Immobilization of iron hydroxide/oxide on reduced graphene oxide: peroxidase-like activity and selective detection of sulfide ions

We prepared nanocomposites of amorphous iron hydroxide/oxide immobilized on reduced graphene oxide (FeOxH-rGO) with peroxidase-like activity for the detection of sulfide (S2-) ions. FeOxH-rGO nanocomposites were prepared by reaction of GO (size similar to 300 nm) partially reduced by ultraviolet irradiation with Fe2+ in Tris-borate solution (5.0 mM, pH 7.0). The amorphous FeO(OH) and Fe(OH)(2) were immobilized on rGO to form FeOxH-rGO nanocomposites. The as-prepared FeOxH-rGO nanocomposites exhibited peroxidase-like catalytic activity in the H2O2-mediated oxidation of Amplex Red (AR) to fluorescent resorufin. Our AR/FeOxH-rGO probe allowed the detection of H2O2 down to 50 nM within 10 min under microwave irradiation (170 W). The catalytic activity of FeOxH-rGO was significantly suppressed in the presence of S2- because of the formation of FeS on the FeOxH-rGO nanocomposites' surfaces. The H2O2/AR-FeOxH-rGO probe provided a limit of detection (signal-to-noise ratio 3) of 50 nM for S2- with high selectivity (>100-fold) with respect to other anions. Taking advantage of their high stability and selectivity, we employed our H2O2/AR-FeOxH-rGO probe for the detection of S2- in hot spring samples (75.1-619.5 mu M) and the results showed good correlation (r = 0.98) with results from inductively coupled plasma mass spectrometry. This label-free, rapid, and simple sensing system shows great potential for the detection of S2- ions in real samples.