Direct synthesis of antimicrobial coatings based on tailored bi-elemental nanoparticles

Abstract

Ultrathin coatings based on bi-elemental nanoparticles (NPs) are very promising to limit the surface-related spread of bacterial pathogens, particularly in nosocomial environments. However, tailoring the synthesis, composition, adhesion to substrate, and antimicrobial spectrum of the coating is an open challenge. Herein, we report on a radically new nanostructured coating, obtained by a one-step gas-phase deposition technique, and composed of bi-elemental Janus type Ag/Ti NPs. The NPs are characterized by a cluster-in-cluster mixing phase with metallic Ag nano-crystals embedded in amorphous TiO2 and present a promising antimicrobial activity including also multidrug resistant strains. We demonstrate the flexibility of the method to tune the embedded Ag nano-crystals dimension, the total relative composition of the coating, and the substrate type, opening the possibility of tailoring the dimension, composition, antimicrobial spectrum, and other physical/chemical properties of such multi-elemental systems. This work is expected to significantly spread the range of applications of NPs coatings, not only as an effective tool in the prevention of healthcare-associated infections but also in other technologically relevant fields like sensors or nano-/micro joining

Exploring the Optical and Morphological Properties of Ag and Ag/TiO2 Nanocomposites Grown by Supersonic Cluster Beam Deposition

“…The atomic force microscopy (AFM) data of Figure 1a,b, respectively, show that the 80 nm thick film of Ag NP and the 40 nm thick film of Ag/TiO 2 50-50 have quite similar surface morphology and a proper insight into the structural and chemical differences of the two films requires further investigations. The apparent lateral size of the NPs spans in the range 15–35 nm but, as already pointed out [6,19,24], actual lateral size of the NP in the film has to be estimated after deconvolution with the actual AFM tip apex radius (typical 10 nm) and by use of vertical height of isolated NP [25]. However, the root mean square (RMS) roughness of the two films are consistent with previous works: 1.7 nm for Ag film, 2.8 nm for Ag/Ti 50-50 nanocomposite.…”

“…Due to the atomic number sensitivity of the HAADF-STEM technique (the higher Z, the higher apparent brightness), Ag (Z Ag = 47) nanocrystals are the brightest objects. The grayscale areas have been shown to be composed by a TiO 2 matrix [24] related to the lower Z numbers of the components (Z Ti = 22, Z O = 8). The Ag NPs are partially encapsulated, more similar to the Janus-like than the core-shell configuration [28], the former being commonly observed for bimetallic noble metal nanoparticles [29].…”

“…The Ag NPs are partially encapsulated, more similar to the Janus-like than the core-shell configuration [28], the former being commonly observed for bimetallic noble metal nanoparticles [29]. Previous investigations about the structure of the oxide matrix performed by X-ray diffraction [24] suggested that the TiO 2 is amorphous, in agreement with the TEM image shown in Figure 1d, where no sign of regular atomic arrangement can be observed in the “gray” areas.…”

“…This indicates that the presence of the amorphous TiO 2 affects the size distribution of Ag NPs. Since the amount of TiO 2 is directly related to the density of Ti in the starting rod for the ablation [24], this effect could be exploited to tune the size of Ag NPs. Moreover, modification of the Ti–Ag precursor rod with Mg–Ag, Al–Ag could lead to the formation of other Janus-type NPs or even multi element alloy NPs.…”

“…The SCBD gas-phase synthesis method [20,21] allows to grow porous NPs films either metallic [6] or semiconducting [22,23] or even metal NP-dielectric nanocomposite films [24] directly from a suitable target source. A table-top spectroscopic ellipsometer (Woollam Alpha-SE) instrument allows indirect assessment of the film structure, especially the film porosity, through the information provided by optical properties of the film in the visible-infrared (IR) wavelength range and the use of a quite simple model.…”