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Photonic resonance modes can be spectrally coupled to the vibrational modes of molecules in the mid‐infrared regime through interactions between localized electric fields and nearby molecules. According to recent studies, radiative loss engineering of coupled systems is a promising approach for tailoring coupling conditions and enhancing the molecular signals. However, this strategy has only been realized using the localized surface plasmon resonances of metal nanostructures, which suffer from increased ohmic loss in the mid‐infrared region and face serious limitations in achieving high quality (Q) factors. In this study, silicon‐based metasurfaces formed on silicon‐on‐insulator wafers are adopted to achieve high Q factors and tune the coupling conditions between the quasi‐bound states in the continuum (qBICs) and molecular vibrations. The coupling between the resonance mode and polymethyl methacrylate molecules is tailored from weak to strong coupling regimes by simply changing the structural asymmetry parameter and utilizing the intrinsically high Q factors of the qBIC modes. In addition, the optimal asymmetry parameter that maximizes the enhanced molecular signal is identified, opening a route toward realizing highly sensitive surface‐enhanced infrared spectroscopy using complementary metal–oxide–semiconductor compatible all‐dielectric materials. [ABSTRACT FROM AUTHOR]

Surface enhanced infrared absorption (SEIRA) spectroscopy is a powerful tool in which plasmonically enhanced electromagnetic fields provide high‐sensitivity molecular detection. Most SEIRA platforms operate at a single resonant frequency, which must be tuned to match that of the target molecule, and commonly rely on time‐consuming lithographic techniques. This study presents a high‐throughput and cost‐effective plasmonic metasurface for broadband, tunable, and strong infrared signal enhancement. The platform is built upon the principle of dispersion‐engineered plasmonic Fabry–Pérot (FP) nanocavity arrays. It offers 1) tight squeezing of infrared (IR) photons into deep sub‐wavelength nano‐volumes and 2) spectrally tunable near‐field enhancements of up to ≈106, two to three orders of magnitude higher than most optical metasurface systems. By coupling multilayer nano‐thin film deposition and nanoskiving fabrication techniques, the dispersive FP metasurfaces can be rapidly and reproducibly constructed in a scalable and lithography‐free manner. Using IR spectroscopy, the selective and sensitive label‐free detection of a molecular monolayer is achieved at a range of frequencies. An enhancement factor of nearly 105 is measured at the carbonyl (C = O) vibrational marker band of the molecule. The confluence of high field enhancement, broadband plasmonic response, and facile fabrication makes this metasurface a promising platform for SEIRA spectroscopy. [ABSTRACT FROM AUTHOR]

Surface enhanced infrared absorption (SEIRA) is an experimental method where trace amount of a compound can be detected with high sensibility. This high detection sensibility is the result of the interaction of the molecules with a localized plasmon, usually from a metallic nanoparticle. In this study we numerically investigate by discrete dipole approximation the origin of the Fano-like response of the system, including the induced transparency when the plasmon resonance and the molecular vibrational mode coincide. The detailed analysis of the localization of the absorption shows that the modification of the absorption cross-section when the molecule is present comes from a change of the plasmonic resonance, not from the direct molecular response which is negligible. This sheds a new light on the SEIRA mechanism. In particular, it demonstrates that the sensibility is associated with the influence of the molecule on the plasmon resonance rather than with the local field enhancement itself.

Abstract Background Extracellular Vesicles (EVs) are sub-micrometer lipid-bound particles released by most cell types. They are considered a promising source of cancer biomarkers for liquid biopsy and personalized medicine due to their specific molecular cargo, which provides biochemical information on the state of parent cells. Despite this potential, EVs translation process in the diagnostic practice is still at its birth, and the development of novel medical devices for their detection and characterization is highly required. Results In this study, we demonstrate mid-infrared plasmonic nanoantenna arrays designed to detect, in the liquid and dry phase, the specific vibrational absorption signal of EVs simultaneously with the unspecific refractive index sensing signal. For this purpose, EVs are immobilized on the gold nanoantenna surface by immunocapture, allowing us to select specific EV sub-populations and get rid of contaminants. A wet sample-handling technique relying on hydrophobicity contrast enables effortless reflectance measurements with a Fourier-transform infrared (FTIR) spectro-microscope in the wavelength range between 10 and 3 µm. In a proof-of-principle experiment carried out on EVs released from human colorectal adenocarcinoma (CRC) cells, the protein absorption bands (amide-I and amide-II between 5.9 and 6.4 µm) increase sharply within minutes when the EV solution is introduced in the fluidic chamber, indicating sensitivity to the EV proteins. A refractive index sensing curve is simultaneously provided by our sensor in the form of the redshift of a sharp spectral edge at wavelengths around 5 µm, where no vibrational absorption of organic molecules takes place: this permits to extract of the dynamics of EV capture by antibodies from the overall molecular layer deposition dynamics, which is typically measured by commercial surface plasmon resonance sensors. Additionally, the described metasurface is exploited to compare the spectral response of EVs derived from cancer cells with increasing invasiveness and metastatic potential, suggesting that the average secondary structure content in EVs can be correlated with cell malignancy. Conclusions Thanks to the high protein sensitivity and the possibility to work with small sample volumes—two key features for ultrasensitive detection of extracellular vesicles- our lab-on-chip can positively impact the development of novel laboratory medicine methods for the molecular characterization of EVs. Graphical Abstract

Graphene nanostructures, exhibiting tunable and nanoscale‐confined mid‐infrared (mid‐IR) plasmons, prevail as a powerful spectroscopic platform for novel surface‐enhanced molecular identification. Particularly, graphene shows exciting opportunities for biosensing applications due to its versatile functionalization methods with different biomolecular building blocks (e.g., enzymes, proteins, and DNA). Here, a quantitative bioassay based on the mid‐IR localized surface plasmon resonance (LSPR) modulation in functionalized graphene nanostructures is demonstrated. Specifically, vitamin B12 (vB12) using the specific recognition elements on modified graphene nanoribbons (i.e., pyrene linkers via π − π stacking + anti‐vB12 antibody fragments via amide bond) is detected. Different concentrations of vB12 spotted on an arrayed panel of a single chip are quantified by the graphene LSPR shifts, where a limit of detection (LOD) of 53.5 ng mL−1 is obtained. The upscaling potential of the bioassay using large area nanostructured graphene films produced by nanoimprinting 2D hole arrays is illustrated. The integration of quantitative bioassay with scalable graphene nanostructures shows promising routes of graphene‐based mid‐IR platforms toward prospective industrial applications. [ABSTRACT FROM AUTHOR]

Abstract Graphene nanostructures, exhibiting tunable and nanoscale‐confined mid‐infrared (mid‐IR) plasmons, prevail as a powerful spectroscopic platform for novel surface‐enhanced molecular identification. Particularly, graphene shows exciting opportunities for biosensing applications due to its versatile functionalization methods with different biomolecular building blocks (e.g., enzymes, proteins, and DNA). Here, a quantitative bioassay based on the mid‐IR localized surface plasmon resonance (LSPR) modulation in functionalized graphene nanostructures is demonstrated. Specifically, vitamin B12 (vB12) using the specific recognition elements on modified graphene nanoribbons (i.e., pyrene linkers via π − π stacking + anti‐vB12 antibody fragments via amide bond) is detected. Different concentrations of vB12 spotted on an arrayed panel of a single chip are quantified by the graphene LSPR shifts, where a limit of detection (LOD) of 53.5 ng mL−1 is obtained. The upscaling potential of the bioassay using large area nanostructured graphene films produced by nanoimprinting 2D hole arrays is illustrated. The integration of quantitative bioassay with scalable graphene nanostructures shows promising routes of graphene‐based mid‐IR platforms toward prospective industrial applications.

Background: Extracellular Vesicles (EVs) are sub-micrometer lipid-bound particles released by most cell types. They are considered a promising source of cancer biomarkers for liquid biopsy and personalized medicine due to their specific molecular cargo, which provides biochemical information on the state of parent cells. Despite this potential, EVs translation process in the diagnostic practice is still at its birth, and the development of novel medical devices for their detection and characterization is highly required. Results: In this study, we demonstrate mid-infrared plasmonic nanoantenna arrays designed to detect, in the liquid and dry phase, the specific vibrational absorption signal of EVs simultaneously with the unspecific refractive index sensing signal. For this purpose, EVs are immobilized on the gold nanoantenna surface by immunocapture, allowing us to select specific EV sub-populations and get rid of contaminants. A wet sample-handling technique relying on hydrophobicity contrast enables effortless reflectance measurements with a Fourier-transform infrared (FTIR) spectro-microscope in the wavelength range between 10 and 3 µm. In a proof-of-principle experiment carried out on EVs released from human colorectal adenocarcinoma (CRC) cells, the protein absorption bands (amide-I and amide-II between 5.9 and 6.4 µm) increase sharply within minutes when the EV solution is introduced in the fluidic chamber, indicating sensitivity to the EV proteins. A refractive index sensing curve is simultaneously provided by our sensor in the form of the redshift of a sharp spectral edge at wavelengths around 5 µm, where no vibrational absorption of organic molecules takes place: this permits to extract of the dynamics of EV capture by antibodies from the overall molecular layer deposition dynamics, which is typically measured by commercial surface plasmon resonance sensors. Additionally, the described metasurface is exploited to compare the spectral response of EVs derived from cancer cells with increasing invasiveness and metastatic potential, suggesting that the average secondary structure content in EVs can be correlated with cell malignancy. Conclusions: Thanks to the high protein sensitivity and the possibility to work with small sample volumes—two key features for ultrasensitive detection of extracellular vesicles- our lab-on-chip can positively impact the development of novel laboratory medicine methods for the molecular characterization of EVs. [ABSTRACT FROM AUTHOR]

• Unique quantitative data concerning mercaptosuccinic acid (MSA) adsorption at Au(111) electrode were determined as a function of pH and the electrode potential. • Surface enhanced IR spectroscopy demonstrated that totally protonated MSA is adsorbed at pH<2 and totally deprotonated at pH>4. • Analysis of integrated intensity of the symmetric and asymmetric carbonyl stretch bands showed that MSA assumes nearly perpendicular at pH<2 and a tilted orientation at pH>4. The adsorption of mercaptosuccinic acid (MSA) on the Au (111) surface in 0.1 M HClO 4 and 0.1 M NaOH aqueous solution was examined with electrochemical methods and in situ FTIR spectroscopy. Surface concentrations of MSA molecules at the air-solution interface were determined. The horizontal touch method was used to transfer a known amount of MSA molecules from the air-solution interface onto the gold electrode surface. Chronocoulometry was then applied to determine the amount of charge flowing to the surface and the charge number per adsorbed molecule (the electrosorption valency). The electrosorption valency was used to calculate the amount of adsorbed species from charge densities measured for monolayers assembled overnight from solutions of different pH. Their values change from ∼3.9 × 10−10 mol/cm2 at pH ≤ 2.3 to ∼2.0 × 10−10 mol/cm2 at pH ≥ 4.2 and correspond to the area 0.42 and 0.81 nm2/molecule (or 42 and 81 Å2/ molecule), respectively. The IR spectra (SEIRAS) reveal that adsorbed MSA molecules are fully protonated at pH≤2.3 and fully deprotonated at pH≥4.2. The integrated intensities of the IR bands were used to determine the tilt angle between the direction of all trans-axis of the MSA molecule and surface normal. It is equal to 24 ± 5° for monolayer in 0.1 M HClO 4 and to 41 ± 5o in 0.1 M NaOH. The tilt angle data are consistent with the vertical and tilted orientations of MSA molecules determined from the surface coverage data. [Display omitted] [ABSTRACT FROM AUTHOR]

While infrared spectroscopy is a powerful technique that provides molecular information such as chemical constituents and chemical structures of analytes, it suffers from low absorption cross-section resulting in low sensitivity and poor signal-to-noise or signal-to-background ratios. Surface-enhanced infrared absorption (SEIRA) spectroscopy, which is supported by nanometer scale structures, is a promising technology to overcome these problems in conventional infrared (IR) spectroscopy and enhances IR signals using the field enhancement properties of surface plasmon resonance. Recently resonant SEIRA technique was proposed, and signal enhancement factor was significantly improved. In this review, we present an overview of the recent progresses on resonant SEIRA technologies including nanoantenna- and metamaterial-based SEIRA, and also SEIRA techniques with nanoimaging capabilities.

Metasurfaces can enable the confinement of electromagnetic fields on huge surfaces and zones, and they can thus be applied to biochemical sensing by using surface-enhanced Raman scattering (SERS) and surface-enhanced infrared absorption (SEIRA). Indeed, these metasurfaces have been examined for SERS and SEIRA sensing thanks to the presence of a wide density of hotspots and confined optical modes within their structures. Moreover, some metasurfaces allow an accurate enhancement of the excitation and emission processes for the SERS effect by supporting resonances at frequencies of these processes. Finally, the metasurfaces allow the enhancement of the absorption capacity of the solar light and the generation of a great number of catalytic active sites in order to more quickly produce the surface reactions. Here, we outline the latest advances in metasurfaces for SERS and SEIRA sensors as well as photocatalysis. [ABSTRACT FROM AUTHOR]

Because of the localized surface plasmon resonance (LSPR), molecules adsorbed at the surfaces of the metallic nanostructures exhibit a strongly enhanced electric field. The enhanced field around the nanoscale morphology amplifies the Raman scattering signal and excites the local field across the infrared (IR) vibrational modes, enabling high-sensitivity chemical and biological sensing. Herein, we achieve strong enhancement in surface-enhanced Raman and IR absorption (SERS and SEIRA) spectroscopies with scalable nanocomposite substrates, consisting of ultrathin nanoscale plasmonic Ag-SiO2 films fabricated by cosputtering. The plasmonic hotspots of a 25-nm-thick nanocomposite film successfully amplify the SERS and SEIRA signals of methylene blue with ultralow detection of 10–10 M in the SERS mode. The LSPRs of topping silver particles and near-field plasmonic coupling among the neighboring granular silver nanoparticles and topping particle make a combinatorial impact and lead to signal enhancement, with a predicted factor of up to 109 orders of magnitude for Raman scattering and 102 under the IR vibrational modes. These simple nanocomposite films with a high density of plasmonic hotspots are highly suitable as sensors-on-a-chip for label-free chemical and biomolecular identification with outstanding performance. [ABSTRACT FROM AUTHOR]

In this paper, silver nanoparticles (AgNPs) were prepared as enhanced substrates for the detection of glutathione in dairy products by polyol reduction of silver nitrate. The infrared spectra were collected and analyzed by surface-enhanced infrared absorption spectroscopy (SEIRA) method of transmission mode using a cell of calcium fluoride window sheet immobilization solution for the study. The disappearance of the thiol (–SH) absorption peak in the infrared spectrum, and the shift of its characteristic absorption peak when glutathione was bound to AgNPs solvate indicated the Ag–S bond interaction and the aggregation of AgNPS. AgNPs accumulate to form “hot spots”, resulting in enhanced electromagnetic fields and thus enhanced infrared signals of glutathione. The intensity of the characteristic absorption peak at 1,654 cm−1 (carbonyl C=O bond stretching) was used for the quantitative analysis of glutathione. After optimizing the conditions, glutathione content in pretreated pure milk and pure ewe's milk was determined using AgNPs in combination with SEIRA. Good linearity was obtained in the range of 0.02–0.12 mg/mL with correlation coefficients (R2) of 0.9879 and 0.9833, respectively, and LOD of 0.02 mg/mL with average spiked recoveries of 101.3 and 92.5%, respectively. The results show that the method can be used for accurate determination of glutathione content in common dairy products.

Keywords: infrared spectroscopy; nano-imaging; nanostructure; metamaterials; SEIRA; surface plasmons EN infrared spectroscopy nano-imaging nanostructure metamaterials SEIRA surface plasmons 2541 2561 21 05/19/22 20220601 NES 220601 1 Introduction Spectroscopy is a powerful optical and photonic technique. This is because AFM-IR has a high sensitivity to IR absorption inside the entire nanostructure, whereas s-SNOM exhibits surface sensitivity on the IR absorption of nanostructures. 2.2 Dielectric nanostructures All-dielectric nanostructures with a high refractive index have recently emerged as an alternative to plasmonic nanostructures for highly sensitive SEIRA spectroscopy. Since it is difficult to separate these two topics, we categorize SEIRA supported by simple nanoantenna structures or having broad and weak plasmonic absorption bands as nanoantenna-based SEIRA, and that using rather complicated or artificial structures and strong resonant absorption close to unity is categorized as metamaterial-based SEIRA. On the other hand, AFM-IR mechanically probes the IR absorption of a sample and transduces IR absorption signals using sharp metallic or dielectric tips in the near-field, unlike s-SNOM that optically probes the IR absorption of samples. [Extracted from the article]

[Display omitted] • A green, fast, and effective multivariate method for determine atrazine with ATR-IR; • Ag 2 Se stabilized with mercaptopropionic acid quantum dots as substrate for SEIRA analysis; • SEIRA strategy proved to be able to enhance the atrazine signal up to 86-fold; • SEIRA detection of ATZ at concentrations as low as 0.001 µg/mL; A green, fast and effective multivariate method for the determination of atrazine (ATZ) was developed using conventional infrared equipment furnished with an attenuated total reflectance module (ATR-IR), providing limit of detection (LOD) and limit of quantification (LOQ) in the ranges from 1.9 to 4.6 µg/mL and from 5.6 to 14 µg/mL, respectively. Furthermore, the surface-enhanced infrared absorption (SEIRA) approach was investigated to improve the sensitivity of the measurements and detect ATZ at low concentrations, addressing the compatibility with reference methods. To this end, a substrate formed by silver selenide quantum dots stabilized with mercaptopropionic acid (Ag 2 Se/MPA), synthesized in aqueous medium by an one-pot synthesis, was used. The spectral data were investigated by univariate and multivariate calibrations, allowing to calculate the enhancement factor (EF) and the multivariate enhancement factor (MEF), respectively. The SEIRA strategy proved to be able to enhance the atrazine signal up to 86-fold, allowing the detection of ATZ at concentrations as low as 0.001 µg/mL. [ABSTRACT FROM AUTHOR]

[Display omitted] • Novel chlorpromazine conjugates with gold nanoparticles were prepared in an electrostatically-driven self-organization process. • pH-dependent electrokinetic properties of chlorpromazine conjugates with gold nanoparticles were determined. • The chemical structure of chlorpromazine deposited on gold nanoparticles was determined using SERS and SEIRA. • The stability of novel conjugates under controlled conditions of pH was confirmed based on spectroscopic and electrokinetic investigations. Scientific studies have demonstrated that conjugates of anticancer drugs with metal nanoparticles (MeNPs) lead to a more effective deactivation of tumor cells compared to free drugs. Similarly, it has been established that conjugates of antibiotics with MeNPs exhibit higher biocidal activity against bacteria than their unbound counterparts. However, limited information is available regarding conjugates formed from drugs other than anticancer and antibiotics. Therefore, our research aims to develop synthesis methods for conjugates of chlorpromazine (CPZ), a neuroleptic, with gold nanoparticles (AuNPs). CPZ-AuNP conjugates were prepared through a ligand exchange reaction conducted on the surface of quasi-spherical, negatively charged citrate-stabilized TC-AuNPs with an average size of 55 ± 5 nm. UV–vis spectroscopy was employed to determine the stability range of the conjugates under controlled conditions of pH and ionic strength. Based on electrokinetic measurements, it was observed that the zeta potential of CPZ-AuNP conjugates strongly depends on the amount of CPZ adsorbed on the TC-AuNP surface. Additionally, the conjugates exhibited an isoelectric point at pH 8.8. Surface-enhanced Raman spectroscopy (SERS) and surface-enhanced infrared absorption spectroscopy (SEIRA) were employed to elucidate the adsorption structure of CPZ on TC-AuNPs. The interpretation of the spectra was conducted based on the Raman and FTIR spectra of CPZ, along with calculations performed using Density Functional Theory (DFT). The results indicated that CPZ primarily interacts with the TC-AuNP surface through the angularly oriented phenothiazine ring and the propylene bridge. Furthermore, it was demonstrated that the C-N-C fragment is perpendicular to the surface of the TC-AuNP with which it interacts. The findings from this analysis suggest the potential for further research on the use of these conjugates in biomedical applications. [ABSTRACT FROM AUTHOR]

An approach which allows both electrochemical studies and surface enhanced infrared characterization of electrodeposited Cytochrome C is presented. This approach is based on in-plane disordered arrays of resonant slits engraved in Au substrates using focused ion beam. For light-polarized perpendicular to the slit, the reflectivity spectra of the slit arrays show dips related to the excitation of the slit plasmon resonance, whose position depends on the slit length. Due to the presence of the continuous Au layer around the slits, the very same substrates can be used to perform electrochemical studies. By varying the slit length, we have tuned the plasmon resonance to match the absorption bands of electrodeposited Cytochrome C, demonstrating the detection of minute amounts of this protein, all the way down to a single monolayer. [ABSTRACT FROM AUTHOR]

The increasing demand for more reliable and cost effective biosensors has steered development of various novel biosensor platforms. Sensors based on optical techniques have attracted much attention because of their advantages, such as immune to electromagnetic interference, multiplex and cost effective. Surface enhanced infrared absorption (SEIRA) is a powerful vibrational label-free analytical technique that has benefited from collective excitation of surface plasmon to enhance vibrational signals of thin molecular layers. Owing to surface plasmon phenomenon to enhanced vibrational signal, SEIRA has attracted much research attention t as an alternate promising biosensor platforms and in recent years, continuous SEIRA sensing platforms are emerging. In this brief review, we outline the principle of SEIRA, in particular, theoretical models that give insight into the light interactions with plasmonic nanostructures and the coupling between nanostructures and vibrational molecules. With this, commonly used active SEIRA substrates and their optimization methods are discussed, ranging from materials, geometrical design and commonly used fabrication methods. Also discussed are advancements in analytical applications of SEIRA and brief future perspectives on SEIRA sensing platform.

Absorption, scattering, and fluorescence are processes that increase with electric field intensity. The most prominent way to enhance electric field intensity is to use localized or propagating surface plasmon polaritons (SPPs) based on metallic particles and nanostructures. In addition, several other, much less well-known, photonic structures that increase electric field intensity exist. Interference enhancement provided by thin dielectric coatings on reflective substrates is able to provide electric field intensity enhancement over the whole substrate and not only at certain hotspots, thereby being in particular suitable for the spectroscopy of thin surface layers. The same coatings on high refractive index substrates may be used for interference-enhanced total internal reflection-based spectroscopy in much the same way as Kretschmann or Otto configuration for exciting propagating SPPs. The latter configurations can also be used to launch Bloch surface waves on 1D photonic crystal structures for the enhancement of electric field intensity and thereby absorption, scattering, and fluorescence-based spectroscopies. High refractive index substrates alone can also, when nanostructured, enhance infrared absorption or Raman scattering via Mie-type resonances. As a further method, this review will cover recent developments to employ phonon polaritons in the reststrahlen region.

Metasurfaces can enable the confinement of electromagnetic fields on huge surfaces and zones, and they can thus be applied to biochemical sensing by using surface-enhanced Raman scattering (SERS) and surface-enhanced infrared absorption (SEIRA). Indeed, these metasurfaces have been examined for SERS and SEIRA sensing thanks to the presence of a wide density of hotspots and confined optical modes within their structures. Moreover, some metasurfaces allow an accurate enhancement of the excitation and emission processes for the SERS effect by supporting resonances at frequencies of these processes. Finally, the metasurfaces allow the enhancement of the absorption capacity of the solar light and the generation of a great number of catalytic active sites in order to more quickly produce the surface reactions. Here, we outline the latest advances in metasurfaces for SERS and SEIRA sensors as well as photocatalysis.

[Display omitted] • Extracellular vesicles sparked large interest as nanosized biological messengers. • EV characterization presents challenges due to their multifaceted heterogeneity. • Mid-IR spectroscopy provides a label-free biochemical fingerprint of EVs. • Literature is revised, highlighting emerging IR technologies and Machine Learning. • An extensive collection of spectral peaks assigned to EVs is reported. Extracellular vesicles (EVs) are lipid vesicles secreted by all cells into the extracellular space and act as nanosized biological messengers among cells. They carry a specific molecular cargo, composed of lipids, proteins, nucleic acids, and carbohydrates, which reflects the state of their parent cells. Due to their remarkable structural and compositional heterogeneity, characterizing EVs, particularly from a biochemical perspective, presents complex challenges. In this context, mid-infrared (IR) spectroscopy is emerging as a valuable tool, providing researchers with a comprehensive and label-free spectral fingerprint of EVs in terms of their specific molecular content. This review aims to provide an up-to-date critical overview of the major advancements in mid-IR spectroscopy of extracellular vesicles, encompassing both fundamental and applied research achievements. We also systematically emphasize the new possibilities offered by the integration of emerging cutting-edge IR technologies, such as tip-enhanced and surface-enhanced spectroscopy approaches, along with the growing use of machine learning for data analysis and spectral interpretation. Additionally, to assist researchers in navigating this intricate subject, our manuscript includes a wide and detailed collection of the spectral peaks that have been assigned to EV molecular constituents up to now in the literature. [ABSTRACT FROM AUTHOR]

Detecting the building blocks of all living organisms plays a vital role in medical diagnosis and biological research. Infrared (IR) spectroscopy is one of the techniques for detecting biomolecules, such as DNA, RNA, and lipids, through their vibrational fingerprints. IR spectroscopy provides biosensing by directly measuring changes in absorption spectra; however, nanometric-size molecules reveal a weak signal-to-noise ratio with IR light, which is a disadvantage for sensitive bio-detection. Surface-Enhanced Infrared Spectroscopy (SEIRA) based on different structures and materials has been widely used to overcome this problem. In this study, a SEIRA platform based on a hybrid graphene-metal nanoantenna array is designed by combining the enhanced sensitivity of graphene with its electrical tunability and strong-field enhancement with metallic structures. The plasmonic resonance of graphene nano-slit is dynamically tuned to detect fingerprints of protein monolayer at different frequencies. The same detection behavior has been statically demonstrated by metallic antennas. Our results indicate that the sensitivity of the SEIRA sensor platform is quite high due to the combination of graphene and metal hybrid structure compared to the metal resonator alone because of the strong light confinement in the graphene layer. The proposed biosensor can detect the Amid-I and Amid-II bonds, which create relatively strong vibrational fingerprints, as well as the Amide-III bond, which is a very weak bond of a monolayer protein-goat-mouse Immunoglobulin (IgG) protein. It can also be a very useful characterization tool for identifying the molecular fingerprints of unknown chemicals and molecules with its capability to span a large spectral range either dynamically or statically. The strong light absorption via metallic structures compensates for the large areal coverage of graphene sheets, which is quite a challenge for dynamic tuning in real applications. • A graphene-metal hybrid biosensor that consists of an array of H-shaped nanoantennas and graphene layers on top of dielectric-metal layers has been introduced to detect protein goat anti-mouse immunoglobin G (IgG). • Our hybrid biosensor platform is tunable and capable of sensing Amid-I, II, and III bands effectively. • Biomolecular detection can be achieved in a broader spectral range to detect even the weakest vibrational mode of the Amide-III bond along with the other two Amide bonds. • Our proposed platform exhibits two orders of magnitude sensitivity compared to metal-based sensors due to the combination of strong field enhancement in the metal with the strong spatial confinement of graphene plasmons. • The proposed structure offers dynamic tuning via the graphene layer to adjust the resonance frequency of the device for detecting different molecular fingerprints, which is impossible with metallic plasmonics. [ABSTRACT FROM AUTHOR]

The past two decades have seen the full expansion of all fields of Nanotechnology, Chemometrics, Recycling, and Vibration spectroscopy into most of the research areas. The proposed method involves the harmonization of the previously mentioned fields as a vital tool to fulfill the concepts of sustainability and green analytical chemistry. This may reduce the negative impact of analytical laboratory activities on the surrounding environment and enables the implementation of sustainable development principles to analytical laboratories. This work compares the performance of surface enhanced infrared spectroscopy (SEIRA) with traditional chromatographic techniques for quantification of active pharmaceutical ingredients concerning the twelve principles of green analytical chemistry. The used aluminum TLC slides were recycled to be used as a SEIRA substrate. Citrate capped silver nanoparticles were synthesized via one step chemical reduction method, characterized, and deposited on the surface of the recycled aluminum TLC slides to be used as an active mid-infrared surface for quantification of the active pharmaceutical ingredient's combinations. SEIRA coupled with PLSR chemometric tool was developed, validated and successfully applied to mixtures having diverged concentration ranges (5, 30 and 500 μg ml−1) of Pholcodine, Pseudoephedrine and Paracetamol, respectively. Pholcodine is a synthetic or semi-synthetic opium alkaloid that derived from morphine. Pseudoephedrine is a sympathomimetic agent that is prohibited in sports competitions by the world antidoping agency at certain concentration levels. Paracetamol has analgesic and antipyretic actions. After optimization of the method parameters and number of latent factors, a good linear calibration model of the PLSR strategy was obtained as indicated by the lowest root mean square error of calibration and prediction obtained and the regression coefficients R2 of 0.9912, 0.9888, and 0.9992, respectively. The calibration ranges for the three drugs in their pharmaceutical combinations was 2.5–12.5, 15–75 and 200–600 μg ml−1, respectively. The method showed high resolving power for the three drugs in presence of excipients and good recoveries were obtained in a range of 97–102% with relative standard deviation < 2. The developed lab on a chip SEIRA analyzer in comparison to the traditional chromatographic techniques does not only fulfill the twelve principles of GAC but also it combines the merits of high throughput straightforward fingerprint analyzers, portable to measure samples on its place, cost effective, reduced sample volume and solvent consumption, coupled with intelligent chemometric tools to analyze multiple samples, reduced trials and time to get results. Image 1 • Surface enhanced infrared spectroscopy coupled to chemometric tools for quantification of pharmaceutical combinations. • One step synthesis of citrate capped silver nanoparticles. and its characterization using different techniques • A cost-effective substrate was prepared using the nanoparticles deposited on recycled aluminum TLC plates. • The method has been applied for quantification of pholcodine, pseudoephedrine and paracetamol pharmaceutical combinations. • The opportunities for SEIRA to fulfill the twelve principles of GAC in comparison to traditional techniques were discussed. [ABSTRACT FROM AUTHOR]

Seirinae is one of the most diverse subfamilies of Collembola. To date no detailed phylogeny of Seirinae has been proposed, which leads to difficulties in the understanding of evolutionary patterns regarding this taxon. The main aim of this study is to clarify the phylogenetic relationships within the Neotropical Seirinae, by generating and analysing the mitochondrial genomes of 26 terminal taxa of Entomobryidae, and one species of Paronellidae. Specifically, we first generated Illumina HiSeq 2000 shotgun sequence data from each species, then reconstructed the mitochondrial genome of each species using two methods: MitoZ and MIRA/MITOBim. Using these data, we were able to generate a well‐supported phylogeny that combined all the above species as well as three publicly available mitogenomes from other species. Bayesian and maximum likelihood methods were applied using all 13 protein coding genes. In this way, monophyly for the internal groups of Seirinae was obtained based on molecular evidence for the first time, as was the potential validity of three main internal taxa of the subfamily. We furthermore validated that Tyrannoseira is a distinct lineage and propose the elevation of Lepidocyrtinus to genus. Lastly, we anticipate that these newly available mitogenomes will serve as a useful dataset for future studies on the evolution of the Collembola and Hexapoda. [ABSTRACT FROM AUTHOR]

Infrared spectroscopy is widely used technique for observing bioorganic materials, but sometimes scientist have to work with small amount of investigated materials and infrared light interacts poorly with nanometric size molecules. Taking into account unique electro-optical properties of graphene and metal we demonstrated possibility to use metal-graphene nanostructures for label-free detection of thymine. It was shown that IR spectra of thymine adsorbed on the composite nanostructures, such as Au "nanostars" with graphene, is more enhanced than whenthese nanoparticles are used without graphene. The enhancement in IR absorption for complex thymine/Au/graphene depends on size of Au nanoparticlesand thymine's molecular group. [ABSTRACT FROM AUTHOR]

Tailored plasmonic nanoantennas are needed for diverse applications, among those sensing. Surface-enhanced infrared absorption (SEIRA) spectroscopy using adapted nanoantenna substrates is an efficient technique for the selective detection of molecules by their vibrational spectra, even in small quantity. Highly doped semiconductors have been proposed as innovative materials for plasmonics, especially for more flexibility concerning the targeted spectral range. Here, we report on rectangular-shaped, highly Si-doped InAsSb nanoantennas sustaining polarization switchable longitudinal and transverse plasmonic resonances in the mid-infrared. For small array periodicities, the highest reflectance intensity is obtained. Large periodicities can be used to combine localized surface plasmon resonances (SPR) with array resonances, as shown in electromagnetic calculations. The nanoantenna arrays can be efficiently used for broadband SEIRA spectroscopy, exploiting the spectral overlap between the large longitudinal or transverse plasmonic resonances and narrow infrared active absorption features of an analyte molecule. We demonstrate an increase of the vibrational line intensity up to a factor of 5.7 of infrared-active absorption features of vanillin in the fingerprint spectral region, yielding enhancement factors of three to four orders of magnitude. Moreover, an optimized readout for SPR sensing is proposed based on slightly overlapping longitudinal and transverse localized SPR.

Polycyclic aromatic hydrocarbons (PAHs) constitute a class of universally prevalent carcinogenic environmental contaminants. It is increasingly recognized, however, that PAHs derivatized with oxygen, sulfur, or nitrogen functional groups are frequently more dangerous than their unfunctionalized counterparts. This much larger family of chemicals─polycyclic aromatic compounds─PACs─is far less well characterized than PAHs. Using surface-enhanced Raman and IR Absorption spectroscopies (SERS + SEIRA) combined on a single substrate, along with density functional theoretical (DFT) calculations, we show that direct chemical detection and identification of PACs at sub-parts-per-billion concentration can be achieved. Focusing our studies on 9,10-anthraquinone, 5,12-tetracenequinone, 9-nitroanthracene, and 1-nitropyrene as model PAC contaminants, detection is made possible by incorporating a hydroxy-functionalized self-assembled monolayer that facilitates hydrogen bonding between analytes and the SERS + SEIRA substrate. 5,12-Tetracenequinone was detected at 0.3 ppb, and the limit of detection was determined to be 0.1 ppb using SEIRA alone. This approach is straightforwardly extendable to other families of analytes and will ultimately facilitate fieldable chemical detection of these dangerous yet largely overlooked environmental contaminants.

Highlights • An extensive study on Silver - Ge20Se70Te10 film system as a substrate for SEIRA spectroscopy is carried out. • SEIRA response of the system was analyzed by recording FTIR transmission spectra of analyte Hexa Decane Thiol (HDT). • Silver structures were developed on Ge 20 Se 70 Te 10 film via oblique angle deposition and ideal Ag thickness for maximum SEIRA enhancement is found. • The response of the system to variations in the analyte concentration is also explored. Abstract Surface-enhanced infrared absorption (SEIRA) spectroscopy is a powerful tool for characterizing and identifying chemical/biological species. Though SEIRA technique has enabled detection up to few molecule levels with sophisticated device structures, there is still room for improvement (can extend to detect down to a single molecule). Superior sensor platforms can be developed by incorporating advanced substrate material, so as to be actively employed in trace analysis, forensic sciences etc. In this work, chalcogenide glass of composition Ge 20 Se 70 Te 10 is characterized to probe its usability as a SEIRA substrate. Silver island structures were developed on Ge 20 Se 70 Te 10 film via oblique angle deposition and its SEIRA response was recorded using FTIR spectrometer with Hexa Decane Thiol (HDT) as the analyte. Investigations reveal an optimum silver thickness at which maximum absorption enhancement is obtained. The response of the system to variations in the analyte concentration is also explored. Studies prove them to be a promising candidate as an IR substrate which can be used to develop integrated optical waveguide for highly sensitive SEIRA spectroscopy. [ABSTRACT FROM AUTHOR]

In this study, carbon nanodots (CNDs) with excellent aqueous dispersibility, narrow size distribution, and oxygen-rich functional groups have been prepared via a green electrochemical method. Graphite electrodes were directly electrolyzed at ambient temperatures to form uniform CNDs in deionized water, which is free from additional oxidant/reductant. As-synthesized CNDs have been applied to coat an attenuated total reflection (ATR) waveguide enabling surface-enhanced infrared absorption (SEIRA) spectroscopic studies for detecting a variety of analytes in aqueous phase with remarkably enhanced IR band intensities. Finally, the proposed ATR-SEIRA strategy enabled quantitatively analyzing adenine in aqueous solution after optimizing the amount of CNDs, the solution pH, and potential CND aggregation. Graphical abstract [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • A multiband perfect absorber has been demonstrated for SEIRA applications. • A fine-tuning mechanism for optical responses based on geometrical parameters has been theoretically shown. • Sensing capability of the perfect absorber has been theoretically demonstrated for protein layers and polymers. • Experimentally demonstration of SEIRA capability has been shown with a polymer film. Abstract Recently perfect absorbers (PAs) have received significant interest due to their characteristics of complex electric permittivity (ε) and magnetic permeability (μ). By rationally designing these artificial structures, the impedance of the perfect absorber can be matched to free space with an independent adjustment in the electric and magnetic resonances, where this structure leads to strong absorption from mid- to near-IR wavelength. In this article, we proposed a multiband PA platform, which simultaneously operates with a near unity absorption at different resonances that could be an ideal candidate for multiple sensing of molecular fingerprints. We numerically analyzed the dependence of the optical response of the PA platform through finite-difference time domain (FDTD) simulations for a fine-tuning mechanism of the PA platform. We theoretically demonstrated the surface enhanced infrared absorption (SEIRA) capability of our PA platform by studying its optical response with a thin protein bilayer and a polymethyl-methacrylate (PMMA) film. As an initial step we experimentally showed the vibrational modes of a thin PMMA film. We believe, our findings could open new avenues for reliable SERIA platforms through providing multiple vibrational finger print information compared to its conventional counterparts relying only on a single sensing data. [ABSTRACT FROM AUTHOR]

p-Aminothiophenol (PATP) is a preferred molecule in research on surface-enhanced Raman scattering (SERS) because of its unique characteristics of high spectral activity, easily induced charge-transfer (CT), and sensitivity to molecular structural changes. However, some aspects are still unclear, such as the initial steady state of PATP on noble metallic substrates without strong additional excitation with incident and/or induced electromagnetic radiation. Information about the initial steady state, especially the intrinsic CT state, is of great importance to elucidate the dynamic processes of CT and/or molecular structural changes under additional excitation. To investigate the native state of an adsorbed molecule, a suitable probe method that does not disrupt the native state of the whole system, including both molecules and substrates, is required. SERS is not applied in this context because of its use of high-energy visible and near-infrared light. Herein, a low-energy probe method, surface-enhanced infrared-absorption (SEIRA) spectroscopy, is employed as a suitable method for studying the native adsorption state of PATP on silver nanoisland films. The molecular structure and adsorption state were investigated. The intrinsic CT state received particular attention by analyzing the CT-related vibration of B 2 modes. Using Fourier transform infrared (FTIR), transmission SEIRA and reflection SEIRA spectroscopy, we explained why the relative intensities of some bands were different under different conditions. A quasi-standing orientation of PATP adsorbed on the substrates was also confirmed. More importantly, we demonstrated that there is no perceptible CT between PATP and silver nanoisland films; in contrast, CT generally occurs in a disruptive manner in SERS. Density functional theory (DFT) calculations and the selection rules for infrared (IR) transmission and reflection-absorption spectroscopy were used to analyze the spectra throughout the paper. SEIRA proved to be an effective technique to explore the native adsorption state of molecules without the excessive external disturbance induced by excitation. The results are very important in providing insight into molecules in surface-interface chemistry, enhanced spectroscopy and photoelectronics. [ABSTRACT FROM AUTHOR]

Passive proton translocation across membranes through proton channels is generally measured with assays that allow a qualitative detection of the H+-transfer. However, if a quantitative and time-resolved analysis is required, new methods have to be developed. Here, we report on the quantification of pH changes induced by the voltage-dependent proton channel Hv1 using the commercially available pH-sensitive fluorophore Oregon Green 488-DHPE (OG488-DHPE). We successfully expressed and isolated Hv1 from Escherichia coli and reconstituted the protein in large unilamellar vesicles. Reconstitution was verified by surface enhanced infrared absorption (SEIRA) spectroscopy and proton activity was measured by a standard 9-amino-6-chloro-2-methoxyacridine assay. The quantitative OG488-DHPE assay demonstrated that the proton translocation rate of reconstituted Hv1 is much smaller than those reported in cellular systems. The OG488-DHPE assay further enabled us to quantify the KD-value of the Hv1-inhibitor 2-guanidinobenzimidazole, which matches well with that found in cellular experiments. Our results clearly demonstrate the applicability of the developed in vitro assay to measure proton translocation in a quantitative fashion; the assay allows to screen for new inhibitors and to determine their characteristic parameters.ᅟ [ABSTRACT FROM AUTHOR]

In this present work, we have redesigned the well-known Turkevich protocol for promoting versatile galvanic replacement, resulting in the synthesis of hollow Au nanostructures by the sacrificial reduction of HAuCl 4 on the as-prepared Ag nanoparticles in the presence of slight excess NaCl in order to dictate their core size to cavity ratio in a highly reproducible manner. The significance of chloride ion interaction in tuning the size/shape control was corroborated with the contrasting effect of other halide ions, namely bromine and iodine. The structure-property functional relationship of these artificial hollow metal nanostructures were not only established using the systematic optical absorption and TEM measurements, but also through enhanced spectroscopy measurements such as SEIRA and SERS, elucidating the dynamic advantage of hollow nanostructures over and above their solid monometallic counterparts. Further, the familiar 4-NA to p-PDA catalytic reduction kinetics demonstrate the unusual zeroth order characteristics in the presence of hollow metal nanostructures, unequivocally distinguishing it from the common first order characteristics associated with the corresponding solid metal nanoparticles, essentially attributed to the morphology tuned accessible higher total surface area, thus exemplifying the aesthetic compliance for future technological applications. [ABSTRACT FROM AUTHOR]

Nanofluidic devices have offered us fascinating analytical platforms for chemical and bioanalysis by exploiting unique properties of liquids and molecules confined in nanospaces. The increasing interests in nanofluidic analytical devices have triggered the development of new robust and sensitive detection techniques, especially label-free ones. IR absorption spectroscopy is one of the most powerful biochemical analysis methods for identification and quantitative measurement of chemical species in the label-free and non-invasive fashion. However, the low sensitivity and the difficulties in fabrication of IR-compatible nanofluidic devices are major obstacles that restrict the applications of IR spectroscopy in nanofluidics. Here, we realized the bonding of CaF2 and SiO2 at room temperature and demonstrated an IR-compatible nanofluidic device that allowed the IR spectroscopy in a wide range of mid-IR regime. We also performed the integration of metal-insulator-metal perfect absorber metamaterials into nanofluidic devices for plasmon-enhanced infrared absorption spectroscopy with ultrahigh sensitivity. This study also shows a proof-of-concept of the multi-band absorber by combining different types of nanostructures. The results indicate the potential of implementing metamaterials in tracking several characteristic molecular vibrational modes simultaneously, making it possible to identify molecular species in mixture or complex biological entities.

Tailored plasmonic nanoantennas are needed for diverse applications, among those sensing. Surfaceenhanced infrared absorption (SEIRA) spectroscopy using adapted nanoantenna substrates is an efficient technique for the selective detection of molecules by their vibrational spectra, even in small quantity. Highly doped semiconductors have been proposed as innovative materials for plasmonics, especially for more flexibility concerning the targeted spectral range. Here, we report on rectangularshaped, highly Si-doped InAsSb nanoantennas sustaining polarization switchable longitudinal and transverse plasmonic resonances in the mid-infrared. For small array periodicities, the highest reflectance intensity is obtained. Large periodicities can be used to combine localized surface plasmon resonances (SPR) with array resonances, as shown in electromagnetic calculations. The nanoantenna arrays can be efficiently used for broadband SEIRA spectroscopy, exploiting the spectral overlap between the large longitudinal or transverse plasmonic resonances and narrow infrared active absorption features of an analyte molecule. We demonstrate an increase of the vibrational line intensity up to a factor of 5.7 of infrared-active absorption features of vanillin in the fingerprint spectral region, yielding enhancement factors of three to four orders of magnitude. Moreover, an optimized readout for SPR sensing is proposed based on slightly overlapping longitudinal and transverse localized SPR. [ABSTRACT FROM AUTHOR]

A scalable nanofabrication approach for the fabrication of hexagonal packed complementary vertically coupled plasmonic (CVCP) structures for surface-enhanced infrared absorption (SEIRA) applications is reported in this study. This fabrication approach consists of nanosphere lithography, reactive ion etching, and metal deposition and can be implemented on a four-inch wafer scale with low cost and high uniformity. The CVCP structure contains dense plasmonic nanoparticles inside a three-dimensional cavity nanoantenna array. The localized surface plasmon resonance between the top-bottom metallic nanoantenna couple generates a solid localized electric field inside the cavity. A high simulated and experimental SEIRA electric-field enhancement was achieved by optimizing the height of the silicon nanopedestals. Using a representative monolayer octadecanethiol, an enhancement factor of 2.1 × 103 was demonstrated with an optimized structure geometry. When the detection area was extended to square millimeters, the limit of detection of monolayer octadecanethiol on the CVCP substrate reached 10 nM, which is four orders of magnitude lower than that on a flat gold substrate. This study demonstrates a feasible fabrication approach for producing three-dimensional nanoantenna structures with high enhancement factors in a scalable fashion, empowering the practical application of SEIRA substrates. [Display omitted] • Four-inch wafer scale CVCP structure was produced via nanosphere lithography. • Self-assembled metallic nanoparticles on the CVCP structure sidewalls strengthened plasmonic resonance. • Monomolecular octadecanethiol was sensed with a high enhancement of 2.1 × 103 and LOD of 10 nM. [ABSTRACT FROM AUTHOR]

Surface-enhanced infrared absorption (SEIRA) spectroscopy has outstanding potential in chemical detection as a complement to surface-enhanced Raman spectroscopy (SERS), yet it has historically lagged well behind SERS in detection sensitivity. Here we report a new ultrasensitive infrared antenna designed to bring SEIRA spectroscopy into the few-molecule detection range. Our antenna consists of a bowtie-shaped Au structure with a sub-3 nm gap, positioned to create a cavity above a reflective substrate. This three-dimensional geometry tightly confines incident mid-infrared radiation into its ultrasmall junction, yielding a hot spot with a theoretical SEIRA enhancement factor of more than 107, which can be designed to span the range of frequencies useful for SEIRA. We quantitatively evaluated the IR detection limit of this antenna design using mixed monolayers of 4-nitrothiophenol (4-NTP) and 4-methoxythiolphenol (4-MTP). The optimized antenna structure allows the detection of as few as -500 molecules of 4-NTP and -600 molecules of 4-MTP with a standard commercial FTIR spectrometer. This strategy offers a new platform for analyzing the IR vibrations of minute quantities of molecules and lends insight into the ultimate limit of single-molecule SEIRA detection. [ABSTRACT FROM AUTHOR]

The application of attenuated total reflection surface-enhanced infrared absorption spectroscopy (ATR SEIRA) to the analysis of fatty acids on silver nanoparticles was investigated. Attenuated total reflection measurements using four types of internal reflection elements (IREs)--zinc selenide, diamond, silicon, and germanium--were performed for silver nanoparticles modified with fatty acids, and germanium IRE was shown to be suitable for the analysis of silver nanoparticles, even when the sample had a high refractive index. Fatty acids coating the silver nanoparticles could be directly identified by SEIRA enhancement, because both symmetric carboxylate stretching vibration and methylene wagging vibration were strongly detected. Furthermore, the peak positions for methylene wagging vibration differed depending on the carbon number of the fatty acid, so that information from the ATR SEIRA spectra makes it possible to identify substances coating silver nanoparticles. Therefore, ATR SEIRA would appear to have significant potential as a technique for the identification of substances coated on metal nanoparticle surfaces. [ABSTRACT FROM AUTHOR]

In this paper, a disease transmission model of SEIR type with stage structure is proposed and studied. Two kinds of time delays are considered: the first one is the mature delay which divides the population into two stages; the second one is the time lag between birth and being able to move freely, which we call the freely-moving delay. Our mathematical analysis establishes that the global dynamics are determined by the basic reproduction number . If , then the disease free equilibrium is globally asymptotically stable, and the disease will die out. If , then a unique positive equilibrium exists, and is locally asymptotically stable when the freely-moving delay is less than the critical value. We show that increasing this delay can destabilize and lead to Hopf bifurcations and stable periodic solutions. By using the normal form theory and the center manifold theory, we derive the formulae for determining the direction of the Hopf bifurcation and the stability of the bifurcating periodic solutions. Finally, some numerical simulations are carried out to verify the theoretical analysis and some biological implications are discussed. [ABSTRACT FROM AUTHOR]

Doped metal oxides are plasmonic materials that boast both synthetic and postsynthetic spectral tunability. They have already enabled promising smart window and optoelectronic technologies and have been proposed for use in surface enhanced infrared absorption spectroscopy (SEIRA) and sensing applications. Herein, we report the first step toward realization of the former utilizing cubic F and Sn codoped In2O3 nanocrystals (NCs) to couple to the C-H vibration of surface-bound oleate ligands. Electron energy loss spectroscopy is used to map the strong near-field enhancement around these NCs that enables localized surface plasmon resonance (LSPR) coupling between adjacent nanocrystals and LSPR-molecular vibration coupling. Fourier transform infrared spectroscopy measurements and finite element simulations are applied to observe and explain the nature of the coupling phenomena, specifically addressing coupling in mesoscale assembled films. The Fano line shape signatures of LSPR-coupled molecular vibrations are rationalized with two-port temporal coupled mode theory. With this combined theoretical and experimental approach, we describe the influence of coupling strength and relative detuning between the molecular vibration and LSPR on the enhancement factor and further explain the basis of the observed Fano line shape by deconvoluting the combined response of the LSPR and molecular vibration in transmission, absorption and reflection. This study therefore illustrates various factors involved in determining the LSPR-LSPR and LSPR-molecular vibration coupling for metal oxide materials and provides a fundamental basis for the design of sensing or SEIRA substrates. [ABSTRACT FROM AUTHOR]

In this paper, we report on a general method to optimise the optical characteristics of 2D-arrays of plasmonic gold nanoantennas performing as band-pass filter functionalised metasurfaces to be used as high-sensitivity mid-infrared spectroscopic sensors. We demonstrate that it is possible to increase their sensitivity in the detection of chemical and biological substances when the sensors are used in the surface-enhanced infrared absorption (SEIRA) technique. This technique allows revealing the presence of a substance adsorbed on the nanoantennas by measuring its optical absorption under the conditions for which the maximum value of the functionalised metasurface reflectivity occurs at the same wavelength of the substance maximum absorption peak. In particular, numerical simulations based on finite element method of the metasurface detection response demonstrate the possibility to increase the sensor sensitivity of more than four orders of magnitude with respect to that one achievable if the same amount of the substance is deposited on an unstructured planar metal surface. These results can be obtained by acting on the 2D-array periodicity, nanoantenna shape (i.e. rod and cross), size and thickness independently from the wavelength at which the substance absorption occurs. Moreover, in the case of cross-shaped nanoantennas, we report a complete numerical characterisation of the dependence of the metasurface maximum reflectivity and peak wavelength on the variation of the geometrical parameters of both the nanoantennas and the 2D-array. [ABSTRACT FROM AUTHOR]

Surface enhanced infrared absorption spectroscopy (SEIRAS) with attenuated total reflection (ATR) configuration has been used to determine bovine serum albumin (BSA) protein adsorbed onto bare gold nanoparticles (AuNPs). The AuNPs forming the SEIRA-active substrate were directly synthesized inside the ATR liquid cell taking advantage of stainless steel assisted synthesis via the walls composing the ATR compartment. The formation of the AuNPs can be directly monitored via the enhancement of the corresponding water absorption features. The absorbance of BSA at the AuNPs deposited onto the Si ATR waveguide is significantly enhanced when compared to bare Si, thereby improving the sensitivity of detection. Apparently, the presence of the AuNPs layer at the ATR waveguide surface at the measured conditions does not affect the secondary structure of the protein. Measurements were performed in water and confirmed in deuterium oxide, which significantly reduces the strongly absorbing mid-infrared background of water in the spectral regime of interest. The limits of detection achieved for BSA protein analysis in water and deuterium oxide media are 1.93 and 4.15 mg·L, respectively, and the precisions at a 250 mg·L concentration are 11.9% and 8.1%, respectively. [ABSTRACT FROM AUTHOR]

Triangular gold microprisms and spherical silica nanoparticles with attached gold nano-islands were examined as an active nanostructures for the surface enhanced Raman and infrared spectroscopy. These particles were probed for the detection of pyridostigmine bromide as a safe analog of military compound sarin. Raman and infrared spectral bands of the pyridostigmine bromide were measured. Detailed correlation of obtained spectral bands with specific vibrations in pyridostigmine bromide was done. Silica nanoparticles with attached gold nano-islands showed more essential enhancement of the Raman signal than gold microcrystals. The reasons of such behaviour are discussed. [ABSTRACT FROM AUTHOR]

[Display omitted] • Corrosion process of copper NPs/titanium surface in the presence of tryptophan. • Complex investigations: EIS, PDP, AFM, SEM, XPS, Raman, FT-IR, SERS, SEIRA, nano-IR. • Tryptophan triggered formation of Cu-Trp complex and nano-galvanic coupling of CuNPs-Ti. • Conformational changes of Trp (indole ring, amine group) on the corroded CuNPs-Ti surface. A combination of electrochemical and spectroscopic studies allows for understanding and describing the processes that occur on a nano-modified commercial pure Ti by Cu nanoparticles (CuNPs) in the presence and absence of tryptophan (Trp). The electrochemical results confirmed that the deposition of a thin CuNPs layer on the Ti substrate improves the corrosion resistance of the substrate under simulated physiological conditions. The addition of Trp to the corrosive environment accelerated the degradation of the CuNPs coating likely via the formation of a Cu-Trp complex. The degradation of the coating led to the formation of nano-galvanic sites at the substrate/ CuNPs coating interface, which in turn had a detrimental effect on the substrate and further increased the degradation of the coating. The conformational changes of Trp on the corroded CuNPs-Ti surface have been investigated by surface-enhanced vibrational techniques. Trp was adsorbed on the corroded CuNPs-Ti surface through the indole ring, which adopts a more/less horizontal orientation, and the protonated amine group in the presence of chloride and phosphate ions on the metallic surface. The application of a combination of infrared spectroscopy with atomic force microscopy (AFM-IR) proved that Trp covered the bimetal surface and caused the significant degradation of the surface. [ABSTRACT FROM AUTHOR]

Using rigorous finite element electromagnetic calculations, we study the performance of a localized surface plasmons resonance array infrared sensor, from an uncommon perspective, by analyzing electromagnetic hot spots density. We show that the hot spots density strongly depends on near-field interaction between plasmonic nanoantennas. We provide important theoretical evidence that the degree of the interaction depends on both material and geometrical properties of an array. To this end, we consider arrays of conventional metal (CM) and plasmonic transparent conducting oxide (TCO) at different nanoantennas density. We establish that a single CM nanoantenna has higher field intensity enhancement than a TCO counterpart. On the other hand, an array of TCO nanoantennas provides 30 times larger density of the hotspots and 15 times higher signal-to-noise ratio, as compared to a CM array. [ABSTRACT FROM AUTHOR]

It is demonstrated that the forbidden lines, which exist in the SERS and SEIRA spectra of molecules with sufficiently high symmetry are absent in these spectra of the fullerene C 60 . In addition the enhancement coefficient in Single molecule SERS on C 60 is ∼10 8 that is significantly less than the value 10 14 –10 15 , characteristic for other molecules, which do not belong to the ones with cubic and icosahedral symmetry groups. These results can be explained by existence of so-called electrodynamical forbiddance arising due to belonging of C 60 to the icosahedral symmetry group and due to the electrodynamical law div E = 0. [ABSTRACT FROM AUTHOR]

Because of its extended surface area porous gold is of potential interest for surface-enhanced spectroscopy methods. Optical properties of porous and smooth gold nanowires of similar diameter are analyzed with infrared spectroscopy and modeled with finite-difference time-domain simulations. By electrochemical deposition in ion-track etched polymer smooth gold and gold-silver alloy nanowires are synthesized. Porous gold nanowires are subsequently obtained by dealloying. The porosity clearly affects important plasmonic characteristics, resulting in a strong redshift of the resonant wavelength, and significant line broadening, which can be convincingly explained by effective Drude parameters related to a lowered average electron density and a higher electron scattering in the porous gold, respectively. Finally, the sensing performance of porous wires is tested by surface-enhanced infrared absorption. The measurements show a similar vibrational signal contrast for smooth and porous wires. This is explained by simulations which reveal that the nanowire near-field modeled with bulk gold data is higher and thus accordingly the vibrational signal is enhanced compared to nanowires modeled with the effective Drude parameters of porous gold. This means that the advantages offered by the larger surface of porous wires are counterbalanced by lower near-field strength. [ABSTRACT FROM AUTHOR]