Polyoxometalate-based iron-organic complex nanozymes with peroxidase-like activities for colorimetric detection of...

As a new type of artificial enzyme, a nanozyme is an ideal substitute for natural enzymes and has been successfully applied in many fields. However, in the application of biomolecular detection, most nanozymes have the disadvantages of long reaction times or high detection limits, prompting researchers to search for new efficient nanozymes. In this work, the enzyme-like activities of three polyoxometalate-based iron-organic complexes ([Fe(bpp)₂](Mo₆O₁₉), [Fe(bpp)₂]₂(Mo₈O₂₆)·2CH₃OH, and [Fe(bpp)₂]₄H[Na(Mo₈O₂₆)]₃), namely, FeMo₆, Fe₂Mo₈, and Fe₄Mo₈Na, were analyzed. All three polyoxometalate-based iron-organic complexes were found to be capable of catalyzing hydrogen peroxide (H₂O₂) to oxidize 3,3',5,5'-tetramethylbenzidine and o-phenylenediamine, resulting in visible color changes, further exhibiting peroxidase-like activity. Results showed that Fe₄Mo₈Na had more active sites due to its long chain structure, endowing more prominent peroxidase-like activity compared with Fe₂Mo₈ and FeMo₆. A colorimetric sensing platform for H₂O₂ and ascorbic acid detection based on Fe₄Mo₈Na was established. The linear response range for H₂O₂ detection was 0.5-100 μM, and the detection limit was 0.143 μM. The linear response for ascorbic acid detection ranges from 0 to 750 μM with a detection limit of 1.07 μM. This study provides a new perspective for developing new nanozymes and expanding the sensing and detection application of nanozymes.