Influence of Temperature, Light and Surfactants on the Longevity of Silver Nanoparticles Synthesised From Ipomoea carnea for the Control of Rhizoctonia solani

Abstract

This study explores the long-term effectiveness and stability of silver nanoparticles (AgNPs) synthesised using Ipomoea carnea extract against Rhizoctonia solani. AgNPs were stored under four conditions: room temperature (25°C) with light exposure, room temperature in darkness, 4°C in light and at 4°C in darkness; their antifungal activity was assessed over 360 days. AgNPs stored at 4°C in the dark showed sustained antifungal activity, while light exposure accelerated their degradation, reducing effectiveness by 120 days. UV–vis spectroscopy, particle size analysis and zeta potential confirmed increased nanoparticle oxidation due to light exposure. Under a higher concentration of NaCl (3 M), polyvinylpyrrolidone (PVP) and polyethylene glycol (PEG) were evaluated as stabilising agents. PVP exhibited the best protection against aggregation of AgNPs, followed by PEG. PVP offered superior protection against aggregation and maintained stability for up to 270 days, particularly at 4°C in darkness. Zeta potential analysis showed a moderate decline in nanoparticle stability over time, with PVP-stabilised AgNPs retaining a range of −28.7 to −22.1 mV. Antifungal assays demonstrated over 91.4% efficacy of PVP-stabilised AgNPs for 270 days, highlighting their potential as long-term antifungal agents. This study emphasises the importance of storage conditions and stabilisers in maintaining the efficacy of biosynthesised AgNPs.