Biological sensing using frequency based interrogation of functionalized silicon nanowires

Silicon nanowires can be made into sensitive molecular sensors. When being functionalized with antibodies they are capable of detecting femto molar concentrations of antigens in real time. To date, detection methods have been based upon directly measuring the change in DC conductance. This is difficult and requires sensitive low noise amplifiers and high resolution Analog to Digital Converters. This is not ideal for low cost and highly integrated systems. In this paper it is demonstrated that nanowires exhibit a gate dependent AC-transfer function that resembles that of a high pass filter. To the authors´ knowledge this is the first time this effect has been reported. Furthermore it is illustrated that as molecules with a higher net charge attach to the nanowire, and displace more charge carriers within the nanowire channel, the filter´s corner frequency decreases. This property of silicon nanowires is exploited to build a low cost real time antigen detection system.