Hot Charge Carriers Mediate Regioselective Thiol Cleavage and Biofunctionalization of Gold Nanoparticles

Laser excitation of plasmonic particles represents an attractive avenue to tailor and catalyze surface chemical reactions at the nanoscale. However, it remains unclear how interfacial chemistry is catalyzed by the interplay between photothermal heating and hot carriers, let alone how these processes are spatially dependent. Here, we study gold-sulfur (Au-S) cleavage at the single-particle and single-molecule level using DNA-functionalized gold particles. We find very effective cleavage by continuous-wave (CW) irradiation rather than the usually employed pulsed laser, whose time and wavelength dependence we quantify by single-molecule microscopy of DNA-interaction kinetics. We find that direct interband excitation is far more effective at cleaving Au-S bonds compared to intraband or plasmon excitation. We attribute this to the 5d band that is narrowed and shifted to lower energies compared to bulk gold. Surprisingly, we uncover a location-dependent cleavage where cleavage of tip-bound DNA is enhanced irrespective of irradiation polarization. This provides an all-optical pathway for regioselective cleavage and refunctionalization that does not require chemical additives. We demonstrate its application toward tip-selective biofunctionalization of nanorods for improved plasmon-enhanced fluorescence sensing. The presented results improve our understanding of hot-carrier chemistry at the single-particle and single-molecule level and will aid in developing tools for nanoscale catalysis and sensing.