Real-time tracking of colloidal stability based on collision behaviors probed by surface-enhanced Raman spectroscopy

The dynamic behaviors of colloidal particles have already been considered as one of the key issues in their practical application, such as aggregation and dispersion. However, it is still remained significant challenge in developing the real time techniques to capture their dynamic tracks. The nano/subnanometer scale gap generated during the colloidal collisions served as the critical location for amplifying the Raman signal, so called as gap ("hot spots") based surface enhanced Raman spectroscopy (SERS). The alternating reversible "spike" of SERS intensity and irreversible step in baseline intensity are contributed to the preferred stability and the aggregation of colloid respectively.

A facile approach is developed to track colloidal stability in real-time based on collisions and SERS. The effects of particle concentration, the dispersion medium, and solution pH on colloidal stability are systematically investigated, and the SERS intensity of a simulated single-like "hot spot" was calculated by combining a SEM position with SERS mapping technology to estimate the intensity of single-particle collision.

The colloidal particles exhibited higher stability in the solution with lower particle concentration, higher viscosity and neutral medium. The SERS intensity of single-particle collision was estimated to be about 2.06 × 10^-7 counts, and the average number of collisions for the 0.13 mmol/dm³ SiO₂@Ag solution was about 1.11 × 10⁸ times/spike in the "spikes" with SERS intensity of 23.0 cps. It is believed that the SERS based strategy would be developed as a promising tool for obtaining the deeper insight into the nature of collisions in the colloidal science.