Antimicrobial activity of sodium dodecyl sulfate-capped silver nanoparticles via green synthesis of continuous wave fiber laser

Continuous wave (CW) fiber laser operating at 1064 nm with 50 watts has been used for the eco-friendly synthesis of sodium dodecyl sulfate (SDS)-capped silver nanoparticles (AgNPs) using a silver acetate precursor and SDS dissolved in an aqueous medium. The selected laser parameters (50 W, 50 min exposure) were optimized through systematic preliminary experiments, with lower powers or shorter exposure times failing to initiate nanoparticle formation. A novel photothermal reduction mechanism is proposed wherein SDS serves a dual function: (i) as the reducing agent under laser activation, facilitating electron transfer from its negatively charged sulfate heads to Ag⁺ ions, and (ii) as a capping agent providing electrostatic stabilization. The concentration of both SDS and silver acetate was varied to produce nine samples (AgS1-AgS9) with different particle sizes (40–100 nm) and concentrations. UV-Vis spectroscopy confirmed the presence of stable SDS-capped AgNPs through their surface plasmon resonance, enabling the determination of particle size, concentration, and optical extinction cross-section. XRD, EDX, and SEM analyses confirmed the formation of crystalline, spherical AgNPs with SDS capping. Control experiments using alternative capping agents (citric acid, PVA) under identical conditions yielded no nanoparticles, confirming SDS's essential role in the reduction mechanism. As an application, the antimicrobial activity was tested against the Gram-positive bacteria ( Staphylococcus aureus , S. epidermidis ), Gram-negative bacteria ( Escherichia coli , Pseudomonas aeruginosa ), and the pathogenic fungus Candida albicans using the well diffusion method. Results showed a clear inverse correlation between particle size and antimicrobial activity, with 40 nm particles (AgS1, AgS3, AgS6) exhibiting 2.2–2.8 fold greater inhibition than 80 nm particles. The highest concentration sample (AgS1) recorded the strongest inhibitory effect against P. aeruginosa (46.1% over positive control) and C. albicans. The amphiphilic nature of the SDS capping enhanced interaction with the bacterial cell wall, facilitating Ag⁺ ion delivery. In conclusion, CW fiber laser-synthesized SDS-capped AgNPs with controlled sizes demonstrate efficient antimicrobial activity ( in-vitro assay), offering a green, cost-effective alternative to conventional antibacterial and antifungal agents.