Evaluating antibacterial, antioxidant and apoptosis-mediated anticancer activities of green-synthesised silver nanoparticles using unicellular cyanobacterium Synechocystis pevaleikii

The escalating threat of multidrug-resistant pathogens and aggressive malignancies demands sustainable alternatives to conventional therapeutics. Aligning with the One-Health approach, this study establishes an eco-friendly green nanotechnology platform utilising the unexploited marine unicellular cyanobacterium Synechocystis pevaleikii to biosynthesise stable, multifunctional silver nanoparticles ( Sp -AgNPs). The synthesis using a 100 mg/10 mL aqueous biomass extract and 1 mM silver nitrate (AgNO 3 ) at 40 °C was visually confirmed by a green-to-brown colour transition. Comprehensive physical mapping revealed a sharp UV-visible surface plasmon resonance peak at 441 nm. FTIR spectroscopy identified a robust bio-organic capping matrix composed of proteins, carbohydrates, and polyphenols. Crystallographic analysis (P-XRD and SAED) confirmed a highly pure, face-centered cubic lattice with an average core crystallite size of 24.6 nm. FESEM and TEM imaging demonstrated spherical, polydisperse morphologies with a core size distribution of 11–56 nm and a mean particle diameter of 51 ± 1.2 nm. EDX validated elemental purity with 84.80 wt% silver. DLS measurements had a mean hydrodynamic diameter of 103.6 nm, while a highly negative zeta potential of − 21.43 mV excellent colloidal stability. In biological evaluations, Sp -AgNPs demonstrated broad-spectrum antibacterial efficacy, producing zones of inhibition of 16 mm against Escherichia coli and 14 mm against Arthrobacter globiformis , with highly potent MIC values of 6.25 µg/mL and 12.5 µg/mL, respectively. Quantitative microtiter assays confirmed substantial dose-dependent antibiofilm activity, achieving up to 93% ( A. globiformis ) and 77% ( E. coli ) eradication at peak concentrations. Furthermore, the nanostructures exhibited exceptional free-radical scavenging capacity with an IC 50 value of 9.2 µg/mL. Most crucially, Sp -AgNPs displayed powerful selective cytotoxicity against the breast cancer MCF-7 cell line, yielding an IC 50 value of 12.09 µg/mL in MTT assays. Confocal microscopy (Calcein-AM/PI and Annexin V-PI) confirmed that this cytotoxicity is driven by robust intracellular reactive oxygen species overproduction, triggering targeted cellular death.