A comparative study on chemically and phytogenically synthesized TiO₂ nanoparticles and their role in modulating plant growth and metabolic dynamics

Abstract

The present research provides a comprehensive investigation of the synthesis, characterization, and agricultural applications of titanium dioxide nanoparticles (TiO₂-NPs) developed via a conventional and eco-friendly (green synthesis method) route, focusing on their interactions with plant growth-promoting microorganisms (PGPMs) in order to boost the physiological and antioxidant performance of Capsicum annuum cultivars. The TiO₂-NPs synthesized through the molten salt method exhibited a nano-cuboid structure, a negative surface charge, and a moderate surface area. While green-synthesized TiO₂-NPs obtained from blueberry natural extracts using isopropanol (TiO₂-I.P) and methanol (TiO₂-M) exhibited mesoporous polyhedral anatase structures (E₉ ≈ 3.0 eV), hydrodynamic sizes of 130–150 nm, and stable ζ-potentials ranging from −33 to −50 mV. The extracts rich in flavonoid and phenolic compounds provided distinctive surface functionalities, improving the stability and bioactivity of the nanoparticles (NPs). In-vitro compatibility studies indicated that TiO₂-NPs facilitated microbial proliferation up to 150 µg/mL without exhibiting toxicity, thereby enhancing Bacillus thuringiensis (B.t) (1.56–2.92×10⁸ CFU/mL) and Trichoderma harzianum (Th) (2.50–3.90 × 10⁸ spores/mL), greenhouse experiments revealed significant enhancements in plants shoot and root growth, as well as increases in fresh weight (F.W) and dry weight (D.W) biomass and chlorophyll content. When TiO₂-NPs were utilized either independently or in combination with PGPMs B.t, Th. The synergistic treatments significantly improved antioxidant and enzymatic responses. Including peroxidase (69.90 UA/g F.W), β-1,3-glucanase (2.45 nkat/g FW), total phenolic content (29.50 GA/g FW), and chlorophyll accumulation (210.8 ± 11.4 mg/mg FW). In the context of green formulations were observed, TiO₂-I.P increased number of leaves and height of plant, whereas the root elongation not greater than control. Specifically with individual microorganism B.t, Th combined with at moderate concentration of TiO₂-I.P improved F.W and D.W. Peroxidase levels significantly increased when 50 µg/mL of TiO₂-M combined with microorganisms B.t+Th, While TiO₂-I.P stimulated a wider range of antioxidant responses, at 150 µg/mL of both formulation increased the total proteins. In case of total chlorophyll content increased at 150 µg/mL of TiO₂-I.P alone or combination of microorganism B.t+Th. The results emphasize biphasic behavior that is dependent on both formulation and dose, influenced by the surface chemistry of NPs and their compatibility with beneficial PGPMs. This work advances a practical framework for precision and sustainable agriculture through the integration of nanotechnology and microbial biotechnology. Where the surface chemistry of NPs and their biological compatibility can be tailored to ensure reliable and useful outcomes in agricultural fields.