Quenching of tryptophan fluorescence by colloidal Cu2S nanoparticles through static and dynamic modes under different solution pH

[Display omitted] •UV–visible spectroscopy indicates binding of tryptophan with the Cu2S NPs at pH 10.6.•FTIR data suggests binding of tryptophan via indole chromophore to the Cu2S NPs at pH 10.6.•Dynamic quenching of the tryptophan fluorescence by the Cu2S NPs at pH 6.•Static quenching of the tryptophan fluorescence by the Cu2S NPs at pH 10.6. The study of the interaction between biomolecules and nanoparticles (NPs) is interesting since the dimensions of the two overlap to some extent. Herein, the interaction of an essential amino acid, tryptophan, with Cu2S NPs was investigated by using various spectroscopic techniques. The 220 nm absorption band of tryptophan was found to be blue-shifted by 2 and 5 nm at pH 6 and 10.6 respectively. The binding of tryptophan with the Cu2S NPs at pH 10.6 via its indole chromophore was established by the Fourier transform infrared (FTIR) spectroscopic measurements. The fluorescence emission of tryptophan was quenched by the semiconductor NPs. The fluorescence quenching was found to be dynamic in nature at pH 6. However, the static mode of quenching was found to be operative at pH 10.6. The binding constants and thermodynamic parameters were calculated for the tryptophan-Cu2S NPs complex at pH 10.6.