*2.2. Preparation of Fe3O4@ZnS*

The chemical coprecipitation method was employed to synthesize Fe3O4@ZnS core/shell nanocomposites. First, 10 mL of Fe3O<sup>4</sup> was diluted to 100 mL and the solution was kept neutral. Then, 2.5 mmol of Zn(Ac)2·2H2O and Na2S·9H2O were dissolved in turn under the condition of water bath stirring, and were stirred for 6 h. The item was attracted by a magnetic force and then underwent a thorough cleansing process with ultrapure water and ethanol. The Fe3O4@ZnS nanoprobe was completed and water was added to make a dispersion for further modification [22].
