Synthesis of bio-inspired silver nanoparticles using Geranium wallichianum D. Don ex Sweet. (Geraniaceae) leaf extract for antibacterial activity and colorimetric detection of Hg2+

Abstract The rise in antimicrobial resistance and heavy metal contamination poses major risks to human health and the environment. This study reports the green synthesis of silver nanoparticles (AgNPs) using a polar extract of Geranium wallichianum D. Don ex Sweet. to evaluate antibacterial activity and Hg ²⁺ -sensing. This is the first reported use of G. wallichianum as a dual reducing and stabilizing agent, enabling a rapid sunlight-assisted synthesis completed within 15 min. Characterization confirmed successful formation of AgNPs: UV–Vis spectroscopy monitored stability, FT-IR verified functional group interactions, PXRD confirmed the crystalline phase, SEM revealed an average particle size of 26 nm, and hydrodynamic size and zeta potential were 39 nm and − 28 mV, respectively. Antibacterial activity was assessed using 30 µg/mL AgNPs, 30 µg/mL erythromycin as a positive control, 30 µg/mL plant extract, and DI water as a negative control. All tests were conducted in triplicate and analyzed using one-way ANOVA ( p < 0.05). The biogenic AgNPs exhibited strong antibacterial activity against Staphylococcus epidermidis (20 mm ZOI), Klebsiella pneumoniae (18 mm ZOI), and Escherichia coli (19 mm ZOI). The MIC and MBC values ranged from 15 to 30 µg/mL, confirming the dose-dependent antibacterial potency. Additionally, AgNPs showed excellent colorimetric response toward Hg ²⁺ , with a linear detection range of 1–100 µM and a limit of detection (LOD) of 6.68 µM. The sensor demonstrated high selectivity and practical applicability in real-water samples. Overall, the unique sunlight-driven synthesis strategy, coupled with the strong antibacterial potential and exceptional Hg ^{2 +} selectivity, underscores the novelty and sustainability of G. wallichianum -mediated AgNPs as a versatile nanoplatform for biomedical and environmental applications.