Assembly of polyoxometalates/polydopamine nanozymes as a multifunctional platform for glutathione and Escherichia coli O157:H7 detection

A new P2W18Fe4/PDA (P2W18Fe4 = K10P2W18Fe4(H2O)2O68 and PDA = polydopamine) nanocomposite has been synthesized with peroxidase activity for glutathione (GSH) and Escherichia coli O157:H7 (E. coli O157:H7) detection. The size of P2W18Fe4/PDA is about 104 ± 16 nm, which is the smallest among the reported polyoxometalates (POMs)/PDA composites. The polydopamine functionalization not only provides an adhesive surface for the immobilization of biomolecules onto P2W18Fe4, but also, significantly increases the peroxidase-like activity of P2W18Fe4, probably due to its enhanced affinity to organic substrates. P2W18Fe4/PDA can catalyze the oxidation of o-phenylenediamine (OPD) to form yellow 2, 3-diaminophenazine (DAB) in the presence of H2O2 through hydroxyl radical. The GSH can efficiently react with the hydroxyl radicals from H2O2 catalyzed by P2W18Fe4/PDA to inhibit the production of DAB. Thus, we can determination the concentration of GSH with the decreasing spectrometric signal of the DAB. The limit of colorimetric detection was 0.18 mM with the linear range from 2 to 8 mM. The limit of fluorescent detection was 4.02 μM with the linear range from 15.63 to 250 μM. The assay was successfully applied to the detection of GSH in SH-SY5Y cells lysate samples with higher sensitivity and specificity. The detection of E. coli O157:H7 was achieved by the sandwich immunoassay with the P2W18Fe4/PDA nanozymes as labeling markers. A linear correlation was established between absorbance intensity and E. coli O157:H7 from 103 to 106 CFU / mL with a detection limit of 4.2 × 102 CFU/mL. These primary results enlarge the POMs’ analytic application field.