Abstract
Here, cadmium sulphide quantum dots (CdS QDs) have been synthetized and functionalized with Bovine Serum Albumin (BSA) in a colloidal aqueous solution with a stability of over 3 months. Specific synthesis conditions, in homogeneous phase and at low temperature, have allowed limitation of S2− concentration, hence, as a consequence, there is restricted growth of the nanoparticles (NPs). This fact allows binding with BSA in the most favorable manner for the biomolecule. The presence of Cd2+ ions on the surface of the CdS nanoparticle is counteracted by the negatively charged domains of the BSA, resulting in the formation of small NPs, with little tendency for aggregation. Temperature and pH have great influence on the fluorescence characteristics of the synthetized nanoparticles. Working at low temperatures (4 °C) and pH 10–11 have proven the best result as shown by hydrolysis kinetic control of the thioacetamide precursor of S2− ion. Biological activity of the coupled BSA is maintained allowing subsequent bioconjugation with other biomolecules such as antibodies. The chemical conjugation with anti-Glutathione S-transferase (α-GST) antibody, a common tag employed in human recombinant fusion proteins, produces a strong quenching of fluorescence that proves the possibilities of its use in biological labelling. Finally, p53, onco-human recombinant protein (GST tagged in COOH terminus), has been in situ IVTT (in vitro transcription-translation) expressed and efficiently captured by the α-GST-CdS QD conjugate as a proof of the biocompatibility on IVTT systems and the functionality of conjugated antibody.
Highlights
Quantum dots (QDs) are semiconductor nanomaterials that have attracted considerable attention in several research areas in the last years
In most biological applications, nanomaterials are coated with proteins to generate biocompatibility and/or adsorbed proteins inherently presented in the biological fluid
The preparation of protein-conjugated QDs is a laborious process with multiple stages that usually start with the synthesis of a colloidal QD and its solubilization, and follow by further functionalization with biomolecules
Summary
Quantum dots (QDs) are semiconductor nanomaterials that have attracted considerable attention in several research areas in the last years. The direct synthesis of protein conjugated QDs under mild conditions (pH, incubation times, T, etc.) has been quite successful in the production of highly luminescent QDs with adequate range of emission wavelengths, high quantum yield and photostability for bioimaging applications For this purpose, it has been reported that preparation of QDs enriched with some metallic ions could be combined with some amino acid functional groups (such as carboxylic groups, amino, thiol, etc.) to obtain a covalent bound between chemically reactive moieties of the protein and QD surface [17]. Due to its low cost, easy availability, biotechnological relevance and biomedicinal importance, BSA is currently used as a model protein in biomedical research [20] Aside from these properties, BSA has been previously reported as a capping/stabilizing agent for the synthesis of several semiconductor nanomaterials based on noble metals [21,22,23,24,25]. Compared to other conventional protein expression systems, IVTT can produce functional properly folded proteins of any size in a less complex manner while still being a highly efficient procedure; it has been adopted as a useful strategy in the Human Proteome Project (www.hupo.org) [26,27]
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