Bioinspired Synthesis of Copper Nanoparticles and its Efficacy on Seed Viability and Seedling Growth in Mungbean (Vigna radiata L.)

Background: Copper is an important micronutrient required for the growth of the plants. It activates enzymes and helps in protein synthesis in plants. Nanoparticles in the size range from 1 to 100 nm possess unique properties, such as the high surface area to volume ratio, size-dependent capabilities and unique optical properties, and hence, copper nanoparticles (CuNPs) were evaluated for growth promotion of mung bean (Vigna radiata L.). Objective: The main aim of the study was to synthesize CuNPs using neem extracts, and evaluate their activity on viability of seeds and growth of seedlings in V. radiata. Methods: Here, we synthesized CuNPs by the neem (Azadirachta indica) leaf extract, which was treated with copper sulphate and ascorbic acid. The reduction of copper sulphate to CuNPs was confirmed by the UV-Visible spectrophotometer and was further characterized by XRD, FTIR, NTA, and Zeta potential measurement. The efficacy of biogenic CuNPs (size <50 nm) was evaluated on germination and growth promotion of V. radiata seeds. The copper content was confirmed in CuNPs treated plants after analysis by Atomic Absorption Spectroscopy (AAS). Results: CuNPs were synthesized by the neem (A. indica) leaf extract as brown precipitation. Preliminary detection was performed by UV-Visible spectrophotometer, which showed a peak at 619 nm. Further characterization by X-ray diffraction confirmed the Face Centered Cubic crystal structure. Fourier Transform Infra Red spectroscopy analysis revealed the presence of amino acids as functional groups in the leaf extract. Nanoparticle tracking and analysis (NTA) demonstrated an average size of 41±21 nm with the concentration of 3.3×109 particles/ml. Zeta potential value was found to be -18.2 mV. The growth promotion effect showed the maximum germination recorded at 100 ppm of CuNPs; while copper ions showed an adverse effect on root growth. The AAS analysis demonstrated the increased copper content in the CuNPs treated seedlings than that of the control. Conclusion: It is a first report to demonstrate the positive effect of biogenic CuNPs on growth, nutrition and enhanced seed germination, and hence, CuNPs could be used as a nano-fertilizer after further extensive nursery trials.