The impact of bacteria exposure on the plasmonic response of silver nanostructured surfaces

Abstract

Silver, in the form of nanostructures, is widely employed as an antimicrobial agent. The origin of the biocidal mechanism has been elucidated in the last decades, originating from silver cation release due to oxidative dissolution followed by cellular uptake of silver ions, a process that causes a severe disruption of bacterial metabolism, leading to eradication. Despite the large body of work addressing the effects of nanosilver shape/size on the antibacterial mechanism and on the (bio)physical chemistry pathways that drive bacterial eradication, little effort has been devoted to the investigation of nanostructured silver plasmon response upon interaction with bacteria. We investigate the bacteria-induced changes of the plasmonic response of silver nanoplates after exposure to the bacterial model Escherichia coli. Ultrafast pump-probe measurements indicate that the dramatic changes on particle size/shape and crystallinity, which likely stem from a bacteria-induced oxidative dissolution process, translate into a clear modification of the plasmonic response. Specifically, exposure to bacteria causes a decrease in the electron–phonon coupling time and an increase in lattice-environment coupling time, effects explained by an increase in the free electron density and amorphization of the silver particles. Coherent oscillations that are observed in pristine silver are completely damped in contaminated samples, which can be attributed again to amorphization of the nanoplates at the surface and an increase in polydispersivity of particle geometries. This study opens innovative avenues in the biophysics of bio-responsive materials, with the aim of providing reliable biophysical signatures of the interaction of plasmonic materials with complex biological environments.

Tamm Plasmon Resonance as Optical Fingerprint of Silver/Bacteria Interaction

“…The nanostructured Ag film has an important role here due to three important reasons: (i) it leads to the appearance of the TP spectral feature. This is considerably narrower than the PBG (FWHM = 27 vs 138 nm), implying that its intensity and position is a relatively sensitive read-out upon exposure of analytes; (ii) the intrinsic and high bio-responsivity of nanosilver, which results in bacteria-driven modifications of silver plasmonic properties; , and (iii) the corrugation at the nanoscale that does not hamper the emergence of the TP resonance while allowing direct access to its field, as demonstrated in a recent publication . Hence, our main idea is to exploit all these three advantages to build up an optical sensor capable of detecting the presence of bacteria, as well as being able to map out their metabolic activity with the broad view to develop drug-testing platforms.…”

“…In this context, photonic-based devices can be in principle portable and easy-to-read alternatives to traditional state-of-the-art methods . In our first attempt, we incorporated a thin layer of silver (8 nm) on top of DBRs, relying on the well-known capability of silver to interact with bacteria, an effect that in turn induces marked changes in the structural, morphological, and optical properties of the metal. , Although we could observe a clear PBG blue shift upon exposure to bacteria in our initial studies (∼10 nm, accompanied by a strong broadening), , we realized that this originated simply from a change in the refractive index conditions experienced by the DBR, without the excitation/involvement of any well-defined plasmonic resonance. Thus, our sensing information was essentially photonic and encoded entirely on the broad PBG feature (full width half-maximum, FWHM, exceeding largely 100 nm), rendering the read-out difficult to be interpreted.…”

“…As briefly mentioned above, we proposed that the bacterial-driven modification of the silver plasmon resides on the release of positive metal ions, within the scheme of silver oxidative dissolution. 13,14,51 This can be essentially rationalized as a "biological doping", 15 as removal of Ag + will leave behind an excess of negative charge. The results plotted in Figure 4 are thus fully consistent with this interpretation, for both phenomena, lead to an accumulation of negative charges in the plasmonic metal.…”

Leachability and Anti-Mold Efficiency of Nanosilver on Poplar Wood Surface

“…The antifungal element of the nano-metallic material existed at the nanoscale, with unique features of large specific surface area and abundant surface charges, possessing strong affinity with the polar components of wood, which could not be easily washed away by water flow, and thus exhibited higher leaching resistance than the correspondingly water-soluble ionic element [ 26 ]. Previous studies reported that the leaching rate of antifungal nanomaterials on wood surface was closely related to their physical and chemical environments, such as particle size, particle species, solution concentration, stabilizer type, wood species, water flow rate, water volume, pH value of leachate, light irradiating area, and ambient temperature [ 26 , 31 , 32 ]. In general, the larger the particle size, the more difficult it is for it to traverse within wood components, and the lower the leaching rate.…”

Unraveling the Intrinsic Biocidal Activity of the SiO2–Ag Composite against SARS-CoV-2: A Joint Experimental and Theoretical Study

“…The SiO 2 –Ag composite takes advantage of the distinctive properties of Ag as a potent antimicrobial agent − and the porous inorganic 3D network structure of SiO 2 , resulting in fast mass transport, high thermal and mechanical stability, a large specific surface area, biocompatibility, and easy functionalization. − Over the last few years, our research group has reported that the SiO 2 –Ag composite with anti-SARS-CoV-2 properties is a versatile, low-cost, and tolerant additive to functionalize textiles and surfaces, representing a safe alternative for its application and the prevention of microbial proliferation and transmission. Indeed, the experimental results indicated that the as-fabricated samples exhibited a high antibacterial activity towardE.…”