Enhanced photothermal signal in Thiol-capped single gold nanoparticles

Metallic nanoparticles are strong absorbers and scatterers of visible light due to surface plasmon resonance (SPR), which is the coherent oscillation of free electrons in conduction band induced by interacting with light. As shape and size are significant for the properties of the nanoparticles, single-particle spectroscopy techniques need to be used to characterize the nanoparticles without ensemble averaging. In this work, we made two samples with 90-nm AuNPs. In addition, 1-decanethiol was used to coat the surface of AuNPs. To introduce the thiol, we added two drops of 10 mM thiol solution onto the top of one of the two samples and allowed enough time for drying. We then measured two samples under the same experimental conditions and compared the photo-thermal signal. In this study, SEM characterization was carried out using a Quanta ESEM2 SEM (FEI) operated under low vacuum in a water vapor atmosphere at 30 kV. In conclusion, we presented a novel approach toward enhancing the sensitivity of photothermal imaging by capping the surface of AuNPs with 1-decanethiol. We found that the photothermal signal can be increased by a factor of ~10 for thiol-capped AuNPs. Further experiments to clarify the capping effect are underway. The result shows a potential application of a photothermal imaging method together with thiolated DNA molecules in biological studies