A novel photo-biological engineering method for Salvia miltiorrhiza-mediated fabrication of silver nanoparticles using LED lights sources and its effectiveness against Aedes aegypti mosquito larvae and microbial pathogens

In this study, Salvia miltiorrhiza-synthesized Ag nanoparticles (AgNPs) fabricated using sunlight or various LED lights were studied for their biophysical features and evaluated as larvicides against Aedes aegypti mosquitoes and growth inhibitors on different species of microbial pathogens. AgNPs production post-exposure to sunlight or different LED light conditions (i.e. blue, red, green, and white) was confirmed by characteristic surface Plasmon resonance (SPR) at maximum λ of 430, 420, 460, 450, and 460 nm, respectively. Optimization of pH, reducing extract concentration, metal ion concentration and time elapsed from the nano-biosynthesis was achieved. High-resolution transmission electron microscopy (HR-TEM) showed that most AgNPs was spherical, triangular and oval, with average size of 18.5, 28.02, 50.22, 16.26 and 10.12 nm for white, green, red, blue and sunlight, respectively. XRD confirmed the all the obtained AgNPs showed face centered cubic (fcc) crystal lattice. FT-IR analysis of all synthesized AgNPs indicated the involvement of phenol, amine, hydroxyl and amino groups in the reduction of nano-Ag. All tested AgNPs inhibited the growth of Brevibacterium linens (KACC-14346), Propionibacterium acnes (KACC 11946), Staphylococcus aureus (KACC-10768) and Staphylococcus epidermidis. As a general trend, larvicidal assays conducted on dengue and Zika virus vector Aedes aegypti showed that, after 48 h of exposure, the toxicity achieved by sunlight-fabricated AgNPs was slightly higher if compared to AgNPs fabricated using various LED lights. Overall, our research highlighted the importance of abiotic parameters, with special reference to light condition, during green nanosynthesis of antimicrobials and larvicides.