*3.1. Materials*

All chemicals used in this work were reagent-grade and were used without further purification. Diethylene glycol ((HOCH2CH2)2O, DEG, 99%) was supplied by Alfa Aesar (Thermo Fisher, Kandel, Germany); Orange II (C16H10N2Na2O7S2, >85%), zinc(II) acetate dihydrate (Zn(CH3CO2)2·2H2O, >98%), silver nitrate (AgNO3, >99%) and absolute ethanol (CH3CH2OH, >99.8%) were supplied by Sigma-Aldrich (St. Louis, MI, USA). Silver nanoclusters (Ag-AQCs DS0481) were provided by NANOGAP SUB-NM POWDER, S.A (ZIP code 15895 O Milladoiro, A Coruña, Spain). This sample contains a mixture of Ag nanoclusters with <sup>≤</sup>10 silver atoms per nanocluster (100 mg L<sup>−</sup>1) and Ag(I) ions (400 mg L<sup>−</sup>1).
