Temperature Dependent Synthesis of Tryptophan-Functionalized Gold Nanoparticles and Their Application in Imaging Human Neuronal Cells

Abstract

The growth kinetics and temporal evolution of the UV-vis spectrum of gold nanoparticles (AuNPs) by following tryptophan reduction in different temperature conditions were studied systematically. The results revealed the productivity and overall reaction mechanism were mostly determined by the temperature, which was in turn affected by the concentration of tryptophan. Two considerably different reaction pathways were observed. The first pathway occurred at ambient temperature (35 degrees C) and consisted of three corresponding steps: nucleation, growth, and oriented attachment. The second pathway occurred above the ambient temperature (45, 65, and 95 degrees C) and was responsible for the well-known nucleation growth route. The second pathway was used to develop a facile synthetic route for the preparation of functionalized AuNPs with the size about 20 nm. Consequently, the stability and functionalization of the AuNPs were demonstrated using dilution studies, zeta potential, and FTIR measurements. The imaging of human neuronal (SH-SYSY) cells showed that the fluorescent signal from the tryptophan-functionalized AuNPs was significantly brighter than that from autofluorescence of the cells. The strong signal, resistance to photobleaching, excellent stability, ease of synthesis, simplicity of functionalization, and biocompatibility make AuNPs an attractive option for imaging and biomedical applications.