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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.

Microplastic particles (MPs) contamination of aquatic environments has raised a growing concern in recent decades because of their numerous potential toxicological effects. Although fish are among the most studied aquatic organisms, reports on MPs ingestion in freshwater environments are still scarce. Thus, there is still much to study to understand the uptake mechanisms, their potential accumulation among the food webs and their ecotoxicological effects. Here, MPs presence in the digestive system of one of the most widespread and commercially exploited freshwater fish, the perch (Perca fluviatilis, Linnaeus 1758), was investigated in four different south-alpine lakes, to assess the extent of ingestion and evaluate its relation to the body health condition. A total of 80 perch specimen have been sampled from the Italian lakes Como, Garda, Maggiore and Orta. Microplastic particles occurred in 86% of the analysed specimens, with average values ranging from 1.24 ± 1.04 MPs fish -1 in L. Como to 5.59 ± 2.61 MPs fish -1 in L. Garda. The isolated particles were mainly fragments, except in L. Como where films were more abundant. The most common polymers were polyethylene, polyethylene terephthalate, polyamide, and polycarbonate, although a high degree of degradation was found in 43% of synthetic particles, not allowing their recognition up to a single polymer. Despite the high number of ingested MPs, fish health (evaluated by means of Fulton's body condition and hepatosomatic index) was not affected. Instead, fullness index showed an inverse linear relationship with the number of ingested particles, which suggests that also in perch MPs presence could interfere with feeding activity, as already described for other taxa., (Copyright © 2021 Elsevier Ltd. All rights reserved.)

The many fundamental roto-vibrational resonances of chemical compounds result in strong absorption lines in the mid-infrared region (λ ∼ 2-20 μm). For this reason, mid-infrared spectroscopy plays a key role in label-free sensing, in particular, for chemical recognition, but often lacks the required sensitivity to probe small numbers of molecules. In this work, we propose a vibrational sensing scheme based on Bloch surface waves (BSWs) on 1D photonic crystals to increase the sensitivity of mid-infrared sensors. We report on the design and deposition of CaF 2 /ZnS 1D photonic crystals. Moreover, we theoretically and experimentally demonstrate the possibility to sustain narrow σ-polarized BSW modes together with broader π-polarized modes in the range of 3-8 μm by means of a customized Fourier transform infrared spectroscopy setup. The multilayer stacks are deposited directly on CaF 2 prisms, reducing the number of unnecessary interfaces when exciting in the Kretschmann-Raether configuration. Finally, we compare the performance of mid-IR sensors based on surface plasmon polaritons with the BSW-based sensor. The figures of merit found for BSWs in terms of confinement of the electromagnetic field and propagation length puts them as forefrontrunners for label-free and polarization-dependent sensing devices., Competing Interests: The authors declare no competing financial interest., (© 2020 American Chemical Society.)

A novel spectroscopy technique to enable the rapid characterization of discrete mid-infrared integrated photonic waveguides is demonstrated. The technique utilizes lithography patterned polymer blocks that absorb light strongly within the molecular fingerprint region. These act as integrated waveguide detectors when combined with an atomic force microscope that measures the photothermal expansion when infrared light is guided to the block. As a proof of concept, the technique is used to experimentally characterize propagation loss and grating coupler response of Ge-on-Si waveguides at wavelengths from 6 to 10 µm. In addition, when the microscope is operated in scanning mode at fixed wavelength, the guided mode exiting the output facet is imaged with a lateral resolution better than 500 nm i.e. below the diffraction limit. The characterization technique can be applied to any mid-infrared waveguide platform and can provide non-destructive in-situ testing of discrete waveguide components.

We study radiative relaxation at terahertz frequencies in n-type Ge/SiGe quantum wells, optically pumped with a terahertz free electron laser. Two wells coupled through a tunneling barrier are designed to operate as a three-level laser system with non-equilibrium population generated by optical pumping around the 1→3 intersubband transition at 10 THz. The non-equilibrium subband population dynamics are studied by absorption-saturation measurements and compared to a numerical model. In the emission spectroscopy experiment, we observed a photoluminescence peak at 4 THz, which can be attributed to the 3→2 intersubband transition with possible contribution from the 2→1 intersubband transition. These results represent a step towards silicon-based integrated terahertz emitters.

We demonstrate the use of plasmonic effects to boost the near-infrared sensitivity of metal-semiconductor-metal detectors. Plasmon-enhanced photodetection is achieved by properly optimizing Au interdigitated electrodes, micro-fabricated on Ge, a semiconductor that features a strong near IR absorption. Finite-difference time-domain simulations, photocurrent experiments and Fourier-transform IR spectroscopy are performed to validate how a relatively simple tuning of the contact geometry allows for an enhancement of the response of the device adapting it to the specific detection needs. A 2-fold gain factor in the Ge absorption characteristics is experimentally demonstrated at 1.4 µm, highlighting the potential of this approach for optoelectronic and sensing applications.

Photosensitive proteins embedded in the cell membrane (about 5 nm thickness) act as photoactivated proton pumps, ion gates, enzymes, or more generally, as initiators of stimuli for the cell activity. They are composed of a protein backbone and a covalently bound cofactor (e.g. the retinal chromophore in bacteriorhodopsin (BR), channelrhodopsin, and other opsins). The light-induced conformational changes of both the cofactor and the protein are at the basis of the physiological functions of photosensitive proteins. Despite the dramatic development of microscopy techniques, investigating conformational changes of proteins at the membrane monolayer level is still a big challenge. Techniques based on atomic force microscopy (AFM) can detect electric currents through protein monolayers and even molecular binding forces in single-protein molecules but not the conformational changes. For the latter, Fourier-transform infrared spectroscopy (FTIR) using difference-spectroscopy mode is typically employed, but it is performed on macroscopic liquid suspensions or thick films containing large amounts of purified photosensitive proteins. In this work, we develop AFM-assisted, tip-enhanced infrared difference-nanospectroscopy to investigate light-induced conformational changes of the bacteriorhodopsin mutant D96N in single submicrometric native purple membrane patches. We obtain a significant improvement compared with the signal-to-noise ratio of standard IR nanospectroscopy techniques by exploiting the field enhancement in the plasmonic nanogap that forms between a gold-coated AFM probe tip and an ultraflat gold surface, as further supported by electromagnetic and thermal simulations. IR difference-spectra in the 1450-1800 cm -1 range are recorded from individual patches as thin as 10 nm, with a diameter of less than 500 nm, well beyond the diffraction limit for FTIR microspectroscopy. We find clear spectroscopic evidence of a branching of the photocycle for BR molecules in direct contact with the gold surfaces, with equal amounts of proteins either following the standard proton-pump photocycle or being trapped in an intermediate state not directly contributing to light-induced proton transport. Our results are particularly relevant for BR-based optoelectronic and energy-harvesting devices, where BR molecular monolayers are put in contact with metal surfaces, and, more generally, for AFM-based IR spectroscopy studies of conformational changes of proteins embedded in intrinsically heterogeneous native cell membranes.

We have conducted a comprehensive investigation of the optical and vibrational properties of the binary semiconductor SnSe as a function of temperature and pressure by means of experimental and ab initio probes. Our high-temperature investigations at ambient pressure have successfully reproduced the progressive enhancement of the free carrier concentration upon approaching the Pnma → Bbmm transition, whereas the pressure-induced Pnma → Bbmm transformation at ambient temperature, accompanied by an electronic semiconductor → semi-metal transition, has been identified for bulk SnSe close to 10 GPa. Modeling of the Raman-active vibrations revealed that three-phonon anharmonic processes dominate the temperature-induced mode frequency evolution. In addition, SnSe was found to exhibit a pressure-induced enhancement of the Born effective charge. Such behavior is quite unique and cannot be rationalized within the proposed effective charge trends of binary materials under pressure.

Background. In the current scientific literature there are only few studies on the immediate functional loading of single implants. The aim of the present present study was to evaluate the 4-year survival rate, complication rate and peri-implant marginal bone loss (PIMBL) of immediately loaded single implants inserted in healed ridges and fresh post-extraction sites. Methods. Six centers were involved in this prospective study. The surgical and prosthetic protocol was defined in detail, before the start of recruiting patients. Recruitment of patients and performance of surgeries took place between February 2012 and February 2013. Criteria for inclusion were single-tooth gaps in healed ridges and fresh post-extraction sockets. All the fixtures (Anyridge®, Megagen Corporation, Gyeongbuk, South Korea) were functionally loaded immediately after insertion and followed for a period of 4 years. Outcome measures were implant survival, complications and PIMBL. Results. Forty-six patients (18‒73 years of age) were selected. In total, 57 fixtures were placed (10 in fresh post-extraction sockets). After 4 years of functional loading, only one fixture was lost; therefore, high survival rates (97.6% patient-based; 98.1% implant-based) were reported. In addition, a limited incidence of biologic (4.8% patient-based; 3.8% implant-based) and prosthetic (9.7% patient-based; 7.6% implant-based) complications was reported. The overall 4-year PIMBL amounted to 0.38±0.21 mm (healed ridges: 0.4±0.21 mm; fresh post-extraction sockets: 0.33±0.20 mm). Conclusion. Loading single implants immediately seems to be a highly successful treatment modality. However, long-term data are needed to confirm these positive outcomes.

The development of Ge and SiGe chemical vapor deposition techniques on silicon wafers has enabled the integration of multi-quantum well structures in silicon photonics chips for nonlinear optics with potential applications to integrated nonlinear optics, however research has focused up to now on undoped quantum wells and interband optical excitations. In this work, we present model calculations for the giant nonlinear coefficients provided by intersubband transitions in hole-doped Ge/SiGe and Si/SiGe multi-quantum wells. We employ a valence band-structure model for Si 1-x Ge x to calculate the confined hole states of asymmetric-coupled quantum wells for second-harmonic generation in the mid-infrared. We calculate the nonlinear emission spectra from the second-order susceptibility tensor, including the particular vertical emission spectra of valence-band quantum wells. Two possible nonlinear mid-infrared sensor architectures, one based on waveguides and another based on metasurfaces, are described as perspective application.

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.

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., (© 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

The aim of this prospective multicenter study was to evaluate the outcomes of single implants subjected to immediate functional loading. Inclusion criteria were single-tooth placement in postextraction sockets or fully healed sites, and sufficient bone height and width to place an implant of at least 3.5 × 10.0 mm. All implants were functionally loaded immediately after placement and followed for 2 years. Outcome measures were implant survival, complications, and peri-implant marginal bone loss (MBL). A total of 57 implants (38 maxilla, 19 mandible) were placed in 46 patients (23 men, 23 women, aged 18-73 years). Of these, 10 implants were placed in postextraction sockets. One implant failed, in a healed site, giving a patient-based overall 2-year survival rate of 97.6%. The incidence of biologic complications was 1.8%; prosthetic complications amounted to 7.5%. The peri-implant MBL was 0.37 ± 0.22 mm (healed sites: 0.4 mm ± 0.22; postextraction sockets: 0.3 mm ± 0.22). The immediate functional loading of single implants seems to represent a safe and successful procedure. Long-term follow-up studies on a larger sample of patients are needed to confirm these results.

A 3D Topological Insulator (TI) is an intrinsically stratified electronic material characterized by an insulating bulk and Dirac free electrons at the interface with vacuum or another dielectric. In this paper, we investigate, through terahertz (THz) spectroscopy, the plasmon excitation of Dirac electrons on thin films of (Bi1-xInx)2Se3 TI patterned in the form of a micro-ribbon array, across a Quantum Phase Transition (QPT) from the topological to a trivial insulating phase. The latter is achieved by In doping onto the Bi-site and is characterized by massive electrons at the surface. While the plasmon frequency is nearly independent of In content, the plasmon width undergoes a sudden broadening across the QPT, perfectly mirroring the single particle (free electron) behavior as measured on the same films. This strongly suggests that the topological protection from backscattering characterizing Dirac electrons in the topological phase extends also to their plasmon excitations.

In this work we present an integrated biosensor that enables FTIR (Fourier Transform-Infrared) detection of analytes contained in diluted solutions. The fabricated nanosensor allows for the detection of proteins through the identification of the fine structure of their amide I and II bands, up to the nanomolar concentration range. We exploited two distinct effects to enhance the sensitivity: (i) the concentration effect due to the presence of the superhydrophobic surface that conveys molecules dispersed in solution directly inside the focus of a FTIR spectromicroscope; (ii) the plasmonic resonance of the nanoantenna array that provides electromagnetic field enhancement in the amide I and II spectral region (1500-1700 cm(-1)). We demonstrate the detection of ferritin in the nanomolar concentration range, a blood protein that is usually available in small amounts in typical blood samples.

Purpose: The aim of this prospective multicentre study was to evaluate the clinical outcome of immediately loaded single implants., Materials and Methods: Patients were recruited at six clinical centres. Inclusion criteria were singletooth replacement in fully healed sites or post-extraction sockets with adequate bone height and width, to place an implant of at least 3.5 mm in diameter and 10.0 mm in length. All implants (AnyRidge, MegaGen, Gyeongbuk, South Korea) were functionally loaded immediately after placement. After 3 months, final crowns were delivered. All implants were followed for 1 year. Outcome measures were: implant stability; complications; peri-implant marginal bone level changes; probing pocket depth., Results: Fifty-seven implants (38 in the maxilla and 19 in the mandible) were placed in 46 patients (23 males, 23 females, aged between 18 to 73 years). Ten implants were placed in post-extraction sockets. Two patients (two implants) withdrew from the study and were classified as drop-outs. At the end of the study, only one implant was lost in a healed site. All the surviving implants were stable, giving an overall 1-year survival rate of 97.7% (patient-based). A few complications (one patient experienced swelling after surgery, two had loosened abutments and another patient had a ceramic crown fracture) were encountered. After 1 year of functional loading, the patients had lost an average of 0.32 mm (± 0.22) of peri-implant marginal bone; the mean probing pocket depth (PPD) was 2.16 mm (± 0.68)., Conclusions: Within its limit (limited number of patients treated and self-evaluation of the outcomes), this study supports the concept that immediate functional loading of single dental implants can be a successful treatment procedure, with satisfactory clinical outcomes.

The active site of several oxygen binding proteins can be mimicked with the ferric iron protoporphyrin IX derivative hemin, coordinating two imidazole molecules and embedded in sodium dodecyl sulfate (SDS) micelles; the detergent simulates the hydrophobic cavity of heme proteins. We studied the low-frequency vibrational modes of the porphyrin-iron-imidazole bonding in infrared absorbance spectra. Assignment of the metal-ligand vibrations to signals at 396, 387, and 378 cm(-1) was performed by isotope labeling of the imidazole ligand. These modes were also found to be temperature-dependent and to display a linear increase of signal intensity between 25 and 150 K and, with a different slope, between 150 and 300 K. The modes at 396 and 399 cm(-1) show for 25 K an up-shift about 4 cm(-1) and the signal at 378 cm(-1) a small downshift, indicating the involvement of antisymmetric stretching modes and, in the latter, of bending motions. Anharmonic couplings to doming modes are discussed, and the doming mode and hydrogen-bonding signature spectral range between 300 and 100 cm(-1) is presented.