Colorimetric Detection of Acid Phosphatase and Malathion Using NiCo₂O₄ Nanosheets as Peroxidase-Mimicking Activity

The establishment of a low-cost and facile approach for the assay of acid phosphatase (ACP) and its inhibitor is a research focus. In this paper, we successfully synthesized NiCo₂O₄ nanosheets with peroxidase-mimicking activity in alkaline deep eutectic solvents (DESs) composed of NaOH and PEG-200, which can catalyze 3,3′,5,5′-tetramethylbenzidine (TMB) to the oxidation state TMB (ox-TMB) in the presence of H₂O₂. Due to L-ascorbic acid-2-phosphate can be hydrolyzed into ascorbic acid by ACP, the peroxidase-like activity of NiCo₂O₄ nanosheets is inhibited. However, the addition of malathion, an inhibitor of ACP, can inhibit the activity of ACP and thus limit the production of ascorbic acid (AA). Therefore, a colorimetric approach can be established for highly sensitive and selective detection of ACP and malathion with detection limits of 0.032 U/L and 0.65 nmol/L, respectively. More importantly, this method can be successfully applied to malathion detection in environmental samples tap water and food cucumber juice, indicating that it has potential application prospects in environmental and agricultural fields.