UV-light-actuated in-situ preparation of paper@ZnCd quantum dots for paper-based enzymatic nanoreactors

Abstract

Quantum dots (QDs) have been widely applied in the analytical field including sensitive fluorescent assays on paper-based devices. A facile in-situ synthesis of QDs after a simple reagent deposition on paper could enable a rapid low-cost fabrication of QD–modified paper with a variety of properties and purposes such as enzymatic nanoreactors. Herein, for the first time, fluorescent ZnCd QDs were prepared by in-situ synthesis in the paper matrix using thiol-containing precursors and irradiation by UV light. A successful creation of the immobilized ZnCd QDs on paper (paper@ZnCd QDs) was monitored by their intrinsic fluorescence while their peroxidase mimetic activity was evaluated by a catalytic reaction between H2O2 and a substrate (3,3′,5,5′-tetramethylbenzidine, TMB) producing a blue coloured product of charged transfer complex of TMB (oxTMB). From three thiol precursors investigated, the insulin precursor provided a greater activity than glutathione (GSH) and both considerably larger than BSA. Finally, a QDs precursor mixture deposition onto the paper matrix was evaluated by the peroxidase-mimetic activity, which was comparable with a reference method. The in-situ preparation of paper@ZnCd QDs is simple, rapid and ‘green’, with potential in biomedical applications primarily as fluorescence imaging agent and enzyme mimetic paper-based nanoreactors.