Biosynthesis of zinc oxide nanoparticles using aqueous extract of Andrographis alata: Characterization, optimization and assessment of their antibacterial, antioxidant, antidiabetic and anti-Alzheimer's properties

•By using Andrographis alata aqueous extract zincoxide nanoparticles (ZnO NPs) were synthesized.•Biosynthesized A.alata ZnO NPs were characterized by UV–Vis, FT-IR, XRD, SEM, EDAX, HR-TEM and DLS.•Synthesized A.alata ZnO NPs antibacterial, antioxidant, antidiabetic and anti-Alzeimers potential were evaluated with their corresponding references streptomycin, ascorbic acid, acarbose and galantamine respectively.•Enzyme inhibition kinetic studies were performed for α-glucosidase and acetylcholine esterase.•This study will contribute to novel outlooks such as drugs, biomedicals and pharmaceuticals industries. Recently, great attention was paid on the synthesis of nano particles via green protocols, explicitly using plant materials. In view of this, currently, zinc oxide nano particles (ZnO NPs) were synthesized with the aid of an aqueous extract of whole plants of Andrographis alata. As a part of extensive characterisation, the UV–Vis spectrum manifested absorption maxim at 372 nm, characteristic for bio-reduced ZnO NPs. The XRD study demonstrated the hexagonal wurtzite structures for ZnO NPs which is consistent with the JCPDS card no: 01–089–1397. FTIR analysis has assured the role of phytoconstituents of A.alata in reduction and capping of ZnO NPs by disclosing absorptions for O ̶ H, N ̶ H, C=O, C=C, C ̶ O, C ̶ N stretching vibrations. Morphological studies via EDS, DLS, SEM and HR-TEM analysis illustrated crystalline flower shaped flakes like structures for ZnO NPs with size in the range of 35–53 nm. The photosynthesized ZnO NPs displayed strong anti-bacterial activities against various pathogenic bacterial strains. Moreover, bio-reduced ZnO NPs also had strong anti-oxidant, anti-Alzheimer and anti-diabetic potencies with IC50 values in micro gram ranges. All in all, the ZnO NPs synthesized using A.alata has substantial efficacy for further use in biomedical, pharmaceutical and food processing industries. [Display omitted]