Understanding gold nanoparticles interactions with chitosan: Crosslinking agents as novel strategy for direct covalent immobilization of biomolecules on metallic surfaces

The development of a new method for covalent immobilization of biomolecules on the surface of bare gold nanoparticles (AuNPs) by using crosslinking agents in one step is presented. A very compatible biopolymer such as chitosan has been used as a target molecule to probe the viability of the proposed methodology. Click chemistry, based on biocompatible reactions and coupling with 1-Ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride and N-hydroxysuccinimide allow to analyze the covalent interactions between the metal nanoparticles and the biopolymer. Spectra deconvolution technique and Zeta potential measurements confirm the covalent interaction. The present study allows to quantify the proportion of AuNPs covalently adhered to the chitosan, which depends on the solution pH. The obtained results indicates that covalent interactions can be increased up to 25% in relation to total system interactions, which are mostly electrostatic. The proposed strategy opens up a new pathway for biomedical applications because the control of the chemical linkage can be directly performed on the nanoparticle surface without using any molecular intermediate, which may improve the encapsulation efficiency on drug delivery therapies.