Correlation of antibacterial and time resolved photoluminescence studies using bio-reduced silver nanoparticles conjugated with fluorescent quantum dots as a biomarker

This report lays the foundation stone for the real time detector to control and monitor antibiotic resistant bacteria's. To start with, firstly, the green synthesis of silver nanoparticles were done by the bio-reduction of silver nitrate using different concentrations of medicinal plant extract taken from the leaves of Azadirachta indica (neem). The well-known standard surface plasmon resonance (SPR) wavelength of 430 nm and the characteristic brown color of the solution confirms the formation of eco-friendly silver nanoparticles. The silver nanoparticle size in the range of 10–20 nm was observed from TEM measurements for the sample showing best SPR which was further selected for conjugation with QDs. Secondly glutathione capped ZnS:Mn QDs were synthesized and conjugated with silver nanoparticles (0.09–0.1 mg/mL) and then their zone of inhibition studies were done using antibiotic resistant gram positive as well as gram negative bacteria's i.e. Staphylococcus aureus and Escherichia coli respectively. Lastly, time resolved photoluminescence studies of the conjugated system were done to correlate zone of inhibition (antibiotic sensitivity) with silver nanoparticle concentration in both the cases of a gram positive bacteria and gram negative bacteria. Luminescence intensity of glutathione capped QDs conjugated silver nanoparticles decreases with increasing concentration of silver nanoparticles in tune with the increasing zone of inhibition (antibiotic sensitivity). This is very important for making a fluorescence based detector to monitor antibiotic resistant bacteria's.