Surface Enhanced Spectroscopy of Molecules on Plasmonic Nanostructures

Abstract

Metal nanoparticles have a great importance in Photoacoustic imaging (PAI) technique and in Surface enhanced Raman Spectroscopy (SERS). The size effect of gold nanospheres (AuNSs) used as a contrast agent for the PAI of breast cancer cell line MDA-MB 231 have been assessed. The decrease in the AuNS size, at the same optical density (OD), results in an improved PA signal, due to the increase in the total surface area of the particles resulting in more heating. The PA signal generally increases linearly with increasing OD, with almost the same rate of increase for the three used particle sizes. It is observed that PEGylation of AuNPs, as contrast agent, diminishes the PA images of cancer cells due to their increased resistance to uptake the AuNP, which results in diminishing the PA image compared to the image obtained for cells incubated with unPEGylated AuNSs. An enhanced PA image contrast is obtained for cells loaded with silica coated Gold nanorods (AuNRs) as compared to cells loaded with PEGylated AuNRs. This is because of the enhanced cellular uptake for Silica coated AuNRs and the decrease of the interfacial thermal impedance between gold and surrounding solvent, which allows the particle to generate more heat to the environment and hence increase the PA signal.