Green synthesis, phytochemical characterization of black shea nut cake-derived silver nanoparticles and evaluation of biological activities

Sustainable nanotechnology has increased the promotion of agrowaste-based synthesis of different nanoparticles for multifarious applications. In this study, the extract of black shea nut cake (BLSNC) which is a phytochemical-rich waste from the processing of shea butter fruit was evaluated for the biosynthesis of silver nanoparticles (AgNPs) for the first time. Aqueous BLSNC extract was reacted with 1 mM silver nitrate at 30 °C under static conditions. The BLSNC-AgNPs were characterized by UV-Vis spectroscopy, Fourier transform infrared (FTIR) spectroscopy, transmission electron microscopy (TEM), selected area electron diffraction (SAED), and energy dispersive X-ray spectroscopy (EDX). The chemical fingerprints of the nanoparticles were also studied using gas chromatography-mass spectrometry (GC-MS). The BLSNC-AgNPs which absorbed maximally at 433 nm were crystalline and spherical-shaped having sizes of 8.4–26.5 nm. FTIR spectra revealed that compounds rich in O-H, C-O, and C = O functional groups were involved in the capping and stabilization of BLSNC-AgNPs. GC-MS identified 22 compounds in BLSNC-AgNPs which were dominated by oleic acid (10.50%), and 9-Octadecenal, (Z)- (8.15%). However, further analytical techniques such as LC-MS, HRMS, and NMR will be needed to establish the full mechanisms of phytochemical evolution during the biosynthesis of BLSNC-AgNPs. The nanoparticles showed strong antibacterial activities (65.37–88.03%) against Pseudomonas aeruginosa , Klebsiella oxytoca , Staphylococcus aureus , Proteus mirabilis , and Escherichia coli. Elevated absorbance values obtained at 260 and 280 nm showed the impacts of BLSNC-AgNPs to release DNA and proteins from the treated cells of E. coli and S. aureus . The nanoparticles completely inhibited the growth of Aspergillus species, while 69% inhibition was achieved against Candida albicans . The nanoparticles scavenged 2,2-diphenyl-1-picrylhydrazyl (DPPH), nitric oxide (NO), and hydrogen peroxide (H 2 O 2 ) to the tune of 71.46–90.97%, inhibited α-amylase by 80.92%, and completely prevented blood clot formation, thereby showing its multifunctional biomedical potentials. Thus, shea nut cake can serve as a viable renewable material for sustainable biofabrication of AgNPs with biological activities that may be explored for biomedical applications for the promotion of circular bioeconomy and contributions to the attainment of good health and wellbeing (SDG 3).