Enhancement of antibacterial activity of synthesized ligand-free CdS nanocrystals due to silver doping

Recently, different nanocrystals have been reported to be the alternative, optimistic, and novel antimicrobial agent against the many antibiotic-resistant bacteria. Here, ligand-free CdS and Ag-doped CdS (Ag/CdS) nanocrystals have been synthesized by chemical methods for the study of the antimicrobial activity on Escherichia coli and Staphylococcus aureus by Kirby-Bauer diffusion method to see the effect against Gram-positive and Gram-negative bacteria. These prepared nanocrystals have been characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM), and X-ray diffraction (XRD). TEM and SEM images confirm the spherical morphology of both the sample and the respective XRD patterns indicate polycrystalline nature having a cubic zinc blende structure. Antibacterial activities have been tested with CdS and Ag/CdS, considering concentrations ranging from 10 to 200 mu g/ml. After 24 h of incubation, the zone of inhibition (ZOI) is measured for each concentration, which shows that both the nanocrystals are ineffective against E. coli but much effective against S. aureus at this low concentration range. Furthermore, Ag/CdS nanocrystals have been found to show much more ZOI than CdS. Differences in the antibacterial activity can be due to the presence of different cell wall in E. coli and S. aureus.