Enzyme Modified Field Effect Transistor Research Articles

Graphene-based enzyme-modified field-effect transistor biosensor for monitoring drug effects in Alzheimer’s disease treatment

A reduced graphene oxide-based enzyme-modified field-effect transistor (RGO-EnFET) was fabricated to study the enzymatic kinetics between acetylcholinesterase (AChE) and acetylcholine (ACh), which are related to the progression and treatment of Alzheimer’s disease (AD). The RGO-EnFET exhibited typical ambipolar transfer characteristics with a charge neutrality point (the Dirac point, VDirac) in an aqueous environment, and biological events occurring on the RGO surface were evaluated by observing the Dirac point shift (ΔVDirac) according to reactions. First, the pH sensitivity of the RGO-EnFET was measured to be 24.12 mV pH−1 for a pH range of 4–10 with excellent repeatability. Then, ACh quantification in the concentration range of 1 μM–10 mM was evaluated, with a linear slope of 13.9 mV dec−1 being obtained between ΔVDirac and the ACh concentration on a logarithmic scale. The effects of AChE inhibitors (donepezil and rivastigmine) on the AChE enzymatic activity were also investigated. The distinguishable inhibition rates were acquired for donepezil and rivastigmine at saturation levels of 90% and 75%, respectively. These results indicate that the RGO-EnFET biosensor was successfully exploited as an in vitro analytical tool and has potential of future application in the study of enzymatic kinetics and drug screening for therapeutic purposes.

Glucose Sensing by an Enzyme-modified ZnO-based FET

Characteristics of an enzyme-modified field-effect transistor (EnFET) made of a ZnO-based ion-sensitive FET with immobilized glucose oxidase on the gate surface are studied for the application to healthcare chips. The EnFET was found to be able to detect reversibly and repeatedly the β-D glucose in solution in the range of 0.2-40 mmol/L with an apparent Michaelis constant of 3.3 mmol/L, indicating the suitability for diabetic plasma glucose sensors.

Glycine gated spiking inhibitory postsynaptic membrane at the synaptic cleft.

Enzyme modified field effect transistor (ENFET) may be used to represent the variable conductance of transmitter-gated ion channels in the postsynaptic region of the neuron. The objective of this work is to develop a simple analog circuit model that can simulate the function of neurotransmitter glycine gated ion channels of postsynaptic membrane at the synaptic cleft. In this paper, Glycine sensitive ENFET is incorporated into the Hodgkin-Huxley (H-H) circuit model of the postsynaptic membrane at the synaptic cleft. Simulation of the circuit model yields an output representing the membrane potential of the synaptic region. Simulation is performed in MATLAB environment for inhibitory action of synapses. This model can be used in neuro-bioengineering fields for simulation of binding activity and electrical activity of the postsynaptic region.

Laser-unzipped carbon nanotube based glucose sensor for separated structure of enzyme modified field effect transistor

A glucose sensing film composed of unzipped multiwalled carbon nanotubes (MWCNTs) via continuous-wave laser irradiation is investigated. Some structural defects decorate on MWCNTs after an acid treatment, and the MWCNTs are unzipped into sheet-shaped layers initiated from these defects after the laser irradiation. The laser-irradiated carbon nanotube thin films (CNTFs) possess higher conductance owing to larger contact area, and the side edges of unzipped CNTs could act as sensing sites for hydrogen ions. Thus the laser-irradiated CNTF as a glucose sensing film could achieve a higher sensitivity of 0.302mV(mg/dl)−1, equal to 7.55mV(mg/dl)−1 per centimeter square, and a larger linearity of 0.9947 than the as-sprayed one. Moreover, the fully low-temperature processes of this work also reveal the potentials for flexible and disposable biosensors.

Biologically inspired circuit model for simulation of glutamate gated ion channels of the postsynaptic membrane at synaptic cleft.

Enzyme modified field effect transistor (ENFET) may be used to represent the variable conductance of transmitter-gated ion channels in the postsynaptic region of the neuron. The objective of this work is to develop a simple analog circuit model that can simulate the function of neurotransmitter glutamate gated ion channels of postsynaptic membrane at the synaptic cleft. In this paper, Glutamate sensitive ENFET is incorporated into the Hodgkin-Huxley (H-H) circuit model of the postsynaptic membrane at the synaptic cleft. Simulation of the circuit model yields an output representing the membrane potential of the synaptic region. Simulation is performed in MATLAB environment for excitatory action of synapses. This model can be used in neuro-bioengineering programs for simulation of binding activity and electrical activity of the postsynaptic region.

Modeling Neuron for Simulation of Transmitter Gated Ion Channels of Postsynaptic Membrane at Synaptic Cleft

The variable conductance of postsynaptic membrane of neuron dependence on the neurotransmitterreceptor binding activity is represented by ion sensitive field effect transistor (ISFET). ISFET functions not only as a voltage controlled conductance but can also be converted into an enzyme modified field effect transistor (ENFET) and therefore can provide a means of measurement of specific neurotransmitters that bind with the receptor sites of postsynaptic membrane. This analog is incorporated into the Hodgkin-Huxley (H-H) model of neuron to substitute the variable Na + and Cl - conductances. Simulation is performed in MATLAB environment both for excitatory and inhibitory states and results are presented.

Enzyme-Modified Field Effect Transistors Based on Surface-Conductive Single-Crystalline Diamond

Enzyme-modified field effect transistors (ENFETs) were realized using surface-conductive single-crystalline diamond films. The enzymes penicillinase and acetylcholinesterase were immobilized onto the active area of diamond-based electrolytic solution gated FETs, using different organic linker molecules and cross-linking chemistries. The active area of the devices was patterned to generate enzyme-modified regions next to surface-conductive regions. Penicillinase was chosen as a robust model system, but the main focus of the present paper is on acetylcholinesterase, an enzyme essential for many neuronal signal transduction processes. All the different ENFETs show a clear and specific response to the corresponding substrate, penicillin and acetylcholine. The device response is based on the pH sensitivity of the surface-conductive active area and is enabled by the local pH change induced during the enzymatic reaction. The devices demonstrate promising stability and characteristic variations of the enzymatic activity with measurement conditions. Furthermore, the results from the ENFET measurements were compared with the results of spectrophotometric experiments, carried out with enzymes immobilized on diamond substrates and also with free enzymes in solution. This allows an analysis of the enzyme kinetics, as well as qualitative comparison of the different functionalization methods employed in this study.

Catalytic activity of enzymes immobilized on AlGaN∕GaN solution gate field-effect transistors

Enzyme-modified field-effect transistors (EnFETs) were prepared by immobilization of penicillinase on AlGaN∕GaN solution gate field-effect transistors. The influence of the immobilization process on enzyme functionality was analyzed by comparing covalent immobilization and physisorption. Covalent immobilization by Schiff base formation on GaN surfaces modified with an aminopropyltriethoxysilane monolayer exhibits high reproducibility with respect to the enzyme/substrate affinity. Reductive amination of the Schiff base bonds to secondary amines significantly increases the stability of the enzyme layer. Electronic characterization of the EnFET response to penicillin G indicates that covalent immobilization leads to the formation of an enzyme (sub)monolayer.

酸化亜鉛表面の有機分子修飾

Toward the fabrication of biosensing medical devices with enzyme-modified field effect transistors based on zinc oxide (ZnO), surface modifications using organic molecules were employed. In case of molecules containing thiol groups, it was found that molecules on ZnO surfaces were desorbed during water immersion, while ZnO surfaces modified by a silane-coupling agent were stable in water. Glucoseoxidase (GOX), an enzyme, specifically reacting with glucose, could be immobilized on molecular modified ZnO surfaces.

Control of chemical bonding of the ZnO surface grown by molecular beam epitaxy

Toward the fabrication of enzyme modified field effect transistors (EnFETs) as one of organic/inorganic hybridized structures, surface bonding of the ZnO grown by molecular beam epitaxy was controlled by ex situ treatments. Angle resolved X-ray photoelectron spectroscopy (XPS) measurement revealed that OH bonds exist at the surface of ZnO. It was found that the number of OH bond could be changed with reversibility using plasma and thermal treatments.

High resistive layers toward ZnO-based enzyme modified field effect transistor

One of the key issues for the realization of ZnO-based enzyme modified field effect transistors (FET) is growth of a high resistive layer underneath the active layer of the device structure. For that purpose, nitrogen-doped ZnO (ZnO:N) and ZnMgO layers were grown on a-plane sapphire substrates by molecular beam epitaxy (MBE). Although photoluminescence (PL) spectra indicated that nitrogen atom was incorporated as acceptor, ZnO:N layers showed still n-type conductivity probably due to generation of donor-like defects during nitrogen doping. On the other hand, ZnMgO layers showed high resistive and flat surface, which will be utilized underlying layers for successive growth of ZnO-based biosensors.

Study on separative structure of EnFET to detect acetylcholine

In this study, our laboratory used a separative structure of extended gate field effect transistor (EGFET) to detect pH value and constructed an enzyme modified field effect transistor (EnFET) by coupling them with a membrane containing immobilized acetylcholinesterase (AcChE). The enzyme-catalyzed hydrolysis reaction of acetylcholine seemed to be resulted in the pH change of the membrane due to the formation of acetic acid. This structure has a lot of advantages, such as being insensitive toward light, being simple to in its passivation and package, and the flexibility of shape in the extended gate area, etc. In addition, it is easier to fabricate and package the sensors, and the measurement is simple for the application of disposable biosensor.

Bio-field-effect transistors for process control in biotechnology

The application of enzyme-modified field-effect transistors (BioFETs) in biotechnological process control is presented. Penicillin, glucose and urea are detected with these devices in cultivation media and on-line in biotechnological processes. In these applications, the BioFETs are used as detectors in flow injection analysis (FIA) systems. Special flow cells with a small volume, constructed for this purpose, guarantee an optimum sample transport to the sensor. Therefore, 15–20 determinations per hour can be performed. The BioFET/FIA system gives good results for the on-line monitoring of glucose and urea during cultivations of S. cerevisiae and E. coli in different types of bioreactors.

Response characteristics of the glucose-sensitive field-effect transistor. Computer simulation of the effect of gluconolactonase coimmobilization in a glucose oxidase membrane

The bienzyme system consisting of glucose oxidase and gluconolactonase was investigated using a conventional diffusion-kinetics model for an enzyme-modified field-effect transistor (FET) to clarify the effect of gluconolactonase coimmobilization in a glucose oxidase membrane on the steady-state response amplitude of a glucose sensor based on a FET. The model includes spontaneous and enzymatic hydrolysis reactions of d-glucono-δ-lactone and it elucidated the following experimental results: a glucose sensor with a membrane (about 1 μm in thickness) coimmobilizing these enzymes showed a sufficient response amplitude, whereas without coimmobilization of gluconolactonase no detectable response was observed up to 3 mM glucose; and the response amplitude depended strongly on the amount of lactonase in the membrane. The model also predicted an optimum enzyme ratio for coimmobilization in a membrane.

A flow-through cell for use with an enzyme-modified field effect transistor without polymeric encapsulation and wire bonding

A new type of flow-through cell for an enzyme-modified field effect transistor (FET) is described. The cell makes it possible to use a FET without polymeric encapsulation and wire bonding. Electrical evaluation of a FET used with the flow cell demonstrates that the flow cell has no practical problems causing sensor malfunctions. The noise and drift levels of tbe FET sensor with the flow cell are shown to be similar to those of an epoxy-encapsulated FET sensor. The application of the flow cell with a urease-modified FET is described. Useful responses are obtained for 0.25–50 mg l −1 urea with relative standard deviations of <3%.