UC Irvine

Monoclonal antibodies are being increasingly utilized as highly-specific sensing elements and linkers for biosensing and chemical detection applications. Ideally, such sensors would demonstrate a real-time response to analyte concentration, but devices incorporating antibodies are often limited by the kinetics of antibody-antigen binding, which can take tens of minutes to measure accurately. Fast, single-molecule techniques show potential for reducing measurement time and revealing kinetics that are otherwise hidden during ensemble measurements. In this work, field effect transistors (FET) based on carbon nanotubes were used to record the binding activity of antibody 3C6 molecules with paclitaxel at the microsecond timescale. Single-molecule measurements revealed individual antibody-antigen binding and unbinding events, with statistics correlated to paclitaxel concentration, while ensemble measurements exhibited no consistent dependence on paclitaxel concentration. Further analysis of the single-molecule binding statistics showed deviations from simple receptor-ligand binding, suggesting the presence of cooperative binding dynamics between the individual binding sites on the 3C6 molecule. The measurement accuracy of the binding dynamics was limited by bandwidth, suggesting that measurements performed at higher bandwidth could increase the accuracy of the binding kinetics values obtained. Equilibration times for the single-molecule carbon nanotube FETs were under 60 seconds, demonstrating rapid response times that can be used in real-time sensing applications.