Article

Tuning the Resonant Frequency of Resonators Using Molecular Surface Self-assembly Approach

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Abstract

In this work, a new method to tune the resonant frequency of micro-fabricated resonator using molecular layer-by-layer (LbL) self-assembly approach is demonstrated. By simply controlling the polymer concentration and the number of layers deposited, precisely tuning the frequency of micro-fabricated resonators is realized. Due to its selective deposition through specific molecular recognitions, such technique avoids the high-cost and complex steps of conventional semiconductor fabrications and is able to tune individual diced device. Briefly, Film Bulk Acoustic Resonator (FBAR) is used to demonstrate the tuning process and two types of LbL deposition methods are compared. The film thickness and morphology have been characterized by UV-vis reflection spectra, ellipsometer and AFM. As a result, the maximum resonant frequency shift of FBAR reaches more than 20 MHz, meaning 1.4% tunability at least. The minimum frequency shift is nearly 10 kHZ per bilayer, indicating 7 ppm tuning resolution. Besides, Pressure Cooker Test (PCT) is performed to evaluate the reliability of LbL coated FBAR. Furthermore, applications for wireless broadband communication and chemical sensors of LbL coated FBAR have been demonstrated.

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... More recently, Henze et al. [381] demonstrated a post-production hydrofluoric acid etching process for fine-tuning microresonators to reach an arbitrary frequency, and a controllable resonant frequency 10 GHz was observed using this effective approach. More recently, Liu et al. [382] presented a new method to tune the resonant frequency of microfabricated film bulk acoustic resonator (FBAR) using molecular layer-by-layer (LbL) self-assembly approach for wireless broadband communication, as shown in Figure 35. The maximum resonant frequency shift of FBAR reaches more than 20 MHz, meaning 1.4% tunability at least. ...
... Figure 35. Frequency tuning of microresonator using molecular LbL self-assembly approach reported by Liu et al. [382]. Optical microscope images of the FBAR filter (a) before and (b) after LbL assembly. ...
... Electrical performance of (c) wide band and (d) pass band (red) before and (blue) after LbL assembly. Reused with permission from [382], Copyright 2015, American Chemical Society. ...
Article
Advances in micro- and nanofabrication technologies have enabled the development of novel micro- and nanomechanical resonators which have attracted significant attention due to their fascinating physical properties and growing potential applications. In this review, we have presented a brief overview of the resonance behavior and frequency tuning principles by varying either the mass or the stiffness of resonators. The progress in micro- and nanomechanical resonators using the tuning electrode, tuning fork, and suspended channel structures and made of graphene have been reviewed. We have also highlighted some major influencing factors such as large-amplitude effect, surface effect and fluid effect on the performances of resonators. More specifically, we have addressed the effects of axial stress/strain, residual surface stress and adsorption-induced surface stress on the sensing and detection applications and discussed the current challenges. We have significantly focused on the active and passive frequency tuning methods and techniques for micro- and nanomechanical resonator applications. On one hand, we have comprehensively evaluated the advantages and disadvantages of each strategy, including active methods such as electrothermal, electrostatic, piezoelectrical, dielectric, magnetomotive, photothermal, mode-coupling as well as tension-based tuning mechanisms, and passive techniques such as post-fabrication and post-packaging tuning processes. On the other hand, the tuning capability and challenges to integrate reliable and customizable frequency tuning methods have been addressed. We have additionally concluded with a discussion of important future directions for further tunable micro- and nanomechanical resonators.
... The gravimetric-based measurement leads to a sensing signal, which carries information about the adsorption of analytes [24]. In recent years, rapid progress has been made in the field of gas sensing using thin film bulk acoustic resonators (FBARs) [25][26][27][28][29]. Due to their GHz-level resonant frequency and high quality-factor, FBARs show higher sensitivity than conventional acoustic wave devices [30,31]. ...
... As shown in Figure 2f-j, the 2.44 GHz FBAR was fabricated with a standard microelectromechanical system (MEMS) fabrication process as described before [26]. First, an air cavity was etched on a single-side polished silicon wafer by deep reactive ion etching (DRIE). ...
Article
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In this paper, we develop a novel dual-mode gas sensor system which comprises a silicon nanoribbon field effect transistor (Si-NR FET) and a film bulk acoustic resonator (FBAR). We investigate their sensing characteristics using polar and nonpolar organic compounds, and demonstrate that polarity has a significant effect on the response of the Si-NR FET sensor, and only a minor effect on the FBAR sensor. In this dual-mode system, qualitative discrimination can be achieved by analyzing polarity with the Si-NR FET and quantitative concentration information can be obtained using a polymer-coated FBAR with a detection limit at the ppm level. The complementary performance of the sensing elements provides higher analytical efficiency. Additionally, a dual mixture of two types of freons (CFC-113 and HCFC-141b) is further analyzed with the dual-mode gas sensor. Owing to the small size and complementary metal-oxide semiconductor (CMOS)-compatibility of the system, the dual-mode gas sensor shows potential as a portable integrated sensing system for the analysis of gas mixtures in the future.
... As shown in Figure 2e-g, FBAR was first exposed to the air plasma for 5 min to form hydroxyl groups on a passivation layer [23], followed by amino-silanization with APTES in a chemical gas deposition system (Yield Engineering Systems, Inc., Livermore, CA, USA). Then we adopted both dipping-assisted and spinning-assisted methods to realize the molecular surface self-assembly of PETs in a layer-by-layer fashion. ...
... Since PET thin films are not rigid films, excessive assembly of PSS/PDDA bilayers on FBAR surface leads to the dissipation of acoustic energy from the piezoelectric layer, which causes the loss of quality factor, resulting in the consequent decrease of sensitivity. Additionally, the classic Sauerbrey equation is valid only when the maximum mass load of PET thin films does not exceed two percent of the resonant frequency [23]. Therefore, we controlled the frequency shift resulting from the PET assembly within 1.44 × 10 9 Hz × 2% = 2.88 × 10 7 Hz. Figure 6 displays the frequency shift of FBAR and the thickness growth of PSS/PDDA films during the molecular surface assembly on FBAR surface. ...
Article
We developed a highly sensitive humidity sensor based on the combination of ultrahigh-frequency film bulk acoustic resonator (FBAR) and nano-assembled polyelectrolyte (PET) thin films. The water molecule absorption efficiency was optimized by forming loosely-packed PET nanostructures. Then, the humidity sensing characteristics were analyzed in terms of sensitivity, linearity, reversibility, stability and detection limit. As a result, PET-coated FBAR exhibits excellent humidity sensitivity of 2202.20 Hz/ppm, which is five orders of magnitude higher than quartz crystal microbalance (QCM). Additionally, temperature dependence was investigated with the result that PET-coated FBAR possessed a higher sensitivity at low temperature. Furthermore, we realized the selective detection of water vapor from volatile organic compounds (VOCs) with respect to the polarity property. Owing to the high sensitivity, miniaturized size and ultrahigh operating frequency, PET-coated FBAR is uniquely favorable as a wireless humidity sensor node to integrate into wireless sensor networks (WSNs).
... It has been demonstrated that LbL assembly of poly(acrylic acid) (PAA) and poly(4vinylpyridine) (PVP) on the FBAR surface could be used in tuning the resonance frequency of devices. Moreover, the LbL polymer coating offered a direct method for modification of the FBAR surface and facilitation of VOC sensing applications (Liu et al. 2014). ...
... Device fabrication. The 4.44 GHz FBARs in this work (shown in Fig. S8) were conveniently fabricated by a standard MEMS fabrication process as described before 53 . In brief, an air cavity was initially generated on a single-side polished silicon wafer by deep reactive ion etching (DRIE). ...
Article
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In this paper, we have modeled and analyzed affinities and kinetics of volatile organic compounds (VOCs) adsorption (and desorption) on various surface chemical groups using multiple self-assembled monolayers (SAMs) functionalized film bulk acoustic resonator (FBAR) array. The high-frequency and micro-scale resonator provides improved sensitivity in the detections of VOCs at trace levels. With the study of affinities and kinetics, three concentration-independent intrinsic parameters (monolayer adsorption capacity, adsorption energy constant and desorption rate) of gas-surface interactions are obtained to contribute to a multi-parameter fingerprint library of VOC analytes. Effects of functional group's properties on gas-surface interactions are also discussed. The proposed sensor array with concentration-independent fingerprint library shows potential as a portable electronic nose (e-nose) system for VOCs discrimination and gas-sensitive materials selections.
... As a result, the mass of PAH in the first PETs bilayer is 9.89 μg/m 2 , considering the fitted value of is 0.66 F/m 2 (see Supporting Information). In case of the SMR, the mass assembled on sensing surface is determined by the classic Sauerbrey Eq. (5)[40]: ...
Article
The advancement in micro/nanotechnologies has been continuously providing possibilities for inventing novel biochemical sensors. However, variations in the transducer type can cause different sensing results due to the differences in their mechanisms of analyzing biomolecular interactions. In this work, we focused on the comparative analysis of static and non-static assays for molecular interactions using on-chip integrated extended-gate field effect transistor (EGFET) as a static sensing interface and solidly mounted resonator (SMR) as a non-static sensing interface. Analysis of polyelectrolytes (PETs) surface assembly and antigen-antibody interaction using the two types of biochemical sensors presented consistent and complementary sets of information. Meanwhile, due to the difference in their operating mechanisms, variations on the detection efficiency, kinetics and thermodynamics were observed. Our results highlighted the critical dependence of signal detection on biochemical sensors’ operating mechanisms and provided a valuable guidance for static and non-static assays for biomolecular detections.
... In the end, to demonstrate the utility of an mFBAR gas sensor in MDGC, a preliminary GC-GC system, with the mFBAR installed between separation columns, was configured and tested in a 11-component mixture. [36] and is briefly described as in the following steps (see Figure S1). Step 1: an air cavity was etched on the silicon substrate by deep-reactive ion etching (DRIE). ...
Article
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A microfluidic film bulk acoustic wave resonator gas sensor (mFBAR) adapted specifically as an in-line detector in gas chromatography was described. This miniaturized vapor sensor was a non-destructive detector with very low dead volume (0.02 μL). It was prepared by enclosing the resonator in a microfluidic channel on a chip with dimensions of only 15 mm × 15 mm × 1 mm. The device with polymer coating showed satisfactory performance in the detection of organophosphorus compound, demonstrating a very low detection limit (a dozen parts per billion) with relatively short response time (about fifteen seconds) toward the simulant of chemical warfare agent, dimethyl methylphosphonate. The in-line detection of the mFBAR sensor with FID was constructed and employed to directly measure the concentration profile on the solid surface by the mFBAR with the controlled concentration profile in the mobile phase at the same time. The difference of peak-maximum position between mobile phase and solid phase could be a convenient indicator to measure mass transfer rate. With the response of the mFBAR and FID obtained in one injection, an injection mass-independent parameter can be calculated and used to identify the analyte of interest.
... The hydrophobic Teflon film coating not only reduces the required sample volume but also blocks the physical adsorption of target molecules on non-active areas, therefore, improving the adsorption/binding kinetics. Meanwhile, Liu et al. (2015) recently demonstrated that the f r of an individual FBAR device can be tuned by coating polymeric layers (poly(acrylic acid) (PAA) and poly(4-vinylpyridine)(PVP)) on top of the devices through either dipping or spin coating method. A maximum f r shift of more than 20 MHz can be achieved. ...
Article
Biosensors play important roles in different applications such as medical diagnostics, environmental monitoring, food safety, and the study of biomolecular interactions. Highly sensitive, label-free and disposable biosensors are particularly desired for many clinical applications. In the past decade, film bulk acoustic resonators (FBARs) have been developed as biosensors because of their high resonant frequency and small base mass (hence greater sensitivity), lower cost, label-free capability and small size. This paper reviews the piezoelectric materials used for FBARs, the optimisation of device structures, and their applications as biosensors in a wide range of biological applications such as the detection of antigens, DNAs and small biomolecules. Their integration with microfluidic devices and high-throughput detection are also discussed.
... The powerdependent characteristics of the resonator-induced concentration effect render the resonator as a regulator to control the biomolecular interaction rate via adjusting the power, which plays a key role in enzymology and other biological research. Except for the power, the resonator with higher Q value is characterized by larger vibration amplitude and has a stronger streaming effect in solution, 44 which will lead to a more efficient molecular concentration effect. As shown in Figure 4F, after incubation and actuation of the resonator for 15 min, the resulting fluorescence intensity for the resonator with Q = 41 is 3.7 times larger than that for the resonator with Q = 33. ...
Article
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In designing bioassay systems for low-abundance biomolecule detection, most research focuses on improving transduction mechanisms while ignoring the intrinsically fundamental limitations in solution: mass transfer and binding affinity. We demonstrate enhanced biomolecular surface binding using an acoustic nano-electromechanical system (NEMS) resonator, as an on-chip biomolecular concentrator which breaks both mass transfer and binding affinity limitations. As a result, a concentration factor of 10⁵ has been obtained for various biomolecules. The resultantly enhanced surface binding between probes on the absorption surface and analytes in solution enables us to lower the limit of detection for representative proteins. We also integrated the biomolecular concentrator into an optoelectronic bioassay platform to demonstrate delivery of proteins from buffer/serum to the absorption surface. Since the manufacture of the resonator is CMOS-compatible, we expect it to be readily applied to further analysis of biomolecular interactions in molecular diagnostics.
... Owning to the development of microsystem and nanotechnology, acoustic devices based on piezoelectric materials have gained increasing attention in biochemical research field [41][42][43][44] which is due to their low cost, batch manufacturing, small volume and noninvasive to biomolecules [45][46][47]. Here, we demonstrated a novel and versatile controlled release approach using gigahertz ultrasound (hypersound) induced by a nano-electromechanical acoustic resonator composed of ultra-thin material layers (several tens to hundreds of nanometers thick). ...
Article
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Background Controllable and multiple DNA release is critical in modern gene-based therapies. Current approaches require complex assistant molecules for combined release. To overcome the restrictions on the materials and environment, a novel and versatile DNA release method using a nano-electromechanical (NEMS) hypersonic resonator of gigahertz (GHz) frequency is developed. Results The micro-vortexes excited by ultra-high frequency acoustic wave can generate tunable shear stress at solid–liquid interface, thereby disrupting molecular interactions in immobilized multilayered polyelectrolyte thin films and releasing embedded DNA strands in a controlled fashion. Both finite element model analysis and experiment results verify the feasibility of this method. The release rate and released amount are confirmed to be well tuned. Owing to the different forces generated at different depth of the films, release of two types of DNA molecules with different velocities is achieved, which further explores its application in combined gene therapy. Conclusions Our research confirmed that this novel platform based on a nano-electromechanical hypersonic resonator works well for controllable single and multi-DNA release. In addition, the unique features of this resonator such as miniaturization and batch manufacturing open its possibility to be developed into a high-throughput, implantable and site targeting DNA release and delivery system.
... In this work, film bulk acoustic resonators (FBARs) were fabricated using standard microfabrication according to a previous published process (see also Supporting Information). 40 The series resonant frequency signal of FBAR was obtained by network analyzer (Agilent E5061B). ...
Article
This paper describes the detection of volatile organic compounds (VOCs) using an e-nose type integrated microfabricated sensor array, in which each resonator is coated with different supramolecular monolayers: p-tert-butyl calix[8]arene (Calix[8]arene), 2,3,7,8,12,13,17,18-octaethyl-21H,23H-porphine (Porphyrin), beta-cyclodextrin (β-CD) and cucurbit[8]uril (CB[8]). Supramolecular monolayers fabricated by Langmuir-Blodgett techniques work as specific sensing interface for different VOCs recognition which increase the sensor selectivity. Microfabricated ultra-high working frequency transducers (4.4 GHz) enable their high sensitivity towards monolayer sensing which facilitate the analyses of VOCs adsorption isotherms and kinetics. Two affinity constants (K1, K2) are obtained for each VOC, which indicate the gas molecule adsorption happen inside and outside of the supramolecular cavities. Additional kinetic information (adsorption/desorption rate constants (ka, kd)) are obtained, thus enrich the sensing matrix (△f, K1, K2, ka, kd) which can be used as fingerprint patterns for highly specific detection and discrimination of VOCs.
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Chapter
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The surface of a fused silica and oxidized silicon wafer (SiO2/Si(100)) was treated with (4-aminophenyl)trimethoxysilane (1), (3-aminopropyl)triethoxysilane (2), (3-aminopropyl)diethoxymethylsilane (3), and (3-aminopropyl)ethoxydimethylsilane (4) in solution. The thickness of thus formed aminosilane layers was determined with ellipsometry. In most cases silane coupling agents produce monolayers of 6−10 Å thickness, but reagent 2 gives multilayers with variable thickness (6−100 Å) depending upon the dipping time. The aminosilane layers were allowed to react with 4-nitrobenzaldehyde, and formation of the corresponding imines was confirmed by UV−vis spectroscopy. Relative surface density of the amines was calculated from the observed absorbance. In aqueous medium the imines were easily hydrolyzed to regenerate the amine group. The process, the formation, and the subsequent hydrolysis of the imines, can be repeated several times without any noticeable degradation of the absorption characteristics. The ellipsometric data and the measured absorbance show that 3 gives the most uniform molecular layer with the highest surface density of the amine functionality. Meanwhile, 2 provides multilayers lacking uniformity, and the other reagents produce uniform thin layers but with lower surface density of the amine.
Article
A highly sensitive film bulk acoustic resonator (FBAR) mass sensor in liquid environments is described in this paper. A transmission line model is used to theoretically predict the dependence of the FBAR's resonant frequency on added mass. FBAR performance in a liquid environment is experimentally characterized for the first time and the effects of the liquid nature and conductivity on the FBAR series and parallel resonant frequencies are investigated. A TiO2-coated FBAR is developed for sensitive mass sensing of metal ions in a liquid environment.
Article
Two self-assembled monolayers (SAMs), 6-mercaptonicotinic acid (6-MNA) and hydrophobic heptadecafluorodecyltrimethoxysilane (FAS-17), are used to specifically modify the two surfaces of a piezoresistive SiO2 cantilever for functionalizations of both specific explosive-sensing improvement and non-specific molecular-adsorption suppression. With the dual-SAM modification technique, the on-chip-integrated ultra-sensitive microcantilever sensor behaves more sensitively and has quicker sensing properties to trace trinitrotoluene (TNT) than the previously reported cantilever functionalized with 4-MBA SAM, as well as being able to significantly suppress the cross-talk influence from environmental air humidity. Measurement results show that the high-performance sensor achieves a rapid, reversible and reproducible response to TNT vapour, with a detecting resolution of tens of ppt.
Article
Variations in the linear charge density of a weak polyacid brought about by controlling solution pH in a layer-by-layer sequential adsorption process were used to systematically control the layer thickness, level of layer interpenetration, and surface wettability of sequentially adsorbed layers of poly(acrylic acid) (PAA) and poly(allylamine) (PAH). The thickness contributed by an individual polyion layer was found to depend primarily on the pH of the polymer's dipping solution and, within the pH range examined, was not influenced by the thickness or level of interpenetration of the previously adsorbed layer. Contact angle and methylene blue adsorption measurements revealed that the deposited layers are typically highly interpenetrated and that the deposition process is a surface charge dominated adsorption process. Using this simple molecular-level blending approach, it is possible to create surfaces with advancing water contact angles that vary from essentially zero (completely wettable surfaces) to as high as 50°, all using the same simple polycation/polyanion combination.
Article
Silicon bulk micromachined FBAR filters and duplexer have been developed. The proposed filters are comprised of several resonators and the duplexer is made with two filters and a phase delay line. The fabricated FBAR filters have insertion losses (IL) of −1.46 and −1.86 dB, return losses of −13 and −10 dB, stop band rejection of −14 and −33 dB, central frequency of 1.88 and 1.96 GHz, and size of 1.3 mm × 1.5 mm, respectively. The fabricated FBAR duplexer has insertion loss (IL) of −3.5 dB (Max.) in pass band and absolute attenuation of −42 dB (Min.) at transmitter to antenna ports, while it has IL of −4.5 dB (Max.) in pass band and absolute attenuation of −52 dB (Min.) at antenna to receiver ports. © 2006 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 339–342, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22133
Article
The layer-by-layer (LbL) formation of Smart particle coatings using oppositely charged block copolymer micelles is discussed. The formation of micelle multilayers requires that the two types of micelle are oppositely charged at a given pH. Further evidence for the absorption of the copolymer micelles and the build-up of a multilayer coating on the silica particles was obtained from transmission electron microscopy (TEM). The absorption of copolymer micelles leads to an increase in the apparent roughness of the micelle-coated silica particles with increasing number of micelle layers. Particle size analysis indicated an increase in hydrodynamic particle radius from 126 nm to 130 nm for the first micelle monolayer. The two types of micelles share the same pH-responsive core, and the same hydrophobic activity can be absorbed within each micelle layer, providing the micelle overlayer with an increased capacity for the delivery of activities.
Article
Communication: pH-Controlled encapsulation in and release of macromolecules from polyelectrolyte capsules of a few microns in diameter is demonstrated. Capsules were prepared via alternating adsorption of the oppositely charged polymers poly(allylamine hydrochloride) and poly(styrene sulfonate) onto decomposable melamin formaldehyde cores. The capsules were open for macromolecules at pH values below 6 and closed at pH > 8. Permeation and encapsulation of FITC-dextran (MW 75 000) into polyelectrolyte multilayer capsules. Top: pH 10, center: pH 3, bottom: pH increased to 10 after the capsules were loaded with FITC-dextran at pH 3. The bulk FITC-dextran was removed by washings at pH 10.
Article
The spin self-assembly (SA) process utilizing interactions which causes adsorption, the rearrangement of polymer chains onto a substrate, and the desorption of weakly bound chains in a very short time of approximately 10 s was demonstrated. This new ultrathin film-forming process yields a highly ordered internal structure far superior to the structure obtained with the dip SA process. In addition, it allows to predict and control precisely the bilayer thickness as well as the surface roughness.
Article
In this Full Paper, we develop a novel approach for the generation of stable molecularly imprinted sites in polymeric films by combining the layer-by-layer (LbL) technique and photochemical crosslinking of the layered structure. After photo-crosslinking, the imprinted films show high reproducibility and rapid loading and unloading of imprinted sites by the template molecules. Moreover, the competitive adsorption of template molecules and redox labels into the imprinted film using electrochemical methods indicates that the imprinted film has higher affinity for template molecules. We believe this approach may have some advantages over traditional ways of preparing imprinted sites in polymer matrices and it may open a new avenue for the functionalization of LbL films.
Article
Recent years have seen increasing interest in the construction of nanoscopically layered materials involving aqueous-based sequential assembly of polymers on solid substrates. In the booming research area of layer-by-layer (LbL) assembly of oppositely charged polymers, self-assembly driven by hydrogen bond formation emerges as a powerful technique. Hydrogen-bonded (HB) LbL materials open new opportunities for LbL films, which are more difficult to produce than their electrostatically assembled counterparts. Specifically, the new properties associated with HB assembly include: 1) the ease of producing films responsive to environmental pH at mild pH values, 2) numerous possibilities for converting HB films into single- or two-component ultrathin hydrogel materials, and 3) the inclusion of polymers with low glass transition temperatures (e.g., poly(ethylene oxide)) within ultrathin films. These properties can lead to new applications for HB LbL films, such as pH- and/or temperature-responsive drug delivery systems, materials with tunable mechanical properties, release films dissolvable under physiological conditions, and proton-exchange membranes for fuel cells. In this report, we discuss the recent developments in the synthesis of LbL materials based on HB assembly, the study of their structure–property relationships, and the prospective applications of HB LbL constructs in biotechnology and biomedicine.
Article
Localized-mass sensors using thin-film bulk acoustic resonators (FBAR) have been implemented for the study of sensitivity and possible configurations in biological applications. In a first experiment, a group of resonators are loaded with the same amount of mass but different contact areas, achieving responsivities as high as 10(-19) g/Hz, and potential sensitivities in the order of 10(-14) g. These numbers are at least one order of magnitude higher than those obtained for uniform thin-film loadings, although it is clear that sensitivity decreases with the area of the localized-mass. The current phase-noise levels and the quality factor of resonators would allow measuring frequency changes of 30kHz - the minimum measured frequency shifting has been 500 kHz so far - due to a mass deposition of 9.0 x 10(-15) g. In a second experiment, localized-loadings with the same mass are located in different positions of the top electrodes of the corresponding FBARs. It was found out that a location change of the mass in the electrode causes different magnitudes of frequency shifting. A discussion on these topics is opened, in order to define future applications and research lines concerning localized-mass sensing in FBARs. (C) 2007 Elsevier B.V. All rights reserved.
Article
Nano-assembled thin films prepared by a layer-by-layer approach on QCM resonators were used as sensitive elements for monitoring relative humidity. Different types of films, polymer-based (PDDA/PSS)n film and porphyrin-based (PDDA/TSPP)n and (PDDA/MnTSPP)n films (where n = 5, 10, and 15), showed linear responses to relative humidity changes in the range of 4–94%. Increase of the number of bilayers deposited on the QCM electrode enhanced the sensitivity to relative humidity. The porphyrin-based films showed ca. 4.5 times higher sensitivity towards relative humidity than the polymer-based films, owing to presence of the higher number of free sulfonic acid groups. Incorporation of the metal ion into the porphyrin pyrrole ring was not significant in sensitivity. However, all films showed a good reversibility to the stepwise changes of relative humidity and the response and recovery times (t90) were very fast within 15 s.
Article
Piezoelectric microelectromechanical systems (MEMS) resonant sensors, known for their excellent mass resolution, have been studied for many applications, including DNA hybridization, protein-ligand interactions, and immunosensor development. They have also been explored for detecting antigens, organic gas, toxic ions, and explosives. Most piezoelectric MEMS resonant sensors are acoustic sensors (with specific coating layers) that enable selective and label-free detection of biological events in real time. These label-free technologies have recently garnered significant attention for their sensitive and quantitative multi-parameter analysis of biological systems. Since piezoelectric MEMS resonant sensors do more than transform analyte mass or thickness into an electrical signal (e.g., frequency and impedance), special attention must be paid to their potential beyond microweighing, such as measuring elastic and viscous properties, and several types of sensors currently under development operate at different resonant modes (i.e., thickness extensional mode, thickness shear mode, lateral extensional mode, flexural mode, etc.). In this review, we provide an overview of recent developments in micromachined resonant sensors and activities relating to biochemical interfaces for acoustic sensors.
Article
The immobilization of two 30-mer oligonucleotides, one biotinylated (biotin-DNA) and the other having a mercaptohexyl group at the 5'-phosphate end (BS1-SH), onto modified gold surfaces has been examined using a quartz crystal microbalance (QCM). Both single-layer and multilayer DNA films were prepared. The single-layer films of biotin-DNA were constructed by binding to a precursor layer of avidin, which had been attached to the QCM either covalently using a water-soluble carbodiimide hydrochloride (EDC) and N-hydroxysuccinimide (NHS) or via electrostatic interaction with poly(allylamine hydrochloride) (PAH). Single-layer films of BS1-SH were also formed on PAH via the electrostatic attraction between the amine groups on PAH and the negatively charged phosphate backbone of DNA. Multilayer films of DNA were fabricated by the successive deposition of avidin and poly(styrenesulfonate) (PSS), up to a total of nine avidin/PSS layers, followed by DNA adsorption. DNA immobilization and hybridization of the immobilized DNAs was monitored in situ from QCM frequency changes. Hybridization was induced by exposure of the DNA-containing films to complementary DNA in solution. Equal frequency changes were observed for the DNA immobilization and hybridization steps for the single-layer films, indicating a DNA probe-to-hybridized DNA target ratio of 1:1. The multilayer DNA films also exhibited DNA hybridization, with a greater quantity of DNA hybridized compared with the single-layer films. The multilayer films provide a novel means for the fabrication of DNA-based thin films with increased capacity for nucleic acid detection.
Article
We fabricated large arrays of suspended, single-layer graphene membrane resonators using chemical vapor deposition (CVD) growth followed by patterning and transfer. We measure the resonators using both optical and electrical actuation and detection techniques. We find that the resonators can be modeled as flat membranes under tension, and that clamping the membranes on all sides improves agreement with our model and reduces the variation in frequency between identical resonators. The resonance frequency is tunable with both electrostatic gate voltage and temperature, and quality factors improve dramatically with cooling, reaching values up to 9000 at 10 K. These measurements show that it is possible to produce large arrays of CVD-grown graphene resonators with reproducible properties and the same excellent electrical and mechanical properties previously reported for exfoliated graphene.
Article
DNA methylation catalyzed by methyltransferase (MTase) is a significant epigenetic process for modulating gene expression. Traditional methods to study MTase activity require a laborious and costly DNA labeling process. In this article, we report a simple, colorimetric, and label-free methylation-responsive DNAzyme (MR-DNAzyme) strategy for MTase activity analysis. This new strategy relies on horseradish peroxidase (HRP) mimicking DNAzyme and the methylation-responsive sequence (MRS) of DNA which can be methylated and cleaved by the MTase/endonuclease coupling reaction. Methylation-induced scission of MRS would activate the DNAzyme that can catalyze the generation of a color signal for the amplified detection of methylation events. Taking Dam MTase and DpnI endonuclease as examples, we have developed two colorimetric methods based on the MR-DNAzyme strategy. The first method is to utilize an engineered hairpin-DNAzyme hybrid probe for facile turn-on detection of Dam MTase activity, with a wide linear range (6-100 U/mL) and a low detection limit (6 U/mL). Furthermore, this method could be easily expanded to profile the activity and inhibition of restriction endonuclease. The second method involves a methylation-triggered DNAzyme-based DNA machine, which achieves the ultrahigh sensitive detection of Dam MTase activity (detection limit = 0.25 U/mL) by a two-step signal amplification cascade.
Article
The covalent functionalization of GaN and AlN surfaces with organosilanes is demonstrated. Both octadecyltrimethoxysilane and aminopropyltriethoxysilane form self-assembled monolayers on hydroxylated GaN and AlN surfaces, confirmed by x-ray photoelectron spectroscopy and atomic force microscopy. The monolayer thickness on GaN was determined to 2.5 +/- 0.2 nm by x-ray reflectivity. Temperature-programmed desorption measurements reveal a desorption enthalpy of 240 kJ/mol. The realization of micropatterned self-assembled monolayers and the hybridization of deoxyribonucleic acid molecules on biofunctionalized GaN surfaces are shown.
Article
The layer-by-layer (LbL) desposition of oppositely charged polyelectrolytes from adsorption solutions of different ionic strength onto ∼7 nm diameter carboxylic acid-derivatized gold nanoparticles has been studied. The polyelectrolyte-modified nanoparticles were characterized by UV-vis spectrophotometry, microelectrophoresis, analytical ultracentrifugation, and transmission electron microscopy. UV-vis data showed that the peak plasmon absorption wavelength of the gold nanoparticles red-shifted after each adsorption step, and microelectrophoresis experiments revealed a reversal in the surface charge of the nanoparticles following deposition of each layer. These data are consistent with the formation of polyelectrolyte layers on the nanoparticles. Analytical ultracentrifugation showed an increase in mean nanoparticle diameter on adsorption of the polyelectrolytes, confirming the formation of gold-core/polyelectrolyte-shell nanoparticles. Transmission electron microscopy studies showed no signs of aggregation of the polyelectrolyte-coated nanoparticles. The adsorption of the polyelectrolyte-coated gold nanoparticles onto oppositely charged planar supports has also been examined. UV-vis spectrophotometry and atomic force microscopy showed increased amounts of nanoparticles were adsorbed with increasing ionic strength of the nanoparticle dispersions. This allows control of the nanoparticle surface loading by varying the salt content in the nanoparticle dispersions used for adsorption. The LbL strategy used in this work is expected to be applicable to other nanoparticles (e.g., semiconductors, phosphors), thus providing a facile means for their controlled surface modification through polyelectrolyte nanolayering. Such nanoparticles are envisaged to have applications in the biomedical and bioanalytical fields, and to be useful building blocks for the creation of advanced nanoparticle-based films.
Article
A polyelectrolyte multilayer was assembled on top of a patterned PDMS stamp employing the layer-by-layer (LbL) assembly technique. By post-treatment with a base and further cross-linking, a porous multilayer-coated PDMS composite stamp was obtained. With the pore structures acting as an ink reservoir, the multiple printing of proteins was successfully achieved without the need to re-ink the stamp.
Article
We have observed the transversal vibration mode of suspended carbon nanotubes at millikelvin temperatures by measuring the single-electron tunneling current. The suspended nanotubes are actuated contact-free by the radio frequency electric field of a nearby antenna; the mechanical resonance is detected in the time-averaged current through the nanotube. Sharp, gate-tunable resonances due to the bending mode of the nanotube are observed, combining resonance frequencies of up to nu(0) = 350 MHz with quality factors above Q = 10(5), much higher than previously reported results on suspended carbon nanotube resonators. The measured magnitude and temperature dependence of the Q factor shows a remarkable agreement with the intrinsic damping predicted for a suspended carbon nanotube. By adjusting the radio frequency power on the antenna, we find that the nanotube resonator can easily be driven into the nonlinear regime.
Article
Ultraminiaturized mass spectrometers are highly sought-after tools, with numerous applications in areas such as environmental protection, exploration, and drug development. We realize atomic scale mass sensing using doubly clamped suspended carbon nanotube nanomechanical resonators, in which their single-electron transistor properties allows self-detection of the nanotube vibration. We use the detection of shifts in the resonance frequency of the nanotubes to sense and determine the inertial mass of atoms as well as the mass of the nanotube. This highly sensitive mass detection capability may eventually enable applications such as on-chip detection, analysis, and identification of compounds.
Article
Shrinking mechanical resonators to submicrometer dimensions (approximately 100 nm) has tremendously improved capabilities in sensing applications. In this Letter, we go further in size reduction using a 1 nm diameter carbon nanotube as a mechanical resonator for mass sensing. The performances, which are tested by measuring the mass of evaporated chromium atoms, are exceptional. The mass responsivity is measured to be 11 Hz x yg(-1) and the mass resolution is 25 zg at room temperature (1 yg = 10(-24) g and 1 zg = 10(-21) g). By cooling the nanotube down to 5 K in a cryostat, the signal for the detection of mechanical vibrations is improved and corresponds to a resolution of 1.4 zg.
Article
We have employed a chip-bending method to exert continuous and reversible control over the tensile stress in doubly clamped nanomechanical beam resonators. Tensile stress is shown to increase the quality factor of both silicon nitride and single-crystal silicon resonators, implying that added tension can be used as a general, material-independent route to increased quality factor. With this direct stretching technique, we demonstrate beam resonators with unprecedented tunability of both frequency and quality factor. Devices can be tuned back and forth between a high and low stress state, with frequency tunability as large as several hundred percent demonstrated. Over this wide range of frequency, quality factor is also tuned by as much as several hundred percent, providing insights into the loss mechanisms in these materials and this class of nanoresonator. Devices with frequencies in the 1-100 MHz range are studied, with quality factor as high as 390,000 achieved at room temperature, for a silicon nitride device with cross-sectional dimensions below 1 microm, operating in a high stress state. This direct stretching technique may prove useful for the identification of loss mechanisms that contribute to the energy balance in nanomechanical resonators, allowing for the development of new designs that would display higher quality factors. Such devices would have the ability to resolve smaller addendum masses and thus allow more sensitive detection and offer the potential for providing access to previously inaccessible dissipation regimes at low temperatures. This technique provides the ability to dramatically tune both frequency and quality factor, enabling future mechanical resonators to be used as variable frequency references as well as variable band-pass filters in signal-processing applications.
Article
The immobilization scheme of monodispersed gold nanoparticles (10-nm diameter) on piezoelectric substrate surfaces using organosilane molecules as cross-linkers has been developed for lithium niobate (LiNbO3) and silicon oxide (SiO2)/gold-covered lithium tantalate (LiTaO3) of Rayleigh and guided shear horizontal- (guided SH) surface acoustic wave (SAW) sensors. In this study, comparative measurements of gold nanoparticle adsorption kinetics using high-resolution field-emission scanning electron microscopy and SAW sensors allow the frequency responses of SAW sensors to be quantitatively correlated with surface densities of adsorbed nanoparticles. Using this approach, gold nanoparticles are used as the "nanosized mass standards" to scale the mass loading in a wide dynamical range. Rayleigh-SAW and guided SH-SAW sensors are employed here to monitor the surface mass changes on the device surfaces in gas and liquid phases, respectively. The mass sensitivity ( approximately 20 Hz.cm2/ng) of Rayleigh-SAW device (fundamental oscillation frequency of 113.3 MHz in air) is more than 2 orders of magnitude higher than that of conventional 9-MHz quartz crystal microbalance sensors. Furthermore, in situ (aqueous solutions), real-time measurements of adsorption kinetics for both citrate-stabilized gold nanoparticles and DNA-gold nanoparticle conjugates are also demonstrated by guided SH-SAW (fundamental oscillation frequency of 121.3 MHz). By comparing frequency shifts between the adsorption cases of gold nanoparticles and DNA-gold nanoparticle conjugates, the average number of bound oligonucleotides per gold nanoparticle can also be determined. The high mass sensitivity ( approximately 6 Hz.cm2/ng) of guided SH-SAW sensors and successful detection of DNA-gold nanoparticle conjugates paves the way for real-time biosensing in liquids using nanoparticle-enhanced SAW devices.
Article
We demonstrate that the surface morphology and surface-wetting behavior of layer-by-layer (LbL) films can be controlled using different deposition methods. Multilayer films based upon hydrogen-bonding interactions between hydrophobically modified poly(ethylene oxide) (HM-PEO) and poly(acrylic acid) (PAA) have been prepared using the dip- and spin-assisted LbL methods. A three-dimensional surface structure in the dip-assisted multilayer films appeared above a critical number of layer pairs owing to the formation of micelles of HM-PEO in its aqueous dipping solution. In the case of spin-assisted HM-PEO/PAA multilayer films, no such surface morphology development was observed, regardless of the layer pair number, owing to the limited rearrangement and aggregation of HM-PEO micelles during spin deposition. The contrasting surface morphologies of the dip- and spin-assisted LbL films have a remarkable effect on the wetting behavior of water droplets. The water contact angle of the dip-assisted HM-PEO/PAA LbL films reaches a maximum at an intermediate layer pair number, coinciding with the critical number of layer pairs for surface morphology development, and then decreases rapidly as the surface structure is evolved and amplified. In contrast, spin-assisted HM-PEO/PAA LbL films yield a nearly constant water contact angle due to the surface chemical composition and roughness that is uniform independent of layer pair number. We also demonstrate that the multilayer samples prepared using both the dip- and spin-assisted LbL methods were easily peeled away from any type of substrate to yield free-standing films; spin-assisted LbL films appeared transparent, while dip-assisted LbL films were translucent.
Conference Paper
We present results of balanced Rx filters based on thin-film bulk acoustic resonator (FBAR) technology for GSM handset front-end module applications. The balanced filtering is achieved by using a lattice filter topology. The filter is hermetically sealed using wafer-level packaging with solder bumps on each terminal, ready for flip-chip assembly. The size of the filter is less than 1 mm∧2 and the height is less than 0.35 mm. The typical broadband rejection is better than 35 dB, and in-band insertion loss is less than 2 dB. The small size and good temperature stability make FBAR filters an ideal choice for front-end module applications.
Article
The design, finite element modeling, fabrication, and characterization of a novel surface acoustic wave (SAW) delay line for bio/chemical and telecommunication applications in CMOS technology are introduced. A full modeling was carried out. The devices are designed in a standard semiconductor foundry 1.5-mum two-metal two-poly process. A unique maskless postprocessing sequence is designed and completed. The three postprocessing steps are fully compatible with any standard integrated circuit technology such as CMOS. This allows any signal control/processing circuitry to be easily integrated on the same chip. ZnO is used as the piezoelectric material for SAW generation. A thorough characterization and patterning optimization of the sputtered ZnO was carried out. The major novelties that are introduced in the SAW delay line features are the embedded heater elements for temperature control, compensation, and acoustic absorbers that are designed to eliminate edge reflections and minimize triple transit interference that is amplified by edge reflections. Both of these attributes are designed by using CMOS materials without disturbing SAW performance
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