Antimicrobial surfaces containing cationic nanoparticles: how immobilized, clustered, and protruding cationic charge presentation affects killing activity and kinetics

Colloids Surf B Biointerfaces. 2015 Jan 1:125:255-63. doi: 10.1016/j.colsurfb.2014.10.043. Epub 2014 Oct 31.


This work examines how the antimicrobial (killing) activity of net-negative surfaces depends on the presentation of antimicrobial cationic functionality: distributed versus clustered, and flat clusters versus raised clusters. Specifically, the ability to kill Staphylococcus aureus by sparsely distributed 10 nm cationic nanoparticles, immobilized on a negative surface and backfilled with a PEG (polyethylene glycol) brush, was compared with that for a dense layer of the same immobilized nanoparticles. Additionally, sparsely distributed 10 nm poly-L-lysine (PLL) coils, adsorbed to a surface to produce flat cationic "patches" and backfilled with a PEG brush were compared to a saturated adsorbed layer of PLL. The latter resembled classical uniformly cationic antimicrobial surfaces. The protrusion of the cationic clusters substantially influenced killing but the surface concentration of the clusters had minor impact, as long as bacteria adhered. When surfaces were functionalized at the minimum nanoparticle and patch densities needed for bacterial adhesion, killing activity was substantial within 30 min and nearly complete within 2 h. Essentially identical killing was observed on more densely functionalized surfaces. Surfaces containing protruding (by about 8 nm) nanoparticles accomplished rapid killing (at 30 min) compared with surfaces containing similarly cationic but flat features (PLL patches). Importantly, the overall surface density of cationic functionality within the clusters was lower than reported thresholds for antimicrobial action. Also surprising, the nanoparticles were far more deadly when surface-immobilized compared with free in solution. These findings support a killing mechanism involving interfacial stress.

Keywords: Anti-fouling surfaces; Bacteriocidal activity; Charge clustering; Charge density threshold; Interfacial stress; Killing efficiency.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Adsorption
  • Anti-Bacterial Agents / chemistry*
  • Anti-Bacterial Agents / toxicity
  • Bacterial Adhesion
  • Biomechanical Phenomena
  • Cations
  • Colony Count, Microbial
  • Kinetics
  • Microbial Viability / drug effects
  • Nanoparticles / chemistry*
  • Nanoparticles / toxicity
  • Polyethylene Glycols / chemistry*
  • Polylysine / chemistry*
  • Staphylococcus aureus / drug effects*
  • Staphylococcus aureus / growth & development
  • Static Electricity
  • Stress, Mechanical
  • Structure-Activity Relationship
  • Surface Properties


  • Anti-Bacterial Agents
  • Cations
  • Polylysine
  • Polyethylene Glycols