Biosynthesis of copper nanoparticles using senna didymobotrya root extract and their efficacy activity against escherichia coli and staphylococcus aureus

Abstract

The economic burden and high mortality associated with multi-drug resistance in Escherichia coli and Staphylococcus aureus is a major public health concern. This study investigated nanomaterials as antimicrobial agents. Copper (Cu) nanoparticles exhibit better antimicrobial efficacy than copper in bulk form. Cu nanoparticles can offer a solution to antibiotic resistance. Senna didymobotrya roots contain phytochemicals capable of synthesizing Cu nanoparticles. The aim of this study was to synthesize Cu nanoparticles using S. didymobotrya plant root extract and test their efficacy against E. coli and S. aureus. The specific objectives were to: perform extraction, qualitative and quantitative phytochemical screening; synthesis and characterization of Cu nanoparticles; and evaluation of the antimicrobial efficacy of Cu nanoparticles. All the experiments were performed at the Chemistry laboratory in Moi University, Kenya. Extraction was done by soxhlet method. Phytochemical screening was done. Total flavonoid content and total phenolic content was determined. GC-MS analysis was performed to identify compounds in S. didymobotrya root extracts. Cu-nanoparticles were synthesized by adding 10 mL of S. didymobotrya root extracts to 90 mL of 0.0125-0.05 M aqueous CuSO4.5H2O solution at varying temp of 40-80 ℃ and pH of 3-10. Box Behnken design was used to obtain optimal synthesis conditions as determined using Nanotrac particle analyzer. Characterization was done using UV-Vis, Particle size analyzer, X-ray diffraction, Zeta potentiometer, GC-MS and FT-IR. Antibacterial tests were conducted using Kirby-Bauer disk diffusion susceptibility test involving 30 μL solution of Cu nanoparticles. Amoxicillin clavulanate was positive control and dimethyl sulfoxide was negative control. Extraction yield of Senna root methanol extract was 9.94 %. Phytochemical screening showed positive for phenols, tannins, saponins, gladiac glycosides, anthraquinones, alkaloids, and flavonoids; and negative for steroids and terpenoids. Total Flavonoid Content was 48.3 ±1.5 mgQE/g dry weight while Total Phenolic Content was 34.5 ± 0.1 mg GAE/g dry weight. The major compounds identified by GC-MS in reference to NIST library were; Benzoic acid, Thymol, N-Benzyl-2-phenethylamine, Vanillin, Phenyl acetic acid, and Benzothiazole. UV-Vis spectrum showed characteristic peak at 571 nm indicating the formation of Cu-nanoparticles. The optimum synthesis conditions were temperature of 80 °C, pH 3.0 and Cu ion concentration of 0.0125 M. FT-IR spectrum showed absorptions in the range 3500-3100 cm-1 (N-H stretch), 3400-2400 cm-1 (O-H stretch), 988-830 cm-1 (C-H bend), peak at 1612 cm-1 (C=C stretch), and 1271 cm-1 (C-O bend). Cu- nanoparticles sizes ranged between 5.55 and 63.60 nm. The zeta potential value was -69.4 mV indicating that they were stable. The nanoparticles exhibited significant antimicrobial activity on E. coli and S. aureus with Zone of Inhibition 26 ± 0.58 mm and 30 ± 0.58 mm compared to amoxicillin clavulanate (standard) with 20 ± 0.58 mm and 28 ± 0.58 mm, respectively. In conclusion, Senna has high amounts of flavonoids and phenols; the biosynthesized Cu nanoparticles are stable and displayed better antimicrobial activity against E. coli and S. aureus compared to amoxicillin clavulanate (standard). The study recommends the testing of biosynthesized Cu nanoparticles against other potential multi-drug resistant microbes to enable their development into antimicrobial agents.