Synthesis, Characterization and Stability of Gold Nanoparticles (AuNPs) in Different Buffer Systems

Abstract

In the present study, colloidal gold nanoparticles (AuNPs) were synthesized by the citrate reduction method. The physical properties and their stability were studied in the various buffer systems at different pH and time intervals. Monodisperse AuNPs were used to assess their stability and aggregation in 0.1 M of buffers. We analyzed the stability of the colloidal gold nanoparticles in borate, phosphate, Tris–citrate and Tris–HCl buffers with variable pH and time-dependent manner. For understanding the stability and aggregation of AuNPs in different buffers, AuNPs and buffer mixture was incubated at 4 °C for different time-periods. The surface plasmon resonance (SPR) spectra and colorimetric changes were recorded at time interval. Absorbance spectra revealed that different ratios of AuNPs in borate buffer were stable at pH 7.5 to 9.3. Wine red colour with maximum absorbance at 520 nm was obtained due to lack of the aggregation. The phosphate buffer was not suitable for monodisperse gold nanoparticles and got aggregated. In Tris–citrate buffer, the absorbance A520 (*P < 0. 05 and ***P < 0. 001) and correlation coefficient changed with incubation time and λmax shifts to longer wavelengths at pH 8.5. Tris–HCl buffer revealed significant changes A520 with incubation period and did not correlate with time. There were changes in A520 with incubation time and λmax shifts towards longer wavelength at pH 4.0 while AuNPs was stable at pH 10.5. The phosphate buffer, Tris–citrate buffer and Tris–HCl buffer made complexes and got aggregated colorimetric response was shifted wine red color to blue –black color.