Shape- and nitric oxide flux-dependent bactericidal activity of nitric oxide-releasing silica nanorods

Silica nanorods (SNRs) are synthesized and then functionalized with aminoalkoxysilanes to prepare a new class of nitric oxide (NO)-releasing materials. The aspect ratio and size of the SNRs are tuned by varying the temperature, pH, and silane concentration used during the surfactant-templated synthesis. N-Diazeniumdiolate nitric oxide (NO) donors are formed on the secondary amine-functionalized SNRs by reaction with NO gas under basic conditions. Particle surface modifications are employed to manipulate the NO release kinetics. The diverse morphology (i.e., aspect ratio ∼1-8), NO-release kinetics (2000-14,000 ppb NO/mg particle) and similar sizes (i.e., particle volume ∼0.02 μm³) of the resulting NO-releasing SNRs facilitates further studies of how particle shape and NO flux impacts bactericidal activity against Gram-positive Staphylococcus aureus (S. aureus) and Gram-negative Pseudomonas aeruginosa (P. aeruginosa) bacteria. The bactericidal efficacies of these materials improves with increasing particle aspect ratio and initial NO flux. Both chemical (i.e., NO-release kinetics) and physical (i.e., morphology) properties greatly influenced the bactericidal activity of these materials.