*2.6. Procedure for the Fluorescent Detection of Ag<sup>+</sup>*

Certain volumes of Ag<sup>+</sup> solutions were added to 0.4 mg of the Fe3O4@ZnS@MPS suspension, whose final volume was tuned to 5 mL by PBS buffer solution. After a 5 min reaction, the emission spectra were measured at an excitation wavelength of 370 nm. The selectivity performance of Fe3O4@ZnS@MPS assay for the detection of Ag<sup>+</sup> was carried out by measuring its fluorescence response in the presence of various common ions (Co2+ , Pb2+, Ni2+, Hg2+, Al3+, Cu2+, Zn2+, Cd2+, Fe3+, Fe2+, K<sup>+</sup> , Ca2+, Na<sup>+</sup> ).
