Electrical detection of immobilized proteins with ungated AlGaN∕GaN high-electron-mobility Transistors

Ungated $\mathrm{AlGaN}∕\mathrm{GaN}$ high-electron-mobility transistor (HEMT) structures were functionalized in the gate region with aminopropyl silane. This serves as a binding layer to the AlGaN surface for attachment of fluorescent biological probes. Fluorescence microscopy shows that the chemical treatment creates sites for specific absorption of probes. Biotin was then added to the functionalized surface to bind with high affinity to streptavidin proteins. The HEMT drain-source current showed a clear decrease of $4\mu \mathrm{A}$ as this protein was introduced to the surface, showing the promise of this all-electronic detection approach for biological sensing.