Abstract
Biological applications where nanoparticles are used in a cell environment with laser irradiation are rapidly emerging. Investigation of the localized heating effect due to the laser irradiation on the particle is required to preclude unintended thermal effects. While bulk temperature rise can be determined using macroscale measurement methods, observation of the actual temperature within the nanoscale domain around the particle is difficult and here we propose a method to measure the local temperature around a single gold nanoparticle in liquid, using white light scattering spectroscopy. Using 40-nm-diameter gold nanoparticles coated with thermo-responsive polymer, we monitored the localized heating effect through the plasmon peak shift. The shift occurs due to the temperature-dependent refractive index change in surrounding polymer medium. The results indicate that the particle experiences a temperature rise of around 10 degrees Celsius when irradiated with tightly focused irradiation of ~1 mW at 532 nm.
Highlights
Metal nanoparticles exposed to incident laser irradiation at wavelengths close to the surface plasmon resonance efficiently couple the optical energy and generate heat
Emerging applications build on the biocompatible, or relatively nontoxic, nature of the particle, combined with some unique optical physics which allows plasmonic photothermal therapy, photoacoustic tomography, photothermal imaging, and surface enhanced Raman spectroscopy [1,2,3,4,5,6,7]
The difficulty of such local temperature measurement lies in the fact that a thermal contrast mechanism as well as a spatial resolution of several nanometers is necessary to selectively observe the near-field heating of the nanoparticle
Summary
Metal nanoparticles exposed to incident laser irradiation at wavelengths close to the surface plasmon resonance efficiently couple the optical energy and generate heat. For the successful application of gold nanoparticles, the investigation of the localized heating effects must be carried out in order to firstly understand the influence on the biological samples, and subsequently preclude unwanted thermal effects The difficulty of such local temperature measurement lies in the fact that a thermal contrast mechanism as well as a spatial resolution of several nanometers is necessary to selectively observe the near-field heating of the nanoparticle. We have investigated the local temperature of a laser irradiated single nanoparticle by white light scattering spectroscopy. The heating effect was monitored by measuring the peak scattering wavelength derived from the surface plasmon of gold nanoparticles, which varied with the refractive index of the surrounding polymer. The heating effect of single gold nanoparticles under different laser powers and wavelengths are measured and discussed
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