Fabrication and characteristics of MOSFET protein chip for detection of ribosomal protein

A metal oxide silicon field effect transistor (MOSFET) protein chip for the easy detection of protein was fabricated and its characteristics were investigated. Generally, the drain current of the MOSFET is varied by the gate potential. It is expected that the formation of an antibody-antigen complex on the gate of MOSFET would lead to a detectable change in the charge distribution and thus, directly modulate the drain current of MOSFET. As such, the drain current of the MOSFET protein chip can be varied by ribosomal proteins absorbed by the self-assembled monolayer (SAM) immobilized on the gate (Au) surface, as ribosomal protein has positive charge, and these current variations then used as the response of the protein chip. The gate of MOSFET protein chip is not directly biased by an external voltage source, so called open gate or floating gate MOSFET, but rather chemically modified by immobilized molecular receptors called self-assembled monolayer (SAM). In our experiments, the current variation in the proposed protein chip was about 8% with a protein concentration of 0.7 mM. As the protein concentration increased, the drain current also gradually increased. In addition, there were some drift of the drain current in the device. It is considered that these drift might be caused by the drift from the MOSFET itself or protein absorption procedures that are relied on the facile attachment of thiol (-S) ligands to the gate (Au) surface. We verified the formation of SAM on the gold surface and the absorption of protein through the surface plasmon resonance (SPR) measurement.     

Direct protein detection with a nano-interdigitated array gate MOSFET

A new protein sensor is demonstrated by replacing the gate of a metal oxide semiconductor field effect transistor (MOSFET) with a nano-interdigitated array (nIDA). The sensor is able to detect the binding reaction of a typical antibody Ixodes ricinus immunosuppressor (anti-Iris) protein at a concentration lower than 1 ng/ml. The sensor exhibits a high selectivity and reproducible specific detection. We provide a simple model that describes the behavior of the sensor and explains the origin of its high sensitivity. The simulated and experimental results indicate that the drain current of nIDA-gate MOSFET sensor is significantly increased with the successive binding of the thiol layer, Iris and anti-Iris protein layers. It is found that the sensor detection limit can be improved by well optimizing the geometrical parameters of nIDA-gate MOSFET. This nanobiosensor, with real-time and label-free capabilities, can easily be used for the detection of other proteins, DNA, virus and cancer markers. Moreover, an on-chip associated electronics nearby the sensor can be integrated since its fabrication is compatible with complementary metal oxide semiconductor (CMOS) technology.     

Molecular charge contact biosensing based on the interaction of biologically modified magnetic beads with an ion-sensitive field effect transistor

In this article, we report a novel method of biomolecular recognition based on the molecular charge contact (MCC). As one of the MCC biosensing method, the interaction between DNA-coated magnetic beads and a silicon-based semiconductor, an ion-sensitive field effect transistor (ISFET) could be detected for DNA molecular recognition events using the principle of the field effect, which enables detecting ionic or molecular charges. After DNA-coated magnetic beads had been introduced and brought in contact with the gate surface by a magnet, the threshold voltage of the ISFET was shifted in the positive direction by immobilization, hybridization and extension reaction of DNA molecules on magnetic beads. This positive shift was based on the increase in negative charges of the phosphate groups in them. Then, the ISFET device could be reused a couple of dozen times continuously and cost-effectively because the oligonucleotide probes were tethered to the magnetic beads, but this was not done directly on the gate surface of the ISFET. Moreover, the MCC biosensing method enabled discrimination of a single nucleotide polymorphism. By creating an interaction of magnetic beads with the semiconductor, we can expect enhancement of the reaction efficiency in a solution and reuse of the device by separating the reaction field from the sensing substrate.     

Tribovoltaic Effect on Metal–Semiconductor Interface for Direct‐Current Low‐Impedance Triboelectric Nanogenerators

The triboelectric nanogenerator (TENG) is a new energy technology that is enabled by coupled contact electrification and electrostatic induction. The conventional TENGs are usually based on organic polymer insulator materials, which have the limitations and disadvantages of high impedance and alternating output current. Here, a tribovoltaic effect based metal–semiconductor direct‐current triboelectric nanogenerator (MSDC‐TENG) is reported. The tribovoltaic effect is facilitated by direct voltage and current by rubbing a metal/semiconductor on another semiconductor. The frictional energy released by the forming atomic bonds excites nonequilibrium carriers, which are directionally separated to form a current under the built‐in electric field. The continuous average open‐circuit voltage (10–20 mV), short‐circuit direct‐current output (10–20 µA), and low impedance characteristic (0.55–5 kΩ) of the MSDC‐TENG can be observed during relative sliding of the metal and silicon. The working parameters are systematically studied for electric output and impedance characteristics. The results reveal that faster velocity, larger pressure, and smaller area can improve the maximum power density. The internal resistance is mainly determined by the velocity and the electrical resistance of semiconductor. This work not only expands the material candidates of TENGs from organic polymers to semiconductors, but also demonstrates a tribovoltaic effect based electric energy conversion mechanism.     

DNA hybridization sensor based on pentacene thin film transistor

A DNA hybridization sensor using pentacene thin film transistors (TFTs) is an excellent candidate for disposable sensor applications due to their low-cost fabrication process and fast detection. We fabricated pentacene TFTs on glass substrate for the sensing of DNA hybridization. The ss-DNA (polyA/polyT) or ds-DNA (polyA/polyT hybrid) were immobilized directly on the surface of the pentacene, producing a dramatic change in the electrical properties of the devices. The electrical characteristics of devices were studied as a function of DNA immobilization, single-stranded vs. double-stranded DNA, DNA length and concentration. The TFT device was further tested for detection of λ-phage genomic DNA using probe hybridization. Based on these results, we propose that a "label-free" detection technique for DNA hybridization is possible through direct measurement of electrical properties of DNA-immobilized pentacene TFTs.     

Electrical detection of biomolecular interactions with metal-insulator-semiconductor diodes

We report the label-free detection of DNA hybridization using a metal-insulator-semiconductor (MIS) diode or capacitor. Upon immobilization of single-stranded DNA on the gold gate of a MIS capacitor, the capacitance versus voltage characteristics show a significant shift in the direction of negative voltages as expected from the immobilization of negative charges on the gate. The hybridization with the complementary strand gives rise to a further significant shift in the same direction as before, which is consistent with the increase of negative charges on the gate brought about by the hybridization. Fluorescence studies indicate that the immobilization and hybridization of DNA can be electrostatically promoted by electric fields externally applied to the MIS capacitors. The MIS diode detection method is applicable to all biomolecular interactions that affect the surface dipole at the interface between the metal gate and the electrolyte and can be extended to other chemical and biochemical systems such as proteins and cells.     

Gate Length Variation Effect on Performance of Gate-First Self-Aligned In0.53Ga0.47As MOSFET

A multi-gate n-type In_0.53Ga_0.47As MOSFET is fabricated using gate-first self-aligned method and air-bridge technology. The devices with different gate lengths were fabricated with the Al₂O₃ oxide layer with the thickness of 8 nm. In this letter, impact of gate length variation on device parameter such as threshold voltage, high and low voltage transconductance, subthreshold swing and off current are investigated at room temperature. Scaling the gate length revealed good enhancement in all investigated parameters but the negative shift in threshold voltage was observed for shorter gate lengths. The high drain current of 1.13 A/mm and maximum extrinsic transconductance of 678 mS/mm with the field effect mobility of 364 cm²/Vs are achieved for the gate length and width of 0.2 µm and 30µm, respectively. The source/drain overlap length for the device is approximately extracted about 51 nm with the leakage current in order of 10⁻⁸ A. The results of RF measurement for cut-off and maximum oscillation frequency for devices with different gate lengths are compared.     

Electrochemical sensor based on photopolymeric membranes for determining urea

A new electrochemical enzymatic sensor based on the ion selective field effect transistors (ISFETs) and photocurable membrane was developed for the determination of urea. For the immobilization of urease on the gate surface of the ISFET a simple method, involving the use of liquid photocurable compositions on the basis of vinylpirollidone, oligouretanemetacrylate and oligocarbonatemetacrylate, was applied. The linearange of the response of the developed electrochemical sensor lies in the range 0.05-20 mM. The latter corresponds to the claims of the medical practice. The overall time of the analysis is 5-10 min. The effects of the buffer concentration and its pH as well as temperature and presence of ammonia ions in the measuring medium on the amplitude of the sensor response were estimated. The duration of sensor work is as shortest 40 days. The proposed sensor on the basis of the ISFET is promising for the express analysis of the level urea in blood, while the developed method of membrane preparation with entrapped enzyme can be combined with the integral technology of producing of the biosensors semiconductor transducers.     

Development of FET-type albumin sensor for diagnosing nephritis

An albumin biosensor based on a potentiometric measurement using Biofield-effect-transistor (BioFET) has been designed and fabricated, and its characteristics were investigated. The BioFET was fabricated using semiconductor integrated circuit (IC) technology. The gate surface of the BioFET was chemically modified by newly developed self-assembled monolayer (SAM) synthesized by a thiazole benzo crown ether ethylamine (TBCEA)-thioctic acid to immobilize anti-albumin. SAM formation, antibody immobilization, and antigen-antibody interaction were verified using surface plasmon resonance (SPR). The output voltage changes of the BioFET with respect to various albumin concentrations were obtained. Quasi-reference electrode (QRE) and reference FET (ReFET) has been integrated with the BioFET, and its output characteristic was investigated. The results demonstrate the feasibility of the BioFET as the albumin sensor for diagnosing nephritis.     

Pressure sensing using a completely flexible organic transistor

In this paper, we report on pressure sensors based on completely flexible organic thin film transistors (OTFTs). A flexible and transparent plastic foil (Mylar) is employed both as substrate and gate dielectric. Gold source and drain electrodes are patterned on the upper side of the foil while the gate electrode lies on the opposite side; a vacuum-sublimed pentacene film is used as active layer. The pressure dependence of the output current has been investigated by applying to the gate side of the device a mechanical stimulus by means of a pressurized airflow. Experimental results show a reversible dependence of the current on the pressure. The data analysis suggests that the current variations are due to pressure-induced variations of mobility, threshold voltage and possibly contact resistance. The drain current variation is reproducible, linear and reversible even though it displays a hysteresis. Moreover, the sensor responds very fast to the mechanical stimulus (i.e. within tens–hundreds of milliseconds) but the time required to reach the steady state is much higher (tens–hundreds of seconds). Electrical characteristics with and without applied pressure have been carried out in air without any extra ad hoc read-out circuit or equipment.

The reported devices show potential advantages of flexibility of the structure, low cost and versatility of the device structure for sensor technologies. Many innovative and attractive applications as wearable electronics, e-textiles, e-skin for robots can be considered.     

Effect of Geometric Parameters on the Performance of P-Type Junctionless Lateral Gate Transistors

This paper examines the impact of two important geometrical parameters, namely the thickness and source/drain extensions on the performance of low doped p-type double lateral gate junctionless transistors (DGJLTs). The three dimensional Technology Computer-Aided Design simulation is implemented to calculate the characteristics of the devices with different thickness and source/drain extension and based on that, the parameters such as threshold voltage, transconductance and resistance in saturation region are analyzed. In addition, simulation results provide a physical explanation for the variation of device characteristics given by the variation of geometric parameters, mainly based on investigation of the electric field components and the carries density variation. It is shown that, the variation of the carrier density is the main factor which affects the characteristics of the device when the device''s thickness is varied. However, the electric field is mainly responsible for variation of the characteristics when the source/drain extension is changed.     

Labelfree fully electronic nucleic acid detection system based on a field-effect transistor device

The labelfree detection of nucleic acid sequences is one of the modern attempts to develop quick, cheap and miniaturised hand-held devices for the future genetic testing in biotechnology and medical diagnostics. We present an approach to detect the hybridisation of DNA sequences using electrolyte-oxide-semiconductor field-effect transistors (EOSFETs) with micrometer dimensions. These semiconductor devices are sensitive to electrical charge variations that occur at the surface/electrolyte interface, i.e. upon hybridisation of oligonucleotides with complementary single-stranded (ss) oligonucleotides, which are immobilised on the oxide surface of the transistor gate. This method allows direct, time-resolved and in situ detection of specific nucleic acid binding events without any labelling. We focus on the detection mechanism of our sensors by using oppositely charged polyelectrolytes (PAH and PSS) subsequently attached to the transistor structures. Our results indicate that the sensor output is charge sensitive and distance dependent from the gate surface, which pinpoints the need for very defined surface chemistry at the device surface. The hybridisation of natural 19 base-pair sequences has been successfully detected with the sensors. In combination with nano-transistors a PCR free detection system might be feasible in future.     

Detection of DNA recognition events using multi-well field effect devices

We proposed the multi-well field effect device for detection of charged biomolecules and demonstrated the detection principle for DNA recognition events using quasi-static capacitance-voltage (QSCV) measurement. The multi-well field effect device is based on the electrostatic interaction between molecular charges induced by DNA recognition and surface electrons in silicon through the Si(3)N(4)/SiO(2) thin double-layer. Since DNA molecules and DNA binders such as Hoechst 33258 have intrinsic charges in aqueous solutions, respectively, the charge density changes due to DNA recognition events at the Si(3)N(4) surface were directly translated into electrical signal such as a flat band voltage change in the QSCV measurement. The average flat band shifts were 20.7 mV for hybridization and -13.5 mV for binding of Hoechst 33258. From the results of flat band voltage shifts due to hybridization and binding of Hoechst 33258, the immobilization density of oligonucleotide probes at the Si(3)N(4) surface was estimated to be 10(8) cm(-2). The platform based on the multi-well field effect device is suitable for a simple and arrayed detection system for DNA recognition events.     

Label-free DNA sensor based on organic thin film transistors

Organic thin film transistors (OTFTs) are excellent candidates for the application on disposable sensors due to their potentially low-cost fabrication process. A novel DNA sensor based on OTFTs with semiconducting polymer poly(3-hexylthiophene) has been fabricated by solution process. Both single- and double-strand DNA molecules are immobilized on the surface of the Au source/drain electrodes of different OTFT devices, producing a dramatic change in the performance of the devices, which is attributed to the increase of the contact resistances at the source/drain electrodes. Single-strand DNA and double-strand DNA are differentiated successfully in the experiments indicating that this is a promising technique for sensing DNA hybridization without labelling.     

Direct transduction of allele-specific primer extension into electrical signal using genetic field effect transistor

We have developed a genetic field effect transistor (FET) for single nucleotide polymorphism (SNP) genotyping, which is based on potentiometric detection of molecular recognition on the gate insulator. Here, we report direct transduction of allele-specific primer extension on the gate surface into electrical signal using the genetic FETs. This method is based on detection of intrinsic negative charges of polynucleotide synthesized by DNA polymerase. The charge density change at the gate surface could be monitored during primer extension reaction. Moreover, three different genotypes could be successfully distinguished without any labeling for target DNA by the use of the genetic FET in combination with allele-specific primer extension. The platform based on the genetic FETs is suitable for a simple, accurate and inexpensive system for SNP genotyping in clinical diagnostics.     

Effect of Direct-Current Electric Field on Enzymatic Activity and the Concentration of Laccase

This work investigates the effect of direct-current electric field on the extracellular enzymatic activity, concentration and other experimental parameters of laccase from Trametes versicolor. The results showed that laccase could significantly contribute to the change of pH at the end of graphite electrode. In addition, it increased the electrical conductivity of the water. In the experiment, the optimum pH and catalytic pH range for laccase activity were 3.0 and pH 2.5–4.0. The application of 6 V direct current showed significant effects on the laccase enzyme activity. The activity of laccase was enhanced in the anodic region, but at the same time was strongly inhibited at the cathode. The electric charge characteristics of laccase were changed when exposed to electric field, and some laccases molecules moved to the anode, which produced a slight migration phenomenon. This study is the basis of combination of laccase and electrical technology, at the same time, providing a new direction of enhancing laccase activity. Compared to immobilization, using electric field is simple, no chemical additives, and great potential.     

Inactivation of the sodium channel. II. Gating current experiments

Gating current (Ig) has been studied in relation to inactivation of Na channels. No component of Ig has the time course of inactivation; apparently little or no charge movement is associated with this step. Inactivation nonetheless affects Ig by immobilizing about two-thirds of gating charge. Immobilization can be followed by measuring ON charge movement during a pulse and comparing it to OFF charge after the pulse. The OFF:ON ratio is near 1 for a pulse so short that no inactivation occurs, and the ratio drops to about one-third with a time course that parallels inactivation. Other correlations between inactivation and immobilization are that: (a) they have the same voltage dependence; (b) charge movement recovers with the time coures of recovery from inactivation. We interpret this to mean that the immobilized charge returns slowly to "off" position with the time course of recovery from inactivation, and that the small current generated is lost in base-line noise. At -150 mV recover is very rapid, and the immobilized charge forms a distinct slow component of current as it returns to off position. After destruction of inactivation by pronase, there is no immobilization of charge. A model is presented in which inactivation gains its voltage dependence by coupling to the activation gate.     

Development of DNA electrochemical biosensor based on covalent immobilization of probe DNA by direct coupling of sol-gel and self-assembly technologies

A new procedure for fabricating deoxyribonucleic acid (DNA) electrochemical biosensor was developed based on covalent immobilization of target single-stranded DNA (ssDNA) on Au electrode that had been functionalized by direct coupling of sol-gel and self-assembled technologies. Two siloxanes, 3-mercaptopropyltrimethoxysiloxane (MPTMS) and 3-glycidoxypropyltrimethoxysiloxane (GPTMS) were used as precursors to prepare functionally self-assembly sol-gel film on Au electrode. The thiol group of MPTMS allowed assembly of MPTMS sol-gel on gold electrode surface. Through co-condensation between silanols, GPTMS sol-gel with epoxide groups interconnected into MPTMS sol-gel and enabled covalent immobilization of target NH(2)-ssDNA through epoxide/amine coupling reaction. The concentration of MPTMS and GPTMS influenced the performance of the resulting biosensor due to competitive sol-gel process. The linear range of the developed biosensor for determination of complementary ssDNA was from 2.51 x 10(-9) to 5.02 x 10(-7)M with a detection limit of 8.57 x 10(-10)M. The fabricated biosensor possessed good selectivity and could be regenerated. The covalent immobilization of target ssDNA on self-assembled sol-gel matrix could serve as a versatile platform for DNA immobilization and fabrication of biosensors.     

Organic Field‐Effect Transistor for Energy‐Related Applications: Low‐Power‐Consumption Devices,Near‐Infrared Phototransistors,and Organic Thermoelectric Devices

The organic field‐effect transistor (OFET) is the basic building block of integrated circuits. The charge carrier mobility and operating frequency of OFETs have continued to increase; therefore, the power dissipation of OFETs can no longer be ignored. Many research efforts have been made to develop low‐power‐consumption OFETs and complementary circuits. Despite the switching function, OFETs can also be utilized in emerging energy‐related applications, such as near‐infrared (NIR) photodetectors and organic thermoelectric devices. Organic phototransistors show considerably higher photo responsivity than other photodetector architectures due to field‐effect charge modulation. The photoinduced gate modulating largely suppresses the dark current while simultaneously providing gain. These characteristics may favor NIR light detection and suggest that the organic phototransistor is a promising candidate for optoelectronic applications in the NIR regime. For organic thermoelectric applications, OFETs can work as a powerful tool for examining the charge and energy transport in the organic semiconductor, thus giving insight into organic thermoelectric studies. In this review, the authors highlight recent advances in OFET‐ related energy topics, including low‐power‐consumption OFETs, NIR photodetectors, and organic thermoelectric devices. The remaining challenges in the field will also be discussed.     

Microscopic Kinetics of DNA Translocation through synthetic nanopores

We have previously demonstrated that a nanometer-diameter pore in a nanometer-thick metal-oxide-semiconductor-compatible membrane can be used as a molecular sensor for detecting DNA. The prospects for using this type of device for sequencing DNA are avidly being pursued. The key attribute of the sensor is the electric field-induced (voltage-driven) translocation of the DNA molecule in an electrolytic solution across the membrane through the nanopore. To complement ongoing experimental studies developing such pores and measuring signals in response to the presence of DNA, we conducted molecular dynamics simulations of DNA translocation through the nanopore. A typical simulated system included a patch of a silicon nitride membrane dividing water solution of potassium chloride into two compartments connected by the nanopore. External electrical fields induced capturing of the DNA molecules by the pore from the solution and subsequent translocation. Molecular dynamics simulations suggest that 20-basepair segments of double-stranded DNA can transit a nanopore of 2.2 x 2.6 nm(2) cross section in a few microseconds at typical electrical fields. Hydrophobic interactions between DNA bases and the pore surface can slow down translocation of single-stranded DNA and might favor unzipping of double-stranded DNA inside the pore. DNA occluding the pore mouth blocks the electrolytic current through the pore; these current blockades were found to have the same magnitude as the blockade observed when DNA transits the pore. The feasibility of using molecular dynamics simulations to relate the level of the blocked ionic current to the sequence of DNA was investigated.