Biosynthesis, Characterization, and Antimicrobial Activity of Gold Nanoparticles Using Chitosan Isolated From Portunus Sanguinolentus Shells

Abstract

Marine bio-nanotechnology has emerged as a promising field for developing eco-friendly nanomaterials with biomedical applications. This study reports the biosynthesis, characterization, and antimicrobial evaluation of chitosan-gold nanoparticles (CHS-AuNPs) using chitosan extracted from the exoskeleton of Portunus sanguinolentus (three-spot swimming crab). Chitosan was successfully isolated from crab shell waste through sequential demineralization, deproteinization, decolorization, and deacetylation processes. The Chitosan-mediated AuNPs were characterized using UV-Visible spectroscopy, FT-IR, XRD, SEM-EDX, HR-TEM with SAED, DLS, and AFM techniques. UV-Vis spectroscopy revealed a characteristic surface plasmon resonance band at 529 nm, confirming the formation of gold nanoparticles. FT-IR analysis indicated the involvement of hydroxyl and amine groups in the reduction and stabilization of nanoparticles. XRD patterns confirmed the face-centered cubic crystalline structure of metallic gold, with Bragg reflections from the (111), (200), and (220) planes. SEM and HR-TEM images revealed predominantly spherical, polydisperse nanoparticles with sizes ranging from 8–10 nm (AFM) to 51.43 nm (DLS hydrodynamic diameter). EDAX analysis confirmed the elemental composition with a strong gold signal. The antimicrobial activity of CHS-AuNPs was evaluated against six bacterial strains ( E. coli , Enterobacter , P. aeruginosa , K. pneumonia e, S. aureus, and E. faecalis ) and four fungal strains ( A. niger , Penicillium , Rhizopus , and A. flavus ) using the agar well diffusion method. The Chitosan-mediated AuNPs exhibited significant dose-dependent antibacterial activity, with the maximum zone of inhibition against S. aureus (22 ± 0.77 mm) and P. aeruginosa (22 ± 1.47 mm) at 40 µg/mL. Antifungal activity was highest against Penicillium (15 ± 0.57 mm) at the same concentration. The Chitosan-mediated AuNPs demonstrated superior antimicrobial efficacy compared to chitosan alone, highlighting their potential as promising therapeutic agents in biomedical applications, particularly in drug delivery and infection control.

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