Studies on quantum dots synthesized in aqueous solution for biological labeling via electrostatic interaction
Section snippets
Materials
3-Mercaptopropyl acid (MPA) (99+%), tellurium powder (∼200 mesh, 99.8%), CdCl2 (99+%), and NaBH4 (99%) were purchased from Aldrich Chemical Com. Papain was used as obtained from Roche Diagnostics GmbH (Mannheim, Germany). The isoelectric point (pI) of papain is 8.75 [16]. All other reagents were of analytical reagent grade and used without further purification. Purified water (>18 MΩ cm) was used.
Preparation of water-soluble CdTe nanoparticles
MPA-modified CdTe nanoparticles were synthesized in aqueous solution using previously described
Results and discussion
The absorption spectrum of QDs–papain bioconjugates is flatter than that of the free QDs (Fig. 1); at the same time, the absorbance increases. The emission peak of the unconjugated QDs is at 542 nm; however, the emission peak of QDs–papain undergoes a red shift (557 nm), but the intrinsic spectral width is unchanged.
The changes of the absorption and fluorescence spectra result from the shortened distances between QDs owing to the electrostatic attraction between negatively charged CdTe quantum
Conclusions
CdTe nanoparticles synthesized in aqueous solution are effectively bound to a protein via electrostatic interaction. The method for labeling biomacromolecules with semiconductor nanoparticles presented in this paper is simple and feasible and can be applied to other inorganic nanomaterials with charged surfaces. These new types of nanoparticles–biomolecules conjugates could find their own potential application in cell surface labeling, intracellular tracking studies, and other imaging
Acknowledgements
This work was supported by the National Natural Science Foundation of China (No. 20075009). The authors thank Ms. Huijun Yu (College of Chemistry, Jilin University) for help with the enzymic activity measurement.
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Also corresponding author.