Characterization of the Effects of 3-Aminopropyl Triethoxysilane on Stability, Optical Properties and Morphology of Colloidal Gold Nanoparticles

Aggregation of gold nanoparticles in gold colloidal solutions can be induced via the addition of an aminosilane or a change in pH. This aggregation may affect the optics, morphology and stability of these nanomaterials. Therefore, thoroughly detailing the changes will serve as a reference for individuals manipulating these parameters, especially in the field of biomedical applications and diagnostics. A systematic study utilizing several concentrations ranging from 48 mM to 475 mM of 3-aminopropyl triethoxysilane were utilized throughout the duration of the study. Ultraviolet–visible absorption spectra and photoluminescence emissions were monitored as a function of concentration and time. In addition, scanning electron and transmission electron microscopy images were taken to study the morphology. To quantify the extent of aggregation, the Nanotrac Wave (a dynamic light scattering technique) was used to determine size and size distribution of aggregates. This study demonstrates the degree to which an aminosilane could impact the stability, optics and morphology of gold nanoparticles in colloidal solutions. Ultraviolet–visible absorption spectra display systematic and extensive red shifts from 500 nm to 650 nm as the test parameters were changed. Morphology studies indicate that red shifts are largely associated with aggregation of nanoparticles as opposed to particle growth. With the addition of 3-aminopropyl triethoxysilane, the photoluminescence of the gold nanoparticles also increases as a function of concentration and time. This paper also comments on opportunities for misinterpretation of data results while using 3-aminopropyl triethoxysilane. Keywords: Aggregation, aminosilane, colloids, gold nanoparticles, morphology, optical properties.