Biosynthesis of selenium nanoparticles from backhousia citriodora and exploring their antibacterial and larvicidal activities

Abstract

Antimicrobial resistance (AMR) and mosquito-borne diseases continue to pose serious global health challenges, including Malaysia. The rampant use of synthetic antibiotics and insecticides contributes to ecological harm and the emergence of resistant pathogens and vectors. This study explored the green synthesis of selenium nanoparticles (SeNPs) using aqueous leaf extract of Backhousia citriodora (BCAE), and evaluated their antibacterial and larvicidal properties. Phytochemical compounds in BCAE were identified through qualitative screening. The synthesised SeNPs from B. citriodora (BC-SeNPs) were characterised using advanced analytical techniques to determine their structure, morphology and composition. The antibacterial efficacy of BC-SeNPs was evaluated using agar well diffusion and broth microdilution methods. The larvicidal activity against Aedes aegypti was conducted following the WHOstandard bioassay protocol, including morphological and morphometric analysis. Phytochemical analyses of BCAE revealed the presence of phenols and phenolics, flavonoids, alkaloids, tannins, carbohydrates, and steroids. The BC-SeNPs synthesised using 25 mM of Na2SeO3, 0.2 M ascorbic acid, 37 ˚C, pH 7.5, and 48 hours of reaction time exhibited a significant UV-Vis absorption peak at 234 nm. EDX analysis detected 40.9% selenium element in BC-SeNPs, while FESEM and TEM demonstrated welldispersed spherical nanoparticles sized between 30 -145 nm. XRD analysis validated the particles as SeNPs with 18.5% crystalline structure. The zeta potential (–39.1 mV) indicated good nanoparticle stability, while FTIR analysis identified various functional groups from BCAE responsible for the biosynthesis and stabilization of BC-SeNPs. The BC-SeNPs remained stable for 30 days at room temperature (25 ˚C) without aggregation. Antibacterial testing indicated that BC-SeNPs had significantly (P<0.05) higher efficacy than BCAE against gram-positive Staphylococcus aureus and Staphylococcus epidermidis, producing the largest inhibition halos (15.11-22.67 mm) and lowest MICs (0.02-0.78 mg/mL) and MBCs (1.56-3.13 mg/mL). However, both BC-SeNPs and BCAE showed no inhibitory effects on gram-negative Escherichia coli and Klebsiella pneumoniae. The larvicidal results indicated that BC-SeNPs demonstrated significantly (P<0.05) greater toxicity against Ae. aegypti larvae than BCAE alone, with LC₅₀ values of 481.35 ppm (24 h) and 419.09 ppm (48 h), compared to 6068.17 ppm and 5864.49 ppm for BCAE, respectively. Larvae treated with BCSeNPs showed severe morphological deformities and morphometric changes. Overall, BC-SeNPs demonstrated promising antibacterial and larvicidal effects, highlighting their potential as a green and effective alternative tool in addressing AMR and vectorborne diseases.