Stirring continued at room temperature for 20 minutes in the dark. The mixture was then centrifuged in 1.5 mL Eppendorf tubes to eliminate excess polyelectrolyte. Approximately 1.46 -1.48 mL of the supernatant was discarded, and the remaining dark-brown pellet was redispersed in ultrapure water. This centrifugation and redispersion process was repeated as a washing step, yielding a final 12 mL colloidal solution. The synthesized Au@PAH core-shell nanoparticle colloid is further diluted to 15 mL and 1mL of 10 mM titanium bis(ammonium lactato) dihydroxide (TALH) was added in 100 µL steps.