Antimicrobial activity of silver sulfide quantum dots functionalized with highly conjugated Schiff bases in a one-step synthesis

In the present paper, low-dimensional Ag2S QDs were fabricated for the first time, with four different dithiocarbazate derivative Schiff bases (SB) as capping agents in a one-pot synthesis. These SB-capped Ag2S QDs were almost spherical with an average size range of 4.0 to 5.6 nm, which is slightly smaller than conventional thioglycolic acid (TGA)-capped Ag2S QDs. We demonstrate that the growth of Gram-positive bacteria (Bacillus subtillus and Staphylococcus aureus), Gram-negative bacteria (Escherichia coli and Pseudomonas aeruginosa), and a prevalent fungal pathogen (Candida albicans) are inhibited more when the bacterial and fungal cells were nurtured with the synthesized SB-Ag2S QDs, compared with TGA-Ag2S QDs or free unbound Schiff bases. The minimum inhibitory concentration (MIC) results confirmed that even low concentrations of SB-Ag2S QDs were able to inhibit bacterial (MIC 5-75 mu g mL(-1)) and fungal growth (MIC 80-310 mu g mL(-1)), and in some cases they performed better than streptomycin (8-25 mu g mL(-1)). Lethality bioassay results confirmed that SB-Ag2S QDs were not toxic to brine shrimp (Artemia salina). The results show that capping agents are essential in the design of functional Ag2S QDs, and highlight that Schiff bases provide an excellent opportunity to optimize the biological activities of silver based QDs.

Automated summary

In this study, low-dimensional Ag2S quantum dots capped with four different dithiocarbazate derivative Schiff bases were synthesized for the first time. It was found that these quantum dots exhibited better inhibitory effects on the growth of bacteria and fungi. The minimum inhibitory concentration results confirmed that even at low concentrations, the synthesized Ag2S quantum dots with Schiff base capping agents were able to inhibit the growth of bacteria and fungi, and in some cases, they performed better than streptomycin. Additionally, it was found that these quantum dots were not toxic to brine shrimp.