Enhanced optical trapping of ZrO₂@TiO₂ photonic force probe with broadened solvent compatibility

Optical trapping and manipulating nanoparticles are essential tools for interrogating biomedicine at the limits of space and time. Typically, silica or polystyrene microspheres are used as photonic force probes. However, adapting those probes to organic solvents is an ongoing challenge due to the limited solvent compatibility and low refractive index mismatch. Here we report on the optical force enhancement and solvent compatibility that utilizes ZrO₂@TiO₂ core-shell nanoparticles. We experimentally demonstrate that the 450-nm-diameter ZrO₂@TiO₂ core-shell nanoparticles achieve the lateral and axial trap stiffness up to 0.45 pN µm^-1 mW^-1 and 0.43 pN µm^-1 mW^-1 in water, showing more than fivefold and ninefold improvement on the ordinary SiO₂ particle of the same size. In addition, ZrO₂@TiO₂ core-shell nanoparticles can realize stable three-dimensional trapping in both polyethylene glycol and glucose solutions. This optical trapping enhancement property, coupled with solvent compatibility, expands the range of feasible optical trapping experiments and will pave the way toward more advanced biological applications.