Characterization and assessment of antioxidant and antimicrobial efficacy of environment-friendly rGO nanosheets

The growing interest in the production of nanoparticles using environmentally friendly procedures supports the recent developments in materials science and nanomedicine. The current paper discusses reduced graphene oxide nanosheet (rGO) synthesized through a sustainable green method by using Costus igneus leaf extract, which has a high nutrient content and potential medical application. The formation of rGO was successful, as indicated by Fourier-transform infrared spectra showing the reduction of oxygen-containing functional groups when compared to graphene oxide peaks and morphological analysis depicting ultra-thin fragmented sheets capped with phytoconstituents. The BHT and CIrGO EC₅₀ values were 47.68 µg/ml and 78.91 µg/ml, respectively, suggesting that the antioxidant activity of both compounds is high. The EC₅₀ of the aqueous and methanolic leaf extracts was significantly lower (p ≤ 0.0001), indicating less activity. In antimicrobial assays, rGO was a potent inhibitor of Staphylococcus aureus with the largest ZOIs recorded compared to other microbes, i.e., 15.7 ± 0.10 mm for methanolic leaf extract, 15.93 ± 0.10 mm for aqueous leaf extract, and 16.1 ± 0.2 mm for CIrGO, as well as with the lowest value of MIC (0.735 mg/ml). Escherichia coli and Enterococcus faecium were less susceptible, maybe due to their different cell wall structure. The rGO also demonstrated moderate antifungal effects against Candida albicans with ZOIs of 6.1-6.5 mm and at a relatively high MIC (25 mg/ml), showing that there is an opportunity in this direction to be optimized as well. In brief, there are possibilities that this rGO synthesis coupled with Costus igneus combination can be a cheap and sustainable technique, and the possible antimicrobial and antioxidant activity can be positive, which is also consistent with the historic remedial use of the plant.