While the sensitivity of ion-sensitive FET (ISFET)-based enzyme sensors that detect an enzyme-catalyzed reaction as a local pH change are strongly affected by the buffer conditions such as pH and buffer capacity, the sensitivity of the proposed FET-based enzyme sensor is not affected by them in principle. We developed a field-effect transistor (FET)-based enzyme sensor that detects an enzyme-catalyzed redox-reaction event as an interfacial potential change on an 11-ferrocenyl-1-undecanethiol (11-FUT) modified gold electrode. The results went a step further to realize the albumin BioFET sensor for diagnosing nephritis and to develop a BioFET sensor array for the detection of multi biomarkers simultaneously. The output drain current characteristics of the BioFET with respect to various albumin concentrations were obtained. A mixture of albumin and C-reactive protein (CRP) and an albumin-only solution were used to prove high specificity of biorecognition element on the BioFET to target molecule, albumin. Surface plasmon resonance (SPR) analysis has been utilized to verify formation of SAM, immobilization of anti-albumin, prevention of non-specific binding and selective interaction between anti-albumin and albumin. For the detection of a biomarker, albumin, in urine the gate surface of the BioFET was modified by an engineered self-assembled monolayer, thiazole benzo crown ether ethylamine (TBCEA)-thioctic acid to immobilize anti-albumin. The BioFET was fabricated using the conventional CMOS process technology. FETs appear in vast numbers in microprocessor chips and similar devices.Characteristics of a label-less electrochemical immunosensor based on a field-effect transistor (FET) for the detection of a biomarker in urine have been investigated.
Junction FETs have relatively slow switching speeds compared with MOSFETs and bipolar transistors, and are therefore not used in logic circuits. Unlike the bipolar transistor both types of FET require virtually no input current to the gate except a pulse to charge or discharge the gate capacitance. In the MOSFET the gate is insulated from the source and drain regions and the channel forms when the gate voltage is applied. In the junction FET the channel is a composite part of the structure. In contrast to bipolar transistors, FETs are unipolar devices the current flow is electrons (in n-channel devices) or holes (in p-channel devices). Devices with p-type source, drain, and channel are called p-channel devices. If the source and drain regions are composed of n-type semiconductor the conduction channel is n-type these devices are known as n-channel devices. Current flow in a narrow conduction channel between drain and source is controlled by the voltage applied between gate and source, which can deplete the conduction channel of charge carriers. Field-effect transistor ( FET) A semiconductor device having three terminals: source, gate, and drain.
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