Article

Improved QD-BRET conjugates for detection and imaging

Molecular Imaging Program at Stanford (MIPS), Department of Radiology, School of Medicine, Stanford University, Stanford, CA 94305, USA.
Biochemical and Biophysical Research Communications (Impact Factor: 2.28). 09/2008; 372(3):388-94. DOI: 10.1016/j.bbrc.2008.04.159
Source: PubMed

ABSTRACT Self-illuminating quantum dots, also known as QD-BRET conjugates, are a new class of quantum dot bioconjugates which do not need external light for excitation. Instead, light emission relies on the bioluminescence resonance energy transfer from the attached Renilla luciferase enzyme, which emits light upon the oxidation of its substrate. QD-BRET combines the advantages of the QDs (such as superior brightness and photostability, tunable emission, multiplexing) as well as the high sensitivity of bioluminescence imaging, thus holding the promise for improved deep tissue in vivo imaging. Although studies have demonstrated the superior sensitivity and deep tissue imaging potential, the stability of the QD-BRET conjugates in biological environment needs to be improved for long-term imaging studies such as in vivo cell tracking. In this study, we seek to improve the stability of QD-BRET probes through polymeric encapsulation with a polyacrylamide gel. Results show that encapsulation caused some activity loss, but significantly improved both the in vitro serum stability and in vivo stability when subcutaneously injected into the animal. Stable QD-BRET probes should further facilitate their applications for both in vitro testing as well as in vivo cell tracking studies.

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    • "Bioluminescence resonance energy transfer (BRET) is similar to FRET (Fluorescence Resonance Energy Transfer), except that the energy comes from a chemical reaction catalyzed by the donor enzyme rather than from absorption of excitation photons. Compared to fl uorescence imaging, bioluminescence has tremendously high sensitivity for in vivo imaging purposes (Xing et al. 2008) (Figure 4). "
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    • "However, two challenges facing in vivo fluorescent imaging are that the strong background autofluorescence is difficult to avoid, and a part of the external exciting light is absorbed and scattered by the tissue,19 so that the fluorescence intensity emitted by the QDs in deep tissue is sometimes too low to be detected or just simply too weak to be distinguished from the background autofluorescence. To overcome this limitation, So et al,20,21 Xing et al,22 Ma et al,23 and Kim et al,24 developed self-illuminating QDs based on the principle of bioluminescence resonance energy transfer (BRET). The fluorescence emitted by these QDs can be illuminated by the bioluminescence produced by the reaction between the enzymes and substrate around the QD surface. "
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