Ion-sensitive field-effect transistors with Si3N4 and TaO2 gate insulator for studying self-assembly of photosynthetic proteins

The reaction center (RC) protein from photosynthetic purple bacteria is an organic structure with the capability of absorbing photons at low light intensities and generating electron-hole pairs with a high efficiency. Application of this biomaterial for energy harvesting and sensor devices has been studied before. A key in employing RCs in an electrochemical device is to immobilize the proteins on an electrode. In this work, ion-sensitive field-effect transistors with Si3N4 and TaO2 gate insulator were tested to measure the success rate in immobilizing the proteins. The results show that by far Si3N4 is a better choice than TaO2, due to the effective self- assembly of the linker molecules. The density of the attached proteins to the Si3N4 transistor was estimated to be 5x10(9) proteins/cm(2) by analyzing the drift in the threshold voltage of the transistor. The fabricated device also presented the feasibility of using the RCs in an integrated photo-transistor.