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Journal of Sensors
Volume 2008, Article ID 797436, 10 pages
Research Article

Monitoring of Enzymatic Proteolysis Using Self-Assembled Quantum Dot-Protein Substrate Sensors

1Division of Optical Sciences, Code 5611, U.S. Naval Research Laboratory, 4555 Overlook Ave, SW, Washington, DC 20375, USA
2Department of Chemical & Biological Engineering, Iowa State University, Ames, IA 50011, USA
3Center for Bio/Molecular Science and Engineering, Code 6900, U.S. Naval Research Laboratory, 4555 Overlook Ave, SW, Washington, DC 20375, USA
4Promega Biosciences, Inc., 277 Granada Dr., San Luis Obispo, CA 93401, USA
5Center for Biomedical Genomics, George Mason University, Fairfax, VA 22030, USA

Received 9 May 2008; Accepted 28 June 2008

Academic Editor: Francesco Baldini

Copyright © 2008 Aaron R. Clapp et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


We have previously utilized hybrid semiconductor quantum dot- (QD-) peptide substrates for monitoring of enzymatic proteolysis. In this report, we expand on this sensing strategy to further monitor protein-protease interactions. We utilize QDs self-assembled with multiple copies of dye-labeled proteins as substrates for the sensing of protease activity. Detection of proteolysis is based on changes in the rate of fluorescence resonance energy transfer (FRET) between the QDs and the proximal dye-labeled proteins following protein digestion by added enzyme. Our study focused on two representative proteolytic enzymes: the cysteine protease papain and the serine protease endoproteinase K. Analysis of the enzymatic digestion allowed us to estimate minimal values for the enzymatic activities of each enzyme used. Mechanisms of enzymatic inhibition were also inferred from the FRET data collected in the presence of inhibitors. Potential applications of this technology include drug discovery assays and in vivo cellular monitoring of enzymatic activity.