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

Abstract

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; λ_em-408 nm) and an acceptor silver nanoparticle (Ag NP; λ_abs-406 nm). When the S₄PNL ligand interacts with Ag NPs, the quenching in their luminescence intensity at 408 nm is noticed, with a Stern-Volmer constant of 0.8 × 10⁴ M^-1. The present donor-acceptor pair displays a binding constant of 2.8 × 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.).

Keywords: Antimicrobial activity; Gram-positive bacteria; Heterocyclic ligand; Nanometal surface energy transfer; Silver nanoparticles.