A waste to wealth strategy for developing antioxidant and antibacterial gold nanoparticles

Agro-waste-derived nanomaterials have gained attention due to their sustainability and multifunctionality. In this study, coffee leaf infusion (CLI), an agro-industrial waste extract, was used for the green synthesis of gold nanoparticles (CLI-AuNPs). The process yielded stable spherical nanoparticles with an average size of 9.1 ± 2.0 nm and a zeta potential of − 37.1 ± 4.0 mV. FTIR analysis confirmed the role of CLI phytochemicals in Au³⁺ reduction and nanoparticle stabilization. The CLI-AuNPs showed enhanced antioxidant activity (DPPH IC₅₀ = 483.15 µg/mL) compared to CLI (IC₅₀ = 686.25 µg/mL), along with intracellular ROS modulation indicating context-dependent antioxidant/pro-oxidant behavior. The CLI-AuNPs exhibited strong antibacterial activity against E. coli and S. aureus , with a maximum inhibition zone of 18.4 ± 1.0 mm at 16 µg/mL. MIC and MBC values ranged from 10 to 15 µg/mL. SEM and EDS analyses confirmed bacterial membrane disruption and structural damage. Overall, CLI-AuNPs represent a simple waste-to-wealth platform for stable, biofunctional gold nanoparticles with promising antioxidant and antibacterial applications.