Bacterial responses to Ephedra aphylla stem extract and green-synthesized Ag-TiO2 and Ag-SeO2 core/shell nanocomposites: unveiling antimicrobial and antioxidant properties†

Abstract

This study reports an efficient and green protocol for the green synthesis of Ag-TiO₂ and Ag-SeO₂ nanocomposites using the extracted stems of Ephedra aphylla. Results of spectroscopic and analytical analyses confirmed the successful synthesis, stability, and crystalline nature of the nanomaterials. The phytochemical profile and antioxidant and antimicrobial activities of the E. aphylla extract and the nanocomposites were also studied. E. aphylla extract and both the nanomaterials exhibited significant levels of active phytochemical compounds. These compounds contributed to their potent antioxidant activity, with E. aphylla extract and Ag-TiO₂ NC demonstrating the highest antioxidant activity. Besides, Ag-SeO₂ NC displayed remarkable antibacterial properties against different pathogenic bacteria with 31.0 ± 1.27 mm against K. pneumonia, 31.0 ± 1.72 mm against S. aureus, and 44.0 ± 1.09 mm against B. subtilis, and antifungal properties against Candida glabrata and Aspergillus niger. The enhanced antimicrobial activity of Ag-SeO₂ NC can be attributed to the synergistic effects of silver and selenium nanoparticles, which can disrupt cell membranes, induce oxidative stress, and interfere with essential cellular processes. The minimum inhibitory concentration values of Ag-SeO₂ NC against S. aureus and K. pneumoniae were found to be 0.2956 mg mL⁻¹ and 4.73 mg mL⁻¹, respectively. The mechanism of action of Ag-SeO₂ NC against both fungal strains was investigated using FTIR and HR-TEM analyses.