Antimicrobial, antibiofilm, antioxidant, molecular docking studies, and cytotoxicity evaluations of green synthesized selenium nanoparticles using soft coral Litophyton mollis alone or combined with chitosan

Microbial resistance and biofilm formation represent critical global health threats, necessitating the development of innovative, eco-friendly antimicrobial platforms. This study reports the first-ever green synthesis of a selenium/chitosan nanocomposite (Se/CS) bio-augmented with secondary metabolites from the Red Sea soft coral, Litophyton mollis. The Se/CS platform was comprehensively characterized via UV-Vis, FT-IR, XRD, and TEM, confirming the formation of stable, spherical nanoparticles (37–45 nm) with a strong positive surface charge (+ 35.88 mV) essential for colloidal stability and electrostatic membrane interaction. The Se/CS nanocomposite exhibited superior antimicrobial potency against a broad spectrum of pathogens, including methicillin-resistant Staphylococcus aureus (MRSA) and P. aeruginosa. Notably, the nanocomposite achieved a significantly lower minimum inhibitory concentration (MIC) for MRSA (40 µg/ml) compared to bare Se NPs (110 µg/ml). Furthermore, the system demonstrated robust anti-biofilm activity, inhibiting up to 60% of biofilm formation at 100 µg/ml. Ultrastructural TEM analysis confirmed severe cellular damage, characterized by cell wall distortion and cytoplasmic lysis. The final nanocomposite also displayed excellent antioxidant activity (76.5% DPPH scavenging). Importantly, cytotoxicity assays on Vero cells revealed that while Se NPs alone had a cytotoxic concentration 50% (CC50) of 56.1 ± 3.5 µg/ml, the CS-mediated nanocomposite significantly enhanced biocompatibility, increasing the CC50 to 124.1 ± 2.9 µg/ml. Molecular docking studies supported these results, predicting favorable binding affinities between specific coral metabolites and microbial protein targets. This synergistic, marine-inspired platform offers a promising, non-toxic strategy for mitigating resistant pathogens in diverse biomedical and environmental applications.