Plasmonics refers to the research area of enhanced electromagnetic properties of metallic nanostructures. The term plasmonics is derived from “plasmons”, which are the quanta associated with longitudinal waves propagating in matter through the collective motion of large numbers of electrons. Incident light irradiating these surfaces excites conduction electrons in the metal, and induces excitation of surface plasmons leading to enormous electromagnetic enhancement of spectral signature, such as surface-enhanced Raman scattering (SERS) and surface-enhanced fluorescence (SEF) for ultrasensitive detection of chemical and biological species. Biological process such as cell differentiation, cell division, apoptosis, phagocytosis and necrosis are associated with spatial reorganization of cellular components. Therefore new techniques are being developed in our laboratory to monitor the behavior of the molecules in key processes of the cell’s existence. External labeling of molecules of interest by chemical or recombinant techniques has enabled tracking of individual molecules using fluorescence microscopy with great sensitivity. In our laboratory, novel alternative microscopic techniques such as Surface-enhanced Raman scattering (SERS) that are chemically specific and allow the interrogation of molecules are being investigated.
Nanoparticles are increasingly finding a wide application in the biological studies due to their unique physical and chemical properties. However, biological and medical applications would require nanoparticles to be conjugated to biomolecules. A universal approach for conjugation of silver colloidal nanoparticles to biomolecules has been developed in our group. Surface functionalized silver colloids were labeled with a Raman active dye and bioreceptor molecule and used as labels for cellular imaging. The silver colloidal nanoparticles are efficient substrates that exhibit SERS phenomenon by enhancing the scattering cross sections of conjugated Raman active molecules thus enabling highly sensitive biological probes. In addition SERS nanotechnology and confocal surface-enhanced Raman imaging (SERI) using a acousto-optic tunable filter (AOTF)-based hyperspectral surface-enhanced Raman imaging (HSERI) system equipped with an intensified charged-coupled device has been developed to monitor the intracellular distribution of molecular species associated with biological abnormalities and localization of drugs and other cellular components within cells and thus offering a promising application for molecular signaling monitoring for nanomedicine applications.