Bio-FET

[7] Bio-FETs couple a transistor device with a bio-sensitive layer that can specifically detect bio-molecules such as nucleic acids and proteins.

If the transistor is operated in the subthreshold region, then an exponential increase in current is expected for a unit change in surface potential.

Bio-FETs can be used for detection in fields such as medical diagnostics,[12][11] biological research, environmental protection and food analysis.

Nevertheless, these conventional methods are relatively time-consuming and expensive, involving multi-stage processes and also not compatible to real-time monitoring,[13] in contrast to Bio-FETs.

For example, a microfluidic device can control sample droplet transport whilst enabling detection of bio-molecules, signal processing, and the data transmission, using an all-in-one chip.

[14] Bio-FET also does not require any labeling step,[13] and simply utilise a specific molecular (e.g. antibody, ssDNA[15]) on the sensor surface to provide selectivity.

If the transistor is operated in the subthreshold region then an exponential increase in current is expected for a unit change in surface potential.

[21] One optimization of Bio-FET may be to put a hydrophobic passivation surface on the source and the drain to reduce non-specific biomolecular binding to regions which are not the sensing-surface.

[33][34] Biosensor MOSFETs (BioFETs) were later developed, and they have since been widely used to measure physical, chemical, biological and environmental parameters.

[3] The first BioFET was the ion-sensitive field-effect transistor (ISFET), invented by Piet Bergveld for electrochemical and biological applications in 1970.

[37] Current research in this area has produced new formations of the BioFET such as the Organic Electrolyte Gated FET (OEGFET).

In a typical BioFET, an electrically and chemically insulating layer (e.g. Silica ) separates the analyte solution from the semiconducting device. A polymer layer, most commonly APTES , is used to chemically link the surface to a receptor which is specific to the analyte (e.g. biotin or an antibody ). Upon binding of the analyte, changes in the electrostatic potential at the surface of the electrolyte-insulator layer occur, which in turn results in an electrostatic gating effect of the semiconductor device, and a measurable change in current between the source and drain electrodes. [ 7 ]
Bio-FETs are classified based on the bio recognition element used for detection: En-FET which is an enzyme-modified FET, Immuno-FET which is an immunologically modified FET, DNA-FET which is a DNA-modified FET, CPFET which is cell-potential FET, beetle/chip FET and artificial BioFET-based. [ 7 ]
1957, Diagram of one of the SiO2 transistor devices made by Frosch and Derick [ 26 ]