Chemical Control Over Optical Trapping Force at an Interface

So far, the optical trapping potential is controlled by tuning the physical conditions of the system. Herein, for the first time, an approach, in which the induced optical force or optical potential is controlled, by an external chemical stimulus, is reported. The key to realize this is to design an optical trapping condition in conjunction with resonant excitation, the so-called optical resonance effect (ORE). For this purpose, phenalenone, a well-known triplet photosensitizer, is embedded inside polystyrene particles. The optical resonance effect is achieved through a two-laser system: a 405 nm widefield laser to excite the phenalenone molecules to T₁ state and a 488 nm trapping laser to induce the T₁–T_n–T₁ resonance cycle. Thus, the triplet state is mainly responsible for the optical force enhancement. Since oxygen is an excellent triplet quencher, the triplet populations, and hence, the optical force is controlled by changing the dissolved oxygen concentration. The results presented here pave the way to chemically control the optical force through ORE with promising applications in several research fields ranging from physics to biology.