Infrared Spectroscopy of SARS-CoV-2 Viral Protein: from Receptor Binding Domain to Spike Protein.

Spike (S) glycoprotein is the largest structural protein of SARS-CoV-2 virus and the main one involved in anchoring of the host receptor ACE2 through the receptor binding domain (RBD). S protein secondary structure is of great interest for shedding light on various aspects, from functionality to pathogenesis, finally to spectral fingerprint for the design of optical biosensors. In this paper, the secondary structure of SARS-CoV-2 S protein and its constituting components, namely RBD, S1 and S2 regions, are investigated at serological pH by measuring their amide I infrared absorption bands through Attenuated Total Reflection Infrared (ATR-IR) spectroscopy. Experimental data in combination with MultiFOLD predictions, Define Secondary Structure of Proteins (DSSP) web server and Gravy value calculations, provide a comprehensive understanding of RBD, S1, S2, and S proteins in terms of their secondary structure content, conformational order, and interaction with the solvent.

SAW Humidity Sensing with rr-P3HT Polymer Films.

In the present paper the humidity sensing properties of regioregular rr-P3HT (poly-3-hexylthiophene) polymer films is investigated by means of surface acoustic wave (SAW) based sensors implemented on LiNbO3 (1280 Y-X) and ST-quartz piezoelectric substrates. The polymeric layers were deposited along the SAW propagation path by spray coating method and the layers thickness was measured by atomic force microscopy (AFM) technique. The response of the SAW devices to relative humidity (rh) changes in the range ~5-60% has been investigated by measuring the SAW phase and frequency changes induced by the (rh) absorption in the rr-P3HT layer. The SAW sensor implemented onto LiNbO3 showed improved performance as the thickness of the membrane increases (from 40 to 240 nm): for 240 nm thick polymeric membrane a phase shift of about -1.2 deg and -8.2 deg was measured for the fundamental (~78 MHz operating frequency) and 3rd (~234 MHz) harmonic wave at (rh) = 60%. A thick rr-P3HT film (~600 nm) was deposited onto the quartz-based SAW sensor: the sensor showed a linear frequency shift of ~-20.5 Hz per unit (rh) changes in the ~5-~50% rh range, and a quite fast response (~5 s) even at low humidity level (~5% rh). The LiNbO3 and quartz-based sensors response was assessed by using a dual delay line system to reduce unwanted common mode signals. The simple and cheap spray coating technology for the rr-P3HT polymer films deposition, complemented with fast low level humidity detection of the tested SAW sensors (much faster than the commercially available Michell SF-52 device), highlight their potential in a low-medium range humidity sensing application.

Characterization of CuAg Alloys with Low Ag Concentrations.

Copper-based alloys designed to combine high electronic and thermal conductivities with high mechanical strength find a wide range of applications in different fields. Among the principal representatives, strongly diluted CuAg alloys are of particular interest as innovative materials for the realization of accelerating structures when the use of high-gradient fields requires increasingly high mechanical and thermal performances to overcome the limitations induced by breakdown phenomena. This work reports the production and optical characterization of CuAg crystals at low Ag concentrations, from 0.028% wt to 0.1% wt, which guarantee solid solution hardening while preserving the exceptional conductivity of Cu. By means of Fourier Transform Infrared (FTIR) micro-spectroscopy experiments, the low-energy electrodynamics of the alloys are compared with that of pure Cu, highlighting the complete indistinguishability in terms of electronic transport for such low concentrations. The optical data are further supported by Raman micro-spectroscopy and SEM microscopy analyses, allowing the demonstration of the full homogeneity and complete solubility of solid Ag in copper at those concentrations. Together with the solid solution hardening deriving from the alloying process, these results support the advantage of strongly diluted CuAg alloys over conventional materials for their application in particle accelerators.

On the Dependency of the Electromechanical Response of Rotary MEMS/NEMS on Their Embedded Flexure Hinges' Geometry.

This paper investigates how the electromechanical response of MEMS/NEMS devices changes when the geometrical characteristics of their embedded flexural hinges are modified. The research is dedicated particularly to MEMS/NEMS devices which are actuated by means of rotary comb-drives. The electromechanical behavior of a chosen rotary device is assessed by studying the rotation of the end effector, the motion of the comb-drive mobile fingers, the actuator's maximum operating voltage, and the stress sustained by the flexure when the flexure's shape, length, and width change. The results are compared with the behavior of a standard revolute joint. Outcomes demonstrate that a linear flexible beam cannot perfectly replace the revolute joint as it induces a translation that strongly facilitates the pull-in phenomenon and significantly increases the risk of ruptures of the comb-drives. On the other hand, results show how curved beams provide a motion that better resembles the revolute motion, preserving the structural integrity of the device and avoiding the pull-in phenomenon. Finally, results also show that the end effector motion approaches most precisely the revolute motion when a fine tuning of the beam's length and width is performed.

Biocompatibility and Connectivity of Semiconductor Nanostructures for Cardiac Tissue Engineering Applications.

Nano- or microdevices, enabling simultaneous, long-term, multisite, cellular recording and stimulation from many excitable cells, are expected to make a strategic turn in basic and applied cardiology (particularly tissue engineering) and neuroscience. We propose an innovative approach aiming to elicit bioelectrical information from the cell membrane using an integrated circuit (IC) bearing a coating of nanowires on the chip surface. Nanowires grow directly on the backend of the ICs, thus allowing on-site amplification of bioelectric signals with uniform and controlled morphology and growth of the NWs on templates. To implement this technology, we evaluated the biocompatibility of silicon and zinc oxide nanowires (NWs), used as a seeding substrate for cells in culture, on two different primary cell lines. Human cardiac stromal cells were used to evaluate the effects of ZnO NWs of different lengths on cell behavior, morphology and growth, while BV-2 microglial-like cells and GH4-C1 neuroendocrine-like cell lines were used to evaluate cell membrane-NW interaction and contact when cultured on Si NWs. As the optimization of the contact between integrated microelectronics circuits and cellular membranes represents a long-standing issue, our technological approach may lay the basis for a new era of devices exploiting the microelectronics' sensitivity and "smartness" to both improve investigation of biological systems and to develop suitable NW-based systems available for tissue engineering and regenerative medicine.

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.

In Vitro Evaluation of Structural Factors Favouring Bacterial Adhesion on Orthodontic Adhesive Resins.

Bacterial adhesion to the surface of orthodontic materials is an important step in the formation and proliferation of plaque bacteria, which is responsible for enamel demineralization and periodontium pathologies. With the intent of investigating if adhesive resins used for bracket bonding are prone to bacteria colonization, the surface roughness of these materials has been analyzed, combining information with a novel methodology to observe the internal structures of orthodontic composites. Scanning electron microscopy, combined with focus ion bean micromachining and stylus profilometry analyses, were performed to evaluate the compositional factors that can influence specific pivotal properties facilitating the adhesion of bacteria to the surface, such as surface roughness and robustness of three orthodontic adhesive composite resins. To confirm these findings, contact angle measurements and bacteria incubation on resin slide have been performed, evaluating similarities and differences in the final achievement. In particular, the morphological features that determine an increase in the resins surface wettability and influence the bacterial adhesion are the subject of speculation. Finally, the focused ion beam technique has been proposed as a valuable tool to combine information coming from surface roughness with specific the internal structures of the polymers.

Assessment and Imaging of Intracellular Magnesium in SaOS-2 Osteosarcoma Cells and Its Role in Proliferation.

Magnesium is an essential nutrient involved in many important processes in living organisms, including protein synthesis, cellular energy production and storage, cell growth and nucleic acid synthesis. In this study, we analysed the effect of magnesium deficiency on the proliferation of SaOS-2 osteosarcoma cells. When quiescent magnesium-starved cells were induced to proliferate by serum addition, the magnesium content was 2-3 times lower in cells maintained in a medium without magnesium compared with cells growing in the presence of the ion. Magnesium depletion inhibited cell cycle progression and caused the inhibition of cell proliferation, which was associated with mTOR hypophosphorylation at Serine 2448. In order to map the intracellular magnesium distribution, an analytical approach using synchrotron-based X-ray techniques was applied. When cell growth was stimulated, magnesium was mainly localized near the plasma membrane in cells maintained in a medium without magnesium. In non-proliferating cells growing in the presence of the ion, high concentration areas inside the cell were observed. These results support the role of magnesium in the control of cell proliferation, suggesting that mTOR may represent an important target for the antiproliferative effect of magnesium. Selective control of magnesium availability could be a useful strategy for inhibiting osteosarcoma cell growth.

A Simple Ball Milling and Thermal Oxidation Method for Synthesis of ZnO Nanowires Decorated with Cubic ZnO2 Nanoparticles.

In this work, we propose the synthesis of ZnO nanostructures through the thermal oxidation of ball-milled powders with the introduction of Mg and Sn doping species at the preliminary step of milling. We investigate the advantages and challenges of this two steps process for the production and fabrication of highly crystalline ZnO nanowires. This simple method allows us to fabricate ZnO nanowires with a higher quality core crystal at a much lower temperature and for a shorter processing time than the state-of-the-art, and decorated with by ZnO2 nanoparticles as determined via TEM analysis. The main findings will show that the crystalline core of the nanowires is of hexagonal ZnO while the nanoparticles on the surface are ZnO2 cubic type. Generally, the method proves to be suitable for applications that require a high surface-to-volume ratio, for example, catalysis phenomena, in which the presence of zinc oxides species can play an important role.

Spectral Characterization of Mid-Infrared Bloch Surface Waves Excited on a Truncated 1D Photonic Crystal.

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 CaF2/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 CaF2 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.

The Molecular Weight Dependence of Thermoelectric Properties of Poly (3-Hexylthiophene).

Organic materials have been found to be promising candidates for low-temperature thermoelectric applications. In particular, poly (3-hexylthiophene) (P3HT) has been attracting great interest due to its desirable intrinsic properties, such as excellent solution processability, chemical and thermal stability, and high field-effect mobility. However, its poor electrical conductivity has limited its application as a thermoelectric material. It is therefore important to improve the electrical conductivity of P3HT layers. In this work, we studied how molecular weight (MW) influences the thermoelectric properties of P3HT films. The films were doped with lithium bis(trifluoromethane sulfonyl) imide salt (LiTFSI) and 4-tert butylpyridine (TBP). Various P3HT layers with different MWs ranging from 21 to 94 kDa were investigated. UV-Vis spectroscopy and atomic force microscopy (AFM) analysis were performed to investigate the morphology and structure features of thin films with different MWs. The electrical conductivity initially increased when the MW increased and then decreased at the highest MW, whereas the Seebeck coefficient had a trend of reducing as the MW grew. The maximum thermoelectric power factor (1.87 µW/mK2) was obtained for MW of 77 kDa at 333 K. At this temperature, the electrical conductivity and Seebeck coefficient of this MW were 65.5 S/m and 169 µV/K, respectively.

ZnO Nanostructures and Electrospun ZnO-Polymeric Hybrid Nanomaterials in Biomedical, Health, and Sustainability Applications.

ZnO-based nanomaterials are a subject of increasing interest within current research, because of their multifunctional properties, such as piezoelectricity, semi-conductivity, ultraviolet absorption, optical transparency, and photoluminescence, as well as their low toxicity, biodegradability, low cost, and versatility in achieving diverse shapes. Among the numerous fields of application, the use of nanostructured ZnO is increasingly widespread also in the biomedical and healthcare sectors, thanks to its antiseptic and antibacterial properties, role as a promoter in tissue regeneration, selectivity for specific cell lines, and drug delivery function, as well as its electrochemical and optical properties, which make it a good candidate for biomedical applications. Because of its growing use, understanding the toxicity of ZnO nanomaterials and their interaction with biological systems is crucial for manufacturing relevant engineering materials. In the last few years, ZnO nanostructures were also used to functionalize polymer matrices to produce hybrid composite materials with new properties. Among the numerous manufacturing methods, electrospinning is becoming a mainstream technique for the production of scaffolds and mats made of polymeric and metal-oxide nanofibers. In this review, we focus on toxicological aspects and recent developments in the use of ZnO-based nanomaterials for biomedical, healthcare, and sustainability applications, either alone or loaded inside polymeric matrices to make electrospun composite nanomaterials. Bibliographic data were compared and analyzed with the aim of giving homogeneity to the results and highlighting reference trends useful for obtaining a fresh perspective about the toxicity of ZnO nanostructures and their underlying mechanisms for the materials and engineering community.

Submicron Size Schottky Junctions on As-Grown Monolayer Epitaxial Graphene on Ge(100): A Low-Invasive Scanned-Probe-Based Study.

We report on the investigation of the Schottky barrier (SB) formed at the junction between a metal-free graphene monolayer and Ge semiconductor substrate in the as-grown epitaxial graphene/Ge(100) system. In order to preserve the heterojunction properties, we defined submicron size graphene/Ge junctions using the scanning probe microscopy lithography in the local oxidation configuration, a low-invasive processing approach capable of inducing spatially controlled electrical separations among tiny graphene regions. Characteristic junction parameters were estimated from I-V curves obtained using conductive-atomic force microscopy. The current-voltage characteristics showed a p-type Schottky contact behavior, ascribed to the n-type to p-type conversion of the entire Ge substrate due to the formation of a large density of acceptor defects during the graphene growth process. We estimated, for the first time, the energy barrier height in the as-grown graphene/Ge Schottky junction (φB ≈ 0.45 eV) indicating an n-type doping of the graphene layer with a Fermi level ≈ 0.15 eV above the Dirac point. The SB devices showed ideality factor values around 1.5 pointing to the high quality of the heterojunctions.

A label-free impedimetric aptasensor for the detection of Bacillus anthracis spore simulant.

Herein, we report an impedimetric DNA-based aptamer sensor for a single-step detection of B. anthracis spore simulant (B. cereus spore). Specifically, we designed a miniaturized label-free aptasensor for B. cereus spores based on a gold screen-printed electrode functionalized with B. cereus spores-binding aptamer (BAS-6R). Several parameters were optimized to fabricate the aptasensor such as the concentration of DNA aptamer solution (0.5 µM), the time (48 h), the temperature (4 °C), and the pH (7.5) for aptamer immobilization on the working electrode surface. Once the aptasensor was developed, it was tested against B. cereus spores 14579 evaluating the effect of incubation time and MgCl2 concentration. Under the optimized conditions (incubation time equal to 3 h and absence of MgCl2), B. cereus spores 14579 were detected with a linear range between 104 CFU/ml and 5 × 106 CFU/ml and a detection limit of 3 × 103 CFU/ml. Furthermore, the study of selectivity toward B. cereus 11778, B. subtilis, Legionella pneumophila, and Salmonella Typhimurium has demonstrated the capability of this sensor to detect B. cereus spores, proving the suitability of the DNA-based sensing element combined with a portable instrument for a label-free measurement on site of B. anthracis spore simulant.

Analysis of Polycaprolactone Microfibers as Biofilm Carriers for Biotechnologically Relevant Bacteria.

Polymeric electrospun fibers are becoming popular in microbial biotechnology because of their exceptional physicochemical characteristics, biodegradability, surface-to-volume ratio, and compatibility with biological systems, which give them a great potential as microbial supports to be used in production processes or environmental applications. In this work, we analyzed and compared the ability of Escherichia coli, Pseudomonas putida, Brevundimonas diminuta, and Sphingobium fuliginis to develop biofilms on different types of polycaprolactone (PCL) microfibers. These bacterial species are relevant in the production of biobased chemicals, enzymes, and proteins for therapeutic use and bioremediation. The obtained results demonstrated that all selected species were able to attach efficiently to the PCL microfibers. Also, the ability of pure cultures of S. fuliginis (former Flavobacterium sp. ATCC 27551, a very relevant strain in the bioremediation of organophosphorus compounds) to form dense biofilms was observed for the first time, opening the possibility of new applications for this microorganism. This material showed to have a high microbial loading capacity, regardless of the mesh density and fiber diameter. A comparative analysis between PCL and polylactic acid (PLA) electrospun microfibers indicated that both surfaces have a similar bacterial loading capacity, but the former material showed higher resistance to microbial degradation than PLA.

Single cell versus large population analysis: cell variability in elemental intracellular concentration and distribution.

The quantification of elemental concentration in cells is usually performed by analytical assays on large populations missing peculiar but important rare cells. The present article aims at comparing the elemental quantification in single cells and cell population in three different cell types using a new approach for single cells elemental analysis performed at sub-micrometer scale combining X-ray fluorescence microscopy and atomic force microscopy. The attention is focused on the light element Mg, exploiting the opportunity to compare the single cell quantification to the cell population analysis carried out by a highly Mg-selective fluorescent chemosensor. The results show that the single cell analysis reveals the same Mg differences found in large population of the different cell strains studied. However, in one of the cell strains, single cell analysis reveals two cells with an exceptionally high intracellular Mg content compared with the other cells of the same strain. The single cell analysis allows mapping Mg and other light elements in whole cells at sub-micrometer scale. A detailed intensity correlation analysis on the two cells with the highest Mg content reveals that Mg subcellular localization correlates with oxygen in a different fashion with respect the other sister cells of the same strain. Graphical abstract Single cells or large population analysis this is the question!

Where is it and how much? Mapping and quantifying elements in single cells.

The biological function of a chemical element in cells not only requires the determination of its intracellular quantity, but also the spatial distribution of its concentration. Different strategies can be employed to quantify and map the intracellular concentration of elements in single cells. The assessment of the intracellular elemental concentration, which is the relevant information, requires the measurement of cell volume. This challenging and demanding task requires combining different techniques allowing gathering of both morphological and compositional information on the same cell. Moreover, the need to analyse samples more similar to their natural state requires complex hardware equipment, and supplementary efforts in preparation protocols. Nevertheless, the response to the question: "where is it and how much?" is worth all these efforts. This review aims at providing an insight into the recent and most advanced techniques and strategies for quantifying and mapping chemical elements in single cells. We describe and discuss indirect detection techniques (label based) which make use of fluorescent dyes, and direct ones (label free), such as particle induced X-ray emission, proton backscattering spectrometry, scanning transmission ion spectrometry, nano-secondary ion mass spectrometry, X-ray fluorescence microscopy, complemented by X-ray imaging.

Thermal-electric model for piezoelectric ZnO nanowires.

The behavior of ZnO nanowires under uniaxial loading is characterized by means of a numerical model that accounts for all coupled mechanical, electrical, and thermal effects. The paper shows that thermal effects in the nanowires may greatly impact the predicted performance of piezoelectric and piezotronic nanodevices. The pyroelectric effect introduces new equivalent volumic charge in the body of the nanowire and surface charges at the boundaries, where Kapitza resistances are located, that act together with the piezoelectric charges to improve the predicted performance. It is shown that the proposed model is able to reproduce several effects experimentally observed by other research groups, and is a promising tool for the design of ultra-high efficient nanodevices.

Graphitic Patterns on CVD Diamond Plate as Microheating/Thermometer Devices.

A simple compact temperature sensor and microheater in a wide temperature range has been developed, realizing a laser-patterned resistive structure on the surface of a synthetic polycrystalline diamond plate. Imaging and spectroscopy techniques used to investigate morphology, structure, and composition of the pattern showed that it incorporates different nondiamond carbon phases. Transport experiments revealed the semiconducting behavior of this microresistor. Thermal power measurements versus temperature are presented. A possible application of this device that may easily match compact experimental layouts avoiding both thermal anchoring offset and mechanical stress between sample and sensor is discussed. The patterned structure undergoes testing as a microthermometer, providing fast response and excellent stability versus time. It exhibits a good sensitivity that coupled to an easy calibration procedure minimizes errors and guarantees high accuracy. Plot of temperature versus input power of the resistive patterned line used as microheater shows a linear behavior in an extended temperature range.

Easy to use plastic optical fiber-based biosensor for detection of butanal.

The final goal of this work is to achieve a selective detection of butanal by the realization of a simple, small-size and low cost experimental approach. To this end, a porcine odorant-binding protein was used in connection with surface plasmon resonance transduction in a plastic optical fiber tool for the selective detection of butanal by a competitive assay. This allows to reduce the cost and the size of the sensing device and it offers the possibility to design a "Lab-on-a-chip" platform. The obtained results showed that this system approach is able to selectively detect the presence of butanal in the concentration range from 20 µM to 1000 µM.