Rapid and accurate molecular blood analysis is essential for disease diagnosis and management. Field Effect Transistor (FET) biosensors are a type of device that promise to advance blood point-of-care testing by offering desirable characteristics such as portability, high sensitivity, brief detection time, low manufacturing cost, multiplexing, and label-free detection. By controlling device parameters, desired FET biosensor performance is obtained. This review focuses on the effects of sensing environment, micro/nanoscale device structure, operation mode, and surface functionalization on device performance and long-term stability.

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AlGaN/GaN high electron mobility transistors (HEMTs) were used to measure electrical characteristics of physisorbed gold nanoparticles (Au NPs) functionalized with alkanethiols with a terminal methyl, amine, or carboxyl functional group. Additional alkanethiol was physisorbed onto the NP treated devices to distinguish between the effects of the Au NPs and alkanethiols on HEMT operation. Scanning Kelvin probe microscopy and electrical measurements were used to characterize the treatment effects. The HEMTs were operated near threshold voltage due to the greatest sensitivity in this region. The Au NP/HEMT system electrically detected functional group differences on adsorbed NPs which is pertinent to biosensor applications. With the need for rapid detection of biomolecular analytes in the life sciences and medicine, the research community has made great progress in developing microscale and nanoscale sensors for many biological applications.1,2 One promising biosensor structure is the AlGaN/GaN high electron mobility transistor (HEMT) due to its chemical stability, 2 electrical stability in ionic solutions, 3 biocompatibility, 4,5 and high sensitivity to adsorbed surface charges. 2 These devices have been used for many biomedical and life sciences applications including detection of proteins, 6 DNA,7 pathogens, 8 and cellular signals. 9 A two dimensional electron gas (2DEG) is formed at the interface between the AlGaN and GaN layers due to piezoelectric polarization and spontaneous polarization that is sensitive to adsorbed surface charges.2 Binding of a charged analyte near the gate area of a HEMT biosensor changes the surface potential at the gate that modulates the conductance of the 2DEG charge carrier channel and results in a measureable change in electrical current through the device. 2,10