Potentiometric Detection of Single Nanoparticle Collision Events on a Surface Functionalized Gold Nanoelectrode.

The development of label-free single-entity measurement methods is important for the fundamental studies and applications of biophysics. Recently, we have demonstrated that various nanoparticles and proteins can be detected individually based on the open circuit potential (OCP) changes induced by their collision events on a floating carbon nanoelectrode. However, the carbon nanoelectrode is chemically inert and limited in surface functionalization. Here, I will present our recent progress of using surface-functionalized gold nanoelectrode (GNE) to replace carbon nanoelectrode for potentiometric single-entity studies. The surface functionalization of GNE also enables surface-enhanced Raman spectroscopy (SERS) measurements. However, the gold surface is more likely to be contaminated due to non-specific adsorption making them less suitable for continuous detection of single-entity hit-n-run collision signals. By utilizing the advantage of mixed surface functionalization of GNE with the Raman reporter molecule and polyethylene glycol or zwitterionic molecules, we formed near ‘stealth’ GNE surface and demonstrated that the non-specific adsorptions of nanoparticles to the GNE surface can be minimized, allowing continuous hit-n-run events for over 30 minutes. Also, by using simultaneous time-resolved OCP and SERS measurements, both the OCP and SERS signals induced by the hit-n-run type of collision events can be better understood.