Synthesis of biogenic silver nanoparticles from the extract of Heliotropium eichwaldi L. and their effect as antioxidant, antidiabetic, and anti‐cholinesterase.

Recently, green nanotechnology has received much importance in different fields. It is concerned with the production of small‐size nanoparticles (NPs). It is less toxic to human health and also environmentally benign. Heliotropium eichwaldi (HE) is an herbaceous weed and is widely distributed in Pakistan. The herb is used traditionally for earache, headache, cleaning, and healing ulcers. The aim of this study is to develop an easy and justifiable method for the synthesis of HE‐AgNPs using HE extract and then to investigate the effects of HE‐AgNPs as a free radical scavenger, an inhibitor of the two enzymes, that is, alpha‐amylase (α‐amylase) and acetylcholinesterase (AChE). UV–Vis spectrum at 416 nm confirmed the AgNPs formation, the scanning electron microscopy (SEM) confirmed the irregular‐shaped HE‐AgNPs, the average size of 19.79 nm was calculated using four major peaks (38.41°, 44.48°, 64.56°, and 77.47°) of X‐ray diffraction (XRD) analysis, Fourier transform infrared (FTIR) confirmed the peaks for the functional groups, and electron diffraction X‐ray spectroscopy (EDX) confirmed that silver was the main element (30.68%). The HE‐AgNPs showed an excellent %scavenging of ferric chloride (73 ± 0.098), ammonium molybdenum (72 ± 0.0021), 2,2‐diphenyl‐1‐picrylhydrazyl (DPPH) (64 ± 0.055), H2O2 (63.6 ± 0.001), and 2,2′‐azino‐bis‐(3‐ethylbenzothiazoline‐6‐sulfonic acid) (ABTS) (67.36 ± 0.0014). Hydroxyl radical (67 ± 0.005) showed low IC50 values of 99.93 ± 0.017, 84.58 ± 0.017, 90.14 ± 0.059, 116.02 ± 0.034, 113.02 ± 0.035, and 134.4 ± 0.042 μg as compared with HE extract. Similarly, a maximum inhibition of 67 ± 0.21% (HE extract), 71.4 ± 0.0021% (HE‐AgNPs), and 85 ± 0.11% (glucophage) was reported against α‐amylase with IC50 values of 68 ± 0.27 μg ml−1 for HE extract, 34.43 ± 0.21 μg ml−1 for HE‐AgNPs, and 27.43 ± 0.13 μg ml−1 for glucophage. Statistical analysis showed that HE inhibits α‐amylase in a competitive mode, and HE‐AgNPs in a mixed mode. Similarly, in the case of AChE, the HE plant and HE‐AgNPs exhibited 57 ± 0.21% and 64 ± 0.0021% inhibition with IC50 values of 20 ± 0.014 and 16.81 ± 0.011 μg, respectively. Statistical analysis indicated that the HE plant and HE‐AgNPs caused a non‐competitive type of AChE. Our work suggests the successful generation of HE‐AgNPs, subsequently as significant antioxidant, antidiabetic, and anti‐Alzheimer agent. [ABSTRACT FROM AUTHOR]