Harnessing phytochemicals for nanotechnology: Antimicrobial silver nanoparticles from extracts of Curcuma caesia and Capparis multiflora

The urgent need for sustainable antimicrobial solutions draws tremendous research efforts for the environmentally benign synthesis of nanoparticles. In the present study, silver nanoparticles (Ag- CC and Ag- CM) were synthesised using a cost-effective and environmentally sustainable approach, employing extracts of the rhizomes of Curcuma caesia and the leaves of Capparis multiflora . These plant extracts served as reducing, capping, and stabilising agents, facilitating the formation and stabilisation of the nanoparticles without requiring additional chemical reagents. The synthesis conditions were systematically optimized by varying key parameters, including AgNO 3 concentration (5, 10, 20, 30, 40, and 50 mM), AgNO 3 to extract ratios (1:0.5 – 1:2), reaction temperature (25 °C, 45 °C, 65 °C and 85 °C), and reaction time (2–12 h), to precisely control the size and morphology. Comprehensive characterisation via UV–vis spectroscopy, X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, transmission electron microscopy (TEM), combined with energy-dispersive X-ray spectroscopy (EDS), and selected area electron diffraction (SAED) confirmed successful synthesis. TEM analysis revealed that silver nanoparticles synthesised using Curcuma caesia extract under optimised conditions of 20 mM AgNO 3 , a 1:1.5 volume ratio of AgNO 3 to extract, a reaction temperature of 85 °C, and a 4-hour reaction time, were predominantly spherical with sizes ranging from 3.5 to 12.9 nm. Conversely, nanoparticles produced with Capparis multiflora extract under conditions of 20 mM AgNO 3 , a 1:2 AgNO 3 to extract volume ratio, a 10-hour reaction at 85 °C, mainly adopted spherical shapes with some elongated structures, and sizes ranging from 7.8 to 27.5 nm. Zeta potential measurements indicated that the nanoparticles remained stable for up to one month. Both Ag-CC and Ag-CM exhibited significant antibacterial activity against Klebsiella pneumoniae , Bacillus subtilis , Proteus vulgaris , Staphylococcus aureus and Escherichia coli . The lowest MIC (0.078 mg/mL) and MBC (0.158 mg/mL) values were observed against E. coli . The findings suggest that the synthesized AgNPs possess strong and stable bactericidal activity against a broad spectrum of bacterial strains, including drug-resistant pathogens such as K. pneumoniae and S. aureus , underscoring their potential for application in next-generation antibacterial therapeutics and biomedical fields.