Abstract
Brightly luminescent semiconductor quantum dots (QDs) continue to have an increasing role in biophotonic research and applications such as bioassays. Here, we present methods for the immobilization of QDs on the cellulose fibers of paper substrates for Förster resonance energy transfer (FRET)-based assays of proteolytic activity. Steady-state and time-resolved fluorescence characterization of FRET between immobilized QDs and self-assembled dye-labeled peptides within the paper matrix revealed a substantial enhancement in energy transfer efficiency. Compared to bulk solution, the rate of energy transfer increased approximately 4-fold resulting in a concomitant 7-fold increase in the ratio of FRET-sensitized acceptor dye emission and quenched QD emission. Spots of immobilized QDs with different amounts of dye-labeled peptide had bright luminescence under UV/violet illumination and the net QD and A555 emission was visible by eye as different colors. Tryptic digestion of the peptide linking the QD donor and acceptor dye resulted in loss of FRET. Changes in the dye/QD PL ratio permitted tracking of proteolytic activity, including the effect of increasing amounts of aprotinin, a potent inhibitor of trypsin. The combination of QDs, a paper substrate, and enhanced FRET has strong potential for developing bioassays.
