Coating of gold nanoparticles with natural polymers for imaging and regenerative strategies

Diagnostic, real-time monitoring and treatment can be combined in a single nanoparticle (NP) that will constitute an advantageous theranostic nanomedicine strategy. In this context, gold (Au) NPs are potential theranostic platforms. Indeed, the properties of AuNPs, such as biocompatibility, high chemical stability, facile surface modification, versatile conjugation to biomolecules, allied with the possible detection by a variety of imaging techniques, for example near-infrared irradiation and computed tomographic imaging, make them a very useful tool to be used in several medical applications [1-4].

The coating of AuNPs with polymers provides them advantageous physicochemical properties, such as suspension stability and additional functionality. In this work, AuNPs were coated with natural polymers, namely chitosan and heparin, by the layer-by-layer methodology. The polymers adsorption was monitored by Quartz Crystal Microbalance with Dissipation, as well as by size and zeta-potential analysis. The natural polymers-coated AuNPs presented a spherical shape and a positive surface charge due to chitosan amino groups, enabling their biofunctionalization with monoclonal antibodies to target specific biomolecules. Additionally, cellular assays with the chondrocytic cell line ATDC5 showed that the NPs did not present cytotoxicity at the tested concentrations, and allow cells to proliferate and synthesize proteins along the time course of the experiment. As a proof of concept of their potential application in tissue regeneration, the natural polymers-coated AuNPs were further functionalized with a defined antibody to bind basic fibroblastic growth factor (bFGF). bFGF is, in fact, a potent regulator of cell proliferation, differentiation, migration and survival, as well as of angiogenesis and wound repair [5-7]. The bioactivity of bFGF is maximized when administered in an appropriate carrier that allows enhancing its half-life and ensuring the preservation of its active form [8]. Our results show that our strategy avoids the use of synthetic polymers or crosslinkers, enabling developing functionalized AuNPs as advanced carriers for theranostic applications.