Research On The Photothermal Properties Of Metal Nanoparticles

Due to their unique optical properties resulting from localized surface plasmon resonance (LSPR), noble metal nanoparticles (NPs) have exhibited exciting potential applications in photonic devices, bio-chemical sensing, biological labeling and surface-enhanced Raman scattering in recent two decades. Apart from their superior optical properties, their photothermal properties are becoming a new research hotspot in recent years. Plasmon enhanced metal nanoparticles can be used as efficient, local and flexibly controllable nanosources of heat, enabling nanoscale thermal manipulation. Though metal nanoparticles have been widely used in a variety of applications including photothermal cancer therapy, photothermal imaging and nanofluidics, many questions remain unsolved concerning the underlying physical mechanisms and rules of heat generation and transfer in metal nanoparticles. In the first two chapters of this paper, the optical and photothermal properties, especially the basic theory and computational methods, of plasmonic nanoparticles are reviewed. In the third chapter, the optical and photothermal properties of two interacting nanoparticles are quantitatively investigated using the finite-element method (FEM) based software package COMSOL Multiphysics and the particle temperature is found to be distance dependent. The distance-dependence has two origins, i.e., electromagnetic coupling and thermal accumulative effect. For the particle temperature, a scaling behavior is found, and it suggests that the decay of particle temperature with the interparticle gap for different particle sizes follows a common exponential decay equation. The scaling behavior is qualitatively explained with a simple dipolar-coupling model combined with a point heat source interaction model. Our findings can serve as an excellent guideline for designing and optimizing temperature-based plasmon rulers for nanoscale length measurement. In the fourth part, we numerically investigate the temperature rise of a heated NP near the interface of two kinds of media with different thermal conductivities. It is found that the temperature rise becomes volume-independent if it is scaled by the temperature rise when the particle-interface distance is zero and the particle-interface distance is scaled by the equivalent radius of the NP. This universal scaling behavior is explained with the principle of dimensional homogeneity. A universal scaling equation relating NP temperature increase and particle-interface distance for NP of all shapes and dimensions is derived, which can be used to estimate the actual NP temperature increase of a single metal NP or NP array on a substrate with higher accuracy. Finally, a brief summary and prospects for future research are provided in the last chapter of the paper.