Label-free and reagent-less protein biosensing using aptamer-modified extended-gate field-effect transistors.

We have developed biosensors based on an aptamer-modified field-effect transistor (FET) for the detection of lysozyme and thrombin. An oligonucleotide aptamer as a sensitive and specific ligand for these model proteins was covalently immobilized on a gold electrode extended to the gate of FET together with thiol molecules to make a densely packed self-assembled monolayer (SAM). The aptamer-based potentiometry was achieved in a multi-parallel way using a microelectrodes array format of the gate electrode. A change in the gate potential was monitored in real-time after introduction of a target protein at various concentrations to the functionalized electrodes in a buffer solution. Specific protein binding altered the charge density at the gate/solution interface, i.e., interface potential, because of the intrinsic local net-charges of the captured protein. The potentiometry successfully determined the lysozyme and thrombin on the solid phase with their dynamic ranges 15.2-1040 nM and 13.4-1300 nM and the limit of detection of 12.0 nM and 6.7 nM, respectively. Importantly, robust signals were obtained by the specific protein recognition even in the spiked 10% fetal bovine serum (FBS) conditions. The technique herein described is all within a complementary metal oxide semiconductor (CMOS) compatible format, and is thus promising for highly efficient and low cost manufacturing with the readiness of downsizing and integration by virtue of advanced semiconductor processing technologies.