Investigations on nonlinear optical properties and thermal diffusivity of gold nanoparticle embedded protein complex

Abstract We investigate the modifications in nonlinear optical response and thermal diffusivity of three proteins, viz. Bovine Serum Albumin (BSA), Human Serum Albumin (HSA), and Hen Egg White Lysozyme (HEWL) induced by gold nanoparticles (GNPs) interaction using a single beam z-scan technique and a dual-beam thermal lens technique respectively. Varying concentrations of chemically synthesized gold nanoparticles were added to a fixed concentration of proteins. The size and morphology of gold nanoparticles were analyzed using TEM analysis. The stability of protein-gold nanoparticles was established using zeta potential analysis. The absorption spectra confirmation of a ground state complex between the proteins and gold nanoparticles. The third-order nonlinear optical properties of the samples suggest that proteins exhibit two-photon absorption and reverse saturable absorption. The observed values of nonlinear absorption coefficient and imaginary part of nonlinear susceptibility χ3 for protein-gold nanoparticles are of the order of 10−10 m/W and 10−19 m2/V2. With the increase in gold nanoparticle concentration, both these values are found to decrease due to the formation of the ground-state complex as is evident from absorption spectra. This indicates that gold nanoparticle concentration plays an important role in modulating the nonlinear optical response of the proteins. The nonlinear optical properties of the samples at varying input fluence and wavelength were also investigated. The work is important as it finds application in photothermal therapy for cancer treatment. The optical limiting threshold of the samples is found to decrease with an increase in the concentration of gold nanoparticles. Results suggest that protein-gold nanoparticles can serve as potential candidates for optical limiting applications. Thermal diffusivity values were found to decrease with an increase in gold nanoparticle concentration. Also, a linear variation of thermal diffusivity was obtained with an increase in protein concentration and is a possible method for sensing protein concentration in blood samples.