Colorimetric paper bioassay for the detection of phenolic compounds

A new type of paper based bioassay for the colorimetric detection of phenolic compounds including phenol, bisphenol A, catechol and cresols is reported. The sensor is based on a layer-by-layer (LbL) assembly approach formed by alternatively depositing layers of chitosan and alginate polyelectrolytes onto filter paper and physically entrapping the tyrosinase enzyme in between these layers. The sensor response is quantified as a color change resulting from the specific binding of the enzymatically generated quinone to the multilayers of immobilized chitosan on the paper. The color change can be quantified with the naked eye but a digitalized picture can also be used to provide more sensitive comparison to a calibrated color scheme. The sensor was optimized with respect to the number of layers, pH, enzyme, chitosan and alginate amounts. The colorimetric response was concentration dependent, with a detection limit of 0.86 (±0.1) μg/L for each of the phenolic compounds tested. The response time required for the sensor to reach steady-state color varied between 6 and 17 min depending on the phenolic substrate. The sensor showed excellent storage stability at room temperature for several months (92% residual activity after 260 days storage) and demonstrated good functionality in real environmental samples. A procedure to mass-produce the bioactive sensors by inkjet printing the LbL layers of polyelectrolyte and enzyme on paper is demonstrated.