FET-based biosensor incorporating a conductometric bioreceptor
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FET-based biosensor incorporating a conductometric bioreceptor Andrés Vercik1 1 Basic Sciences Department ZAB/FZEA, University of São Paulo, Av. Duque de Caxias Norte 225, 13635-000, Pirassununga, SP, Brazil. ABSTRACT Novel strategies of transduction may help to improve the biosensor performance by enhancing its sensitivity or linearity or by allowing a better integration with the electronics, which in turn favors the miniaturization of the sensing devices. In this work, a combination of a conductometric element containing the bioreceptor with a MOSFET is proposed as a transduction strategy. Simulations of the gate voltage and drain current versus conductance curves are used to confirm the feasibility of the proposed strategy. One of the advantages of the presented device is that the sensing element can be deposited by back-end processes compatible with current IC technology.
INTRODUCTION A biosensor combines a bio-recognition element in contact with a transducer which converts biochemical event in an electrical signal. Usually, these devices operate according to different principles such as electrochemical, mechanical, piezoelectric or optical techniques. Electrochemical detection strategies, particularly amperometric biosensors are most widely used, followed by the potentiometric devices, mainly those based on field effect transistors. Different strategies or elements are combined frequently to achieve more sensitive or selective devices, aiming a good compatibility with standard microelectronic technologies, for better integration of the sensor with the electronic components for signal conditioning, amplification and displaying, in a compact device. Several materials and structures exhibiting conductance changes in the presence of a chemical or biological species have been used in biosensors, such as arrays of capped metallic nanoparticles or organic films containing nanoparticles and catalytic agents such as enzymes for different target analytes [1-3]. A possible approach to construct biosensors is the combination of conductometric element in the biasing circuit of Metal-Oxide-SemiconductorField-Effect-Transistor (MOSFET). In this work we proposed the use of a conductometric element in series with a tunnel-MOSFET, to provide conductance dependent electrical signals. Simulations are performed to show the feasibility of the propose device and the linear range of operation. According to the results, a linear dependence of the gate voltage on the conductivity is observed. The linear dependence spreads over the whole range of conductivities used in this simulation. On the other hand, the drain current exhibits a linear dependence for higher conductivities, before its saturation. Thus, two different detection strategies of detection can be defined: measure the gate voltage for very low conductivities or measure drain current for higher conductivities.
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THEORY The principle of operation of the biosensor is as follows: a conductometric element, e.g., a polymeric film containing the bioreceptor, a functionalized c
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