Antibacterial activity of MPA-capped CdTe and Ag-doped CdTe nanocrystals: Showing different activity against gram-positive and gram-negative bacteria

Cadmium telluride (CdTe) and silver-doped CdTe (CdTe/Ag) nanocrystals have been used to study the antibacterial activity against gram-positive bacteria (Streptococcus pneumoniae and Staphylococcus aureus) and gram-negative bacteria (Klebsiella pneumoniae and Escherichia coli) by disc diffusion method. Here, CdTe and CdTe/Ag nanocrystals have been prepared by chemical method and characterized by transmission electron microscope (TEM) and X-ray diffraction (XRD). TEM images show that both the nanocrystals are spherical in shape with an average diameter of 6 nm and 5 nm respectively, whereas XRD pattern indicates that these nanocrystals are cubic in structure. Further, nuclear magnetic resonance study as well as FTIR spectral study confirm that prepared nanocrystals are well capped by 3-marcaptopropionic acid. For antibacterial test, different concentrations from 1 to 10 ??g ml???1 of CdTe and CdTe/Ag nanocrystals are placed in the agar broth against all the gram-positive and gram-negative bacterial strains. Here, Ampicillin and water have been used as a standard reference and a control respectively. It is found that both the nanocrystals are effective against all the bacterial strains and the zone of inhibition (ZOI) is measured after 24 h of incubation. But, CdTe/Ag nanocrystals show much more ZOI than CdTe nanocrystals. Among the gram-positive bacteria, these nanocrystals are more effective against S. pneumonia (ZOI-9 mm for 1 ??g ml???1), compared to S. aureus (ZOI-8 mm for 1 ??g ml???1). Whereas, among the gram-negative bacteria, activity is more against the E. Coli (ZOI-8 mm for 1 ??g ml???1) than that in K. pneumonia (ZOI-6.5 mm for 1 ??g ml???1).