Zeev Rosenzweig and colleagues at the University of New Orleans recently modified quantum dots (QDs) to develop a sensor that intrinsically measures the activity of matrix metallo-proteinases (MMPs) in normal and cancerous tissues. In this fluorescence resonance energy transfer assay, the acceptors were rhodamine molecules rather than gold nanoparticles. The rhodamines were attached to the QDs (the donors) via tetrapeptides of RGDC. In the absence of proteases, excited QDs emitted red light (590 nm). When the tetrapeptides were cleaved by the protease, the rhodamine molecules were released, and the QD emission changed to green light (545 nm).
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