Photothermal heating of optically trapped gold nanoparticles quantified using controlled vesicle cargo release

Optically trapped metallic nanoparticles hold great promise as heat transducers in photothermal applications such as drug delivery assays or photothermal therapy. We use the heat dissipated from an optically trapped gold nanosphere to perform a controlled release of a fluorescently labeled vesicle lumen. In the assay, the ambient temperature is kept below the phase transition temperature of the vesicle. When the temperature reaches the phase transition temperature of the lipid, the vesicle becomes leaky and the fluorescently marked lumen diffuses out. We used gel phase vesicles as sensors to quantify the temperature profile around a nanoparticle optically trapped in three dimensions in a similar way as presented in Ref. 1 Trapping of 200 nm gold particles resulted in lower than expected heating, which may be accredited to the displacement of the particle from the optical focus due to high scattering forces experienced by the particle.