Chitosan-stabilized gold nanoparticles for biosensing application

Abstract

Polysaccharide-stabilized gold nanoparticles (AuNPs) were synthesized by two methods. The first method employed chitosan as both reducing and stabilizing agent. The second method used sodium borohydride as a reducing agent and chitosan derivatives; N,N,N-trimethyl chitosan (TMC), N-[(2-hydroxyl-3-trimethylammonium)propyl]chitosan chloride (HTACC), or N-succinyl chitosan (SCC), as a stabilizing agent. The results from transmission electron microscopy showed that the synthesized AuNPs had a spherical morphology, a size range of 7-13 nm, and are stable in aqueous solution for at least 4 months due to the repulsion between the charges on the polymer chains which act as shell coating. According to the photon correlation spectroscopy (PCS), the size, size distribution and stability of particles was found to vary with volume ratio of polymer to HAuCl4, molecular weight of chitosan, concentration of surfactant, and concentration of NaBH4. The synthesis based on sonochemical method using BSA-modified CS (CS-BSA) as a reducing/stabilizing agent yielded BSA-functionalized gold nanoparticles, BSA-CS-AuNPs that were mostly spherical (i.d. average=8.2 nm) with some triangular shape, and were stable in aqueous solution for at least one month. The BSA-CS-AuNPs aggregated in the presence of anti-BSA due to the antigen-antibody specific interactions. The minimum concentration of anti-BSA that can induce the aggregation of BSA-CS-AuNPs that can be visualized by naked eye was 20 µg/mL. These results demonstrated the potential of using AuNPs stabilized by biomolecule-attached chitosan as chromogenic biosensor based on the aggregation of AuNPs.