A green chemistry approach for synthesizing thermostable antimicrobial peptide-coated gold nanoparticles immobilized in an alginate biohydrogel

Developing rapid, green, and cost effective approaches for synthesizing metal nanoparticles with biochemical and biomedical applications is currently a top priority. Here, we report a rapid synthesis of gold nanoparticles (AuNPs) in an alginate polymer using thermostable antimicrobial peptides. At a high temperature, these antimicrobial peptides acted as reducing agents and converted Au3+ to Au-0 in 15 min while retaining their antimicrobial activity. The alginate polymer acted as a stabilizing agent for this reaction. The resulting Au-peptide-alginate biohydrogel was characterized by UV-visible (UV-Vis) spectroscopy, X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), energy dispersive X-ray spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM). TEM analysis showed AuNPs of less than 25 nm in diameter, with peptides present on their surfaces. The Au-peptide-alginate biohydrogel showed effective catalytic activity in reducing 4-nitrophenol and hexacyanoferrate(III) in the presence of sodium borohydride with durable reusability. The Au-peptide-alginate biohydrogel was also demonstrated to have antimicrobial activity against pathogenic bacteria. The method presented here for the synthesis of a metal-polymer conjugate is eco-friendly and robust. Large-scale production of the Au-alginate polymer would be possible in a very short time using this method, which makes it potentially useful for biomedical and industrial applications.