Assessment of polymer-templated gold nanoparticle stability in high ionic strength solution UV-vis is widely used to determine gold nanoparticle stability, as individualized nanoparticles exhibit a characteristic spectrum with a single peak at ~ 520 nm, associated with their well-known wine-red colour. Upon aggregation, the visually observed colour changes to blue-black, and the peak shows a substantial flattening towards higher wavelengths. UV-vis Spectroscopy was measured using NanoDrop™ OneC Microvolume UV-Vis Spectrophotometer, Thermo Fisher Scientific Inc, UK, 2 μL sample size). Polymertemplated gold nanoparticles (3.4 mg(Au)/ml) were respectively mixed with sodium chloride (NaCl) (1M) and magnesium chloride (MgCl2) solutions (1M), in two separate experiments, to give resultant concentrations of 1.7 mg(Au)/ml for the nanoparticles and 0.5 M for each of the electrolytes. UV-Vis spectra were measured at 24h and 72h after mixing.