Callistemon citrinus: A plant-mediated synthesis of sustainable Rhodium nanoparticles and their antimicrobial activity

This work investigates the potential of using Callistemon citrinu flower extract, commonly known as bottlebrush, in the environmentally friendly synthesis of Rhodium nanoparticles (Rh NPs). Callistemon citrinu flower extract contains a high concentration of flavonoids and other phytochemicals. Hence, the extract was used to provide the essential components for an environmentally, sustainable synthesis method of Rh NPs. Different characterization analyses were used to evaluate the different properties of the synthesized particles. UV spectroscopy analysis demonstrated a continuous UV absorption spectrum attributed to the formation of Rh NPs. The XRD data and SAED analysis showed an amorphous nature of the synthesized Rh NPs. The HRTEM imaging provided morphological information about the Rh NPs tested sample, where the efficiency of Callistemon citrinu flower extract as a capping agent was reported. Furthermore, Raman spectra displayed the characteristic vibrational bands of the synthesized Rh NPs. The antimicrobial activity of the synthesized samples was tested against several dental pathogens, that play a role in dental caries, Staphylococcus aureus (SA), Bacillus subtilis (BS), Candida albicans (CA), Escherichia coli (Eco), and Staphylococcus epidermidis (S. Epi). In comparison with the control, Chlorhexidine (CHX), Rh NPs showed a greater impact on C. albicans (20 ≤ Zone of inhibition (ZOI) (mm) ≤ 26). The statistical analysis demonstrated that Rh NPs had a greater mean ZOI than the Callistemon citrinu flower extract. These results reveal the considerable potential and biological capacity Rh NPs have as an antifungal agent for dental applications.