Morphology and oxygen incorporation effect on antimicrobial activity of silver thin films

Abstract

Ag and Ag x O thin films were deposited by non-reactive and reactive pulsed DC magnetron sputtering, respectively, with the final propose of functionalizing the SS316L substrate with antibacterial properties. The coatings were characterized chemically, physically and structurally. The coatings nanostructure was assessed by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS), while the coatings morphology was determined by scanning electron microscopy (SEM). The XRD and XPS analyses suggested that Ag thin film is composed by metallic Ag, which crystallizes in fcc-Ag phase, while the Ag x O thin film showed both metallic Ag and Ag O bonds, which crystalize in fcc-Ag and silver oxide phases. The SEM results revealed that Ag thin film formed a continuous layer, while Ag x O layer was composed of islands with hundreds of nanometers surrounded by small nanoparticles with tens of nanometers. The surface wettability and surface tension parameters were determined by contact angle measurements, being found that Ag and Ag x O surfaces showed very similar behavior, with all the surfaces showing a hydrophobic character. In order to verify the antibacterial behavior of the coatings, halo inhibition zone tests were realized for Staphylococcus epidermidis and Staphylococcus aureus. Ag coatings did not show antibacterial behavior, contrarily to Ag x O coating, which presented antibacterial properties against the studied bacteria. The presence of silver oxide phase along with the development of different morphology was pointed as the main factors in the origin of the antibacterial effect found in Ag x O thin film. The present study demonstrated that Ag x O coating presented antibacterial behavior and its application in cardiovascular stents is promising.

Killing of bacteria by copper, cadmium, and silver surfaces reveals relevant physicochemical parameters

“…However, metallic silver which is not oxidized was shown already in 1937 to be devoid of antibacterial activity. 35 This was subsequently confirmed in various other studies, most recently by Rebelo et al 36 In agreement with these findings, we found that silver does not exhibit detectable contact killing over 6 h and only marginal killing (less than 1 log) in 9 h [ Fig. 3(a)].…”

Electrochemical energy storage of silver and silver oxide thin films in an aqueous NaCl electrolyte

“…increase in crystallinity of the silver oxide thin films due to the increase in the rate of oxygen difusion into the silver oxide thin film deposited at 350W compared to silver oxide thin film deposited at 300W and 250W , resulting in larger grain sizes for silver oxide deposited at 350W [13,[19][20][21][22][23]. This is in agreement with the scanning electron microscopy images, where there are more pronounced micropores on silver oxide films sputtered at higher forward power.…”

“…Figure 2 (a and b) shows the Ag 3d and O 1s spectra, with binding energy observed at 368.3ev consistent with Ag sample [19,[27][28][29][30]. The existence of Ag-O bond was also evident in the O 1s spectra, with peak at 531.8 eV [19,[31][32]. The 531.8 eV peak originates from the subsurface formation of oxygen, which is a mixture of oxygen and the hydroxyl group.…”

Surface Characterization and Copper Release of a-C:H:Cu Coatings for Medical Applications

“…The surface-dependent factors like distribution, size, concentration, shape or charge of the antibacterial substance, the porosity and roughness of the coating's matrix as well as the overall micro-and nanostructure of the coating, are known to influence the ion release kinetics [32]. In this regard, a fine particle size and the incorporation of oxygen species can improve the Ag ions dissolution rate [33]. Additionally, nano-structuring the surface is also a valuable method to control antibacterial activity due to the high surface to volume ratio, which increases the surface reactivity [34].…”