality factors of 2,200 in physiological buffer. We quantitatively detect two gene fragments, SARS-CoV-2 envelope (E) and open reading frame 1b (ORF1b), with high-specificity via DNA hybridization. We also demonstrate femtomolar sensitivity in buffer and nanomolar sensitivity in spiked nasopharyngeal eluates within 5 minutes. Nanoantennas are patterned at densities of 160,000 devices per cm², enabling future work on highly-multiplexed detection. Combined with advances in complex sample processing, our work provides a foundation for rapid, compact, and amplification-free molecular assays.
In view of the relevance of organic thin layers in many fields, the fundamentals, growth mechanisms, and dynamics of thin organic layers, in particular thiol-based self-assembled monolayers (SAMs) on Au(111) are systematically elaborated. From both theoretical and practical perspectives, dynamical and structural features of the SAMs are of great intrigue. Scanning tunneling microscopy (STM) is a remarkably powerful technique employed in the characterization of SAMs. Numerous research examples of investigation about the structural and dynamical properties of SAMs using STM, sometimes combined with other techniques, are listed in the review. Advanced options to enhance the time resolution of STM are discussed. Additionally, we elaborate on the extremely diverse dynamics of various SAMs, such as phase transitions and structural changes at the molecular level. In brief, the current review is expected to supply a better understanding and novel insights regarding the dynamical events happening in organic SAMs and how to characterize these processes.
Despite decades of research on promoting the dropwise condensation of steam, achieving dropwise condensation of low surface tension liquids remains a challenge. The few coatings reported to promote dropwise condensation of low surface tension liquids either require complex fabrication methods, are substrate dependent or have poor scalability. Here, the rational development of a coating, which is applicable to all conventionally used condenser metals, is presented by combining a low contact angle hysteresis polydimethylsiloxane with a low surface energy silane using atmospheric vapor phase deposition. The siloxane-silane coating enables the dropwise condensation of fluids with surface tensions as low as 15 mN m−1 in pure vapor conditions. This siloxane-silane coating enables a 274%, 347%, and 636% heat transfer enhancement during ethanol, hexane, and pentane condensation, respectively, when compared to filmwise condensation on the same un-coated surfaces. Furthermore, this coating exhibits 15 days of steady dropwise condensation with no apparent signs of coating degradation. This study not only demonstrates the possibility of achieving stable dropwise condensation of low surface tension fluids on scalable, structure-less surfaces, it also develops design principles for creating facile, substrate-independent, durable, and scalable omniphobic coatings for a plethora of applications.
Le travail de sortie d’un métal est une propriété fondamentale en physico-chimie des matériaux. C’est l’énergie nécessaire pour extraire un électron depuis le niveau de Fermi vers le niveau du vide. Il est connu que cette grandeur dépend de la nature du métal, mais aussi que d’autres paramètres ont une influence notable. Ainsi ce travail de thèse montre comment le travail de sortie peut être modulé par une couche de molécules auto assemblées sur la surface métallique, et comment il évolue quand le matériau est sous forme de nanoparticules. La présente étude se concentre sur des nanoparticules d’or (AuNPs) de diamètres compris entre 10 et 60 nm, et étudie les effets de fonctionnalisation par quatre molécules : l’hexanedithiol (HDT), l’aminooctanethiol (AOT), l’acide mercaptohexadecanoïque (MDHA) et le dodécanethiol (DDT). Après une étude détaillée des morphologies des surfaces planes d’or fonctionnalisées par microscopie à force atomique (AFM), des mesures de travail de sortie sur ces surfaces sont effectuées par microscopie à sonde de Kelvin (KPFM). En comparant ces résultats à des mesures de photoémission (UPS), l’effet de chaque fonctionnalisation est mis en évidence. Par exemple, le travail de sortie d’une surface fonctionnalisée par MHDA diminue de -0.30 eV par rapport à une surface d’or non fonctionnalisée. Ces résultats montrent aussi l’effet sur le travail de sortie du temps de contact avec l’atmosphère ambiante. Ensuite, nous abordons le cas des AuNPs, synthétisées par voie colloïdale, puis post-fonctionnalisées par AOT ou par MDHA. La fonctionnalisation des AuNPs est suivie par des mesures optiques basées sur la mesure du pic d’absorption (plasmon) des AuNPs dans le visible. Après fonctionnalisation, leur travail de sortie est mesuré par KPFM. Ces mesures mettent en évidence deux phénomènes : la modification du travail de sortie par la fonctionnalisation, ainsi qu’une variation en fonction de la taille de l’AuNP. Dans le but de comprendre précisément cet effet de taille, nos systèmes ont été modélisés par une approche DFT (density functional theory), et les calculs de travaux de sortie ont été confrontés aux mesures expérimentales. Ces calculs sont en très bon accord avec les résultats expérimentaux, notamment sur l’évolution du travail de sortie en fonction de la taille des particules, d’environ 1 meV.nm 1.
The investigation and development of micro/nano biosytem requires a sealed fluidic platform to separate, mix or control the flow of liquids and bio samples as well as a biochemical surface processing to selectively capture or repel biospecies. The first part of this chapter reviews the main techniques used for the fabrication of microchannels, reservoirs, pillars,… in various substrate materials. This includes direct machining techniques such as mechanical cutting, lithography and electroforming, as well as various replication techniques such as PDMS or UV curable resin casting, hot embossing and overall injection molding that is compatible with mass production. The second part describes the recent advances in the development of functionalized surfaces and their applications in biochips. First a focus is put on bioreceptors immobilization and a brief presentation of bioreceptors (antibodies and aptamers) is included. Next the polymers employed against plasmatic proteins fouling are reviewed and finally the surface chemistry preventing bacteria attachment is presented. The two approaches leading to bacteria repelling or killing, depending on the polymers employed, is discussed. The last chapter part is devoted to a critical analysis of bonding and welding techniques proposed to seal fluidic platforms.
A novel and rapid (45 min), quantitative chemiluminescence-based, surface immunoassay is reported for the detection of progesterone and œstriol in artificial saliva. The detection limits for these pregnancy hormones are 2.3 and 2.5 pg mL⁻¹, respectively. The assay is based on the use of ferrocene-tagged, monoclonal antibodies immobilised on a surface, so that the oxidised ferricenium catalyses the reaction between luminol and hydrogen peroxide. The immunoassay is performed in negative, such that increasing the antigen concentration gives rise to decreasing light intensity that is observed, and is unaffected by antibody orientation on the surface. This affords a method of calibration that is readily translated to pregnancy hormone detection in a primary point-of-care environment. Biomolecules with similar structures to these pregnancy hormones found in saliva are demonstrated not to interfere with the immunoassay. © The Royal Society of Chemistry and the Centre National de la Recherche Scientifique.
Amino functionalized surfaces were selectively modified via the combination of a wet agarose stamping technique and microcontact printing technique. Because of the specific reaction environments and diffusion of HNO2 confined in agarose stamp, the reaction of amino groups in the edge of the strip pattern was much more intense than other areas. The modified amino groups in the edge areas show higher affinity to Au-NPs than other areas, consequently, edge enriched Au-NPs patterns were observed after the self-assembly of Au-NPs. A “cylindrical droplet” model, in a manner analogous to “coffee-ring” effect, was proposed to describe the diffusion of HNO2 from the bulk to the edge in agarose stamp. By using such density varied Au-NPs patterns as templates for the growth of ZnO nanorods, we observed high density of Au-NPs resulting in high density and highly (0 0 1) oriented ZnO nanorods. In contrast, sparse and non-oriented ZnO nanorods were grew on low density of Au-NPs areas. Our findings might open new routes for the fabrication of gradient patterns and extend applications of Au-NPs patterns in surface enhanced Raman scattering and catalysis.
This chapter reviews the role of infrared spectroscopy in characterization of surfaces and interfaces of thin organic films. FTIR spectroscopy is widely utilized in studies of chemical bonds addressing questions concerning organization and orientation of the molecules in those films. In-situ FTIR spectroscopy frequently aids in studies of chemical reactions under a variety of experimental conditions, from high vacuum to aqueous solutions. FTIR spectroscopy can be realized in a multitude of setup geometries sensitive to a small amount of surface adsorbates. Anisotropic film properties can be studied by incorporating polarizing optics in an FTIR setup. FTIR modes of operation discussed in this chapter are Attenuated Total Reflection (ATR), transmission and reflection of the IR radiation through (or from) the sample, Polarization Modulation Infrared Reflection Absorption Spectroscopy (PM-IRRAS) and Infrared Spectroscopic Ellipsometry (IRSE). Practical considerations related to the sample properties (such as doping or roughness) and to the measurement conditions are discussed.
Research on surface chirality is motivated by the need to develop functional chiral surfaces for enantiospecific applications. While molecular chirality in 3D has been the subject of study for almost two centuries, many aspects of 2D chiral surface chemistry have yet to be addressed. In 3D, racemic mixtures of chiral molecules tend to aggregate into racemate (molecularly heterochiral) crystals much more frequently than conglomerate (molecularly homochiral) crystals. Whether chiral adsorbates on surfaces preferentially aggregate into heterochiral rather than homochiral domains (2D crystals or clusters) is not known. In this review, we have made the first attempt to answer the following question based on available data: in 2D racemic mixtures adsorbed on surfaces, is there a clear preference for homochiral or heterochiral aggregation? The current hypothesis is that homochiral packing is preferred on surfaces; in contrast to 3D where heterochiral packing is more common. In this review, we present a simple hierarchical scheme to categorize the chirality of adsorbate–surface systems. We then review the body of work using scanning tunneling microscopy predominantly to study aggregation of racemic adsorbates. Our analysis of the existing literature suggests that there is no clear evidence of any preference for either homochiral or heterochiral aggregation at the molecular level by chiral and prochiral adsorbates on surfaces.
In the context of FTIR ATR-based sensors, the organic layer covering the ATR element has to be as stable as possible for optimal spectroscopic measurements. Previously, this self-assembled covering was considered stable after several hours under a PBS flux, probably due to a hydrophobic barrier, which prevents water penetration into the grafted network. Stability and reactivity, measured simultaneously using FTIR ATR, identify the limits of the previously used molecular construction. For the first time, surface etching of the previous functionalised Ge devices (Ge-PEG-NHS), a few minutes after BSA injection, was observed. It was concluded that the molecular chain deformation of Ge-PEG-NHS likely occurred when large molecules were bound. BSA loaded onto a Ge-PEG-NHS surface led to network deprotection, with the probable disruption of hydrogen bonds for single barrier-based networks. This, in turn, was presumably influenced by the random deposition of the NHS moiety on the PEG chain. A new functionalised germanium device, using a rapid three-step in situ procedure, provides an efficient robust network composed of two protective barriers, ideal for the binding of various sized molecules. The Ge-APS-PEG-NHS device has shown exceptional sensitivity with regards to BSA and ethanolamine target molecules while offering homogeneous NHS distribution.
Prior to immobilization of biomolecules or cells onto biosensor surfaces, the surface must be physically or chemically activated for further functionalization. Organosilanes are a versatile option as they facilitate the immobilization through their terminal groups and also display self‐assembly. Incorporating hydroxyl groups is one of the important methods for primary immobilization. This can be done, for example, with oxygen plasma treatment. However, this treatment can affect the performance of the biosensors and this effect is not quite well understood for surface functionalization. In this work, the effect of O2 plasma treatment on EIS sensors was investigated by means of electrochemical characterizations: capacitance–voltage (C–V) and constant capacitance (ConCap) measurements. After O2 plasma treatment, the potential of the EIS sensor dramatically shifts to a more negative value. This was successfully reset by using an annealing process.
ConCap measurement of an EIS sensor. a) Reference measurement, b) after O2 plasma treatment, c) after annealing process.
Despite the wide range and versatility of polymer-grafting methods to produce biopassive interfaces, commonly applied polymer brushes suffer from an intrinsic lack of long-term stability when incubated in aqueous media under physiological conditions. The robustness of brush films in such environments can be greatly improved by applying a hydrophobic, "protecting" layer between the supporting substrate and the interfacial, biopassive brush. Block-copolymer brushes synthesized by sequential surface-initiated atom transfer radical polymerization (SI-ATRP) forming well-defined bilayered architectures can produce coatings with tunable interfacial properties and improved stability when subjected to cell-culture conditions. Three poly(n-alkyl methacrylates) (PAMA), exhibiting different mechanical properties, have been tested as protecting layers. A biopassive, hydrophilic brush is chosen to constitute the interfacial layer in all three cases. On the one hand, the structure of the interfacial layer clearly regulates film biopassivity, as well as its nanomechanical and nanotribological properties, as determined by atomic force microscopy (AFM) techniques. On the other hand, the composition and the mechanical properties of the polymer constituting the substrate-bound layer govern the stability of the entire bilayered film in the aqueous cell-culture environment. Precise control of bilayered brush architecture thus determines the film's applicability for cell manipulation or biomaterials surface engineering.
An important step of fabrication of a high selective DNA probe is the functionalization of semiconducting surfaces with a self-assembled monolayer (SAM) with an appropriate surface termination to interact with DNA. In this work, an immobilization of single strand DNA (ssDNA) is studied using both the heavily exploited aminopropyltriethoxysilane (APTES) and n-(2-aminoethyl)-11-aminoundecyltrimethoxysilane (NAATS), a bi-functional amino silane. A silanization procedure yielding a self-assembled monolayer on the surface of a blanket SiGe substrate was utilized. X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM) techniques were employed to characterize the silanization of SAMs on SiGe surface. The immobilization was characterized using fluorescence intensity measurements. The coverage values of APTES and NAATS SAMs are estimated to be 71.3 and 83%, respectively from the C/Ge ratio. Comparing the performance towards both specific and a non-specific ssDNA complements for both silanes, it was observed that a higher selectivity and sensitivity was obtained by using the NAATS SAM. The results showed that the use of NAATS enhances the selectivity and sensitivity for the target ssDNA compared to APTES. This work highlights the importance of SAM chain length by comparing two used short alkyl chains, APTES with their long-chain counterparts, NAATS. It was observed that a minimum concentration of specific complementary (SCP) ssDNA detected is 1 nM for NAATS immobilized onto SiGe.
Controlling surface coverage and stability of supported aminoalkylsilane monolayers on silica-based substrates still remains a challenge for the development of biosensors and nanomaterials. We have developed protocols using simple surface chemistry and self-assembly from solution without stringent deposition conditions to covalently attach monolayers of 11-aminoundecyltriethoxysilane (AUTES) onto mica and silica substrates. The resulting self-assembled monolayers (SAMs) exhibited excellent hydrolytic stability. The long alkyl chain together with the large grafting density and homogeneity enhanced the monolayer stability by preventing the Sisilane-O-Sisurface bonds from hydrolysis over a wide range of pH values (2 to 10) for long time periods (up to 8 days). The control over the surface density of amino groups was achieved and the reactivity of the amino SAMs was confirmed by covalently attaching carboxyl-functionalized nanoparticles on the SAMs. The immobilized nanoparticles exhibit the same hydrolytic stability as that of the SAMs. The AUTES SAMs prepared in this study exhibited the best hydrolytic stability of similar systems reported so far.
The ability to selectively chemically functionalize silicon nitride (Si3N4) or silicon dioxide (SiO2) surfaces after cleaning would open interesting technological applications. In order to achieve this goal, the chemical composition of surfaces needs to be carefully characterized so that target chemical reactions can proceed on only one surface at a time. While wet-chemically cleaned silicon dioxide surfaces have been shown to be terminated with surficial Si-OH sites, chemical composition of the HF-etched silicon nitride surfaces is more controversial. In this work, we removed the native oxide under various aqueous HF-etching conditions and studied the chemical nature of the resulting Si3N4 surfaces using infrared absorption spectroscopy (IRAS), x-ray photoelectron spectroscopy (XPS), low energy ion scattering (LEIS), and contact angle measurements. We find that HF-etched silicon nitride surfaces are terminated by surficial Si-F and Si-OH bonds, with slightly subsurface Si-OH, Si-O-Si, and Si-NH2 groups. The concentration of surficial Si-F sites is not dependent on HF concentration, but the distribution of oxygen and Si-NH2 displays a weak dependence. The Si-OH groups of the etched nitride surface are shown to react in a similar manner to the Si-OH sites on SiO2, and therefore no selectivity was found. Chemical selectivity was, however, demonstrated by first reacting the -NH2 groups on the etched nitride surface with aldehyde molecules, which do not react with the Si-OH sites on a SiO2 surface, and then using trichloro-organosilanes for selective reaction only on the SiO2 surface (no reactivity on the aldehyde-terminated Si3N4 surface).
A review of the fabrication, characterization and modeling of silicon-on-insulator field-effect-transistor nanoribbon chemical and biological sensors is presented. The impact of mobile ions on the sensor electrical response is shown to depend strongly on the nature of the sensor surface. Appropriate bias conditions for these sensors and a model which predicts sensor operation is described.
Nanocrystal multilayers on different substrates are prepared via self-assembly of quantum dots at the air–liquid interface resulting in highly ordered solids in which each layer can be controlled for use in potential optoelectronic applications. Time-resolved photoluminescence measurements are consistent with the theoretical picture of exciton decay in controlled stratified environment and reveal efficient energy transfer into silicon substrates.
We constructed a self-assembled monolayer (SAM) of mercaptoacetic acid combining functionalized ionic liquid (IL-MAA) by covalent interaction on gold electrode. The formation of IL-MAA SAM on gold electrode has been confirmed by Fourier transform infrared spectroscopy (FT-IR), cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) in this article. The results of CV and EIS revealed that the electrochemical behavior of the [Fe(CN)6]3-/4- redox couple probe improved along with IL's introduction on gold electrode. As IL-MAA is electroactive, hemoglobin (Hb) was modified on the IL-MAA SAM gold electrode subsequently and the direct electrochemistry of Hb was realized. UV-vis spectrum illustrated that the Hb absorbed on the SAM film maintained its natural activity. Upon the optimal conditions, the modified electrode exhibited a high electrocatalytic activity to hydrogen peroxide. Accordingly, an easily-made and cost-effective hydrogen peroxide electrochemical biosensor, accompany with proper fine quality, was accomplished. More importantly, the methodology could provide an effective enzyme immobilization platform based on ionic liquid modifying electrode surface and broaden the use of functionalized ionic liquid in electrochemical biosensor field.
We take advantage of the progresses made in the topic of silicon functionalization. Grafted organic monolayer (GOM) on oxide-free Si have been fabricated using hydrosilylation and characterized using FTIR and XPS. The obtained amine terminated GOM has been used to graft Colloidal gold nanoparticles (AuNP). They have been deposited and single electron transport measurements have been performed using STM under UHV: A double barrier tunneling junction (1: GOM; 2: vacuum between the scanning tip and the AuNP). This structure is known to exhibit single electron transport through Coulomb staircase phenomenon. Evidence for its occurrence and for its reproducibility was obtained at 30K. Experimental and simulated data were compared. The latter were acquired using a recently developed theoretical model that has been modified to model our system more accurately. Our goal is to develop an alternative technology to build single electron transistors that are compatible with current Si-based technology. Nanoquantum dots (NQDs) were also deposited on the GOM. Energy transfers through radiative and non-radiative mechanism between NQDs and substrate were observed on plane surface in recent work using photoluminescence (PL) spectroscopy. We show evidence of optimization of the PL count using GOM on silicon nanopillars and with successive grafting of NQDs to form multilayers. We also show evidence of directed energy transfer from NQDs to the silicon substrate using bilayers of NQDs with a size gradient. All these achievements can be combined for the fabrication of NQDs solar cells prototypes with an enhanced efficiency that could compete with existing technologies.
This chapter reviews the role of infrared spectroscopy in characterization of surfaces and interfaces of thin organic films. FTIR spectroscopy is widely utilized in studies of chemical bonds addressing questions concerning organization and orientation of the molecules in those films. In-situ FTIR spectroscopy frequently aids in studies of chemical reactions under a variety of experimental conditions, from high vacuum to aqueous solutions. FTIR spectroscopy can be realized in a multitude of setup geometries sensitive to a small amount of surface adsorbates. Anisotropic film properties can be studied by incorporating polarizing optics in an FTIR setup. FTIR modes of operation discussed in this chapter are Attenuated Total Reflection (ATR), transmission and reflection of the IR radiation through (or from) the sample, Polarization Modulation Infrared Reflection Absorption Spectroscopy (PM-IRRAS) and Infrared Spectroscopic Ellipsometry (IRSE). Practical considerations related to the sample properties (such as doping or roughness) and to the measurement conditions are discussed.
AlGaN/GaN high electron mobility transistor (HEMT) was successfully fabricated by complementary metal-oxide semiconductor field effect transistor-compatible fabrication method, and the label-free, electrical detection of prostate specific antigen in real time using the biomolecule-gate AlGaN/GaN HEMT sensor was presented. It shows a rapid response when target prostate biomarker in buffer solution was added to the antibody-immobilized sensing area. The linear range for target prostate specific antigen detection has been demonstrated from 0.1 pg/ml to 10.269 ng/ml and a low detection below 0.1 pg/ml level is estimated, which is the best result of AlGaN/GaN HEMT biosensor for prostate specific antigen (PSA) detection till now. The sensitivity of 0.027 % is determined for 0.1 pg/ml prostate specific antigen solution. The electrical result of the biomolecule-gated AlGaN/GaN HEMT biosensor suggested that this biosensor might be a useful tool for the prostate cancer screening.
Most doping research into transition metal dichalcogenides (TMDs) has been mainly focused on the improvement of electronic device performance. Here, the effect of self-assembled monolayer (SAM)-based doping on the performance of WSe2- and MoS2-based transistors and photodetectors is investigated. The achieved doping concentrations are ≈1.4 × 1011 for octadecyltrichlorosilane (OTS) p-doping and ≈1011 for aminopropyltriethoxysilane (APTES) n-doping (nondegenerate). Using this SAM doping technique, the field-effect mobility is increased from 32.58 to 168.9 cm2 V−1 s in OTS/WSe2 transistors and from 28.75 to 142.2 cm2 V−1 s in APTES/MoS2 transistors. For the photodetectors, the responsivity is improved by a factor of ≈28.2 (from 517.2 to 1.45 × 104 A W−1) in the OTS/WSe2 devices and by a factor of ≈26.4 (from 219 to 5.75 × 103 A W−1) in the APTES/MoS2 devices. The enhanced photoresponsivity values are much higher than that of the previously reported TMD photodetectors. The detectivity enhancement is ≈26.6-fold in the OTS/WSe2 devices and ≈24.5-fold in the APTES/MoS2 devices and is caused by the increased photocurrent and maintained dark current after doping. The optoelectronic performance is also investigated with different optical powers and the air-exposure times. This doping study performed on TMD devices will play a significant role for optimizing the performance of future TMD-based electronic/optoelectronic applications.
In this report, we present a ratiometric pH nanoprobe based on stable fluorescent colloidal silica composite nanoparticles encapsulating hydrophilic CdTe quantum dots. Quantum dots, owing to their fascinating optical properties, have been widely used for sensors and bioimaging. To avoid the inherent chemical instability and serious photoluminescence quenching of quantum dots, a facile electrostatic assembly method is developed to prepare sandwich-like silica/CdTe quantum dots/silica composite nanoparticles stabilized by mercaptopropyl trimethoxysilane (SQMS). This approach is of high efficiency, e.g., 98.9% of quantum dots are instantly adsorbed on the surface of silica nanospheres, and nearly 80% of the original fluorescence of the quantum dots is retained for SQMS while traditional silica coating processes caused dramatic quenching. Finally, the bright SQMS with remarkable stability is modified with pH-sensitive fluorescein isothiocyanate to fabricate a high-resolution pH ratiometric nanoprobe. Above all, SQMS shows a uniform sandwich-like structure, narrow size distribution, and stable fluorescence in strongly acidic and highly salted solutions, and the remarkable stability favours quantitative analyses and nanoprobes.
Macroscopically aligned, crystalline layers are a key requirement for high-performance organic field effect transistors from small molecule organic semiconductors. We investigated the crystallization behavior of n-type semiconducting naphthalene and perylene diimides at the liquid/solid/air interface as a solvent meniscus – evaporation-induced – slowly moved along the surface of a monolayer functionalized Si/SiO2. Amine-terminated, triethoxysilane based functional polar monolayers enforce highly oriented crystallization of the respective rylene diimides at the three-phase border. The electron transporting properties of the resulting crystalline layers of rylene diimides were studied in bottom gate-top electrode field effect transistors, which were shown to be improved up to two orders of magnitude over those of solution casted films. Anisotropic effects expected for crystalline devices were also revealed, which corroborated with the macroscopically oriented crystalline planes observed by polarized optical microscopy.
Mesoporous silicon (PSi) has been shown to have extensive application opportunities in biomedicine, whereas it has frequently failed to produce complex systems based on PSi due to the lack of surface functional groups or the instability of the unmodified PSi surface. In the present study, PSi nanoparticles, stabilized by thermal oxidation or thermal carbonization, were successfully modified by grafting aminosilanes on the surface. The modifications were performed by covalently bonding 3-triethoxysilylpropylamine (APTES) or 3-(2-aminoethylamino) propyldimethoxymethylsilane (AEAPMS) on thermally oxidized PSi (TOPSi) and thermally carbonized PSi (TCPSi). These materials were systematically characterized with N2 ad/desorption, TEM, contact angle, zeta potential, FT-IR, 29Si CP/MAS NMR, and elemental analysis. To evaluate their application potentials, a fluorescent dye, fluorescein 5-isothiocyanate (FITC), was coupled on the surface of amine-modified nanoparticles. The effects of PSi matrix and surface amino groups on FITC coupling efficiency, fluorescent intensity, and the stability of fluorescence in simulated body fluid (SBF) were investigated. The nanoparticles modified with AEAPMS had higher FITC coupling efficiency than those modified with APTES. FITC-coupled TOPSi nanoparticles also possessed brighter fluorescence and better fluorescent stability in SBF. Furthermore, due to the protection caused by the mesoporous structure of PSi nanoparticles, the FITC-coupled TOPSi nanoparticles showed superior photostability in photobleaching experiment.
Oxidation of Si(111) surfaces is a procedure widely used for their further functionalization with 3-aminopropyltriethoxysilane (APTES). In the present work, the formation of silicon oxide is carried out by chemical and electrochemical oxidation of the hydrogenated-silicon surfaces, giving rise to Si-OxChem and Si-OxEchem surfaces, respectively. Both surfaces are then functionalized with APTES solution to form an aminopropylsilane (APS) film, using two quite different concentrations of APTES (0.001 and 0.1% v/v), to compare two limiting situations. At the lowest APTES concentration, the comparison of the kinetics of gold nanoparticles (AuNPs) anchoring process on both surfaces is found to be quite different, not only in the initial rate of NPs anchoring but also in the maximum percentage of coverage. In contrast, the kinetics behavior is almost the same when the surfaces are modified with the highest APTES concentration, reaching the same value of surface coverage. The different or similar behavior of both surfaces is analyzed by a careful characterization of Si-OxChem and Si-OxEchem surfaces using XP spectroscopy and AFM measurements, before and after APS functionalization. The significant differences in the surface roughness of the Si-Ox samples, together with the determination of the number of −NH3+ moieties after silanization at both APTES concentrations, leads to the conclusion that the availability of −NH3+ moieties is dependent on two factors: the roughness of the Si-OxChem and Si-OxEchem surfaces as well as the concentration of the APTES solutions. When the APS layer is formed at the lowest APTES concentration, surface roughness controls the number of different types of nitrogen functional groups. In contrast, at the highest APTES concentration, the surface roughness does not have any significant role in the number of −NH3+ moieties present on both surfaces. Because the kinetics of AuNPs anchoring depends mainly on the probability of interacting with the −NH3 + groups, the above characterization allows us to explain in a consistent way the kinetics behavior observed for each particular condition of surface preparation.
A comparative study is presented of the hydrolytic and thermal stability of 24 different kinds of monolayers on Si(111), Si(100), SiC, SiN, SiO2, CrN, ITO, PAO, Au, and stainless steel surfaces. These surfaces were modified utilizing appropriate organic compounds having a constant alkyl chain length (C18), but with different surface-reactive groups, such as 1-octadecene, 1-octadecyne, 1-octadecyltrichlorosilane, 1-octadecanethiol, 1-octadecylamine and 1-octadecylphosphonic acid. The hydrolytic stability of obtained monolayers was systematically investigated in triplicate in constantly flowing aqueous media at room temperature in acidic (pH 3), basic (pH 11), phosphate buffer saline (PBS) and deionized water (neutral conditions), for a period of 1 day, 7 days, and 30 days, yielding 1152 data points for the hydrolytic stability. The hydrolytic stability was monitored by static contact angle measurements and X-ray photoelectron spectroscopy (XPS). The covalently bound alkyne monolayers on Si(111), Si(100), and SiC were shown to be among the most stable monolayers under acidic and neutral conditions. Additionally, the thermal stability of 14 different monolayers was studied in vacuum using XPS at elevated temperatures (25-600 °C). Similar to the hydrolytic stability, the covalently bound both alkyne and alkene monolayers on Si(111), Si(100) and SiC started to degrade from temperatures above 260 °C, whereas on oxide surfaces (e.g., PAO) phosphonate monolayers even displayed thermal stability up to ∼500 °C.
Much of the microelectronic industry and many uses of silicon are based on the stability of silicon oxide and the electrical quality of its interface with the silicon substrate. It is natural therefore to have focused on functionalizing silicon by grafting molecules on its oxide. However, severe issues are associated with organic functionalization of silicon oxide, such as reproducibility in grafting the layers and quality and stability of these layers once grafted. These problems have stimulated recent efforts to prepare and functionalize high quality oxide-free silicon surfaces. In this review, methods for transforming such oxide-free, hydrogen-terminated silicon surfaces are presented, including hydrosilylation (the formation of silicon carbon bonds) and direct replacement of hydrogen by reactive leaving groups (halogens, methoxy, and hydroxyl). These efforts are based on a number of complementary characterization methods, such as infrared absorption and x-ray photoelectron spectroscopy, low energy ion scattering, and capacitance/current voltage measurements. In contrast to previous work on the subject, the focus of this review is on controlled defects on Si(111) surfaces with aim to better understand the surface structure of silicon nanoparticles, the smallest Si object with the highest number of defects. To that end, sections on preparation and selective functionalization of stepped silicon surfaces are included, and the current characterization and understanding of silicon nanoparticles added. The outlook on where the field may be going is presented.
The hydrolysis and condensation reactions of -APS have been studied in different acid content aqueous solution by using Fourier Transform infrared (FT-IR) spectroscopy. The hydrolysis of -APS under the studied conditions can be followed by the increase of the ethanol band located at 882 cm−1 and the decrease of the band due to the (CH3) of -APS molecules located at 959 cm−1. Hydrolysis reaction is faster by increasing both H2O and acid concentrations, and it is completed when 3 moles of H2O per mole of -APS are used. The increase of the vibrational band located at 1146 cm−1 shows that condensation of the hydrolysed -APS molecules take place forming linear chains in poorly cross-linked structures. Besides, both 8-membered cyclic siloxane formations and poorly cross-linked structures are formed and increase as the water and acid content are increased. On the other hand, highly connected cross-linked structures do not appear due to the steric hindrance of the non-hydrolysable aminopropyl group. The silanol band shows that hydrolysis is faster than condensation except for samples with the lowest H2O content.
The detection of biological and chemical species is central to many areas of healthcare and the life sciences, ranging from uncovering and diagnosing disease to the discovery and screening of new drug molecules. Hence, the development of new devices that enable direct, sensitive, and rapid analysis of these species could impact humankind in significant ways. Devices based on nanowires are emerging as a powerful and general class of ultrasensitive, electrical sensors for the direct detection of biological and chemical species.
Organic nanowires self-assembled from small-molecule semiconductors and conducting polymers have attracted an enormous amount of interest for use in organic field-effect transistors. This new class of materials offers solution processability, the potential for elucidating transport mechanisms and structure-property relationships, and the realization of high-performance transistors that rival the performance of amorphous Si. We discuss the self-assembly of one-dimensional, single-crystalline organic nanowires, show the structures of commonly employed organic semiconductors, and review some of the advances in this field.
Boron-doped silicon nanowires (SiNWs) were used to create highly sensitive, real-time electrically based sensors for biological
and chemical species. Amine- and oxide-functionalized SiNWs exhibit pH-dependent conductance that was linear over a large
dynamic range and could be understood in terms of the change in surface charge during protonation and deprotonation. Biotin-modified
SiNWs were used to detect streptavidin down to at least a picomolar concentration range. In addition, antigen-functionalized
SiNWs show reversible antibody binding and concentration-dependent detection in real time. Lastly, detection of the reversible
binding of the metabolic indicator Ca2+ was demonstrated. The small size and capability of these semiconductor nanowires for sensitive, label-free, real-time detection
of a wide range of chemical and biological species could be exploited in array-based screening and in vivo diagnostics.
Semiconducting nanowires have the potential to function as highly sensitive and selective sensors for the label-free detection of low concentrations of pathogenic microorganisms. Successful solution-phase nanowire sensing has been demonstrated for ions, small molecules, proteins, DNA and viruses; however, 'bottom-up' nanowires (or similarly configured carbon nanotubes) used for these demonstrations require hybrid fabrication schemes, which result in severe integration issues that have hindered widespread application. Alternative 'top-down' fabrication methods of nanowire-like devices produce disappointing performance because of process-induced material and device degradation. Here we report an approach that uses complementary metal oxide semiconductor (CMOS) field effect transistor compatible technology and hence demonstrate the specific label-free detection of below 100 femtomolar concentrations of antibodies as well as real-time monitoring of the cellular immune response. This approach eliminates the need for hybrid methods and enables system-scale integration of these sensors with signal processing and information systems. Additionally, the ability to monitor antibody binding and sense the cellular immune response in real time with readily available technology should facilitate widespread diagnostic applications.
A site-binding model of the oxide/aqueous electrolyte interface is introduced, in which it is proposed that the adsorbed counter ions form interfacial ion pairs with discrete charged surface groups. This model is used to calculate theoretical surface charge densities of the potential-determining (H+/OH–) ions and the potential at the Outer Helmholtz Plane, which are shown to be consistent with experimental data for oxides. An explanation is provided for the difference between silica and most other oxides in terms of the dissociation constants of the surface hydroxyl groups.
Highly sensitive and sequence-specific DNA sensors were fabricated based on silicon nanowires (SiNWs) with single stranded (ss) probe DNA molecules covalently immobilized on the nanowire surfaces, Label-free complementary (target) ss-DNA in sample solutions were recognized when the target DNA was hybridized with the probe DNA attached on the SiNW surfaces, producing a change of the conductance of the SiNWs. For a 12-mer oligonucletide probe, 25 pM of target DNA in solution was detected easily (signal/noise ratio > 6), whereas 12-mers with one base mismatch did not produce a signal above the background noise.
A simple route to ω-aminoalkyltriethoxysilanes with variable alkylene chain lengths, (EtO)3Si(CH2)nNH2 (n=5,11) is described. These silyl linkers have been used to prepare urea-based compounds with H-bonding and hydrophobic interactions which enable the self-assembly of the molecules. These molecular precursors are suitable for the obtention of nano-structured hybrid silicas.
The presence of mobile Na+ and K+ ions in biological solutions often lead to instabilities in metal-oxide-semiconductor devices and is therefore an important consideration in developing sensor technologies. Permanent hysteresis is observed on silicon-on-insulator field-effect-transistors based sensors after exposure to Na+-based buffer solutions but not after exposure to K+-based solutions. This behavior is attributed to the difference in mobilities of the ions in silicon dioxide. Mobile charge measurements confirm that ions can be transferred from the solution into the oxide. Self-assembled monolayers are shown to provide protection against ion diffusion, preventing permanent hysteresis of the sensors after exposure to solutions.
The thermal behavior of alkyltrichlorosilane (CH3(CH2)n-1SiCl3) based self-assembled monolayers on the oxidized Si(100) surface has been examined under ultrahigh vacuum conditions for n = 4, 8, and 18. Using high-resolution electron energy loss spectroscopy and contact angle analysis, it is found that the monolayers are stable in vacuum up to about 740 K independent of chain length. Above 740 K the chains begin to decompose through C−C bond cleavage, resulting in the desorption of hydrocarbon fragments. Following this initial desorption step, methyl groups attached to silicon atoms are observed. The siloxane head groups remain on the surface following decomposition of the monolayers until about 1100 K.
In order to understand the mechanism of biosensing of field-effect-based biosensors and optimize their performance, the effect of each of its molecular building blocks must be understood. In this work the effect of the self-assembled linker molecules on the top of a biofield-effect transistor was studied in detail. We have combined Kelvin probe force microscopy, current−voltage measurements, and device simulations in order to trace the mechanism of silicon-on-insulator biological field-effect transistors. The measurements were conducted on the widely used linker molecules (3-aminopropyl)trimethoxysilane (APTMS) and (11-aminoundecyl)triethoxysilane (AUTES), which were self-assembled on an ozone-activated silicon oxide surface covering the transistor channel. The work function of the modified silicon oxide decreased by more then 1.5 eV, while the transistor threshold voltage increased by about 30 V following the self-assembly. A detailed analysis indicates that these changes are due to negative-induced charges on the top dielectric layer, and an effective dipole due to the polar monolayer. The results were compared with metal gated transistors fabricated on the same die, and a factor converting the molecular charge to the metal gate voltage was extracted.
Monolayer assemblies on n-alkyl thiols (CH3(CH2)nSH where n = 1, 3, 5, 7, 9, 11, 15, 17, and 21), adsorbed on gold from dilute solution, have been characterized by optical ellipsometry, infrared (IR) spectroscopy, and electrochemistry. All three techniques show that there are distinct differences in structure between long- and short-chain thiol monolayers. The value of n for the sharpest change varies between 5 and 11 depending upon the specific measurement. The IR spectroscopic and ellipsometric data indicate that the long-chain thiols form a densely packed, crystalline-like assembly with fully extended alkyl chains tilted from the surface normal by 20-30°. As the chain length decreases, the structure becomes increasingly disordered with lower packing density and coverage. Electrochemical measurements of heterogeneous electron-transfer rates and of differential capacitance indicate that the long-chain monolayers are free of measurable pin holes, provide substantial barriers to electron transfer, and are strongly resistant to ion penetration. In contrast, with decreasing chain length the barrier properties become weaker. Taken together, these results demonstrate that monolayer assemblies of long-chain thiols on gold have significant potential as model systems for studies of heterogeneous electron transfer, ion transport, and double-layer phenomena.
The C-H stretching modes of the conformationally disordered polymethylene chain are analyzed. Fermi resonance interaction involving HCH bending overtones is dominant in determining the shape of the Raman C-H stretching spectrum. In addition, however, we have found that the C-H stretching frequencies are significantly affected by the conformation of adjoining C-C bonds. The estimated magnitude of this dependence is consistent with the shifts to higher frequencies that are observed upon melting n-alkanes and that have been reported for the infrared spectra of lipid bilayers in going through the main phase transition to the liquid crystal. However, similarities between the C-H stretching spectra of the ordered and disordered chains indicate that the small frequency dispersion observed for these modes in the crystal is, in part, maintained in the disordered chain, a conclusion that is supported by a simplified vibrational analysis. The effects of Fermi resonance interaction on the spectra of the disordered and ordered chain are also similar. The band near 2930 cm -1 observed in hydrocarbon chain systems containing methyl groups is a composite of two overlapping bands, one from the polymethylene chain (2922 cm -1) and one from the methyl group (2938 cm -1). The 2922-cm -1 component is affected by chain conformation while the 2938-cm -1 component is affected by the solvent. The distinction between the behavior of these bands is important since the peak-intensity ratio I 2930/I 2850 is commonly used to interpret the structure of hydrocarbon assemblies.
Principal goals in organic thin-film transistor (OTFT) gate dielectric research include achieving: (i) low gate leakage currents and good chemical/thermal stability, (ii) minimized interface trap state densities to maximize charge transport efficiency, (iii) compatibility with both p- and n- channel organic semiconductors, (iv) enhanced capacitance to lower OTFT operating voltages, and (v) efficient fabrication via solution-phase processing methods. In this Review, we focus on a prominent class of alternative gate dielectric materials: self-assembled monolayers (SAMs) and multilayers (SAMTs) of organic molecules having good insulating properties and large capacitance values, requisite properties for addressing these challenges. We first describe the formation and properties of SAMs on various surfaces (metals and oxides), followed by a discussion of fundamental factors governing charge transport through SAMs. The last section focuses on the roles that SAMs and SAMTs play in OTFTs, such as surface treatments, gate dielectrics, and finally as the semiconductor layer in ultra-thin OTFTs.
Magnetite nanoparticles coated with (3-aminopropyl)triethoxysilane, NH2(CH2)3Si(OC2H5)3, were prepared by silanization reaction and characterized by X-ray diffractometry, transmission electron microscopy, atomic force microscopy, Fourier transform infrared spectroscopy and magnetization measurements. Both uncoated and organosilane-coated magnetite exhibited superparamagnetic behavior and strong magnetization at room temperature. Basic groups anchored on the external surface of the coated magnetite were observed. The superparamagnetic particles of coated magnetite are able to bind to biological molecules, drugs and metals and in this way remove them from medium by magnetic separation procedures.
In order to understand the biosensing mechanism of field-effect based biosensors and optimize their performance, the effect of each of its molecular building block must be understood. In this work the gating effect of self-assembled linker molecules on field-effect transistor was studied in detail. We have combined Kelvin probe force microscopy, current–voltage measurements, capacitance–voltage measurements, equivalent circuit modeling and device simulations in order to trace the mechanism of silicon-on-insulator biological field-effect transistors. The measurements were conducted on the widely used linker molecules (3-aminopropyl)-trimethoxysilane (APTMS) and 11-aminoundecyl-triethoxysilane (AUTES), which were self-assembled on ozone activated silicon oxide surface covering the transistor channel. In a dry environment, the work function of the modified silicon oxide decreased by more than 1.5 eV, and the transistor threshold voltage increased by about 30 V following the self-assembly. A detailed analysis indicates that these changes are due to negative induced charges on the top dielectric layer, and an effective dipole due to the polar monolayer. However, the self-assembly did not change the silicon flat-band voltage when in contact with an electrolyte. This is attributed to electrostatic screening by the electrolyte.
Chemical functionalization of silicon oxide (SiO(2)) surfaces with silane molecules is an important technique for a variety of device and sensor applications. Quality control of self-assembled monolayers (SAMs) is difficult to achieve because of the lack of a direct measure for newly formed interfacial Si-O bonds. Herein we report a sensitive measure of the bonding interface between the SAM and SiO(2), whereby the longitudinal optical (LO) phonon mode of SiO(2) provides a high level of selectivity for the characterization of newly formed interfacial bonds. The intensity and spectral position of the LO peak, observed upon silanization of a variety of silane molecules, are shown to be reliable fingerprints of formation of interfacial bonds that effectively extend the Si-O network after SAM formation. While the IR absorption intensities of functional groups (e.g., >C=O, CH(2)/CH(3)) depend on the nature of the films, the blue-shift and intensity increase of the LO phonon mode are common to all silane molecules investigated and their magnitude is associated with the creation of interfacial bonds only. Moreover, results from this study demonstrate the ability of the LO phonon mode to analyze the silanization kinetics of SiO(2) surfaces, which provides mechanistic insights on the self-assembly process to help achieve a stable and high quality SAM.
Molecular electronics is an attractive option for low-cost devices because it involves highly uniform self-assembly of molecules with a variety of possible functional groups. However, the potential of molecular electronics can only be turned into practical applications if reliable contacts can be established without damaging the organic layer or contaminating its interfaces. Here, a method is described to prepare tightly packed carboxyl-terminated alkyl self-assembled monolayers (SAMs) that are covalently attached to silicon surfaces and to deposit thin metallic copper top contact electrodes without damage to this layer. This method is based on a two-step procedure for SAM preparation and the implementation of atomic layer deposition (ALD) using copper di-sec-butylacetamidinate [Cu(sBu-amd)](2). In situ and ex situ infrared spectroscopy (IRS), X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), and electrical measurements are used to characterize the chemical modification of the Si/SAM interface, the perturbation of the SAM layer itself, and the metal homogeneity and interaction with the SAM headgroups. This work shows that (i) carboxyl-terminated alkyl monolayers can be prepared with the same high density and quality as those achieved for less versatile methyl-terminated alkyl monolayers, as evidenced by electrical properties that are not dominated by interface defects; (ii) Cu is deposited with ALD, forming a bidentate complexation between the Cu and the COOH groups during the first half cycle of the ALD reaction; and (iii) the Si/SAM interface remains chemically intact after metal deposition. The nondamaging thin Cu film deposited by ALD protects the SAM layer, making it possible to deposit a thicker metal top contact leading ultimately to a controlled preparation of molecular electronic devices.
This Article describes a facile method to prepare smooth and homogeneous polymer brush surfaces of variable grafting density from a solid surface by combining Langmuir-Blodgett (LB) deposition with surface-initiated atom transfer radical polymerization (SI-ATRP). This method is successfully demonstrated by the preparation of thermoresponsive poly(N-isopropylacrylamide) (PNIPAM) brush surfaces on smooth silicon and quartz substrates. With the custom-synthesized inert diluent whose chemical structure, except end-functionality, is the same as that of the reactive initiator, smooth and chemically homogeneous mixed monolayers of initiators and inert diluents are immobilized on a solid surface by LB deposition, allowing the further variation of the grafting density of PNIPAM brushes grafted from the initiator monolayers of varied initiator coverage. With the optimized molar ratio of deactivator, Cu(II) in the Cu(I)-ligand catalyst complex, the brush thickness of PNIPAM brushes at varied grafting density is controlled to grow nearly linearly with reaction time while smoothness and chemical homogeneity of PNIPAM brushes are achieved. For the demonstrated PNIPAM brush surfaces, the thermoresponsive characteristics of PNIPAM brushes are also verified. This combined LB-ATRP method can be applied to graft a variety of polymer brushes, including polyelectrolytes and block copolymers, from different solid substrates.
A dendrimer-modified nanopipette is used to detect hybridization of a specific DNA sequence through evaluation of the extent of rectification of ion currents observed in the measured current-voltage response.
Biotinylation of silicon oxide surfaces, surface stability, and evolution of these functionalized surfaces under biospecific attachment of streptavidin were studied using Fourier transform infrared spectroscopy. Adsorption and stability of species or changes in the resulting surfaces were monitored after each step of the attachment processes. The silicon oxide surface was initially derivatized by 3-aminopropyltriethoxysilane, and the quality of the 3-aminopropylsiloxane (APS) surface was monitored using the Si-O-Si and Si-O-C region of its vibrational spectrum. A strong correlation between surface quality and presilanization atmospheric moisture content was established. The vibrational fingerprint of biotinylation was determined, both for physisorption and chemisorption to the surface. A new band (i.e., not previously associated with biotin) at approximately 1250 cm(-1) was identified as a vibrational mode of the biotin ureido group, making it possible to track changes in the biotinylated surface in the presence of streptavidin. Some of the biotin ureido at the surface was found to be affected by the protein adsorption and rinse steps while remaining chemisorbed to the surface. The stability of the APS was found to impact the behavior of the biotinylated surface (measured using the Si-O-Si/Si-O-C and approximately 1250 cm(-1) absorption bands, respectively).
In this paper, we report a new label-free method for the imaging of immobilized oligonucleotide probes on DNA microarrays. The imaging principle is based on the disruption of orientations of nematic liquid crystals (LCs), 4-cyano-4'-pentylbiphenyl (5CB), by the immobilized oligonucleotides on a surface. Because LCs are birefringent materials, disruption of their orientations by the immobilized oligonucleotides can manifest as optical signals visible to the naked eye. LC cells with two homeotropic boundary conditions, which align 5CB perpendicularly to both surfaces, were developed to deliver a distinct contrast between a dark background and a bright image caused by the immobilized oligonucleotides. This design also allows the quantification of immobilized oligonucleotide concentrations through the interference colors of LCs. The LC-based imaging method has a good signal-to-noise ratio and a clear distinction between positive and negative results and is nondestructive to the immobilized oligonucleotides. These advantages make it a promising means of assessing the quality of DNA microarrays.
Various samples of aminopropyl-functionalized silica (APS) have been prepared by grafting an organosilane precursor 3-aminopropyl-triethoxysilane (APTES) onto the surface of silica gel. The amine group content of the materials has been adjusted by varying the amount of APTES in the reaction medium (toluene). The grafted APS solids have been characterized with using several analytical techniques (N(2) adsorption, X-ray photoelectron spectroscopy, infrared spectrometry) to determine their physico-chemical properties. Their reactivity in aqueous solutions was studied by acid-base titration, via protonation of the amine groups, and by way of complexation of these groups by Hg(II) species. APS stability in aqueous medium was investigated at various pH and as a function of time, by the quantitative analysis of soluble Si- or amine-containing species that have been leached in solution upon degradation of APS. The chemical stability was found to increase when decreasing pH below the pK(a) value corresponding to the RNH(3)(+)/RNH(2) couple, but very low pH values were necessary to get long-term stability because of the high local concentration of the amine groups in the APS materials. Adsorption of mercury(II) ions on APS was also performed to confirm the long-term stability of the grafted solid in acidic medium. Relationship between solution pH and APS stability was discussed. For sake of comparison, the stability of APS in ethanol and that of mercaptopropyl-grafted silica (MPS) in water have been briefly considered and discussed with respect to practical applications of silica-based organic-inorganic hybrids, e.g., in separation science or in the field of electrochemical sensors.
Parameters important to the self-assembly of 3-(aminopropyl)triethoxysilane (APTES) on chemically grown silicon oxide (SiO 2) to form an aminopropyl silane (APS) film have been investigated using in situ infrared (IR) absorption spectroscopy. Preannealing to approximately 70 degrees C produces significant improvements in the quality of the film: the APS film is denser, and the Si-O-Si bonds between the molecules and the SiO 2 surface are more structured and ordered with only a limited number of remaining unreacted ethoxy groups. In contrast, post-annealing the functionalized SiO 2 samples after room temperature reaction with APTES (i.e., ex situ annealing) does not lead to any spectral change, suggesting that post-annealing has no strong effect on the horizontal polymerization as suggested earlier. Both IR and ellipsometry data show that the higher the solution temperature, the denser and thinner the APS layer is for a given immersion time. Finally, the APS layer obtained by preannealing the solution at 70 degrees C exhibits a better stability in deionized water than the APS layer prepared at room temperature.
A new solid-state device has been developed for the measurement of ion activities in electrochemical and biological environments. One can recognize in the device the properties of both a glass electrode and a field-effect transistor. This justifies the name ion-sensitive field-effect transistor. The device makes it possible to measure ion activities without using a reference electrode. For its application, a special electronic circuit is described. Results of measured Na+ and H+ ion activities are given in detail. As an example for electrophysiological application, results are shown of recorded extracellular ion pulses measured with a guinea pig taenia coli.
Considerable attention has been drawn during the last two decades to functionalize noble metal surfaces by forming ordered organic films of few nm to several hundred-nm thickness. Self-assembled monolayer (SAM) provides one simple route to functionalize electrode surfaces by organic molecules (both aliphatic and aromatic) containing free anchor groups such as thiols, disulphides, amines, silanes, or acids. The monolayer produced by self-assembly allows tremendous flexibility with respect to several applications depending upon their terminal functionality (hydrophilic or hydrophobic control) or by varying the chain length (distance control). For example, SAM of long chain alkane thiol produces a highly packed and ordered surface, which can provide a membrane like microenvironment, useful for immobilising biological molecules. The high selectivity of biological molecules integrated with an electrochemical, optical or piezoelectric transduction mode of analyte recognition offers great promise to exploit them as efficient and accurate biosensors. It is demonstrated with suitable examples that monolayer design plays a key role in controlling the performance of these SAM based biosensors, irrespective of the immobilisation strategy and sensing mechanism.
Cell shapes induced by cell-substratum interactions are linked with proliferation, differentiation or apoptosis of cells. To clarify the relevance of specific surface characteristics, we applied self-assembled monolayers (SAM) of alkyl silanes exhibiting a variety of terminating functional groups. We first characterised the SAMs on glass or silicon wafers by measuring wettability, layer thickness and roughness. Water contact angle data revealed that methyl (CH(3)), bromine (Br), and vinyl (CH=CH(2)) groups lead to hydrophobic surfaces, while amine (NH(2)) and carboxyl (COOH) functions lead to moderately wettable surfaces, and polyethylene glycol (PEG) and hydroxyl (OH) groups created wettable substrata. The surfaces were found to be molecular smooth except for one type of NH(2) surface. The SDS-PAGE analysis of proteins adsorbed from bovine serum to the SAMs showed less protein adsorption to PEG and OH than to CH(3), NH(2) and COOH. Immunoblotting revealed that a key component of adsorbed proteins is vitronectin while fibronectin was not detectable. The interaction of human fibroblasts with CH(3), PEG and OH terminated SAMs was similarly weak while strong attachment, spreading, fibronectin matrix formation and growth were observed on COOH and NH(2). The strong interaction of fibroblasts with the latter SAMs was linked to an enhanced activity of integrins as observed after antibody-tagging of living cells.
Devices based on nanowires are emerging as a powerful platform for the direct detection of biological and chemical species, including low concentrations of proteins and viruses.
We study the effect of monolayer quality on the electrical transport through n-Si/C(n)H(2n+1)/Hg junctions (n = 12, 14, and 18) and find that truly high quality layers and only they, yield the type of data, reported by us in Phys. Rev. Lett. 2005, 95, 266807, data that are consistent with the theoretically predicted behavior of a Schottky barrier coupled to a tunnel barrier. By using that agreement as our starting point, we can assess the effects of changing the quality of the alkyl monolayers, as judged from ellipsometer, contact angle, XPS, and ATR-FTIR measurements, on the electrical transport. Although low monolayer quality layers are easily identified by one or more of those characterization tools, as well as from the current-voltage measurements, even a combination of characterization techniques may not suffice to distinguish between monolayers with minor differences in quality, which, nevertheless, are evident in the transport measurement. The thermionic emission mechanism, which in these systems dominates at low forward bias, is the one that is most sensitive to monolayer quality. It serves thus as the best quality control. This is important because, even where tunneling characteristics appear rather insensitive to slightly diminished quality, their correct analysis will be affected, especially if layers of different lengths are also of different quality.
Detection and quantification of biological and chemical species are central to many areas of healthcare and the life sciences, ranging from diagnosing disease to discovery and screening of new drug molecules. Semiconductor nanowires configured as electronic devices have emerged as a general platform for ultra-sensitive direct electrical detection of biological and chemical species. Here we describe a detailed protocol for realizing nanowire electronic sensors. First, the growth of uniform, single crystal silicon nanowires, and subsequent isolation of the nanowires as stable suspensions are outlined. Second, fabrication of addressable nanowire device arrays is described. Third, covalent modification of the nanowire device surfaces with receptors is described. Fourth, an example modification and measurements of the electrical response from devices are detailed. The silicon nanowire (SiNW) devices have demonstrated applications for label-free, ultrasensitive and highly-selective real-time detection of a wide range of biological and chemical species, including proteins, nucleic acids, small molecules and viruses.
The charge coupling between the front and back gates of thin-film silicon-on-insulator (SOI: e.g,, recrystallized Si on SiO 2 ) MOSFET's is analyzed, and closed-form expressions for the threshold voltage under all possible steady-state conditions are derived. The expressions clearly show the dependence of the linear-region channel conductance on the back-gate bias and on the device parameters, including those of the back silicon-insulator interface. The analysis is supported by current-voltage measurements of laser-recrystallized SOI MOSFET's. The results suggest how the back-gate bias may be used to optimize the performance of the SOI MOSFET in particular applications.
- Hafeman