Switchable Electron Transfer in Single Thermoresponsive Core-Shell Plasmonic Hybrid Nanoelectrodes

Active control of electrochemical processes at the nanoscale is promising for applications in switchable electronics. It has been demonstrated that stimuli-responsive polymers can serve as logic gates to switch between “on” and “off” states in response to environmental changes at both the macro- and nanoscale. As the majority of these stimuli-responsive polymers are weak polyelectrolytes, metal ions or conductive monomers are often incorporated into the stimuli-responsive matrix for electrochemical applications. However, the incorporation of conductive components may reduce the gating efficacy of these stimuli-responsive materials. In this work, we investigated the efficacy of switchable electron transfer in nonconductive stimuli-responsive core-shell hybrid nanoelectrodes consisting of thermoresponsive poly(N-isopropylacrylamide) grafted from plasmonic gold nanoparticles, termed pNIPAM@AuNPs. Under applied electrochemical potentials, electron transfer to the plasmonic core can be monitored optically through changes in the linewidth and peak position of the longitudinal surface plasmon resonance. Using single-particle dark-field spectroelectrochemistry, we observed that expanded pNIPAM@AuNPs exhibited hindered electron transfer, but, upon polymer collapse, electron transfer substantially increased. We also determined that, although heterogeneous, the extent of electron transfer in pNIPAM@AuNPs was reversibly switched through temperature cycling. Furthermore, we established that the gating efficiency of the polymer is dependent on the core morphology as a result of the size and shape dependent strength of the plasmonic electric field. These results provide insight into reversibly gated electron transfer in stimuli-responsive hybrid nanoelectrodes and suggest that a conductive polymer matrix is not necessarily required to facilitate electron transfer.