[Show abstract][Hide abstract] ABSTRACT: Antibody mimic proteins (AMPs) are poly-peptides that bind to their target analytes with high affinity and specificity, just like conventional antibodies, but are much smaller in size (2-5 nm, less than 10kDa). In this report, we describe the first application of AMP in the field of nanobiosensors. In2O3 nanowire based biosensors have been configured with an AMP (Fibronectin, Fn) to detect nucleocapsid (N) protein, a biomarker for severe acute respiratory syndrome (SARS). Using these devices, N protein was detected at sub-nanomolar concentration in the presence of 44 μM bovine serum albumin as a background. Furthermore, negative control experiment is carried out to confirm the role of AMPs in N protein detection.
[Show abstract][Hide abstract] ABSTRACT: Biomarker detection based on nanowire biosensors has attracted a significant amount of research effort in recent years. However, only very limited research work has been directed toward biomarker detection directly from physiological fluids mainly because of challenges caused by the complexity of media. This limitation significantly reduces the practical impact generated by the aforementioned nanobiosensors. In this study, we demonstrate an In(2)O(3) nanowire-based biosensing system that is capable of performing rapid, label-free, electrical detection of cancer biomarkers directly from human whole blood collected by a finger prick. Passivating the nanowire surface successfully blocked the signal induced by nonspecific binding when performing active measurement in whole blood. Passivated devices showed markedly smaller signals induced by nonspecific binding of proteins and other biomaterials in serum and higher sensitivity to target biomarkers than bare devices. The detection limit of passivated sensors for biomarkers in whole blood was similar to the detection limit for the same analyte in purified buffer solutions at the same ionic strength, suggesting minimal decrease in device performance in the complex media. We then demonstrated detection of multiple cancer biomarkers with high reliability at clinically meaningful concentrations from whole blood collected by a finger prick using this sensing system.
[Show abstract][Hide abstract] ABSTRACT: Biosensing property and functionalization of In2O3 nanowire and carbon nanotube field effect transistor were investigated. Low-density lipoproteins adsorbed on their surface were found to give complementary effects on their electrical property, e.g., enhanced conductance in NW and suppressed conductance in CNT. Prostate specific antigen was selectively detected by functionalizing the sensors with PSA antibody via linker molecules. It was found that the exposure to 0.14 nM (5 ng/ml) PSA increases the conductance of In2O3 nanowire by 1.3 %, while 1.4 nM (50 ng/ml) PSA decreases that of carbon nanotube by 2 %. Additionally, selective functionalization of Indium Tin Oxide thin film and In2O3 NWs with probe DNA single strand was achieved by selectively converting hydroquinone into quinone using electrochemistry, as confirmed by the fluorescence study.
[Show abstract][Hide abstract] ABSTRACT: We report a comparative study and Raman characterization of the formation of graphene on single crystal Ni (111) and polycrystalline Ni substrates using chemical vapor deposition (CVD). Preferential formation of monolayer/bilayer graphene on the single crystal surface is attributed to its atomically smooth surface and the absence of grain boundaries. In contrast, CVD graphene formed on polycrystalline Ni leads to a higher percentage of multilayer graphene (≥3 layers), which is attributed to the presence of grain boundaries in Ni that can serve as nucleation sites for multilayer growth. Micro-Raman surface mapping reveals that the area percentages of monolayer/bilayer graphene are 91.4% for the Ni (111) substrate and 72.8% for the polycrystalline Ni substrate under comparable CVD conditions. The use of single crystal substrates for graphene growth may open ways for uniform high-quality graphene over large areas.Keywords (keywords): Ni (111); polycrystalline Ni; graphene; chemical vapor deposition; growth mechanism
[Show abstract][Hide abstract] ABSTRACT: Biosensors utilizing carbon nanotube field-effect transistors have a tremendous potential to serve as the basis for the next generation of diagnostic systems. While nanotubes have been employed in the fabrication of multiple sensors, little attention has previously been paid to how the nanotube density affects the biosensor performance. We conducted a systematic study of the effect of density on the performance of nanotube biosensors and discovered that this parameter is crucial to achieving consistently high performance. We found that devices with lower density offer higher sensitivity in terms of both detection limit and magnitude of response. The low density nanotube devices resulted in a detection limit of 1 pM in an electrolyte buffer containing high levels of electrolytes (ionic concentration ∼140 mM, matching the ionic strength of serum and plasma). Further investigation suggested that the enhanced sensitivity arises from the semiconductor-like behavior-strong gate dependence and lower capacitance-of the nanotube network at low density. Finally, we used the density-optimized nanotube biosensors to detect the nucleocapsid (N) protein of the SARS virus and demonstrated improved detection limits under physiological conditions. Our results show that it is critical to carefully tune the nanotube density in order to fabricate sensitive and reliable devices.
[Show abstract][Hide abstract] ABSTRACT: Silver nanowire films are promising alternatives to tin-doped indium oxide (ITO) films as transparent conductive electrodes.
In this paper, we report the use of vacuum filtration and a polydimethylsiloxane (PDMS)-assisted transfer printing technique
to fabricate silver nanowire films on both rigid and flexible substrates, bringing advantages such as the capability of patterned
transfer, the best performance among various ITO alternatives (10 Ω/sq at 85% transparency), and good adhesion to the underlying
substrate, thus eliminating the previously reported adhesion problem. In addition, our method also allows the preparation
of high quality patterned films of silver nanowires with different line widths and shapes in a matter of few minutes, making
it a scalable process. Furthermore, use of an anodized aluminum oxide (AAO) membrane in the transfer process allows annealing
of nanowire films at moderately high temperature to obtain films with extremely high conductivity and good transparency. Using
this transfer technique, we obtained silver nanowire films on a flexible polyethylene terephthalate (PET) substrate with a
transparency of 85%, a sheet resistance of 10 Ω/sq, with good mechanical flexibility. Detailed analysis revealed that the
Ag nanowire network exhibits two-dimensional percolation behavior with good agreement between experimentally observed and
theoretically predicted values of critical volume.
KeywordsAg nanowire-PDMS transfer-transparent electrode-flexible electronics-percolation network
Nano Research 08/2010; 3(8):564-573. DOI:10.1007/s12274-010-0017-5 · 7.01 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Semiconducting nanowires are promising ultrasensitive, label-free sensors for small molecules, DNA, proteins, and cellular function. Nanowire field-effect transistors (FETs) function by sensing the charge of a bound molecule. However, solutions of physiological ionic strength compromise the detection of specific binding events due to ionic (Debye) screening. A general solution to this limitation with the development of a hybrid nanoelectronic enzyme-linked immunosorbent assay (ne-ELISA) that combines the power of enzymatic conversion of a bound substrate with electronic detection is demonstrated. This novel configuration produces a local enzyme-mediated pH change proportional to the bound ligand concentration. It is shown that nanowire FETs configured as pH sensors can be used for the quantitative detection of interleukin-2 in physiologically buffered solution at concentrations as low as 1.6 pg mL(-1). By successfully bypassing the Debye screening inherent in physiological fluids, the ne-ELISA promises wide applicability for ligand detection in a range of relevant solutions.
Small 01/2010; 6(2):232-8. DOI:10.1002/smll.200901551 · 8.37 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Nanowire/nanotube biosensors have stimulated significant interest; however, the inevitable device-to-device variation in the biosensor performance remains a great challenge. We have developed an analytical method to calibrate nanowire biosensor responses that can suppress the device-to-device variation in sensing response significantly. The method is based on our discovery of a strong correlation between the biosensor gate dependence (dI(ds)/dV(g)) and the absolute response (absolute change in current, DeltaI). In(2)O(3) nanowire-based biosensors for streptavidin detection were used as the model system. Studying the liquid gate effect and ionic concentration dependence of strepavidin sensing indicates that electrostatic interaction is the dominant mechanism for sensing response. Based on this sensing mechanism and transistor physics, a linear correlation between the absolute sensor response (DeltaI) and the gate dependence (dI(ds)/dV(g)) is predicted and confirmed experimentally. Using this correlation, a calibration method was developed where the absolute response is divided by dI(ds)/dV(g) for each device, and the calibrated responses from different devices behaved almost identically. Compared to the common normalization method (normalization of the conductance/resistance/current by the initial value), this calibration method was proven advantageous using a conventional transistor model. The method presented here substantially suppresses device-to-device variation, allowing the use of nanosensors in large arrays.
[Show abstract][Hide abstract] ABSTRACT: To add to the understanding of the properties of functionalized carbon nanotubes in biological applications, we report a monotonic pH sensitivity of the intracellular fluorescence emission of single-walled carbon nanotube-fluorescein carbazide (SWCNT-FC) conjugates in human ovarian cancer cells. Light-stimulated intracellular hydrolysis of the amide linkage and localized intracellular pH changes are proposed as mechanisms. SWCNT-FC conjugates may serve as intracellular pH sensors.
[Show abstract][Hide abstract] ABSTRACT: Antibody mimic proteins (AMPs) are polypeptides that bind to their target analytes with high affinity and specificity, just like conventional antibodies, but are much smaller in size (2-5 nm, less than 10 kDa). In this report, we describe the first application of AMP in the field of nanobiosensors. In(2)O(3) nanowire based biosensors have been configured with an AMP (Fibronectin, Fn) to detect nucleocapsid (N) protein, a biomarker for severe acute respiratory syndrome (SARS). Using these devices, N protein was detected at subnanomolar concentration in the presence of 44 microM bovine serum albumin as a background. Furthermore, the binding constant of the AMP to Fn was determined from the concentration dependence of the response of our biosensors.
[Show abstract][Hide abstract] ABSTRACT: A novel hybrid chemical sensor array composed of individual In(2)O(3) nanowires, SnO(2) nanowires, ZnO nanowires, and single-walled carbon nanotubes with integrated micromachined hotplates for sensitive gas discrimination was demonstrated. Key features of our approach include the integration of nanowire and carbon nanotube sensors, precise control of the sensor temperature using the micromachined hotplates, and the use of principal component analysis for pattern recognition. This sensor array was exposed to important industrial gases such as hydrogen, ethanol and nitrogen dioxide at different concentrations and sensing temperatures, and an excellent selectivity was obtained to build up an interesting 'smell-print' library of these gases. Principal component analysis of the sensing results showed great discrimination of those three tested chemicals, and in-depth analysis revealed clear improvement of selectivity by the integration of carbon nanotube sensors. This nanoelectronic nose approach has great potential for detecting and discriminating between a wide variety of gases, including explosive ones and nerve agents.
[Show abstract][Hide abstract] ABSTRACT: In this paper, the use of carbon nanotube biosensors toward alga cell detection was examined. The biosensor devices were fabricated on complete 4 in. wafers by first growing carbon nanotubes (CNTs) and then depositing metal electrodes using a shadow mask. In addition, we decorated the biosensors with metal-clusters resulted in enhancing the sensitivity by 2000-folds and has enabled the detection of streptavidin down to 10 pM concentration. This sensitivity enhancement was attributed to activation of CNT channels due to formation of Schottky junctions between CNTs and metal-clusters. Real-time cell detection has been successfully carried out using the CNT biosensors for two kinds of alga related to brown tides: Aureococcus anophagefferens and BT3. Functionalization of the CNT biosensors with the monoclonal antibody for A. anophagefferens has led to detection at a concentration of 10(4) cells/ml, with sensitivity lower than 10(4) cells/ml projected based on the signal-to-noise ratio of the sensors. Further functionalization with tween 20 led to suppression of non-specific binding of BT3 and enabled label-free and selective detection of A. anophagefferens. These nanobiosensors may find potential applications for environmental monitoring and disease diagnosis.
[Show abstract][Hide abstract] ABSTRACT: We report high-performance fully transparent thin-film transistors (TTFTs) on both rigid and flexible substrates with transfer printed aligned nanotubes as the active channel and indium-tin oxide as the source, drain, and gate electrodes. Such transistors have been fabricated through low-temperature processing, which allowed device fabrication even on flexible substrates. Transparent transistors with high effective mobilities (approximately 1300 cm(2) V(-1) s(-1)) were first demonstrated on glass substrates via engineering of the source and drain contacts, and high on/off ratio (3 x 10(4)) was achieved using electrical breakdown. In addition, flexible TTFTs with good transparency were also fabricated and successfully operated under bending up to 120 degrees . All of the devices showed good transparency (approximately 80% on average). The transparent transistors were further utilized to construct a fully transparent and flexible logic inverter on a plastic substrate and also used to control commercial GaN light-emitting diodes (LEDs) with light intensity modulation of 10(3). Our results suggest that aligned nanotubes have great potential to work as building blocks for future transparent electronics.
[Show abstract][Hide abstract] ABSTRACT: This dissertation presents applications of one-dimensional structured
nanomaterials, carbon nanotubes and In2O3 nanowires, for biosensors and
transparent electronics. Chapter 1 gives the motivation to study
applications of one-dimensional structured nanomaterials, and also brief
introduction to structure, synthesis, and electronic properties of
carbon nanotubes and In2O3 nanowires. In Chapter 2, introduction and
motivation of biosensors using nanotubes/nanowires is given, followed by
an overview on important background knowledge and concepts in
biosensing. In Chapter 3, application of carbon nanotube biosensors
toward brown tide algae detection is presented. Our devices successfully
detected a brown tide marker selectively with real-time response. In
Chapter 4, we demonstrate that In2O3 nanowire biosensors coupled with an
antibody mimic protein (Fibronectin, Fn) can be used to detect
nucleocapsid (N) protein, a biomarker for severe acute respiratory
syndrome (SARS), at concentrations to below the sub-nanomolar range. In
Chapter 5, we develop an analytical method to calibrate nanowire
biosensor responses that can suppress the device-to-device variation in
sensing response significantly. In Chapter 6, we investigate the effect
of nanotube density on the biosensor performance, and proved that it
plays an important role through systematic studies. In Chapter 7, I
propose a future direction of nanobiosensors research, and show
preliminary results along the proposed direction. I first present a
concept of an ideal bioassay system with a list of requirements for the
system, and propose the strategy of multi-integration to establish a
system based on nanobiosensors that satisfies all of the requirements.
In Chapter 8, we demonstrate high performance fully transparent
transistors based on transfer printed aligned carbon nanotubes on both
rigid and flexible substrates. We achieved device mobility as high as
1,300 cm 2V-1s-1 on glass substrates, which is the highest among
transparent transistors reported so far. We also demonstrated fully
transparent PMOS inverters on flexible substrates, and also successfully
controlled commercial GaN light--emitting diodes (LEDs) with light
intensity modulation of 103. Lastly, a brief summary of this thesis is
given in Chapter 9.
[Show abstract][Hide abstract] ABSTRACT: Nanowire (NW)-based FETs are promising devices with potential applications ranging from health monitoring to drug discovery. In fact, these devices have demonstrated the ability to detect a variety of analytes such as particular DNA sequences, cancer biomarkers, and larger entities such as viruses. These sensor devices have also been used to monitor enzymatic activities and study the behavior of potential drug molecules. The detection of the analytes occurs with high specificity and sensitivity in reasonably short time. Here, we review the recent literature produced in the field of NW FET biosensors. We elaborate on the parameters that ultimately influence device performance such as methods of NW production, device dimensionality, and active measurement conditions. Significant progress has been made in this field of technology; however, it is often difficult to compare literature reports due to differences in both measurement conditions and data analysis. The standardization of certain active measurement conditions, such as the ionic strength of the analyte solutions, and manipulation of data are proposed to facilitate comparison between different NW biosensors.
[Show abstract][Hide abstract] ABSTRACT: We report the fabrication of high performance nanowire transistors (NWTs) using In2O3 nanowires as the active channel and a self-assembled nanodielectric (SAND) as the gate insulator. The SAND-based single In2O3 NWTs are controlled by individually addressed gate electrodes. These devices exhibit n-type transistor characteristics with an on-current of similar to 25 mu A for a single In2O3 nanowire at 2.0V(ds), 2.1V(gs), a subthreshold slope of 0.2 V/decade, an on-off current ratio of 10(6), and a field-effect mobility of similar to 1450 cm(2)/V s. These results demonstrate that SAND-based In2O3 NWTs are promising candidates for high performance nanoscale logic technologies.
[Show abstract][Hide abstract] ABSTRACT: Optically transparent, mechanically flexible displays are attractive for next-generation visual technologies and portable electronics. In principle, organic light-emitting diodes (OLEDs) satisfy key requirements for this application-transparency, lightweight, flexibility, and low-temperature fabrication. However, to realize transparent, flexible active-matrix OLED (AMOLED) displays requires suitable thin-film transistor (TFT) drive electronics. Nanowire transistors (NWTs) are ideal candidates for this role due to their outstanding electrical characteristics, potential for compact size, fast switching, low-temperature fabrication, and transparency. Here we report the first demonstration of AMOLED displays driven exclusively by NW electronics and show that such displays can be optically transparent. The displays use pixel dimensions suitable for hand-held applications, exhibit 300 cd/m2 brightness, and are fabricated at temperatures suitable for integration on plastic substrates.