Biosynthesis of NiO nanoparticles using Spirogyra sp. cell-free extract and their potential biological applications

Abstract

Biosynthesis is progressing owing to economical synthesis and the availability of organisms (good source of metabolites) which significantly complex and cap the metallic ions to produce stable nanomaterials. In this study, nickel oxide nanoparticles (NiO NPs) were prepared using cell free extract of Spirogyra sp., a filamentous green macroalgae containing polyols, ammines, and carbonyl compounds. The biomolecules in the extract efficiently convert Ni(NO₃)₂ to NiO as indicated by a change in color from greenish to reddish violet. The formation of NiO NPs was confirmed by the signature peak observed at 350 nm in the UV spectrum and diffraction peaks at 2θ = 37.3, 43.3, 62.9 and 75.6° in the XRD spectra. The crystallite size of the as-synthesized NiO NPs was calculated to be 27.7 nm. The physical characterization techniques like FESEM, HRTEM etc. confirmed the formation of polycrystalline quasi-spherical NPs. The synthesized material was further investigated for its potency for biological applications. Its antibacterial action (IC₅₀:10 mg L⁻¹) against Gram-positive (Bacillus subtilis) and Gram-negative (Escherichia coli) bacterial strains showed concentration dependent activity with MIC (minimum inhibitory concentration) of 10 mg L⁻¹. In addition, the NPs showed a stimulatory effect at lower concentration (5 mg L⁻¹) with a nearly 15% increase in the root length and shoot length, while they exhibited an inhibitory effect at higher concentration (>5 mg L⁻¹) on seed germination and seedling growth of Mung Beans (Vigna radiata (L.) R. Wilczek). In addition, the NiO NPs showed appreciable antioxidant potential, evaluated through assays like DPPH and TAC. Furthermore, it is concluded that the as-synthesized NiO NPs via a green approach showed reliable in vitro biochemical properties, which signifies their potential for use in the biomedical and agricultural fields with future appraisal.