Reflection Surface-enhanced Infrared Absorption Spectroscopy Research Articles

Optimization of a Commercial Variable Angle Accessory for Entry Level Users of Electrochemical Attenuated Total Reflection Surface-Enhanced Infrared Absorption Spectroscopy (ATR-SEIRAS).

An evaluation of several experimental aspects that can optimize electrochemical attenuated total reflection surface-enhanced infrared absorption spectroscopy (ATR-SEIRAS) performance using a commercially available, specular reflection accessory is provided. A comparison of different silicon single-bounce internal reflection elements (IREs) is made with emphasis on different face-angled crystal (FAC) options. Selection of optimal angle of incidence for maximizing signal and minimizing noise is shown to require consideration of the optical throughput of the accessory, reflection losses at the crystal surfaces, and polarization effects. The benefits of wire-grid polarizers and antireflective (AR) coatings on the IREs is discussed. High signal-to-noise ratios can be achieved by omitting polarizers, using an AR-coated FAC with a larger face angle, and working at angles of incidence close to the maximum throughput angle of the accessory.

Antenna array-enhanced attenuated total reflection IR analysis in an aqueous solution.

Attenuated total reflection surface-enhanced infrared absorption spectroscopy (ATR-SEIRAS) is a powerful technique that provides structural and functional information during dynamic reactions in aqueous solutions. One existing limitation is the sensitivity to extract the signals of trace-level analytes from the background water in situ and in real time. Here, we proposed a novel ATR-SEIRAS platform that integrated a large-scale triangle gold antenna array onto a conventional ATR-IR platform to increase the sensitivity of this analytical technique. A square centimeter level well-ordered gold antenna array was fabricated onto an Si prism via nanosphere lithography. The size-dependent antenna array resonance had weak correlation with the incident polarization and antenna orientation, allowing antenna array-enhanced IR detection without the requirement of a microscope. In addition, the antenna resonance shift that occurred due to analyte adsorption-induced refractive index variation could be minimized benefiting from the high refractive index of Si (3.4). As a demonstration, we dynamically monitored the adsorption of the trace levels of proteins on top of the antenna array with a real signal enhancement factor larger than 300. Our platform opens an avenue to apply antenna array-enhanced IR spectroscopy in an aqueous environment measured via commercial IR instruments, which is extremely promising for the interfacial applications that require signal enhancement.

In situ study of EDC/NHS immobilization on gold surface based on attenuated total reflection surface-enhanced infrared absorption spectroscopy (ATR-SEIRAS).

In this study, the time-dependent reaction between 11-mercaptoundecanoic acid (11-MUA) and 1-Ethyl-3-(3-dimethylaminopropyl)carbodiimide/N-hydroxysuccinimide (EDC/NHS) is precisely characterized using surface enhanced infrared absorption spectroscopy (SEIRAS). According to the high correlation between the spectral results of SEIRAS and the electrochemical behavior, it strongly demonstrates that the EDC/NHS reaction would be obviously interfered by phosphate ions in the neutral pH condition (pH = 7.0).

Potential Routes and Mitigation Strategies for Contamination in Interfacial Specific Infrared Spectroelectrochemical Studies

Attenuated total reflectance surface-enhanced infrared absorption spectroscopy (ATR-SEIRAS) is a powerful tool for probing the electrochemical interface; however, inconsistencies in reported spectr...

Graphene Plasmon-Enhanced IR Biosensing for in Situ Detection of Aqueous-Phase Molecules with an Attenuated Total Reflection Mode.

Graphene plasmon has attracted extensive interest due to the unprecedented electromagnetic confinement, long propagation distance, and tunable plasmonic frequency. Successful applications of graphene plasmon as infrared sensors have been recently demonstrated, yet they are mainly focused on solid/solid and solid/gas interfaces analysis. Herein, we, for the first time, propose a graphene plasmon-enhanced infrared sensor based on attenuated total reflection configuration for in situ analysis of aqueous-phase molecules. This IR sensor includes a boron-doped graphene (BG) nanodisk array fabricated on top of a ZnSe prism surface that supports attenuated total reflection surface-enhanced infrared absorption spectroscopy (ATR-SEIRA). Our ATR-SEIRA platform is efficient and straightforward for in situ and label-free monitoring of the interaction of biomolecules without interference from the environments, allowing for the extraction of instant spectroscopic information in a complex biological event. Utilizing the near-field enhancement of graphene plasmon, the binding interaction of L-selectin with its aptamer as a demonstration has been investigated to evaluate the specific protein recognition process. The detection limit of the target protein reaches 0.5 nM. Our work demonstrates that chemical-doped graphene plasmon combined with ATR-SEIRA is a promising signal enhancement platform for in situ aqueous-phase biosensing.

Identification of native charge-transfer status of p-aminothiolphenol adsorbed on noble metallic substrates by surface-enhanced infrared absorption (SEIRA) spectroscopy

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 B2 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.

Examination of Near-Electrode Concentration Gradients and Kinetic Impacts on the Electrochemical Reduction of CO2 using Surface-Enhanced Infrared Spectroscopy

Localized concentration gradients within the electrochemical double layer during various electrochemical processes can have wide-ranging impacts; however, experimental investigation to quantitatively correlate the rate of surface-mediated electrochemical reaction with the interfacial species concentrations has historically been lacking. In this work, we demonstrate a spectroscopic method for the in situ determination of the surface pH using the CO2 reduction reaction as a model system. Attenuated total reflectance surface-enhanced infrared absorption spectroscopy is employed to monitor the ratio of vibrational bands of carbonate and bicarbonate as a function of electrode potential. Integrated areas of vibrational bands are then compared with those obtained from calibration spectra collected in electrolytes with known pH values to determine near-electrode proton concentrations. Experimentally determined interfacial proton concentrations are then related to the resultant concentration overpotentials to exam...

Chain-length dependent interfacial immunoreaction kinetics on self-assembled monolayers revealed by surface-enhanced infrared absorption spectroscopy

Self-assembled monolayer (SAM) has been extensively applied as ideal interface layer for construction of biosensors. Its chain length and end functional groups determine the physical and chemical properties of the modified surfaces, which will affect the performance of constructed biosensors. Herein, we studied the influence of chain length of n-alkanethiols SAMs on the immunoreaction kinetics employing attenuated total reflection surface-enhanced infrared absorption spectroscopy (ATR-SEIRAS). Antibody (rabbit immunoglobulin) is assembled on carboxyl terminated SAMs of n-alkanethiols with different chain lengths (n = 3, 6, 11, 16). The whole fabrication steps of the immunoassay can be monitored in situ by the ATR-SEIRAS. From the time-dependent SEIRA spectra, the interfacial immunoreaction kinetics between the immobilized antibody and antigen (goat anti-rabbit immunoglobulin) can be evaluated. We found that the immunoreaction became faster with increasing the chain length of SAMs. This chain length dependent kinetics might be attributed to different orientations of the assembled antibody caused by different packing densities of SAMs. The present research offers a sensing platform to evaluate immunoassay kinetics and provides fundamentals for construction of immunoassay with high performance.

Attenuated Total Reflection Surface-Enhanced Infrared Absorption (ATR SEIRA) Spectroscopy for the Analysis of Fatty Acids on Silver Nanoparticles.

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.

Attenuated Total Reflection Surface-Enhanced Infrared Absorption Spectroscopy: a Powerful Technique for Bioanalysis

Attenuated total reflection surface-enhanced infrared absorption spectroscopy (ATR-SEIRAS) has recently been proven to be a powerful tool for bioanalysis. It enables in situ and in real-time observation of dynamic processes occurring on specific interface, revealing rich structural and functional information of biomolecules at sub monolayer level. The aim of this general review was to give an overview of the cutting edge applications of ATR-SEIRAS. We start with description of the basic configuration of the standard ATR-SEIRAS platform. The enhanced mechanisms and methods to fabricate enhanced substrates are then presented. We discuss the recent developments, challenges and applications of ATR-SEIRAS in bioanalysis, mainly focusing on DNA analysis, protein behavior and cell properties. Finally, further development of the ATR-SEIRAS technique with enhanced sensitivity, improved time and spatial resolutions will be prospected.

Mechanistic Insights into Electro-Oxidation of Solution CO on the Polycrystalline Gold Surface as Seen by in Situ IR Spectroscopy

Carbon monoxide (CO) adsorption and electro-oxidation on a gold (Au) ultrathin film deposited onto a silicon prism infrared (IR) window in a CO-saturated (≈1 mM) 0.1 M HClO4 supporting electrolyte were investigated by in situ electrochemical attenuated-total-reflection (ATR) surface-enhanced IR reflection absorption spectroscopy (SEIRAS). By varying the reaction environment with sequential (CO and N2) purging of the supporting electrolyte and the Au surface morphology with CO annealing, we were able to assign adsorbed CO to terrace-like and step-like sites to deconvolute the corresponding time- and potential-dependent IR spectra. The results of these spectral deconvolutions suggest strongly that in the CO-saturated supporting electrolyte the weakly bound CO interacted mainly with the strongly adsorbed CO on the step-like sites and likely formed a dipolar-coupled weak interacting pair with the latter. Model ab initio density functional theory (DFT) calculations confirm the existence of the weakly bound CO ...

Enhanced Vibrational Spectroscopies as Tools for Small Molecule Biosensing.

In this short summary we summarize some of the latest developments in vibrational spectroscopic tools applied for the sensing of (small) molecules and biomolecules in a label-free mode of operation. We first introduce various concepts for the enhancement of InfraRed spectroscopic techniques, including the principles of Attenuated Total Reflection InfraRed (ATR-IR), (phase-modulated) InfraRed Reflection Absorption Spectroscopy (IRRAS/PM-IRRAS), and Surface Enhanced Infrared Reflection Absorption Spectroscopy (SEIRAS). Particular attention is put on the use of novel nanostructured substrates that allow for the excitation of propagating and localized surface plasmon modes aimed at operating additional enhancement mechanisms. This is then be complemented by the description of the latest development in Surface- and Tip-Enhanced Raman Spectroscopies, again with an emphasis on the detection of small molecules or bioanalytes.

SEIRAS Studies of Water Structure in a Sodium Dodecyl Sulfate Film Adsorbed at a Gold Electrode Surface.

Surface-enhanced infrared reflection-absorption spectroscopy (SEIRAS) was used to investigate the structure of water that is incorporated within a film of sodium dodecyl sulfate (SDS) adsorbed at a thin gold nanoparticle film deposited onto a silicon substrate. Previous studies on a Au(111) electrode surface showed that SDS molecules form long-range ordered hemicylindrical hemimicelles (phase I) for potentials -0.2 ≤ E ≤ 0.45 V vs Ag/AgCl and a disordered bilayer (phase II) for potentials E ≥ 0.5 V vs Ag/AgCl. The SEIRA spectra demonstrated that the hemimicellar film is water-rich and contains both a network of hydrogen-bonded water and a disturbed network of hydrogen bonds consisting of monomeric and dimeric water in the hydrophobic region of the film. No network water was observed in phase II of the film. However, SEIRAS data showed that sulfate groups in the disordered bilayer are hydrated. The SEIRAS spectra of the film of SDS were compared to the previously measured spectra obtained using subtractively normalized interfacial Fourier transform IR spectroscopy (SNIFTIRS). The complementarity of the spectroscopic information obtained by these two techniques was demonstrated.

Spectroelectrochemical and DFT Study of Thiourea Adsorption on Gold Electrodes in Acid Media

The adsorption of thiourea (TU) at Au(111) and Au(100) single crystal and evaporated gold thin-film electrodes with preferential (111) orientation was studied in perchloric acid solutions with TU concentrations below 0.1 mM. For this purpose, cyclic voltammetry with gold single crystals was combined with external reflection infrared spectroscopy and surface-enhanced infrared reflection-absorption spectroscopy under attenuated total reflection conditions (ATR-SEIRAS) with gold thin film electrodes. In situ surface enhanced Raman spectroscopy (SERS) experiments were also carried out with these latter samples. In addition, optimized geometries and theoretical harmonic vibrational frequencies, obtained from B3LYP/LANL2DZ, 6-31+G(d) calculations for TU and thioureate species adsorbed on Au clusters with (111) orientation, were used for the interpretation of the experimental spectra. ATR-SEIRAS experiments show irreversible adsorption of TU at 0.10 V, whereas the SERS experiments have confirmed the bonding of the TU molecule to the metal surface through the S atom. The optimized geometry obtained from density functional theory (DFT) calculations for adsorbed TU corresponds to unidentate bonding through the sulfur atom, with the Au-S bond slightly tilted (13°) from the surface normal, whereas the C-S bond appears to be tilted by 45°. In the case of adsorbed thioureate, under the application of an external electric field of 0.01 a.u., a bidentate asymmetrical bridge adsorption configuration is obtained with one N(H) and the S atoms bonded to Au in positions close to top adsorption sites and with the molecular plane perpendicular to the metal surface. The observation of an adsorbate band for the asymmetric NCN stretching in the experimental infrared spectra confirms the tilting of the S-C bond of the adsorbed TU at low potentials. Changes of the adsorbate bands in the ATR-SEIRA spectra at potentials around 0.60 vs reversible hydrogen electrode (RHE) can be interpreted on the basis of DFT results as due to the deprotonation of adsorbed TU to form adsorbed thioureate. © 2014 American Chemical Society.

Spectroelectrochemical behavior of 4-aminobenzenethiol on nanostructured platinum and silver electrodes

The adsorption of 4-aminobenzenethiol (4-ABT) on Ag and Pt nanoparticles is studied by spectroelectrochemical means (cyclic voltammetry, Surface-Enhanced Raman Spectroscopy (SERS) and Surface-Enhanced Infrared Reflection Absorption Spectroscopy (SEIRAS)). Similar SERS spectra are obtained when 4-ABT is adsorbed on platinum and silver nanostructured substrates. In addition, unless a low power density of the laser is used, these spectra show, both under open circuit conditions and when applying electrode potentials above −0.50V vs AgCl/Ag, bands not observed in the normal Raman spectrum of 4-ABT. These bands disappear when the electrode potential is shifted to more negative values. Conversely, the SEIRA spectra of 4-ABT adsorbed on Ag do not show any significant change with the electrode potential, which indicates that there are no new species electrochemically formed in the range of potentials considered, which include some anodic and cathodic processes as shown in the corresponding cyclic voltammograms. In this regard, SERS measurements put in evidence the time dependence of the spectra obtained at potentials above −0.50V just after switching on the laser suggesting the formation of new species, probably dimercaptoazobenzene (4-4′-DMAB), formed by a photochemical process of the adsorbed 4-ABT.

Infrared Spectroscopy of Thin Organic Films Adsorbed at a Gold Electrode Surface

This lecture will review our research involving IR spectroscopy at the solid –liquid interface. After a brief review of basic principles of IR spectroscopy and the laws of reflection of light at interfaces, three methods of Infrared Reflection Absorption Spectroscopy (IRRAS) will be described. The first is subtractively normalized interfacial Fourier transform infrared spectroscopy (SNIFTIRS) or in short potential difference IR spectroscopy. This technique finds application to study reversible adsorption of soluble molecules at electrode surfaces. The methods of optimisation of the SNIFTIRS experiment will be discussed. Its application will be illustrated by the case of adsorption of a soluble surfactant such as sodium dodecyl sulphate (SDS) at a gold electrode surface.1 The second technique to measure IR spectra at interfaces is the photon polarization modulation infrared reflection absorption spectroscopy (PM IRRAS). This technique is used to study films of insoluble molecules a various interfaces. I will discuss application of this technique to study model biological membranes supported at a gold electrode surface.2 The third technique is the surface enhanced infrared reflection absorption spectroscopy (SEIRAS). It is performed using attenuated total internal reflection (ATR) element covered by nanoparticles of gold. The intensity of the IR signal is then enhanced by a factor of 100. In addition, since the film of metal nanoparticles is conductive it is used to study phenomena at electrified interfaces. I will describe application of this technique to study structure of water in model biological membrane supported at a gold electrode surface.3 I will emphasize complementarity of SEIRAS and PMIRRAS in application to bio-electrochemical research.Literature1.Jay Leitch, John Collins, K. Andreas Friedrich, Ulrich Stimming, John R. Dutcher, Jacek Lipkowski “Infrared Studies of the Potential Controlled Adsorption of Sodium Dodecyl Sulfate at the Au(111) Electrode Surface”, Langmuir, 2012,28,2455-2464.2. Jacek Lipkowski, “Building model biomimetic membrane at a gold electrode surface”, Phys. Chem. Chem. Phys., 2010,12,13874-13887.3. Taro Uchida, Masatoshi Osawa and Jacek Lipkowski, “SEIRAS studies of water structure at the gold electrode surface in the presence of supported lipid bilayer”, J.Electroanal.Chem. DOI:10.1016/j.jelechem.2013.10.015

Electrocatalysis of Ethanol on a Pd Electrode in Alkaline Media: An in Situ Attenuated Total Reflection Surface-Enhanced Infrared Absorption Spectroscopy Study

In situ attenuated total reflection surface-enhanced infrared absorption spectroscopy in conjunction with H–D isotope replacement is used to investigate the dissociation and oxidation of CH3CH2OH on a Pd electrode in 0.1 M NaOH, with a focus on identifying the chemical nature of the pivotal intermediate in the so-called dual-pathway (C1 and C2) reaction mechanism. Real-time spectroelectrochemical measurements reveal a band at ∼1625 cm–1 showing up prior to the multiply bonded COad band. CH3CD2OH and D2O are used to exclude the spectral interference with this band from interfacial acetaldehyde and H2O, respectively, confirming for the first time that the ∼1625 cm–1 band is due to the adsorbed acetyl on the Pd electrode in alkaline media. The spectral results suggest that the as-adsorbed acetyl (CH3COad) is oxidized to acetate from approximately −0.4 V as the potential moves positively to conclude the C2 pathway. Alternatively, in the C1 pathway, the CH3COad is decomposed to α-COad and β-CHx species on the ...

Surface-Enhanced Infrared Absorption Spectroscopy Study of Anticorrosion Behavior of 2-Mercaptobenzothiazole on Copper

2-Mercaptobenzothiazole (MBT) is a highly efficient inhibitor of Cu. However, the inhibition mechanism is still unclear. In this paper, the anticorrosive effect of MBT on a Cu surface at the macroscopic level was evaluated using a polarization curve technique. The potential-dependent adsorption geometries of MBT at the molecular level were investigated using electrochemical surface-enhanced infrared reflection absorption spectroscopy in attenuated total reflection mode, together with theoretical calculations. The results indicated that the MBT molecules were adsorbed on the Cu surface vertically, in a thiolate form, through exocyclic S atoms at a potential negative of 0 V (vs saturated calomel electrode (SCE)). At a potential positive of 0 V (vs SCE), electrons were transferred between MBT and the Cu substrate, meaning that MBT molecules can interact with the Cu surface via exocyclic S and endocyclic N atoms to form a polymer film, resulting in the formation of a compact protecting layer to prevent Cu dissolution.

In Situ Molecular Level Measurements of Ion Dynamics in an Electrochemical Capacitor

Improving the energy storage capability of batteries and capacitors is inherently dependent on clarifying our understanding of ion dynamics of advanced electrolytes in a variety of materials. Herein we report a new attenuated total reflectance–surface-enhanced infrared absorption spectroscopy technique that can selectively and simultaneously measure both cation and anion transport of an ionic liquid (1-ethyl-3-methylimidazolium triflate (EMIm-Tf)) in a functioning electrochemical pseudocapacitor (actuator). This new capacitor–spectroscopy technique was utilized to probe the gold current collector/RuO2 electrode interface during both square wave and cyclic voltammetry experiments. Results show that the cations and anions transport as aggregates and the cation dominates and dictates the direction of ion transport in these devices. Results also show that ion dynamics in pseudocapacitors is a diffusion-limited process.

A comparative study of the adsorption and oxidation of L-alanine and L-serine on Au(1 0 0), Au(1 1 1) and gold thin film electrodes in acid media

The adsorption and oxidation of l-alanine and l-serine at Au(111) and Au(100) single crystal and evaporated thin-film electrodes with preferential (111) orientation was studied in perchloric acid solutions. For this purpose, cyclic voltammetry experiments were combined with external reflection infrared spectroscopy (gold single crystals) and surface-enhanced infrared reflection–absorption spectroscopy under attenuated total reflection conditions (ATR-SEIRAS) (gold thin films). In addition, theoretical harmonic vibrational frequencies, obtained from B3LYP/LANL2DZ, 6-31+G(d) calculations for the zwitterionic species adsorbed on Au clusters with (111) orientation, were used to interpret the experimental spectra. The optimized geometry obtained from DFT calculations for the corresponding zwitterion plus a water molecule, under the application of an external electric field of 0.01a.u. corresponds to a bidentate asymmetrical bridge adsorption configuration. The absence of an adsorbate band for the asymmetric OCO stretching in the experimental infrared spectra confirms the bidentate bonding of the adsorbed zwitterion through the oxygen atoms of the carboxylate group irrespective of the crystallographic orientation of the electrode surface, the adsorbate coverage and the electrode potential. In addition to typical interfacial water bands associated to perchlorate anions, which are co-adsorbed in order to compensate the positive charge of the ammonium group, the ATR-SEIRA spectra also show bands around 2950cm−1 that can be related to the formation of hydrogen bonds between interfacial water and the ammonium group of the adsorbed zwitterion. The voltammetric experiments have shown that, as in the case of platinum electrodes, l-serine oxidizes at lower potentials than l-alanine. Under these conditions, the in situ infrared experiments show the formation of carbon dioxide and adsorbed cyanide as oxidation products of l-serine. In the case of l-alanine, only carbon dioxide was detected.