An Electronic and Optically Controlled Bifunctional Transistor Based on a Bio-Nano Hybrid Complex.

We report an electronically and optically controlled bioelectronic field-effect transistor (FET) based on the hybrid film of photoactive bacteriorhodopsin and electronically conducting single-walled carbon nanotubes (SWNTs). Two-dimensional (2D) crystals of bacteriorhodopsin form the photoactive center of the bio-nano complex, whereas one-dimensional (1D) pure SWNTs provide the required electronic support. The redshift in the Raman spectra indicates the electronic doping with an estimated charge density of 3 × 10 cm. The hybrid structure shows a conductivity of 19 μS/m and semiconducting characteristics due to preferential binding with selective diameters of semiconducting SWNTs. The bioelectronic transistor fabricated using direct laser lithography shows both optical and electronic gating with a significant on/off switch ratio of 8.5 and a photoconductivity of 13.15 μS/m. An n-type FET shows complementary p-type characteristics under light due to optically controlled, electronic doping by the "proton-pumping" bacteriorhodopsin. The fabricated bioelectronic transistor exhibits both electronically and optically well-controlled bifunctionality based on the functionalized hybrid electronic material.