Multifaceted properties of TiO2 nanoparticles synthesized using Mangifera indica and Azadirachta indica plant extracts: antimicrobial, antioxidant, and non-linear optical activity investigation for sustainable agricultural applications

Abstract

The increasing global food scarcity necessitates the development of nanomaterials with low toxicity for use as antimicrobial agents and sensors to mitigate agricultural losses. In this study, we present an investigation into the green synthesis of titanium dioxide nanoparticles (TiO₂ NPs) utilizing plant extracts derived from Azadirachta indica (A. indica) and Mangifera indica (M. indica) as reducing and stabilizing agents. The antimicrobial activity of the NPs is investigated against a range of pathogenic fungi (A. alternata, C. gloeosporioides, T. harzianum, and A. rolfsii) and a bacterial species (X. oryzae) known to significantly impact crop yield in agriculture. Remarkably, the TiO₂ NPs exhibit potent inhibitory action against all tested microorganisms, suppressing their growth over an extended period as revealed by the zone of inhibition (ZOI) estimated via disc diffusion assay. This can be attributed to the generation of reactive oxygen species (ROS), including hydroxyl radicals, in close proximity to the microbial cell wall. Furthermore, the free radical scavenging activity was confirmed by a dose-dependent response in the 2,2-diphenyl-1-picrylhydrazyl (DPPH) assay, demonstrating their substantial antioxidant activity. Moreover, we also explore the non-linear optical (NLO) properties of the TiO₂ NPs through Z-scan measurements employing femtosecond (fs) laser pulses. Notably, both types of NPs exhibit reverse saturable absorption (RSA) behaviour when excited by femtosecond laser pulses, enabling the determination of the nonlinear absorption coefficient and nonlinear refractive index through fitting open and closed aperture curves. The calculated values of the nonlinear susceptibility of NPs synthesized using M. indica and A. indica are 2.43 × 10⁻¹⁵ + i.7.2 × 10⁻¹⁸ and 3.91 × 10⁻¹⁵ + i.1.06 × 10⁻¹⁸, respectively. These values reflect the robust NLO response of NPs, indicating their potential for a wide range of applications. Combining their potent antimicrobial activity, antioxidant properties, and strong nonlinear optical characteristics, these NPs hold tremendous promise in addressing critical challenges in sustainable agriculture.