Fast lipid vesicles and dielectric particles migration using thermal-gradient-induced forces

Lipid vesicles are small biological particles that can be used for both targeted drug delivery systems and clinical studies. Their optical manipulation, however, is limited by the small difference in refractive indices with the surrounding medium, as well as the requirement for high laser trapping powers. In this work, we combine gradient force and thermal forces to deliver and trap individual lipid vesicles with low-trapping laser powers. The total optothermal force exerted on liposomes causes them to migrate rapidly toward the laser focus with a high average migration velocity of 1.77 µm s−1 under 7.3% w/v polyethylene glycol (PEG) concentration and low trapping laser power of 1 mW. A high normalized experimental trap stiffness of 0.88 (pN µm) mW−1 was obtained at 7.3% w/v PEG/water solution. This work may open new ways for bioparticle sorting and manipulation with potential applications in cellular studies, drug delivery, biosensing, and medicine.