Observation and biomedical application of plasmon-enhanced fluorescence induced multiple stimulated Stokes Raman scattering in FITC-conjugated gold nanoparticles solution

Abstract

This work describes the observation of multi-wavelengths due to stimulated Raman scattering from deep red to near-infrared (NIR) induced by plasmon-enhanced fluorescence (PEF) of fluorescein isothiocyanate (FITC) conjugated gold nanoparticles (F-AuNP) excited by 488 nm diode laser. Coupling between the near-field of localized surface plasmons of AuNP with molecules amplifies the fluorescence signal i.e. brightness hence the quantum yield by several orders of magnitude. Resonance Rayleigh scattering and PEF conditions are satisfied due to the overlapping of 488 nm of the laser beam with the maximum absorbance of FITC, and the SPR of AuNP with FITC emission spectrum at ≈525 nm. PEF acts as Stoke sand secondary pump beam for further optical excitation. Surface-enhanced Raman scattering (SERS) showed FITC molecular bonds at 600, 1680, and a weak deviation at 1280 cm−1, respectively. Longer wavelengths with higher output power were observed between 180° and 270°, and shorter wavelengths with lower power between 90° and 0° respectively. F-AuNPs were incubated and up taken by the oyster mushroom (OM) grown in the lab for bioimaging purposes and studied by phase-contrast microscope (PCM), and fluorescence microscope (FM). The FM results revealed visible colours, which can be utilized for in vitro and in vivo biosensing applications.