The effect of the electromagnetic field on metabolic-active bacterial biofilm experimentallyinduced on titanium dental implants.

Microbial biofilm is of paramount importance in the development of mucositis or peri-implantitis in patients with dental implants. This study was designed to investigate whether an electromagnetic field at high frequency waves directly applied on 33 titanium implants could remove experimentally-induced Enterococcus faecalis bacterial biofilm. A specially designed device (X-IMPLANT) was used to generate the electromagnetic field, with output power of 8 W, supply frequency (action/pause) 3/2s, and an output frequency of 625±5% kHz in plastic devices containing the biofilm-covered implants immersed in sterile saline. The bacterial biofilm on both treated and untreated control implants was quantitatively measured by phenol red-based Bio-Timer-Assay reagent. The kinetic analysis of the curves showed that the electrical treatment generated by the X-IMPLANT device completely removed the bacterial biofilm after 30 minutes of treatment (p<0.01). Elimination of the biofilm was also confirmed by chromatic observation in the macro-method. Our data seem to indicate that the procedure could be considered for clinical application in peri-implantitis to counteract bacterial biofilm on dental implants.

Low-Temperature Stability and Sensing Performance of Mid-Infrared Bloch Surface Waves on a One-Dimensional Photonic Crystal.

The growing need for new and reliable surface sensing methods is arousing interest in the electromagnetic excitations of ultrathin films, i.e., to generate electromagnetic field distributions that resonantly interact with the most significant quasi-particles of condensed matter. In such a context, Bloch surface waves turned out to be a valid alternative to surface plasmon polaritons to implement high-sensitivity sensors in the visible spectral range. Only in the last few years, however, has their use been extended to infrared wavelengths, which represent a powerful tool for detecting and recognizing molecular species and crystalline structures. In this work, we demonstrate, by means of high-resolution reflectivity measurements, that a one-dimensional photonic crystal can sustain Bloch surface waves in the infrared spectral range from room temperature down to 10 K. To the best of our knowledge, this is the first demonstration of infrared Bloch surface waves at cryogenic temperatures. Furthermore, by exploiting the enhancement of the surface state and the high brilliance of infrared synchrotron radiation, we demonstrate that the proposed BSW-based sensor has a sensitivity on the order of 2.9 cm-1 for each nanometer-thick ice layer grown on its surface below 150 K. In conclusion, we believe that Bloch surface wave-based sensors are a valid new class of surface mode-based sensors for applications in materials science.

Grazing-angle reflectivity setup for the low-temperature infrared spectroscopy of two-dimensional systems.

A new optical setup is described that allows the reflectivity at grazing incidence to be measured, including ultrathin films and two-dimensional electron systems (2DES) down to liquid-helium temperatures, by exploiting the Berreman effect and the high brilliance of infrared synchrotron radiation. This apparatus is well adapted to detect the absorption of a 2DES of nanometric thickness, namely that which forms spontaneously at the interface between a thin film of LaAlO3 and its SrTiO3 substrate, and to determine its Drude parameters.

Infrared Spectroscopy of the Topological Surface States of Bi_{2}Se_{3} by Use of the Berreman Effect.

The Berreman effect (BE) allows one to study the electrodynamics of ultrathin conducting films at the surface of dielectrics by use of grazing-angle infrared spectroscopy and polarized radiation. Here, we first apply the BE to the two-dimensional electron system (2DES) at the interface between a high-purity film of the topological insulator Bi_{2}Se_{3} and its sapphire substrate. We determine for the 2DES a charge density n_{s}=(8±1)×10^{12} cm^{-2}, a thickness d=0.6±0.2 nm, and a mobility µ^{IR}=290±30 cm^{2}/V s. Within errors, all of these parameters result in being independent of temperature between 300 and 10 K. These findings consistently indicate that the 2DES is formed by topological surface states, whose infrared response is then directly observed here.

Heterogeneity of the Transmembrane Protein Conformation in Purple Membranes Identified by Infrared Nanospectroscopy.

Cell membranes are intrinsically heterogeneous, as the local protein and lipid distribution is critical to physiological processes. Even in template systems embedding a single protein type, like purple membranes, there can be a different local response to external stimuli or environmental factors, resulting in heterogeneous conformational changes. Despite the dramatic advances of microspectroscopy techniques, the identification of the conformation heterogeneity is still a challenging task. Tip-enhanced infrared nanospectroscopy is here used to identify conformational changes connected to the hydration state of the transmembrane proteins contained in a 50 nm diameter cell membrane area, without the need for fluorescent labels. In dried purple membrane monolayers, areas with fully hydrated proteins are found among large numbers of molecules with randomly distributed hydration states. Infrared nanospectroscopy results are compared to the spectra obtained with diffraction-limited infrared techniques based on the use of synchrotron radiation, in which the diffraction limit still prevents the observation of nanoscale heterogeneity.

Optical properties of (SrMnO3)n/(LaMnO3)2n superlattices: an insulator-to-metal transition observed in the absence of disorder.

We measure the optical conductivity, σ1(ω), of (SrMnO3)n/(LaMnO3)2n superlattices (SL) for n = 1, 3, 5, and 8 and 10 < T < 400 K. Data show a T-dependent insulator to metal transition (IMT) for n ≤ 3, driven by the softening of a polaronic mid-infrared band. At n = 5 that softening is incomplete, while at the largest-period n = 8 compound the MIR band is independent of T and the SL remains insulating. One can thus first observe the IMT in a Manganite system in the absence of the disorder due to chemical doping. Unsuccessful reconstruction of the SL optical properties from those of the original bulk materials suggests that (SrMnO3)n/(LaMnO3)2n heterostructures give rise to a novel electronic state.

Optical performances of SINBAD, the synchrotron infrared beamline at DAphiNE.

SINBAD (Synchrotron Infrared Beamline At DAphiNE) is the first Italian synchrotron radiation beamline operating in the infrared range. It collects the radiation emitted by DANE, an electron-positron collider designed to work at 0.51 GeV with a beam current I> 1 A. The actual performances of the beamline, in terms of brilliance gain with respect to blackbodies and polarization properties, are presented and discussed. Finally, the stability of the SINBAD source, a critical issue for Fourier-transform infrared spectroscopy, is discussed.