Bringing the interaction of silver nanoparticles with bacteria to light

Abstract

In past decades, the exploitation of silver nanoparticles in novel antibacterial and detection devices has risen to prominence, owing to the well-known specific interaction of silver with bacteria. The vast majority of the investigations focus on the investigation over the mechanism of action underpinning bacterial eradication, while few efforts have been devoted to the study of the modification of silver optical properties upon interaction with bacteria. Specifically, given the characteristic localized surface plasmon resonance of silver nanostructures, which is sensitive to changes in the charge carrier density or in the dielectric environment, these systems can offer a handle in the detection of bacteria pathogens. In this review, we present the state of art of the research activity on the interaction of silver nanoparticles with bacteria, with strong emphasis on the modification of their optical properties. This may indeed lead to easy color reading of bacterial tests and pave the way to the development of nanotechnologic silver-based bacterial detection systems and drug-screening platforms.

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.…”

“…coli . By combining ultrafast optical spectroscopy, X-ray diffraction, and imaging, we assigned those changes to the silver oxidative dissolution in the presence of bacteria . In this work, we enhance the detection sensitivity by transducing the bacterial effect into a relatively narrow TP resonance.…”

“…The transmission spectra show a clear shift of the TP peak as a function of applied voltage: the peak undergoes a red shift (11 nm) and increase of transmission under positive bias, while we observe a blue shift (8 nm) and a decrease of transmission under negative bias (Figure a). 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. ,, This can be essentially rationalized as a “biological doping”, as removal of Ag + will leave behind an excess of negative charge. The results plotted in Figure are thus fully consistent with this interpretation, for both phenomena, lead to an accumulation of negative charges in the plasmonic metal.…”

“…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.…”

“…13 By combining ultrafast optical spectroscopy, Xray diffraction, and imaging, we assigned those changes to the silver oxidative dissolution in the presence of bacteria. 14 In this work, we enhance the detection sensitivity by transducing the bacterial effect into a relatively narrow TP resonance. To be quantitative, the blue shift of the silver plasmon resonance upon bacterial exposure divided by its FWHM lies around 5%, 13 whereas for our previous silver/DBR devices (without Tamm resonance), the PBG blue-shift/FWHM ratio amounts to 7%.…”