Silver-doped graphite oxide composites used as antimicrobial agents against Staphylococcus aureus, Escherichia coli and Tatumella terrea evaluated by direct TLC bioautography

Abstract

Silver-doped graphite oxide composites presented mixed Ag and Ag2O crystalline phases accompanied by C/O and ID/IG average ratios of 2.13 and 1.16, associated with a good oxidation degree and high structural disorder or defects in the carbon material, respectively. The low-silver-doped GrO composite showed homogenous silver particle dispersion and a low particle size distribution (96 nm). However, high-silver-doped GrO composites generated materials with high relative crystallinity, silver particle agglomeration, and Ag metal phase promotion. At 3 and 5 mg ml-1 per chromatographic plate, the silver-doped graphite oxide composites were tested by direct TLC bioautography against Staphylococcus aureus, Escherichia coli, and Tatumella terrea microorganisms, where the minimum inhibitory concentration was 3 mg ml-1 per chromatographic plate. At 3.0 mg ml-1 per chromatographic plate, high-silver-doped GrO composite exhibited a 39%, 3.2-fold, and 83% higher retention factor (Rf) compared with the composite with low-silver-doped GrO composite against S. aureus, E. coli, and T. terra microorganisms, respectively. However, both composites showed similar inhibition capacities at 5.0 mg ml-1 per chromatographic plate against the three microorganisms. This behavior may be associated with both composites reaching the threshold limit. In general, the amount of silver acetate used in the silver-doped GrO composites influenced the dispersion, crystalline phase promotion, particle size distribution, and release capacity of the silver particles, which modified the type of electrostatic adsorption between the composites and the bacterial cell walls.