Modular approach for bimodal antibacterial surfaces combining photo-switchable activity and sustained biocidal release

Abstract

Photo-responsive antibacterial surfaces combining both on-demand photo-switchable activity and sustained biocidal release were prepared using sequential chemical grafting of nano-objects with different geometries and functions. The multi-layered coating developed incorporates a monolayer of near-infrared active silica-coated gold nanostars (GNS) decorated by silver nanoparticles (AgNP). This modular approach also enables us to unravel static and photo-activated contributions to the overall antibacterial performance of the surfaces, demonstrating a remarkable synergy between these two mechanisms. Complementary microbiological and imaging evaluations on both planktonic and surfaceattached bacteria provided new insights on these distinct but cooperative effects.The development of smart on-demand antimicrobial surfaces has become a critical research area, addressing the issue of indiscriminate use of biocides implicated in the global emergence of antimicrobial resistance 1 . A significant challenge in this field is the need to combine on-demand antimicrobial functions at surfaces with static long-lasting effects. Static antibacterial surfaces are generally based on the release of metal cations with intrinsic biocidal properties 2 , e.g. sustained Ag + release from surface-attached silver nanoparticles [3][4][5] . In this area we have recently demonstrated that after 24 h such surfaces can reduce the colony forming units (CFU) of planktonic Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) by 5-7 orders of magnitude 4 and reduce the surviving fraction of Staphylococcus epidermidis (S. epidermidis) biofilms by 5 orders of magnitude 5 . Alternatively, the use of light-activated antimicrobial surfaces provides a route towards responsive systems that can be triggered remotely and on-demand 6 . Translation of such technology to in vivo applications (e.g. on the surfaces of prostheses and implants) needs to be restricted to systems responding in the narrow near-infrared (NIR) spectral window (750-900 nm) in which water and living tissues are transparent and, therefore, not susceptible to damage [7][8][9][10][11] . In this context, photothermal conversion by non-spherical plasmonic nanoparticles (e.g. nanorods 12 or nanostars) 7 is becoming particularly interesting, allowing the use of local hyperthermia activated by NIR radiation to kill bacteria. In 2014, the first example of combined use of biocidal metal cations and photothermal conversion of light was published 13 , using biomimetically-coated Au/Ag core/shell nanorods, and demonstrating a synergistic antibacterial effect against planktonic E. coli and S. epidermidis bacteria upon NIR irradiation. More recently, we have developed a different approach, specially designed for surfaces, where glass substrates bearing monolayers of non-coated Ag nanoplates 14 or Ag nanotriangles 15 displayed antibacterial effects significantly enhanced upon NIR irradiation with respect to the intrinsic biocidal effects due to the release of Ag + cations. Remarkably, the amou...

Self‐Assembled Monolayers of Silver Nanoparticles: From Intrinsic to Switchable Inorganic Antibacterial Surfaces

“…The contribution of intrinsic and photothermal antibacterial action was recently separated and unravelled in multilayered materials built with the LbL approach . A GNS monolayer was grafted on glass slides bearing an APTES monolayer and then sealed with a 4 nm SiO 2 layer to give glass|APTES|GNS|SiO 2 slides, presenting an an inert glass‐like surface to the environment.…”

“…Increasing power density by row: (a,b,c) = non irradiated samples; (d,e,f) = samples irradiated with 5× power; (g,h,i) = 20 × power. All scale bars are 500 nm (adapted with permission from ref ,. Copyright 2017, Springer Nature).…”

Evolving Technologies and Strategies for Combating Antibacterial Resistance in the Advent of the Postantibiotic Era

“…There have been promising findings on the in vitro antibacterial impact of stimuli‐responsive antibacterial NPs 110,146. In the field of antimicrobials, the integration of stimuli‐responsive nanomaterials into antibacterial medical products is still at a preclinical or academic research level 147–150. Some examples of wound dressings, catheters, bone cement, and cardiovascular implants containing nanosilver or silver‐loaded nanocomposites as antimicrobial agent is already available, and mainly nanosilver out of all nanomaterials is in clinical use 151–153…”

Suitable Polymeric Coatings to Avoid Localized Surface Plasmon Resonance Hybridization in Printed Patterns of Photothermally Responsive Gold Nanoinks

“…In particular, by decreasing the symmetry of Ag and Au nanoparticles from that of a sphere to those of elongated, branched or more complex shapes, such as nanorods, nanostars, nanoplates and nanoshells, the absorption maximum can be easily shifted from the visible to the Near-IR (NIR) range [3,6] including the so-called 'bio-transparent window' (750-900 nm). Following this, many papers have been published proposing antitumoral [7] and antibacterial [8] photothermal through-tissues therapies by using such non-spherical NP. Besides giving a photothermal response in solution and in-vitro or in-vivo wet conditions, dry surfaces coated with patterns of photothermal NP display an even more intense effect [9,10].…”