Ultrasensitive Electrical Biosensing of Proteins and DNA:  Carbon-Nanotube Derived Amplification of the Recognition and Transduction Events

A new strategy for dramatically amplifying enzyme-linked electrical detection of proteins and DNA using carbon nanotubes (CNTs) for carrying numerous enzyme tracers and accumulating the enzymatically liberated product on CNT-modified transducer is described. Such a CNT-derived double-step amplification pathway (of both the recognition and transduction events) allows the detection of DNA and proteins down to 1.3 and 160 zmol, respectively, in 25−50 μL samples and indicates great promise for PCR-free DNA analysis. The new protocol is illustrated for monitoring sandwich hybridization and antibody−antigen interactions in connection with alkaline-phosphatase tracers. The DNA-linking of CNTs and particles holds promise also for assembling hybrid nanostructures relevant to molecular electronic devices.