Optothermal Effect At The Nanoscale And Application In Bioanalysis

Surface plasmon polaritons have attracted a lot of interest recently.Surface plasmons are the hybrid mods between light and free electrons,and normally exist at metal/dielectric interfaces.Over the last two decades,scientists have made significant progresses in both theory and experiment.With theoretical design and advanced nanofabrication techniques,today the material,geometry and consequently the optical properties of plasmonic nanostructure can be control at will,leading to many new exciting applications in various fields.Localized surface plasmons is an important type of resonances,which can generate great enhancement of the scattering and absorption cross-sections,as well as the field strength in the vicinity of plasmonic nanoparticles.Therefore,metal nanoparticles often have a high absorption efficiency,and extraordinarily strong optothermal effects.Today,optothermal effects of plasmonic nanostructures have been widely used in biomedicine,photothermography,self-assembly of metal nanomaterials,and optothermal control,to name a few.In this paper,we have study the heat transfer of different metal micro-nanostructures and discussed its applications in biochemical detection and local temperature measurement:(1)Optothermal effects of metal nanoparticles on substrates.How the light-induced temperature rise of metal nanoparticles is investigated by simulating the temperature distribution of individual metal nanoparticles with different types of thermal contacts with substrates.(2)Optothermal effects of Au/AAO structures and its application in surface-assisted laser desorption/ionization(SALDI)mass spectrometry(MS).How the ionization efficiency is related to the aperture size,light absorption,heat conduction and heat capacity of SALDI substrates is studied.We found that a larger pore size will lead to higher ionization efficiency and less fragmentation.Theoretical analysis shows that this is caused by the pore-size dependent optical and thermal properties of the Au/AAO substrates.(3)Heat transfer at the tip-sample gap in scanning thermal microscopes and the influences on measurement accuracy.We show that the discrepancy between the measured temperature and the temperature of unperturbed sample can be significant,and it is related to many factors,including the tip size,size of tip-sample gap,heating power and heat source size.Simulation results indicate that the temperature measurement method is accurate only when the sample temperature is not too high and the tip size is much smaller than the sample size.