Self-Assembly of CdSe−ZnS Quantum Dot Bioconjugates Using an Engineered Recombinant Protein

A novel and direct method is described for conjugating protein molecules to luminescent CdSe−ZnS core−shell nanocrystals (Quantum Dots) for use as bioactive fluorescent probes in sensing, imaging, immunoassay, and other diagnostics applications. The approach makes use of a chimeric fusion protein designed to electrostatically bind to the oppositely charged surface of capped colloidal quantum dots (QDs). Preparation of protein-modified QD dispersions with high quantum yield, little or no particle aggregation, and retention of biological activity was achieved. Combining the advantages of lipoic acid capped CdSe−ZnS quantum dots (photochemical stability, a wide range of size-dependent emission wavelengths, and aqueous compatibility) with facile electrostatic conjugation of bioactive proteins, this type of hybrid bioinorganic conjugate represents a powerful fluorescent tracking tool for diverse applications. The design and preparation of a model QD/protein conjugate based on E. coli Maltose Binding Protein is described, together with functional characterization of this new type of nanoassembly using luminescence, laser scanning microscopy, and bioassay.