Chunxiao Hu

NeuroChip: A Microfluidic Electrophysiological Device for Genetic and Chemical Biology Screening of Caenorhabditis elegans Adult and Larvae

Genetic and chemical biology screens of C. elegans have been of enormous benefit in providing fundamental insight into neural function and neuroactive drugs. Recently the exploitation of microfluidic devices has added greater power to this experimental approach providing more discrete and higher throughput phenotypic analysis of neural systems. Here we make a significant addition to this repertoire through the design of a semi-automated microfluidic device, NeuroChip, which has been optimised for selecting worms based on the electrophysiological features of the pharyngeal neural network. We demonstrate this device has the capability to sort mutant from wild-type worms based on high definition extracellular electrophysiological recordings. NeuroChip resolves discrete differences in excitatory, inhibitory and neuromodulatory components of the neural network from individual animals. Worms may be fed into the device consecutively from a reservoir and recovered unharmed. It combines microfluidics with integrated electrode recording for sequential trapping, restraining, recording, releasing and recovering of C. elegans. Thus mutant worms may be selected, recovered and propagated enabling mutagenesis screens based on an electrophysiological phenotype. Drugs may be rapidly applied during the recording thus permitting compound screening. For toxicology, this analysis can provide a precise description of sub-lethal effects on neural function. The chamber has been modified to accommodate L2 larval stages showing applicability for small size nematodes including parasitic species which otherwise are not tractable to this experimental approach. We also combine NeuroChip with optogenetics for targeted interrogation of the function of the neural circuit. NeuroChip thus adds a new tool for exploitation of C. elegans and has applications in neurogenetics, drug discovery and neurotoxicology.

Low-Cost Nanoribbon Sensors for Protein Analysis in Human Serum Using a Miniature Bead-Based Enzyme-Linked Immunosorbent Assay

We describe a low cost thin-film transistor (TFT) nanoribbon sensor for detection of the inflammatory biomarker C-reactive protein (CRP) in human serum via a miniature bead-based enzyme-linked immunosorbent assay (ELISA). The TFT nanoribbon sensor measures the reaction products from the ELISA via pH changes. The bead-based ELISA decouples the protein functionalization steps from the sensor surface, increasing the signal and simplifying the assay. The ability to directly sense proteins in human serum in this way overcomes the Debye length limitation associated with nanowire and nanoribbon biosensors. Compared to classically fabricated nanowires, the TFT nanoribbon sensors are simple, extremely easy to fabricate, and should therefore be much cheaper to manufacture. TFT nanoribbon sensors, configured to measure pH, were used for quantitative detection of CRP spiked into human serum at concentrations as low as 0.2 ng/mL, which is 10 000 times lower than needed for diagnostic purposes, providing the potential for applications that require very high sensitivity.

Effect of subthreshold slope on the sensitivity of nanoribbon sensors

In this work, we investigate how the sensitivity of a nanowire or nanoribbon sensor is influenced by the subthreshold slope of the sensing transistor. Polysilicon nanoribbon sensors are fabricated with a wide range of subthreshold slopes and the sensitivity is characterized using pH measurements. It is shown that there is a strong relationship between the sensitivity and the device subthreshold slope. The sensitivity is characterized using the current sensitivity per pH, which is shown to increase from 1.2% ph(-1) to 33.6% ph(-1) as the subthreshold slope improves from 6.2 V dec(-1) to 0.23 V dec(-1) respectively. We propose a model that relates current sensitivity per pH to the subthreshold slope of the sensing transistor. The model shows that sensitivity is determined only on the subthreshold slope of the sensing transistor and the choice of gate insulator. The model fully explains the values of current sensitivity per pH for the broad range of subthreshold slopes obtained in our fabricated nanoribbon devices. It is also able to explain values of sensitivity reported in the literature, which range from 2.5% pH(-1) to 650% pH(-1) for a variety of nanoribbon and nanowire sensors. Furthermore, it shows that aggressive device scaling is not the key to high sensitivity. For the first time, a figure-of-merit is proposed to compare the performance of nanoscale field effect transistor sensors fabricated using different materials and technologies.

One-Step Electrodeposition of NiCo2S4 Nanosheets on Patterned Platinum Electrodes for Non-Enzymatic Glucose Sensing

The preparation of NiCo2 S4 (NCS) nanosheets on photolithographically patterned platinum electrodes by electrodeposition was explored. The as-prepared nanosheets were systematically characterized by field-emission scanning electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy techniques. The NCS-modified Pt electrode was used as a non-enzymatic glucose sensor. The sensor response exhibited two linear regions in glucose concentration, with a limit of detection of 1.2 μm. The sensors showed that the as-prepared NCS nanosheets have excellent electrocatalytic activity towards glucose with long stability, good reproducibility, and excellent anti-interference properties, and thus, this material holds promise for the development of a practical glucose sensor.

Ultra-fast electronic detection of antimicrobial resistance genes using isothermal amplification and thin film transistor sensors

A low cost thin-film transistor (TFT) nanoribbon (NR) sensor has been developed for rapid real-time detection of DNA amplification using an isothermal Recombinase Polymerase Amplification (RPA) method. The semiconductor chip measures DNA amplification through a pH change, rather than via fluorescence. The utility of the method was demonstrated by amplifying CTX-M and NDM, two genes that confer bacterial resistance to cephalosporins and carbapenems, respectively. It is shown that this approach provides extremely fast and sensitive detection. It can detect <10 copies of the gene in genomic DNA extracted from E. coli or K. pneumoniae clinical isolates within a few minutes. A differential readout system was developed to minimize the effect of primer-dimer amplification on the assay. The simple device has the potential for low cost, portable and real-time nucleic acid analysis as a Point of Care device.

Dual-gate polysilicon nanoribbon biosensors enable high sensitivity detection of proteins

We demonstrate the advantages of dual-gate polysilicon nanoribbon biosensors with a comprehensive evaluation of different measurement schemes for pH and protein sensing. In particular, we compare the detection of voltage and current changes when top- and bottom-gate bias is applied. Measurements of pH show that a large voltage shift of 491 mV pH(-1) is obtained in the subthreshold region when the top-gate is kept at a fixed potential and the bottom-gate is varied (voltage sweep). This is an improvement of 16 times over the 30 mV pH(-1) measured using a top-gate sweep with the bottom-gate at a fixed potential. A similar large voltage shift of 175 mV is obtained when the protein avidin is sensed using a bottom-gate sweep. This is an improvement of 20 times compared with the 8.8 mV achieved from a top-gate sweep. Current measurements using bottom-gate sweeps do not deliver the same signal amplification as when using bottom-gate sweeps to measure voltage shifts. Thus, for detecting a small signal change on protein binding, it is advantageous to employ a double-gate transistor and to measure a voltage shift using a bottom-gate sweep. For top-gate sweeps, the use of a dual-gate transistor enables the current sensitivity to be enhanced by applying a negative bias to the bottom-gate to reduce the carrier concentration in the nanoribbon. For pH measurements, the current sensitivity increases from 65% to 149% and for avidin sensing it increases from 1.4% to 2.5%.

Towards a high-precision, embedded system for versatile sensitive biosensing measurements

This paper demonstrates a versatile, high-accuracy, data-acquisition electronic platform for biosensing measurements, capable of collecting minute current and voltage input signals, stemming from various types of amperometric and potentiometric biosensors. The instrument is able to process the incoming analog signals in a digital manner and export them back to the user either as an amplified analog signal or in digital format through a USB 2.0 interface. The proposed system comprises off-the-shelf IC components and a commercially available FPGA-based DSP unit. The performance of the instrumentation platform has been tested initially by means of very small ideal current and voltage signals generated by precise electronic equipments and subsequently has been validated via proof-of-concept experiments with amperometric and potentiometric sensors. The results shown in this paper exhibit potential for integrating specific sections of the proposed instrumentation board with appropriate biosensors, towards developing affordable, yet reliable Point-Of-Care (POC) diagnostic tools for sensitive biochemical measurements.

Hybrid Dual Mode Sensor for Simultaneous Detection of Two Serum Metabolites

Metabolites are the ultimate readout of disease phenotype that plays a significant role in the study of human disease. Multiple metabolites sometimes serve as biomarkers for a single metabolic disease. Therefore, simultaneous detection and analysis of those metabolites facilitate early diagnostics of the disease. Conventional approaches to detect and quantify metabolites include mass spectrometry and nuclear magnetic resonance that require bulky and expensive equipment. Here, we present a disposable sensing platform that is based on complementary metal–oxide–semiconductor process. It contains two sensors: an ion sensitive field-effect transistor and photodiode that can work independently for detection of pH and color change produced during the metabolite-enzyme reaction. Serum glucose and cholesterol have been detected and quantified simultaneously with the new platform, which shows good sensitivity within the physiological range. Low cost and easy manipulation make our device a prime candidate for personal metabolome sensing diagnostics.

Hybrid localized surface plasmon resonance and quartz crystal microbalance sensor for label free biosensing

We report on the design and fabrication of a hybrid sensor that integrates transmission-mode localized surface plasmonic resonance (LSPR) into a quartz crystal microbalance (QCM) for studying biochemical surface reactions. The coupling of LSPR nanostructures and a QCM allows optical spectra and QCM resonant frequency shifts to be recorded simultaneously and analyzed in real time for a given surface adsorption process. This integration simplifies the conventional combination of SPR and QCM and has the potential to be miniaturized for application in point-of-care (POC) diagnostics. The influence of antibody-antigen recognition effect on both the QCM and LSPR has been analyzed and discussed.

A Sub-30 mpH Resolution Thin Film Transistor-Based Nanoribbon Biosensing Platform

We present a complete biosensing system that comprises a Thin Film Transistor (TFT)-based nanoribbon biosensor and a low noise, high-performance bioinstrumentation platform, capable of detecting sub-30 mpH unit changes, validated by an enzymatic biochemical reaction. The nanoribbon biosensor was fabricated top-down with an ultra-thin (15 nm) polysilicon semiconducting channel that offers excellent sensitivity to surface potential changes. The sensor is coupled to an integrated circuit (IC), which combines dual switched-capacitor integrators with high precision analog-to-digital converters (ADCs). Throughout this work, we employed both conventional pH buffer measurements as well as urea-urease enzymatic reactions for benchmarking the overall performance of the system. The measured results from the urea-urease reaction demonstrate that the system can detect urea in concentrations as low as 25 μM, which translates to a change of 27 mpH, according to our initial pH characterisation measurements. The attained accuracy and resolution of our system as well as its low-cost manufacturability, high processing speed and portability make it a competitive solution for applications requiring rapid and accurate results at remote locations; a necessity for Point-of-Care (POC) diagnostic platforms.