Biomedical and insecticidal efficacy of green synthesized nanoparticles from underexplored Tanzanian medicinal plants: A comparative study using Pueraria montana, Vernonia amygdalina, and Tephrosia vogelii

Abstract

This study explores the biomedical and insecticidal potential of green-synthesized nanoparticles (NPs) from Pueraria montana roots, Vernonia amygdalina, and Tephrosia vogelii leaves. Antibacterial activity of ZnO, CuO, AgNPs, and NiO–CuO nanocomposites was tested against S. aureus, S. pyogenes, and E. coli. The nanoparticles (ROS) generation, disruption of the cell membrane, release of metal ions, and synergistic effects of phytochemical capping agents. The AgNPs showed the strongest activity against gram-positive strains, while ZnO was more effective against E. coli. CuO and AgNPs outperformed ZnO due to smaller size and higher reactivity. At 50 µg/disc, most of these NPs achieved over 70 % of standard antibiotic efficacy. Insecticidal testing against Periplaneta americana showed that T. vogelii derived ZnO NPs caused 33.3 % mortality in 20 min at 50 ppm and over 99 % at 100–200 ppm in 2–6 h. Based on MIC assays conducted using standard broth microdilution methods, AgNPs exhibited the lowest inhibitory concentrations (12.5 ± 0.5 µg/ml) against S. aureus and S. pyogenes, demonstrating stronger antibacterial potency than CuO, ZnO, and NiO–CuO nanoparticles. In contrast, ZnO nanocomposites showed the greatest efficacy against E. coli (MIC value of 14.2 ± 1.4 µg/ml), highlighting differential activity of the green-synthesized nanoparticles depending on bacterial type. These quantitative results provide robust experimental support for the comparative efficacy, linking nanoparticle physicochemical properties, ion release, ROS generation, and phytochemical capping to observed antibacterial performance and thus indicating AgNPs’ superior activity against Gram-positive bacteria. Statistical analysis confirmed significant effects of these plant-based nanoparticles’ type, dose, and exposure. Characterization with UV–Vis, FTIR, SEM, and XRD confirmed desirable physicochemical properties and strong bioactivity. The two-way ANOVA for corrected mortality in (%) showed that both time and treatment type had statistically significant effect (p < 0.05) on insecticidal efficacy (Corrected Mortality). Insecticidal activity was found not only depended on what is applied and nature of treatment such as NPs type, but also how long it has been applied and the dosage or concentration used. Therefore, both formulation type and exposure duration were critical for insect control strategies. The Tukey’s Honestly Significant Difference (HSD) as a post hoc (analysis after ANOVA test) showed that Tephrosia vogelii was significantly more effective than both Puéraria montana (p = 0.001) and Vernonia amygdalina (p = 0.001) in causing insect mortality. Additionally, there was no significant difference between Puéraria montana and Vernonia amygdalina (p = 0.368), suggesting comparable efficacy between them since ANOVA fails to tell where the difference lies. Thus, Tephrosia vogelii appears to be the most promising candidate for insecticidal applications among the three plant extracts tested based on large mean differences and lower p values attested. Synthesized ZnO nanoparticles from Tephrosia vogelii extract exhibited the highest insecticidal activity against Periplaneta americana, surpassing those from Puéraria montana and Vernonia amygdalina. This insecticidal superiority of ZnO NPs from Tephrosia vogelii is probably due to its rich phytochemical profile including rotenone, tephrosine, and degeline enhancing nanoparticle synthesis, surface reactivity, and stability. The fumigant application of nanoparticles was more effective than contact exposure, in inducing faster and higher mortality (notably at 10 % dose within 1–3 h).