"Ghost" Silica Nanoparticles of "Host"-Inherited Antibacterial Action

ACS Appl Mater Interfaces. 2019 Oct 23;11(42):38519-38530. doi: 10.1021/acsami.9b14403. Epub 2019 Oct 14.

Abstract

We fabricated surface-rough mesoporous silica nanoparticles ("ghost" SiO2NPs) by using composite mesoporous copper oxide nanoparticles ("host" CuONPs) as templates, which allowed us to mimic their surface morphology. The "host" CuONPs used here as templates, however, had a very high antibacterial effect, with or without functionalization. To evaluate the surface roughness effect on the "ghost" SiO2NPs antibacterial action, we functionalized them with (3-glycidyloxypropyl)trimethoxysilane (GLYMO) to permit additional covalent coupling of 4-hydroxyphenylboronic acid (4-HPBA). The diol groups on the bacterial membrane can form reversible covalent bonds with boronic acid (BA) groups on the "ghost" SiO2NPs surface and bind to the bacteria, resulting in a very strong amplification of their antibacterial activity, which does not depend on electrostatic adhesion. The BA-functionalized "ghost" SiO2NPs showed a very significant antibacterial effect as compared to smooth SiO2NPs of the same surface coating and particle size. We attribute this to the "ghost" SiO2NPs mesoporous surface morphology, which mimics to a certain extent those of the original mesoporous CuONPs used as templates for their preparation. We envisage that the "ghost" SiO2NPs effectively acquire some of the antibacterial properties from the "host" CuONPs, with the same functionality, despite being completely free of copper. The antibacterial effect of the functionalized "ghost" SiO2NPs/GLYMO/4-HPBA on Rhodococcus rhodochrous (R. rhodochrous) and Escherichia coli (E. coli) is much higher than that of the nonfunctionalized "ghost" SiO2NPs or the "ghost" SiO2NPs/GLYMO. The results indicate that the combination of rough surface morphology and strong adhesion of the particle surface to the bacteria can make even benign material such as silica act as a strong antimicrobial agent. Additionally, our BA-functionalized nanoparticles ("ghost" SiO2NPs/GLYMO/4-HPBA) showed no detectable cytotoxic impact against human keratinocytes at particle concentrations, which are effective against bacteria.

Keywords: antibacterial nanoparticles; bacteria; boronic acid; copper oxide nanoparticles; mesoporous particles; silica nanoparticles; surface roughness; templating.

MeSH terms

  • Boronic Acids / chemistry
  • Cell Line
  • Cell Survival / drug effects
  • Copper / chemistry
  • Escherichia coli / drug effects
  • Humans
  • Nanoparticles / chemistry*
  • Nanoparticles / toxicity
  • Rhodococcus / drug effects
  • Silanes / chemistry
  • Silicon Dioxide / chemistry*
  • Surface Properties
  • Ultraviolet Rays

Substances

  • Boronic Acids
  • Silanes
  • Silicon Dioxide
  • Copper
  • cuprous oxide

Supplementary concepts

  • Rhodococcus rhodochrous