A new approach of near-field thermal imaging of Plasmonic Nanoparticules by nanoscale polymerization
Résumé
Metal nanoparticles have attracted great interest thanks to their original optical, thermal and chemical properties which are related to the Localized Surface Plasmonic Resonance (LSPR) effect. Indeed, the excitation of the LSPR leads to an enhancement of the electromagnetic field at the particle surface. Some of this concentrated energy could be efficiently converted into heat. This ability to locally heat at the nanoscale opens the path for promising achievements in nanotechnology and especially for nanoscale control of temperature allowing for many local chemical and physical processes to be produced upon excitation. These original phenomena are investigated in biological imaging, detection of chemicals, photocatalysis, photothermal cancer therapy, and drug release. In this paper, new approaches of fabrication of metal NPs will be presented. In particular, spatially controlled fabrication methods based on photodewetting or photochemical reduction processes and using a tightly-focused laser beam were developed. Secondly, we investigated the thermal properties of photoexcited GNPs using our approach of nanoscale chemical imaging based on thermo-polymerizable probes. we used molecular thermo-probes to characterize the local heat profile in the vicinity of an isolated GNP under optical excitation. For this, we developed a set of thermopolymerizable formulations. Each one is characterized by a different and controlled polymerization temperature threshold. In particular, we show the possibility of imaging the heat distribution with a spatial resolution better than 40 nm. By tuning the excitation wavelength, we show that the photo-induced heating can be tuned according to the extinction spectrum. The results show that the temperature reached close to the photo-excited nanoparticle (femtosecond laser at 780 nm, 150 fs and 80MHz) exceeds 180 ° C. Finally, we show that is possible to get a near-field thermal signature of single gold nanoparticles at different wavelengths. this approach of thermal imaging at the nanoscale will stimulate further works in thermoplasmonics and their applications to photocatalysis and nanomedicine.