Poly(styryl bisphosphonate) nanoparticles with a narrow size distribution: Synthesis, characterization and antibacterial applications

Bacterial resistance to antibiotics is a major challenge in health research. A recent approach to combat this resistance is by interfering with vital bacterial functional systems. Calcium ions play an important role in bacterial functions such as bacterial cell stability, regulation of virulence genes, and in the function of various intracellular proteins. Bisphosphonate compounds have a high affinity for calcium ions and the antibacterial activity of bisphosphonates in combination with antibiotics has been recently studied. However, the antibacterial behavior of the bisphosphonate group itself has hardly been investigated. New cross-linked poly(styryl bisphosphonate) nanoparticles (poly(StBP) NPs) with a narrow size distribution and high yield were engineered using a dispersion copolymerization of styryl bisphosphonate monomer with the cross-linking monomer triethylene glycol diacrylate and the primary amino monomer N-(3-aminopropyl) methacrylamide hydrochloride. The diameter and size distribution were controlled by changing various polymerization parameters. Fluorescent poly(StBP) NPs were prepared by covalent binding of the primary amino groups on the poly(StBP) NPs surface to the dye BODIPY-FL-NHS ester; these NPs demonstrated a strong affinity for calcium ions. Antibacterial properties of optimal poly(StBP) NPs were studied compared to control NPs, which contain a methoxy group instead the bisphosphonate functional group. Unlike the control NPs, the poly(StBP) NPs demonstrated a significant antibacterial activity for both Gram negative (Escherichia coli and Pseudomonas aeruginosa) and Gram-positive (Staphylococcus aureus and Bacillius subtilis) bacteria.