Multisegment nanowire sensors for the detection of DNA molecules

We describe a novel application for detecting specific single strand DNA sequences using multisegment nanowires via a straightforward surface functionalization method. Nanowires comprising CdTe-Au-CdTe segments are fabricated using electrochemical deposition, and electrical characterization indicates a p-type behavior for the multisegment nanostructures, in a back-to-back Schottky diode configuration. Such nanostructures modified with thiol-terminated probe DNA fragments could function as high fidelity sensors for biomolecules at very low concentration. The gold segment is utilized for functionalization and binding of single strand DNA (ssDNA) fragments while the CdTe segments at both ends serve to modulate the equilibrium Fermi level of the heterojunction device upon hybridization of the complementary DNA fragments (cDNA) to the ssDNA over the Au segment. Employing such multisegment nanowires could lead to the fabrication more sophisticated and high multispecificity biosensors via selective functionalization of individual segments for biowarfare sensing and medical diagnostics applications.     

Optimal signal-to-noise ratio for silicon nanowire biochemical sensors

The signal-to-noise ratio (SNR) for silicon nanowire field-effect transistors operated in an electrolyte environment is an essential figure-of-merit to characterize and compare the detection limit of such devices when used in an exposed channel configuration as biochemical sensors. We employ low frequency noise measurements to determine the regime for optimal SNR. We find that SNR is not significantly affected by the electrolyte concentration, composition, or pH, leading us to conclude that the major contributions to the SNR come from the intrinsic device quality. The results presented here show that SNR is maximized at the peak transconductance.     

The detection properties of ammonia SAW gas sensors based on L-glutamic acid hydrochloride

This study has investigated an improved surface acoustic wave (SAW) ammonia gas sensor based on L-glutamic acid hydrochloride. It presents an excellent reversibility, sensitivity, and repeatability to ammonia. The frequency shift versus ammonia concentration above 40 degrees C was a monotonic function, and the limit of detection of the sensor at 50 degrees C was 80 ppb.     

In-situ detection of C-reactive protein using silicon nanowire field effect transistor

Label-free, sensitive, and real-time c-reactive protein (CRP) sensor was fabricated using p-type silicon nanowire (SiNW) based structures configured as field effect transistors (FET) using the conventional 'top-down' semiconductor processes. The width of SiNWs were distributed 80 nm to 400 nm. Among them to improve signal-to-noise ratio and sensitivity of SiNW FET, 221 nm-SiNW was chosen for biosensing of CRP. Antibody of c-reactive protein (anti-CRP) was immobilized on the SiNW surface through polydimethylsiloxane (PDMS) microfluidic channel for detection of CRP. Specific binding of CRP with anti-CRP on the SiNW surface caused a conductance change of SiNW FET and various injections from 10 and 1 microg/ml to 100 ng/ml solutions of CRP resulted in the conductance changes from 39 and 25 to 16%, respectively. Label-free, in-situ and very sensitive electrical detection of CRP was demonstrated with the prepared SiNW FET.     

Highly ordered nanowire arrays on plastic substrates for ultrasensitive flexible chemical sensors

The development of a robust method for integrating high-performance semiconductors on flexible plastics could enable exciting avenues in fundamental research and novel applications. One area of vital relevance is chemical and biological sensing, which if implemented on biocompatible substrates, could yield breakthroughs in implantable or wearable monitoring systems. Semiconducting nanowires (and nanotubes) are particularly sensitive chemical sensors because of their high surface-to-volume ratios. Here, we present a scalable and parallel process for transferring hundreds of pre-aligned silicon nanowires onto plastic to yield highly ordered films for low-power sensor chips. The nanowires are excellent field-effect transistors, and, as sensors, exhibit parts-per-billion sensitivity to NO2, a hazardous pollutant. We also use SiO2 surface chemistries to construct a 'nano-electronic nose' library, which can distinguish acetone and hexane vapours via distributed responses. The excellent sensing performance coupled with bendable plastic could open up opportunities in portable, wearable or even implantable sensors.     

One-step growth of large-area silicon nanowire fabrics for high-performance multifunctional wearable sensors

Nano Research - Silicon nanowire (SiNW) fabrics are of great interest for fabricating high-performance multifunctional wearable sensors. However, it remains a big challenge to fabricate...     

Ultrasensitive fluorescence detection of single protein molecules manipulated electrically on Au nanowire

Proteins assembled on an Au nanowire are manipulated by an electrical potential applied on the nanowire, which leads to the modulation of molecular fluorescence. The molecular modality can be unequivocally correlated with the modulated fluorescence, which enables the specific fluorescence from a single target protein to be unambiguously distinguished from background noise and nonspecific fluorescence. As demonstrated through a thrombin assay, this simple method can significantly improve the sensitivity and specificity of the protein detection down to the single molecule level.     

Silicon nanowire arrays for label-free detection of DNA

Arrays of highly ordered n-type silicon nanowires (SiNW) are fabricated using complementary metal-oxide semiconductor (CMOS) compatible technology, and their applications in biosensors are investigated. Peptide nucleic acid (PNA) capture probe-functionalized SiNW arrays show a concentration-dependent resistance change upon hybridization to complementary target DNA that is linear over a large dynamic range with a detection limit of 10 fM. As with other SiNW biosensing devices, the sensing mechanism can be understood in terms of the change in charge density at the SiNW surface after hybridization, the so-called "field effect". The SiNW array biosensor discriminates satisfactorily against mismatched target DNA. It is also able to monitor directly the DNA hybridization event in situ and in real time. The SiNW array biosensor described here is ultrasensitive, non-radioactive, and more importantly, label-free, and is of particular importance to the development of gene expression profiling tools and point-of-care applications.     

Tin oxide nanocluster hydrogen and ammonia sensors

We have prepared sensitive hydrogen and ammonia sensors from thin films of tin nanoclusters with diameters between 3 and 10?nm. By baking the samples at 200?°C in ambient air the clusters were oxidized, resulting in very stable films of tin oxide clusters with similar diameters to the original Sn clusters. By monitoring the electrical resistance, it is shown that the cluster films are highly responsive to hydrogen and ammonia at relatively low temperatures, thereby making them attractive for commercial applications in which low power consumption is required. Doping of the films by depositing Pd on top of the clusters resulted in much improved sensor response and response times. It is shown that optimal sensor properties are achieved for very thin cluster films (a few monolayers of clusters).     

Piezotronic effect enhanced Schottky-contact ZnO micro/nanowire humidity sensors

A ZnO micro/nanowire has been utilized to fabricate Schottky-contacted humidity sensors based on a metal-semiconductor-metal （M-S-M） structure. By means of the piezotronic effect, the signal level, sensitivity and sensing resolution of the humidity sensor were significantly enhanced when applying an external strain. Since a higher Schottky barrier markedly reduces the signal level, while a lower Schottky barrier decreases the sensor sensitivity due to increased ohmic transport, a 0.22% compressive strain was found to optimize the performance of the humidity sensor, with the largest responsivity being 1,240%. The physical mechanism behind the observed mechanical-electrical behavior was carefully studied by using band structure diagrams. This work provides a promising way to significantly enhance the overall performance of a Schottky-contact structured micro/nanowire sensor.     

Deep-learning-based nanowire detection in AFM images for automated nanomanipulation

Atomic force microscope(AFM)-based nanomanipulation has been proved to be a possible method for assembling various nanoparticles into complex patterns and devices.To achieve efficient and fully automated nanomanipulation,nanoparticles on the substrate must be identified precisely and automatically.This work focuses on an autodetection method for flexible nanowires using a deep learning technique.An instance segmentation network based on You Only Look Once version 3(YOLOv3)and a fully convolutional network(FCN)is applied to segment all movable nanowires in AFM images.Combined with follow-up image morphology and fitting algorithms,this enables detection of postures and positions of nanowires at a high abstraction level.Benefitting from these algorithms,our program is able to automatically detect nanowires of different morphologies with nanometer resolution and has over 90%reliability in the testing dataset.The detection results are less affected by image complexity than the results of existing methods and demonstrate the good robustness of this algorithm.     

A photothermal interferometer for gas-phase ammonia detection

Detection of gas-phase ammonia is particularly challenging because ambient ammonia concentrations may be less than 1 ppb (molecules of NH(3) per 10(9) molecules of air), ammonia sticks to many materials commonly used to sample air, and particles containing ammonium may interfere with gas-phase measurements. We have built a new and sensitive photothermal interferometer to detect gas-phase ammonia in situ, under typical atmospheric conditions. Ammonia molecules in sampled air absorb infrared radiation from a CO(2) laser at 9.22 μm, with consequent collisional heating, expansion, and refractive index change. This change in refractive index is detected as a phase shift in one arm of a homodyne interferometer. Measurements of vibrational and electrical noise in the interferometer correlate to an instrumental lower limit of detection of 6.6 ppt ammonia in 1 s. The CO(2) laser output is modulated at 1.2 kHz, and the ac signal from the interferometer is measured with a lock-in amplifier. The detector is zeroed by sampling through a H(3)PO(4)-coated denuder tube and is calibrated by dynamic dilution of two permeation tube outputs and by standard addition. Signal gain is insensitive to CO(2) or H(2)O in the sample, and the signal is linear over 5 orders of magnitude. The instrument 2σ precision is 31 ppt when the signal is integrated for 100 s and 250 ppt with a 1-s integration time. The windowless sample cell and inlet is fabricated entirely of glass to minimize sample loss and hysteresis. The instrument response time is demonstrated to be about 1 s.     

All-aerosol-jet-printed highly sensitive and selective polyaniline-based ammonia sensors: a route toward low-cost,low-power gas detection

Journal of Materials Science - We report the design and scalable fabrication of a low-cost and low-power polyaniline-based (PANI) ammonia (NH3) gas sensor on polyimide (PI) substrates using...     

Zinc oxide nanowire gas sensors: fabrication,functionalisation and devices

With the progress in the synthesis of high quality ZnO nanowires, their implementation as gas sensors has gained popularity. Relying on the surface ionosorption, these devices have demonstrated exquisite sensitivity with further improvement achieved through various functionalisation methods. Both resistive and transistor based methodologies are employed for gas sensing while integration of micro-heaters has also been attempted for portability of the devices. In order to achieve successful inclusion amongst semiconductor fabrication processes, top-down approaches are being explored along with conventional bottom-up synthesis routes. Major challenge of low selectivity can be overcome by Electronic Nose systems. This article reviews the progress in synthesis, functionalisation, and device implementation of ZnO nanowire gas sensors, concluding with remarks on associated challenges and future prospects.     

High-strain sensors based on ZnO nanowire/polystyrene hybridized flexible films

A type of strain sensor with high tolerable strain based on a ZnO nanowires/polystyrene nanofibers hybrid structure on a polydimethylsiloxane film is reported. The novel strain sensor can measure and withstand high strain and demonstrates good performance on rapid human-motion measurements. In addition, the device could be driven by solar cells. The results indicate that the device has potential applications as an outdoor sensor system.     

Color matrix refractive index sensors using coupled vertical silicon nanowire arrays

Vivid colors are demonstrated in silicon nanowires with diameters ranging from 105 to 346 nm. The nanowires are vertically arranged in a square lattice with a pitch of 400 nm and are electromagnetically coupled to each other, resulting in frequency-dependent reflection spectra. Since the coupling is dependent on the refractive index of the medium surrounding the nanowires, the arrays can be used for sensing. A simple sensor is demonstrated by observing the change in the reflected color with changing refractive index of the surrounding medium. A refractive index resolution of 5 × 10(-5) is achieved by analyzing bright-field images captured with an optical microscope equipped with a charge coupled device camera.     

Conformable Hybrid Systems for Implantable Bioelectronic Interfaces

Conformable bioelectronic systems are promising tools that may aid the understanding of diseases, alleviate pathological symptoms such as chronic pain, heart arrhythmia, and dysfunctions, and assist in reversing conditions such as deafness, blindness, and paralysis. Combining reduced invasiveness with advanced electronic functions, hybrid bioelectronic systems have evolved tremendously in the last decade, pushed by progress in materials science, micro- and nanofabrication, system assembly and packaging, and biomedical engineering. Hybrid integration refers here to a technological approach to embed within mechanically compliant carrier substrates electronic components and circuits prepared with traditional electronic materials. This combination leverages mechanical and electronic performance of polymer substrates and device materials, respectively, and offers many opportunities for man-made systems to communicate with the body with unmet precision. However, trade-offs between materials selection, manufacturing processes, resolution, electrical function, mechanical integrity, biointegration, and reliability should be considered. Herein, prominent trends in manufacturing conformable hybrid systems are analyzed and key design, function, and validation principles are outlined together with the remaining challenges to produce reliable conformable, hybrid bioelectronic systems.     

Surface cleaning of the nanowire field-effect transistor for gene detection

The efficiency of DNA immobilization by using various surface cleaning methods is studied in this work. The degree of surface cleaning is evaluated by the surface tension measurement to reveal the contribution from the polar and apolar terms. The observation from the fluorescent microscope images indicates the effectiveness of surface clean by the acetone and ethanol mixtures, as well as the sulphuric acid and hydrogen peroxide mixtures. We also fabricate a series of back-gated, 60-nm nanowired (NW) field-effect transistor (FET) sensors for mutation gene detection by following the developed acetone and ethanol mixtures. Electrical properties of the NWFET sensor demonstrate the n-channel depletion characteristics. The current of the sensor is reduced once the attachment of negative charge molecules. The single-stranded capture DNA is chemically immobilized onto the surface of silicon NWFET by three-step reactions. The sensor surface demonstrates the great performance of current shift after the suitable cleaning. The NWFET sensor is successfully applied to detect the BRAF(V599E) mutation genes from the hybridized processes. The sensing behaviour estimated from the electrical signal reaches the femtomolar level.     

Automated target detection system for hyperspectral imaging sensors

Over the past several years, hyperspectral sensor technology has evolved to the point where real-time processing for operational applications is achievable. Algorithms supporting such sensors must be fully automated and robust. Our approach, for target detection applications, is to select signatures from a target reflectance library database and project them to the at-sensor and collection-specific radiance domain using the weather forecast or radiosonde data. This enables platform-based detection immediately following data acquisition without the need for further atmospheric compensation. One advantage of this method for reflective hyperspectral sensors is the ability to predict the radiance signatures of targets under multiple illumination conditions. A three-phase approach is implemented, where the library generation and data acquisition phases provide the necessary input for the automated detection phase. In addition to employing the target detector itself, this final phase includes a series of automated filters, adaptive thresholding, and confidence assignments to extract the optimal information from the detection scores for each spectral class. Our prototype software is applied to 50 reflective hyperspectral datacubes to measure detection performance over a range of targets, backgrounds, and environmental conditions.     

Reusable hydroxyapatite nanocrystal sensors for protein adsorption

Abstract

The repeatability of the adsorption and removal of fibrinogen and fetal bovine serum on hydroxyapatite (HAp) nanocrystal sensors was investigated by Fourier transform infrared (FTIR) spectroscopy and quartz crystal microbalance with dissipation (QCM-D) monitoring technique. The HAp nanocrystals were coated on a gold-coated quartz sensor by electrophoretic deposition. Proteins adsorbed on the HAp sensors were removed by (i) ammonia/hydrogen peroxide mixture (APM), (ii) ultraviolet light (UV), (iii) UV/APM, (iv) APM/UV and (v) sodium dodecyl sulfate (SDS) treatments. FTIR spectra of the reused surfaces revealed that the APM and SDS treatments left peptide fragments or the proteins adsorbed on the surfaces, whereas the other methods successfully removed the proteins. The QCM-D measurements indicated that in the removal treatments, fibrinogen was slowly adsorbed in the first cycle because of the change in surface wettability revealed by contact angle measurements. The SDS treatment was not effective in removing proteins. The APM or UV treatment decreased the frequency shifts for the reused HAp sensors. The UV/APM treatment did not induce the frequency shifts but decreased the dissipation shifts. Therefore, we conclude that the APM/UV treatment is the most useful method for reproducing protein adsorption behavior on HAp sensors.