A Novel Colorimetric Assay for the Detection of Bisphenol A Using Laccase and Mediator Immobilized on Polyvinyl Alcohol Hydrogels

A novel, simple and low-cost colorimetric sensor has been developed for the detection of bisphenol A (BPA). In the assay, laccase catalyses the reaction between BPA and 2,2-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid) [ABTS] radicals, resulting in a colored product showing λ_max at 560 nm. Raman spectroscopy and mass spectra analysis of the product suggests the possible formation of ABTS dication radicals. This assay could detect BPA up to 2 µM by the naked eye, which is lower than the European Union specific migration limit of 2.6 µM. UV–visible spectroscopy showed a linear response in the concentration range of 1.0–10.0 µM with a lower detection limit of 0.5 µM. Sensitivity of the assay was enhanced by 40 folds when laccase and ABTS were fabricated on polyvinyl alcohol (PVA) hydrogel beads, allowing BPA to be detected at concentrations as low as 50 nM. These hydrogel beads were highly stable for long-term storage. Screening of different phenolic contaminants showed that laccase along with ABTS exhibits propensity for para-substituted alkyl-phenols that are considered as xenoestrogens and are highly toxic, estrogenic and carcinogenic in nature. Thus, the assay developed may be utilized for in-situ monitoring of BPA and other toxic xenoestrogens present in the environment. Additionally, its applicability can be extended towards other potential laccase mediators.

Graphical Abstract