Green Synthesis of Silver Nanoparticles from Caesalpinia crista Seed Coat Extract: Effect of Calcination on Physicochemical Properties and Biological Activities

Abstract

Caesalpinia crista seed coats are traditionally useful for treating several diseases, like anthelmintic, tumours, placenta removal, antimicrobial, liver disorders, febrifugal, pain, inflammation, etc. In this process, seed coats from Caesalpinia crista were used to synthesise bioconjugated silver nanoparticles (AgNPs) using the green and calcination methods. The effects of calcination (200°C for 30 min) on the AgNPs' structural properties were examined. UV-visible spectra confirmed the reduction of Ag⁺ to AgNPs, as the peak obtained is at 430 nm for uncalcined bioconjugated AgNPs, while the peak for calcined bioconjugated AgNPs is at 438nm. Scanning electron microscopy (SEM) and X-ray diffraction analysis (XRD) determined uncalcined and calcined bioconjugated AgNPs, found to be spherical crystalline and had sizes of 84.3 nm and 101.15 nm, respectively. Functional groups of bioactive compounds were identified in the uncalcinated and calcinated bioconjugated AgNPs by Fourier Transform Infrared Spectroscopy (FTIR) analysis. EDAX is used for determining the elemental composition of the AgNPs absorption peak in the range of 2.7 to 3.4 keV in both uncalcinated and calcinated bioconjugated AgNPs. The calcined/uncalcined AgNPs were evaluated using the agar-well diffusion method against pathogenic bacteria, including Pseudomonas aeruginosa (11 mm), Escherichia coli (6 mm), Salmonella typhi (3 mm), and Staphylococcus aureus (1 mm). According to in vitro antibacterial research, uncalcined AgNPs significantly reduced the development of tested pathogenic bacteria, but the AgNPs that had been calcined exhibited no growth inhibition activity. Calcination for 30 minutes at 200ºC decreases the bacterial inhibitory action of AgNPs. The calcination temperature affects the antibacterial characteristics of nanoparticles; an increase in temperature results in a decrease in their inhibitory activity. Probably due to calcinations that may have degraded all the phytochemicals adhered to the Ag nanoparticles. The MTT experiment demonstrated that AgNPs and Aq CCSC extract were anticancer agents against MCF-7 breast cancer cells. Aq CCSC extract showed the highest cell viability of 44.28 μg/mL, followed by calcined AgNPs at 40.57 μg/mL and uncalcined AgNPs at 26.67 μg/mL. Uncalcined AgNPs had the strongest anticancer activity.