Description

The fluorescence quenching properties of silver nanoparticles (AgNP) in the presence of tryptophan is well understood. Amino acids introduced into a nanoparticle solution begin binding to the surface in the form of a metal-ligand complex. Interactions such as this are very important in determining how metal nanoparticles such as silver will interact in the presence of proteins. However, it is very difficult to properly calculate the actual number of ligands that will bind to each individual nanoparticle surface. Tryptophan is one of the major amino acids in proteins that strongly fluoresces (tyrosine, and phenylalanine are the other two). By comparing the fluorescence values of a tryptophan solution before and after the addition of AgNP, we can apply these values to a Stern-Volmer plot and find exact binding constants for amino acid complexes. With this analysis, we propose that the relative amount of tryptophan binding per surface of AgNP is very high, covering multiple layers more than expected to be possible. After running some preliminary experiments to find the concentrations of the complexes formed, the amount of tryptophan quenched has been shown to be much greater than initially predicted. Dynamic quenching of the mixture was considered ultimately impossible as the calculated rate constant was much higher than that expected for the diffusion of molecules within the solution. Yet if the process involved static quenching the results would seem to imply that there are multiple layers of tryptophan binding to the surface of each nanoparticle. Our work has now focused on changing the solution conditions individually to understand how each variable affects the overall behavior of the tryptophan-AgNP complex. Such conditions include changing the pH of the environment or adjusting the concentrations of either the AgNP or tryptophan. Once a correlation has been established, a range of tests can then be performed to determine exact calculations for amino acid binding. Further experimentation on both tryptophan concentrations, as well as initial AgNP values, is to be performed within the next few months in order to refine our results into a comprehensive set of conclusions.