Abstract
Medical diagnostics are rapidly evolving to meet the requirements of personalized medicine. We previously developed high field modulated field effect transistor (FET) biosensors for the direct detection of protein biomarkers in whole blood. In this work, we investigate the sensor structure in detail to assess the parameters that govern the sensing characteristics. The basic sensor structure includes a functionalized reference electrode to which gate voltage is applied, placed at a narrow gap from the extended gate metal, which is connected to the FET's gate terminal. It was revealed from our previous studies that there are two ways in which the field generated across the test solution, placed in the gap, can be modulated: by applying higher amplitude of gate voltage and by decreasing the gap between the electrodes. It was found that at smaller gap distances, the potential drop in the solution is linearly dependent on the gap between the electrodes, and hence higher sensitivity can be observed for smaller gap configurations. In this work we initially explore the gap dependence of sensor response for micron scale gap distances. The results indicate that noise characteristics and sensitivity are improved when the gap between the reference electrode and extended gate metal is decreased. The geometry of the sensing areas are also studied to evaluate the optimal electric field distribution across the test solution to generate enhanced sensing characteristics. Finally the surface functionalization is investigated to analyse the effect of surface coverage and number of receptor binding sites on the sensor performance.