Incorporation of laccase into surface-sized paper

The aim of this work was to study the activity and functionality of laccase incorporated into laboratory-coated surface-sized paper. The effects of the physicochemical properties of the studied sized paper grades (permeability, porosity, and wetting) on the enzyme activity were studied. The enzymatic activity of laccase was measured either by following the oxidation of the substrate (mediator) with spectrophotometry or by monitoring the reduction of oxygen by luminescence quenching. The results showed that the initial activity of laccase incorporated into the coating did not decrease during the first 4 weeks and the activity was partly preserved even after 6 months. The functionality of the enzyme in sized papers was examined using 2,2-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt (ABTS) as the substrate. ABTS was inkjet-printed on the sized paper, and the reaction between laccase and ABTS appeared as a color change. The most important factor affecting the color response was the enzyme activity. Other beneficial factors affecting the color response were the hygroscopic nature and wettability of the sized paper. The results showed that the fabrication of bioactive paper is possible with a relatively simple strategy, i.e., by incorporation of the biomolecules in the coating formulation (paste). No major investments would be needed to start the production of this kind of environmentally sustainable, low-cost, and lightweight paper-based bio-indicator, e.g., for authentication applications.