Bioconjugation of Highly Luminescent Colloidal CdSe–ZnS Quantum Dots with an Engineered Two-Domain Recombinant Protein

We present a novel approach, based on molecular self-assembly driven by electrostatic attractions, for conjugating inorganic colloidal semiconductor nanocrystals (quantum dots: QDs) having negatively charged surfaces with a two-domain recombinant protein bearing a positively charged C-terminal leucine zipper domain. Aggregation-free QD/protein conjugate dispersions were prepared. Conjugates retain both properties of the starting materials, i.e., biological activity of the protein and spectroscopic characteristics of the QDs. Such hybrid bio-inorganic conjugates represent a powerful fluorescent tracking tool, because they combine advantages of CdSe–ZnS quantum dots, such as chemical stability and a wide range of size-dependent luminescence emission properties, with a straightforward electrostatic conjugation approach. We describe the design and preparation of a model QD/protein conjugate and present functional characterization of the conjugate using luminescence and bioassays.