Surface-enhanced Infrared Spectroscopy Research Articles

Experimental Insights into the Reaction Intermediates-Selectivity Relationship for Electrochemical CO2 Reduction Reaction

Since the industrial revolution, the use of fossil fuels has increased CO2 concentration in the atmosphere, which has caused global warming to become a serious problem [1]. Thus, to realize a "carbon neutral" society, Electrochemical CO2 Reduction Reaction (CO2RR) has attracted attention. However, there are several challenges to the practical application of CO2RR, one of which is the improvement of product selectivity: the standard electrode potential of each reaction to various products is overlapped [2], and its large overpotential [3], making it difficult to selectively produce a specific product. In the pioneering study by Hori and co-workers, various metal electrodes were investigated and classified into four groups based on their primary reaction product: HCOO–-forming metals, CO-forming metals, hydrocarbon-forming metals, and CO2RR inactive metals (hydrogen-producing metals) [4]. Since the adsorption strength of the reaction intermediates has been considered the primary descriptor for the differences in reaction products, most studies have focused mainly on the adsorption energy. In recent years, more studies have focused on aspects other than the adsorption energies of O-bound and C-bound adsorbates to further improve product selectivity. Rossmeisl et al. suggest that the binding energy of H-bound adsorbates, in addition to O-bound and C-bound adsorbates, is an essential factor in explaining the final product [5]. Furthermore, the focus now expands to electrolyte properties, such as pH [ 6], cations [ 7], and anions [ 8] to control the stability of the reaction intermediates. As such, it is critical to experimentally probe the state of the reaction intermediates in situ to accurately understand the effect of the strategies mentioned above on the reaction pathway.In this study, we experimentally probe the reaction intermediates at various metal electrodes with different product selectivity using operando surface-enhanced infrared spectroscopy (SEIRAS). For the operando SEIRA measurements, we used a metal working electrode composed of a thin metal film electrodeposited on a Si prism coated with a Pt surface enhancement layer. Carbon rods were used as the counter electrode, Ag/AgCl as the reference electrode, and 1 M KHCO3 as the electrolyte. To compare the reactivity of reaction intermediates on different metal electrodes, we conducted linear sweep voltammetry (LSV) from 0.50 to –0.90 V vs RHE and probed the reaction intermediates during the potential sweep using SEIRAS. The result confirms the potential-dependent change in the reaction intermediates as well as the metal-dependent change in the composition of the reaction intermediates, suggesting successful observation of the CO2RR intermediates in different metal catalysts. Through this study, we attempted to interpret the correlation between the reactivity of each electrode and the properties of the reaction intermediates.Reference[1] Choi, S. et al, ChemSusChem 2009, 2, 796-854.[2] Jouny, M. et al, Ind. Eng. Chem. Res. 2018, 57, 2165–2177.[3] Yoo, J. S. et al, ChemSusChem 2016, 9, 358-363.[4] Hori, Y. et al, Modern Aspects of Electrochemistry 2008, 42, 89–189.[5] Bagger, A. et al, ChemPhysChem 2017, 18, 3266–3273.[6] Varela, A.S. et al, Catal. Today 2016, 260, 8-13.[7] Resasco, J. et al, J. Am. Chem. Soc. 2017, 139, 11277-11287.[8] Dunwell, M. et al, J. Am. Chem. Soc. 2017, 139, 3774-3783.

Tuning Hydrogen-Bond Network within Stacked 2D Nanolayer for Enhanced Oxygen Evolution Reaction

Introduction Water splitting is a key to producing hydrogen with renewable electricity. The reaction consists of two reactions: hydrogen evolution and oxygen evolution reaction (OER), and the sluggish reaction kinetics of OER limits the overall energy efficiency1). Although the OER activity was continuously improved, mainly by optimizing the binding ability between reactants and the catalysts, the current strategy is reaching its limits. Recently, it has been reported that the hydrogen bond network of water molecules around the catalyst surface influences OER activity, and Lewis acidic metal cations in electrolytes can be used to tune its structures2). However, the contribution of cations to the OER activity is not noticeably manifested since the cation existence ratio is orders of magnitude lower than that of water molecules.Here, we focused on layered manganese oxide (MnO2)3), which can trap metal complexes, water molecules, and cations within its nanolayer, as an OER catalyst. We synthesized the MnO2 catalysts having Ni2+ complex (for OER active site) and non-catalytic Li+, K+, and Cs+ (for tuning the hydrogen bond network of confined water) co-inserted into the nanolayer. The effect of the hydrogen bond network on the OER activity was clarified by utilizing the nanosized interlayer space of layered MnO2 as a tunable electrochemical reaction field. Methods The layered MnO2 was electrodeposited on an FTO substrate using a solution containing manganese sulfate (MnSO4) and a guest cation (TBA+Cl-). Subsequently, the electrodeposited samples were immersed in various ion exchange solutions to synthesize target catalysts (Ni, Ni-Li, Ni-K, Ni-Cs/MnO2). X-ray diffraction (XRD) was used to estimate the interlayer distances between the crystal phases of samples. The electronic states of Ni active sites were evaluated by X-ray photoelectron spectroscopy (XPS). Linear sweep voltammetry (LSV) was performed using three-electrode cells in 0.1 M TBAOH at a scan rate of 10 mV s– 1 to evaluate the OER activity. Results and discussion The XRD patterns showed the equally spaced peaks for each sample, confirming the layered structure for all synthesized catalysts (Fig.1a). Furthermore, the calculated interlayer distances matched with the hydration radius of expected interlayer cations, suggesting the successful insertion of the target cations. Ni2p peaks from XPS spectra showed the same peak positions throughout the samples, indicating a negligible change in the electronic states of Ni (Fig. 1b). The OER activity changed markedly depending on the non-catalytic alkaline cations, and the OER activity was in the order of Cs+ < K+ < Li+ (Fig.1c). The observed trend was opposite to the activity of Ni disk electrodes in alkaline-cation electrolytes (LiOH < KOH < CsOH) (Fig.1d). The results suggest that alkaline cations differently modulate the hydrogen-bond network in the bulk electrolyte and inside the nanosized interlayer space, thus leading to different OER activity. We will also discuss the correlation between the hydrogen-bond network structure around the Ni2+ complex and OER activity by probing the behavior of confined water within the interlayer with operando surface-enhanced infrared spectroscopy (SEIRAS). Reference 1) Liu, X. Chem. Commun., 52, 5546–5549 (2016). 2)M. Görlin, et al. Nat. Commun., 11, 6181 (2020).3)K. Fujimoto, et al. J. Phys. Chem., 122, 8406–8413 (2018). Figure 1

Surface-enhanced infrared spectroscopic study of extracellular vesicles using plasmonic gold nanoparticles

Extracellular vesicles (EVs), sub-micrometer lipid-bound particles released by most cells, are considered a novel area in both biology and medicine. Among characterization methods, infrared (IR) spectroscopy, especially attenuated total reflection (ATR), is a rapidly emerging label-free tool for molecular characterization of EVs. The relatively low number of vesicles in biological fluids (∼1010 particle/mL), however, and the complex content of the EVs’ milieu (protein aggregates, lipoproteins, buffer molecules) might result in poor signal-to-noise ratio in the IR analysis of EVs. Exploiting the increment of the electromagnetic field at the surface of plasmonic nanomaterials, surface-enhanced infrared spectroscopy (SEIRS) provides an amplification of characteristic IR signals of EV samples. Negatively charged citrate-capped and positively charged cysteamine-capped gold nanoparticles with around 10 nm diameter were synthesized and tested with blood-derived EVs. Both types of gold nanoparticles contributed to an enhancement of the EVs’ IR spectroscopic signature. Joint evaluation of UV-Vis and IR spectroscopic results, supported by FF-TEM images, revealed that proper interaction of gold nanoparticles with EVs is crucial, and an aggregation or clustering of gold nanoparticles is necessary to obtain the SEIRS effect. Positively charged gold nanoparticles resulted in higher enhancement, probably due to electrostatic interaction with EVs, commonly negatively charged.

(Invited) Controlling Electric Fields and Hydration at Electrochemical Junctions Using Surfactants

Tuning the electrostatics and the water structure at the nm and sub-nm scales are two important frontiers towards the broader goal of controlling reactivity at interfaces. Surfactants offer a way to influence both the electrostatics and hydration of an electrochemical interface. Here we report measurements of local electric fields generated between layers of surfactants and an electrode without application of an external potential. We estimate the value of the electric field by measuring the vibrational frequency shift of a well-defined Stark probe that is adsorbed on the electrode. The field generated by the common quaternary ammonium surfactants in aqueous media is estimated to be in the order of 1 V/nm. We show that modest quantities of surfactants (50 mM) can produce polarizing fields similar to those produced by an electrode poised at -0.8 V vs. Ag/AgCl. Furthermore, we show that under electrochemical conditions, surfactants offer a way of modulating the water content near the electrode. In a mixture of water and DMSO, there are two forces that act upon the surfactants to drive them to the interface: they hydrophobic forces and the electrostatic forces from the electrode. We measure the surfactants at the interface as a function of these variables using surface enhanced IR spectroscopy, and arrive at quantitative comparisons between these two effects. These results help in understanding the design principles of modifying interfacial reactions via tailored surfactants.

Basic and Advanced Logical Concept Derived from Surface Enhanced Infrared Spectroscopy (SEIRS) as Sensing Probe for Analysis of Chemical Species: A Brief Review

The worldwide concern for environmental pollution, climate change and health hazards caused by various pollutants has significantly increased in the recent past. Various techniques have so far been employed for sensing applications of such organic as well as inorganic pollutants. Amongst the different techniques, surface enhanced infrared spectroscopy (SEIRS) is a powerful tool which is utilized for label-free and unambiguous identification of molecular species. SEIRS overcomes the limitations of the conventional infrared spectroscopy and has emerged as a potential technique with high surface sensitivity by enhancing the signals by many folds and also facilitates new studies from the fundamental aspect to applied sciences. The current review is dedicated to a comprehension of the SEIRS technique to provide a critical overview of its application as sensing probe for analysis of chemical species. The major features of Fourier Transform Infrared spectroscopy and SEIRS have been critically discussed.

Probing the reactivity of protonated oxygen intermediate in aprotic media with in situ surface-enhanced infrared spectroscopy

A fundamental understanding of electrochemical reactions is essential to drive the practicality of batteries. The oxygen reduction reaction (ORR) that occurs on discharge in aprotic lithium-oxygen (Li-O2) batteries, invariably encounters interference from impurities (e.g., protons) in practical environments. It has been shown that moderate proton-mediated ORR can improve discharge capacity without altering the overall pathway; however, the reactivity of protonated oxygen intermediates formed towards aprotic electrolytes during ORR, remains controversial and unexplored. Herein, we interrogate the reactivity of protonated oxygen intermediates at the model Au | propylene carbonate and Au | trimethyl phosphate interfaces containing phenol as the moderate proton source, using in situ attenuated total reflection surface-enhanced infrared spectroscopy coupled with theoretical calculations. Direct spectroscopic evidence presents that the preferential reaction between superoxide and available protons to form protonated oxygen intermediates (e.g., HO2), can significantly mitigate superoxide anion (O2−)-induced solvent degradations while not triggering additional secondary parasitic reactions. Consequently, practical Li-O2 batteries containing phenol have also exhibited improved electrochemical performance and reversibility. We believe that the fundamental insights will provide important lessons for future practical design (e.g., protons control of electrolytes) of Li-O2 batteries and other related electrochemical devices.

Revisiting the activity origin of the PtAu24(SR)18 nanocluster for enhanced electrocatalytic hydrogen evolution by combining first-principles simulations with the experimental in situ FTIR technique.

Thiolate-protected metal nanoclusters (NCs) have been widely used in various electrocatalytic reactions, yet the dynamic evolution of metal NCs during electrocatalysis has been rarely explored and the activity origin remains largely ambiguous. Herein, using a PtAu24(SCH3)18 NC as a prototype model, we combined advanced first-principles calculations and attenuated total reflection surface-enhanced infrared spectroscopy (ATR-SEIRAS) to re-examine its active site and reaction dynamics in the hydrogen evolution reaction (HER). It has been previously assumed that the central Pt is the only catalytic center. However, differently, we observed the spontaneous desorption of thiolate ligands under moderate potential, and the dethiolated PtAu24 exhibits excellent HER activity, which is contributed not only by the central Pt atom but also by the exposed bridged Au sites. Particularly, the exposed Au exhibits high activity even comparable to Pt, and the synergistic effect between them makes dethiolated PtAu24 an extraordinary HER electrocatalyst, even surpassing the commercial Pt/C catalyst. Our predictions are further verified by electrochemical activation experiments and in situ FTIR (ATR-SEIRAS) characterization, where evident adsorption of Au-H* and Pt-H* bonds is monitored. This work detected, for the first time, the Au-S interfacial dynamics of the PtAu24 nanocluster in electrocatalytic processes, and quantitatively evaluated the essential catalytic role of the exposed Au sites that has been largely overlooked in previous studies.

Regulating Morphological Features of Nickel Single‐Atom Catalysts for Selective and Enhanced Electroreduction of CO2

Single-atom catalysts (SACs) are of interest for chemical transformations of significant energy and environmental relevance because of the envisioned efficient use of active sites and the flexibility in tuning their coordination environment. Future advancement in this vein hinges upon the ability to further increase the number and accessibility of active sites in addition to fine-tuning their chemical environment. In this work, a Ni SAC is reported with a unique hierarchical hollow structure (Ni/HH) that allows increased accessibility of the active sites. The successful obtainment of such a uniquely structured catalystwasenabled by the judiciously chosen solvent mixtures for the preparation of the precursor whose hierarchical feature is maintained during the subsequent pyrolysis and etching of the pyrolysis product. Comparative catalytic and mechanistic studies with reference to three closely related but more compact Ni SACs established the superior performance of Ni/HH for selective electroreduction of CO2 to CO. Experimental analyses by in situ attenuated total reflection surface-enhanced infrared spectroscopy reveal that it is the facilitated formation of the *COOH intermediate in the rate-determining step that leads to the enhanced reaction kinetics and the overall catalytic performance.

Dopamine as a bioinspired adhesion promoter for the metallization of multi-responsive phase change microcapsules

This work reports on an environmentally friendly method to produce encapsulated phase change material with a thin nickel coating, applicable for heat conversion, storage and thermal management of heat-sensitive components and suitable for active heating by electromagnetic radiation. A critical issue for the metallization is the adhesion between the polymer capsule shell and the metal layer. Based on previous studies using the bio-molecule dopamine as adhesion promoter in composites and for plastics metallization, commercial paraffin microcapsules were coated with an ultrathin polydopamine film via a simple wet chemical process. Subsequently, a thin, uniform and compact nickel layer was produced by electroless metallization. The successful deposition of both layers was verified with a broad range of imaging and spectroscopic techniques. For the first time, surface-enhanced IR spectroscopy was used to study the deposition of ultrathin PDA films. The combination of SEM and energy-dispersive X-ray spectroscopy allowed resolving the spatial distribution of the elements Ni, N, and O in the MC shell. Electrically conducting paths in the Ni shell were verified by conductive AFM. Thermal analysis revealed that the coated microcapsules show a phase change enthalpy of approx. 170 J/g, suitable for thermal storage and management. Additionally, the nickel layer enhanced the thermal diffusivity of the microcapsule powders and enables a fast heating of the PCM microcapsules by microwave radiation, demonstrating the applicability of the metallized MCs for controlled heating applications.Graphical abstract

Monitoring the Progression of Cell-Free Expression of Microbial Rhodopsins by Surface Enhanced IR Spectroscopy: Resolving a Branch Point for Successful/Unsuccessful Folding.

The translocon-unassisted folding process of transmembrane domains of the microbial rhodopsins sensory rhodopsin I (HsSRI) and II (HsSRII), channelrhodopsin II (CrChR2), and bacteriorhodopsin (HsBR) during cell-free expression has been investigated by Surface-Enhanced Infrared Absorption Spectroscopy (SEIRAS). Up to now, only a limited number of rhodopsins have been expressed and folded into the functional holoprotein in cell free expression systems, while other microbial rhodopsins fail to properly bind the chromophore all-trans retinal as indicated by the missing visible absorption. SEIRAS experiments suggest that all investigated rhodopsins lead to the production of polypeptides, which are co-translationally inserted into a solid-supported lipid bilayer during the first hour after the in-vitro expression is initiated. Secondary structure analysis of the IR spectra revealed that the polypeptides form a comparable amount of α-helical structure during the initial phase of insertion into the lipid bilayer. As the process progressed (>1 h), only HsBR exhibited a further increase and association of α-helices to form a compact tertiary structure, while the helical contents of the other rhodopsins stagnated. This result suggests that the molecular reason for the unsuccessful cell-free expression of the two sensory rhodopsins and of CrChR2 is not due to the translation process, but rather to the folding process during the post-translational period. Taking our previous observation into account that HsBR fails to form a tertiary structure in the absence of its retinal, we infer that the chromophore retinal is an integral component of the compaction of the polypeptide into its tertiary structure and the formation of a fully functional protein.

Ammonia oxidation on iridium electrode in alkaline media: An in situ ATR-SEIRAS study

• ATR-SEIRAS is extended to study the AOR on Ir electrode in basic media. • NH x ,ad species is attributed to the pivot intermediate. • N 2 H x+y ,ad species is identified as the key active intermediate to generate N 2. • NO 2 − and NO 3 − byproducts arise from NO ad oxidation. Mechanistic understanding of electrochemical ammonia oxidation reaction (AOR) is important for designing efficient AOR catalysts. In this work, in situ attenuated total reflection surface-enhanced infrared spectroscopy (ATR-SEIRAS) is employed to study the AOR at varied potentials on an Ir electrode in alkaline media. The AOR on Ir contains two sequential oxidation peaks in the anodic voltammograms. The in situ ATR-SEIRAS results indicate that the small Peak I at a lower potential is mainly due to dehydrogenation of interfacial ammonia and dimerization of as-generated NH x, ad species to N 2 H x+y, ad species. And the broad and intense Peak II at a higher potential mainly involves the N 2 production from N 2 H x+y, ad species, NO ad species generation from NH x ,ad species and further successive oxidation into the NO 2 − and NO 3 − by-products at higher potentials. It is thus inferred that NH x species are the pivotal intermediates for AOR on Ir electrode, and the N 2 H x+y ,ad and NO ad species the key intermediates for the production of N 2 , NO 2 − and NO 3 − , respectively.

Interaction of CO with Gold in an Electrochemical Environment

We present a joint theoretical–experimental study of CO coverage and facet selectivity on Au under electrochemical conditions. With in situ attenuated total reflection surface-enhanced IR spectroscopy, we investigate the CO binding in an electrochemical environment. At 0.2 V versus SHE, we detect a CO band that disappears upon facet-selective partial Pb underpotential deposition (UPD), suggesting that Pb blocks certain CO adsorption sites. With Pb UPD on single crystals and theoretical surface Pourbaix analysis, we eliminate (111) terraces as a possible adsorption site of CO. Ab initio molecular dynamics simulations of explicit water on the Au surface show the adsorption of CO on (211) steps to be significantly weakened relative to the (100) terrace due to competitive water adsorption. This result suggests that CO is more likely to bind to the (100) terrace than (211) steps in an electrochemical environment, even though Au steps under gas-phase conditions bind CO* more strongly. The competition between water and CO adsorption can result in different binding sites for CO* on Au in the gas phase and electrochemical environments.

Interfacial Acid-Base Equilibria and Electric Fields Concurrently Probed by In Situ Surface-Enhanced Infrared Spectroscopy.

Understanding how applied potentials and electrolyte solution conditions affect interfacial proton (charge) transfers at electrode surfaces is critical for electrochemical technologies. Herein, we examine mixed self-assembled monolayers (SAMs) of 4-mercaptobenzoic acid (4-MBA) and 4-mercaptobenzonitrile (4-MBN) on gold using in situ surface-enhanced infrared absorption spectroscopy (SEIRAS). Measurements as a function of the applied potential, the electrolyte pD, and the electrolyte concentration determined both the relative surface populations of acidic and basic forms of 4-MBA, as well as the local electric fields at the SAM-solution interface by following the Stark shifts of 4-MBN. The effective acidity of the SAM varied with the applied potential, requiring a 600 mV change to move the pKa by one unit. Since this is ca. 10× the Nernstian value of 59 mV/pKa, ∼90% of the applied potential dropped across the SAM layer. This emphasizes the importance of distinguishing applied potentials from the potential experienced at the interface. We use the measured interfacial electric fields to estimate the experienced potential at the SAM edge. The SAM pKa showed a roughly Nernstian dependence on this estimated experienced potential. An analysis of the combined acid-base equilibria and Stark shifts reveals that the interfacial charge density has significant contributions from both SAM carboxylate headgroups and electrolyte components. Ion pairing and ion penetration into the SAM also influence the observed surface acidity. To our knowledge, this study is the first concurrent examination of both effective acidity and electric fields, and highlights the relevance of experienced potentials and specific ion effects at functionalized electrode surfaces.

Adsorption of Halides on Au (111) Electrode in Aprotic Solvents: AC- Voltammetry, EIS, XPS and Surface-Enhanced Infrared Spectroscopy

Specific adsorption of ions on the electrode surface has a significant impact on the electric double layer (EDL) structure and the kinetics of electrode processes[1]. The ion adsorption at aqueous solution interfaces[2] on various metals has been examined intensively, but much fewer studies from non-aqueous solvents have been conducted[3]. Such studies are important because the metal-solvent [4] and ion-solvent interaction energy [5] depend on the chemical nature of the solvent.In this study, three organic solvents (propylene carbonate (PC), diglyme (DG), and dimethyl sulfoxide (DMSO)) were investigated for the adsorption of iodide and bromide ions on Au(111) single crystal electrode. This analysis was conducted by using differential capacity measurements, cyclic voltammetry (CV), Electrochemical Impedance Spectroscopy (EIS), X-ray photoelectron spectroscopy (XPS), and Surface-Enhanced Infrared Spectroscopy (SEIRAS).The magnitude of anion adsorption on Au(111) electrode increases in the series of halides I- ˃ Br- due to better solvation [6] and in the solvent order PC ˃ DG ˃ DMSO[7]. As well, the influence of water content on the adsorption rate of iodide on Au(111) electrode in PC and DMSO was studied. This effect, and the much higher adsorption rate in water is explained by the closer approach of the solvated halogen ion to the surface and the resulting stronger interaction of the transition state with the electrode. Quantification of the adsorbed iodide amount from XPS spectra confirms the coverage estimated from the adsorption charge in CVs. During SEIRAS measurements, a bipolar band is observed at around 1805 cm−1 which correlates to the C-O-vibration of PC as reported on silver electrodes from SERS measurements[8]. A stronger electrical field with decreasing potential is observed in absence of iodine leads to higher absorbance of PC molecules on the surface. Acknowledgments Financial support by the German Federal Ministry of Education and Research (BMBF) of the “LuCaMag” project (Fkz: 03EK3051A) under the framework of “Vom Material zur Innovation” program is acknowledged.

Mapping Adsorbates with Shell-Isolated Nanoparticle Enhanced Raman Spectroscopy to Understand Rapid Superconformal Filling of Cu Trenches

Additive adsorbates are widely used as surfactants to guide morphological and microstructural evolution during electrochemical deposition of thin films. Even though this strategy has been employed for several decades understanding of the mechanisms at play on the interface remain limited. Modern spectroelectrochemical methods, from surface-enhanced Raman spectroscopy (SERS) to surface-enhanced infrared spectroscopy (SEIRAS) and non-linear optical methods like sum frequency generation (SFG) can provide significant insight into the composition, structure, and dynamics of the surfactant adsorbates through their vibrational signatures. on nominally static surfaces. Each strategy is limited to specimen geometry; SERS is closely linked to the use of rough, plasmonically-active surfaces while SEIRAS measurements are constrained to thin, IR-transparent, metallic films. In the last decade, a significant advance was the introduction of nanoparticle reporters, based largely on silica coated Au nanoparticles, that enable Raman spectroscopy studies on well-defined, single-crystal surfaces whereby the nanoparticle serves to channel the plasmonic energy to the nanoparticle-substrate interface. The silica or alternative coating materials are designed to be inert with respect to the chemistry of the adsorbate species under study while remaining thin enough to allow effective focusing of the optical energy. This approach has been adopted by several researchers interested in understanding molecular adsorption on well-defined, single-crystal surfaces, the electrical double layer, and numerous aspects of reactivity related to catalysis, batteries, electrodeposition, etc. The present work demonstrates the use of Au@SiO2 (core-shell) nanoparticles, also known as SHINERS (Shell-Isolated Nanoparticle-Enhanced Raman Spectroscopy), to enable in situ vibrational spectroscopic measurements during electroplating of comparatively smooth, rapidly advancing, surfaces. In particular, the ability of the reporters to float on an advancing surface while responding to area change is used to reveal important, area-driven changes in adsorbate coverage. This study also opens a new avenue for exploring the intersection of analytical surface chemistry and composite electroplating. Figure 1

Is the Use of Surface-Enhanced Infrared Spectroscopy Justified in the Selection of Peptide Fragments That Play a Role in Substrate-Receptor Interactions? Adsorption of Amino Acids and Neurotransmitters on Colloidal Ag and Au Nanoparticles.

This paper describes an application of attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) and surface-enhanced infrared spectroscopy (SEIRA) to characterize the selective adsorption of four peptides present in body fluids such as neuromedin B (NMB), bombesin (BN), neurotensin (NT), and bradykinin (BK), which are known as markers for various human carcinomas. To perform a reliable analysis of the SERIA spectra of these peptides, curve fitting of these spectra in the spectral region above 1500 cm–1 and SEIRA measurements of sulfur-containing and aromatic amino acids were performed. On the basis of the analyses of the spectral profiles, specific conclusions were drawn regarding specific molecule–metal interactions and changes in the interaction during the substrate change from the surface of silver nanoparticles (AgNPs) to gold nanoparticles (AuNPs).

Confined hydration in nanometer-graded plasma polymer films: Insights from surface-enhanced infrared absorption spectroscopy

To shed light on recently explored long-range surface forces generated by subsurface-confined water, the structural characteristics of water molecules penetrating into nanoporous homogeneous and nanograded siloxane plasma polymer films (PPFs) over the time scale of 24 hours are studied by surface-enhanced IR spectroscopy (SEIRAS). Chemically graded PPFs, with embedded hydrophobic-to-hydrophilic gradient, are found to significantly change the average interfacial water orientation due to a unique nanoporous morphology and silanol group coordination. Diffusion of water through the hydrophobic SiO:CH matrix creates an evolution of the coordination of matrix silanol groups, which are eventually deprotonated as soon as the hydration network connects to the aqueous environment. This occurs after ~6 hours of water immersion and coincides with the change of average interfacial water orientation. Both effects are present on hydrophobic samples, but are significantly amplified by the presence of the subsurface vertical amphiphilic gradient (Vgrad), whereas enhanced water uptake in oxygen-plasma modified graded PPFs is covering such effects.

Perfect Absorption Efficiency Circular Nanodisk Array Integrated with a Reactive Impedance Surface with High Field Enhancement.

Infrared (IR) absorbers based on a metal–insulator–metal (MIM) have been widely investigated due to their high absorption performance and simple structure. However, MIM absorbers based on ultrathin spacers suffer from low field enhancement. In this study, we propose a new MIM absorber structure to overcome this drawback. The proposed absorber utilizes a reactive impedance surface (RIS) to boost field enhancement without an ultrathin spacer and maintains near-perfect absorption by impedance matching with the vacuum. The RIS is a metallic patch array on a grounded dielectric substrate that can change its surface impedance, unlike conventional metallic reflectors. The final circular nanodisk array mounted on the optimum RIS offers an electric field enhancement factor of 180 with nearly perfect absorption of 98% at 230 THz. The proposed absorber exhibits robust performance even with a change in polarization of the incident wave. The RIS-integrated MIM absorber can be used to enhance the sensitivity of a local surface plasmon resonance (LSPR) sensor and surface-enhanced IR spectroscopy.

Point mutation in the TGFBI gene: surface-enhanced infrared absorption spectroscopy (SEIRAS) as an analytical method

A novel method to detect DNA mutations based on gold nanoparticles is described. This bioconjugate was prepared by conjugation of the TGFBI gene on the surface of gold nanoparticles. The surface plasmon resonance band observed in the ultraviolet–visible spectrum of the gold nanoparticles showed a shift to a lower energy after the surface was covered with the TGFBI gene. Surface-enhanced infrared spectroscopy (SEIRAS) showed the absorption bands of the bioconjugate due to their proximity to the nanoparticles. The SEIRAS effect was able to detect small and specific changes in the sequence of the TGFBI gene using interactions of the bioconjugates. The study was performed on patients clinically diagnosed with lattice corneal dystrophy (LCD). To our knowledge, this is the first report of FTIR spectroscopy employed to analyse this gene. We used genotyping results previously obtained by next-generation DNA sequencing technology to ensure that the analysed samples had the mutation. Our results show highly reproducible signals, which could be used for analytical studies of mutations in the genome.

Surface-enhanced infrared detection of benzene in air using a porous metal-organic-frameworks film

Infrared (IR) spectroscopy is a powerful technique for observing organic molecules, as it combines sensitive vibrational excitations with a non-destructive probe. However, gaseous volatile compounds in the air are challenging to detect, as they are not easy to immobilize in a sensing device and give enough signal by themselves. In this study, we fabricated a thin nanocrystalline metal-organic framework (nMOF) film on a surface plasmon resonance (SPR) substrate to enhance the IR vibration signal of the gaseous volatile compounds captured within the nMOF pores. Specifically, we synthesized nanocrystalline HKUST-1 (nHKUST-1) particles of ca. 80 nm diameter and used a colloidal dispersion of these particles to fabricate nHKUST-1 films by a spin-coating process. After finding that benzene was readily adsorbed onto nHKUST-1, an nHKUST-1 film deposited on a plasmonic Au substrate was successfully applied to the IR detection of gaseous benzene in air using surface-enhanced IR spectroscopy.