Bioactive paper platform for colorimetric phenols detection

Abstract In this study the development of a low cost, portable and disposable paper-based bioassay for phenolic compounds is described. The colorimetric detection of the analyte is based on an enzymatic assay. The tyrosinase enzyme has been immobilized on a filter paper by simple over-spotting with 3-methyl-2-benzothiazolinone hydrazone (MBTH), that allows the detection of phenols by forming stable coloured adducts with their enzymatic oxidation products. The colour intensity of the adduct (developed after 5 min of reaction) was found to increase proportionally with the increase of the phenolic substrate concentrations. Analyte detection can be achieved by eye and quantification can be simply obtained by using a camera phone and an image analysis software. The response characteristics of the sensor were determined using l -3,4-dihydroxyphenyl-alanine ( l -DOPA), an archetype substrate of tyrosinase, as the analyte. The sensor gave a LOD of 5 μM and a linear response up to 0.5 mM. The polyphenol content in wine was determined by the biosensor and results were compared with that obtained for the phenolic-pool determined by tyrosinase enzymatic assay in solution and for the antioxidant-pool probed by the Folin–Ciocalteau assay. This paper-based platform holds potential for the detection of different types of phenolic compounds. The proposed assay has the advantage of rapidity and simplicity over other detection methods, without need of sophisticated instrumentation and trained personnel.