Trapping and monitoring of single nanoparticle using a metallic nanoantenna

The hopping of a nanoparticle between two adjacent potential wells is a fundamental process in various physical, chemical, and biological phenomena. However, it is tricky to implement an experimental measure to study this process because handling a single nanoparticle is not a simple problem. We propose a 3D tapered metallic nanoantenna with a bow-tie-shaped hole illuminated by two lasers: a continuous-wave (CW) laser and a femtosecond laser. The CW laser produced a double-well potential inside the hole that trapped a single nanoparticle. The femtosecond laser generated a second harmonic signal by enhancing the nonlinear optical effect on the metal surface, which could be easily filtered and monitored. This two-laser platform provides the freedom to choose between the means for capturing a nanoparticle and the means for observing them. We controlled the landscape of the double-well potential by combining the gap size of a nanoantenna and optical pump power. The hopping of trapped nanoparticles over the central potential barrier was monitored and showed a maximum at the specific input laser power. This phenomenon agreed well with the theoretical prediction considering the thermal energy of a nanoparticle.