In the experiments, we used an aqueous dispersion of PSNPs with a diameter of 500 nm that were not surface-modified (Cat# 07307-15, Polysciences, Inc.). These unmodified PSNPs are referred to as bare-PSNP for convenience. The stock solution of the purchased colloids contained a small amount of surfactant for stabilization, which could potentially affect thermophoresis. To address this, the stock solution was centrifuged at 8000 rpm for 3 minutes, and the solvent was replaced with deionized water. This process was repeated twice to remove the surfactant. The density of bare-PSNP was adjusted with deionized water during this process to achieve a suitable concentration for observation under optical microscope.