Abstract

We have developed lipid based assays which can be used to directly quantify the temperature of any nanoscale irradiated object. As a demonstration we apply this to spherical gold nanoparticles irradiated by focused near infrared laser light. By trapping the particles near lipid bilayers having a phase transition temperature just above ambient temperature we observe a gel to fluid phase transition of the lipid bilayer which is directly visualized using fluorescent techniques. Two bilayer systems are used- Giant Unilamellar Vesicles (GUVs) are used to assess the temperature of 3D trapped nanoparticles and secondly, a glass supported lipid bilayer is used to measure the heating in particles confined to 2D by adhesion to the flat bilayer. In both assays fluorescent molecules report about the extent of the melted bilayer region and moreover we observe leakage of GUV content which is a characteristic property of melting bilayers. By measuring the distance from the nanoparticle to the phase boundary we directly obtain the surface temperatures for a range of particle sizes. Interestingly, heating associated with optical trapping in 3D differs significantly from heating of particles confined to 2D. This assay can be directly applied to quantifying heating in nanoscale structures used for photothermal therapy or single molecule applications like nanoshells, rods, or quantum dots which all convert light to heat.

© 2011 Optical Society of America