A new colorimetric protocol for selective detection of phosphate based on the inhibition of peroxidase-like activity of magnetite nanoparticles

Abstract

A simple colorimetric assay for phosphate ion (Pi) has been established based on analyte-induced inhibition of the magnetite nanoparticles (MNPs)-catalyzed oxidation of 3,3′,5,5′-tetramethylbenzidine (TMB) in the presence of H₂O₂. The Fe₃O₄ MNPs can catalyze the H₂O₂-mediated oxidation of TMB and yields a blue oxidized product, which exhibits a maximum absorption at 652 nm. Pi could be absorbed on the surface of the Fe₃O₄ MNPs through coordinating with Fe³⁺, inducing a reduced colorimetric signal. The colorimetric signal change (ΔA₆₅₂) in this process was proportional to the concentration of Pi, ranging from 0.2 μM to 200 μM. The limit of detection (S/N = 3) was as low as 0.11 μM. The as-proposed Fe₃O₄ MNPs–TMB–H₂O₂ probe exhibited a high selectivity toward Pi over other relevant ions that commonly exist in water and has been applied to Pi detection in drinking water, ground water and lake water samples with satisfactory results.