Title: Direct Measurement of Heating by Optically Trapped Gold Nanoparticles Using Molecular Sorting in a Lipid Bilayer
Abstract: Gold nanoparticles have are extremely useful as multi-functional and sensitive probes for investigation and manipulation of biological systems. Particles, as small as tenths of nanometers, can be visualized, optically manipulated, and used as controlled force transducers. Their high absorbance also makes them excellent converters of electromagnetic radiation into thermal energy. If the heating can be quantified it can also be advantageously used to perform controlled thermal treatment. We performed a direct measurement of the heating associated with optical trapping of individual gold nanospheres. A trapped gold nanosphere was embedded in a two dimensional supported gel phase lipid bilayer with incorporated fluorescent molecules which preferentially located, e.g., in the gel phase. Visualization of the melted region gave direct information about the temperature profile around the irradiated particle. The heating is highly dependent on particle size and laser power, with surface temperatures increasing from a few to hundreds of degrees Celcius. This quantification allows for creating controlled and localized temperature gradients which can be utilized for destruction of unwanted biological material such as cancer cells, to create local temperature gradients in lipid bilayers, or for nano-engineering purposes.