Bovine serum albumin capped cadmium sulphide nanoparticles. Synthesis in aqueous solution and interaction with α-GST

Abstract

For the last 20 years, there has been an increasing interest in hybrid materials between inorganic nanoparticles and biomolecules. Today it is simple to control and modify the properties of nanostructures in order to achieve their integration with biological systems. The CdS QDs functionalised with BSA in a colloidal aqueous solution, which are stable over a long period, have been synthesised. The conditions of synthesis, at a homogeneous phase and at low temperature, allow the limiting of the concentration of S2- in solution during the synthesis, which significantly restricts the consequent growth of the NPs. This allows the binding with the BSA in the most favourable manner for the molecule. The existence of Cd2+ ions on the surface of the CdS nanoparticle is counteracted by the negative charge domains of the BSA, the result being the formation of small NPs with a low aggregation tendency. The pH (Fig 1) and the temperature variables have a great influence on the fluorescent characteristics of the nanoparticles synthesised. The best results are obtained by working at low temperatures (4ºC) and at pH values between 10 and 11. Under these conditions the kinetic control of the hydrolysis of the thioacetamide precursor (Fig. 2) has allowed the obtaining of nanoparticles which attain high fluorescence sustained over time and a stability of over 3 months. The BSA bound to the CdS QD (CdS-BSA) maintains its biological activity to allow subsequent bioconjugation with other biological entities such as peptides, proteins, enzymes, or antibodies. Their interaction with the α-GST antibody produces a strong quenching of fluorescence that proves the possibilities of its use in biological labeling.