Optimization of sensing-pad functionalizing strategy toward separative extended-gate FET biosensors for PSA detection.

In this study, separative extended-gate AlGaAs/GaAs high electron mobility transistor (HEMT) biosensor is proposed for prostate-specific antigen (PSA) detection. Zinc oxide nanotetrapods (T-ZnO) with a four-leg structure is introduced onto the sensing pad to form a three-dimensional (3D) and concave detection front. Compared with common plane front, the elaborately-designed-3D and concave detection front can offer more biological modification sites and decrease the Debye volume, resultantly improving both the detection scope and sensitivity. Anti-PSA probes can be fixed at any sites of T-ZnO via a chemical bio-functionalization method, which facilitates better detection performance by comparison with a physical modification scheme. On the other hand, the T-ZnO nanostructures with the four-leg configuration are capable of releasing the stress and erosion effect of the solution on the plane Au film, contributing to a great improvement in the reliability of the biosensors. The optimized biosensors with chemical bio-functionalized T-ZnO detection front demonstrate good linear current/voltage response to label-free PSA target in the concentration range from 5 fg/ml~5 ng/ml and a sensitivity variation ~ 1.3% dec-1.