Sensitive detection of sulfate in PM2.5 via gold nanoparticles/poly-l-lysine/graphene composite film based arylsulfatase-inhibition biosensor

Abstract This work developed a novel sulfate biosensor based on arylsulfatase (AS) inhibition. AS mixed with glutaraldehyde and bovine serum albumin was immobilized on glassy carbon electrode (GCE), which was first modified with poly- l -lysine (PLL)/graphene (GR) hybrid and electrodeposited gold nanoparticles (AuNPs). The characterizations were performed by TEM, SEM, FTIR, Raman spectroscopy and cyclic voltammetry. AS can catalyze 4-nitrocatechol sulfate (NCS) to hydrolyze to sulfate and 4-nitrocatcchol (NC), which is electroactive and an anodic current occurs at ∼0.42 V vs. SCE. However, the production of NC would decrease in the presence of sulfate due to its inhibition effect on the enzymatic hydrolysis reaction, thus leading to a decrease in the oxidation current. The inhibition measurements were carried out by detecting this current decrease after adding sulfate. At optimal conditions, the inhibition rate was linear to −log [sulfate] in the concentration range from 1.0 × 10 −7 to 1.0 × 10 −5  M with the detection limit of 4.0 × 10 −8  M. The introduced biosensor was further applied to assay the sulfate constituent in PM 2.5 , and the results were verified by employing ion chromatography as a reference. It showed that the new biosensor has a promising application for sulfate detection in real samples.