Nanometal surface energy transfer (NSET) from biologically active heterocyclic ligands to silver nanoparticles induces enhanced antimicrobial activity against gram-positive bacteria

Herein we report the formation of a nanometal surface energy transfer (NSET) pair between a donor biologically active heterocyclic luminescent ligand such as 3-(1,3-Dioxoisoindolin-2-yl)-N, N-dimethylpropan-1-ammonium perchlorate (S4PNL; lambda em-408 nm) and an acceptor silver nanoparticle (Ag NP; lambda abs-406 nm). When the S4PNL ligand interacts with Ag NPs, the quenching in their luminescence intensity at 408 nm is noticed, with a SternVolmer constant of 0.8 x 104 M-1. The present donor-acceptor pair displays a binding constant of 2.8 x 104 M-1 and binding sites of 1.12. The current work shows the energy transfer from a molecular dipole (S4PNL) to a nanometal surface (Ag NP) and thus follows the nanometal surface energy transfer (NSET) ruler with an energy transfer efficiency of 80.0%, 50% energy transfer efficiency distance (d0) of 4.9 nm, donor-acceptor distance of 3.4 nm. The alteration in the zeta potential value of S4PNL upon interaction with AgNP clearly demonstrates the strong electrostatic interaction between donor and acceptor. Importantly, the current NSET pair shows enhanced antimicrobial activity against gram-positive bacteria such as Bacillus cereus (B. cereus) in comparison to their parent components i.e. S4PNL ligand and Ag NP. The NSET pair shows maximum inhibition against B. cereus (9202.21 +/- 463.26 CFU/ml.) at 10% while minimum inhibition is observed at 0.01% of it (39,887.19 +/- 242.67 CFU/ml.).