Analysis of configuration of surface-immobilized proteins by Si nanochannel field effect transistor biosensor

We demonstrate the application of ‘top-down’ fabricated Si nanochannel field effect transistor biosensors for measuring charging properties or configuration of proteins immobilized on the Si surface. We have immobilized monoclonal antibodies for prostate specific antigen (anti-PSA) on the p-type Si channel surface, and monitored the channel conductance in response to the variation of ionic strength (salt concentration) and pH of the buffer solution. Effects of the salt concentration at a constant pH is consistent with the screening of protein charges by dissolved counter-ions, enabling analysis of the net protein charge and spatial configuration based on calculated values of Debye screening length (λ_D). The pH-dependence of channel conductance at varying salt concentration has also been investigated, from which the relationship between the pH and net protein charge can be estimated.