Surface-enhanced Infrared Absorption Research Articles

Plasmonic Enhancement of Infrared Vibrational Signals: Nanoslits versus Nanorods

We report on systematic investigations of plasmonically active nanoslits as a beneficial substrate for surface-enhanced infrared absorption (SEIRA). Arranged in arrays, nanoslits with the proper geometry feature strong nanorod-like resonances in the infrared spectral range, as predicted by Babinet’s principle for the same geometrical dimensions. SEIRA enhancement as studied with a thin self-assembled molecular layer of octadecanethiol reaches the values obtained with nanorods if the slit geometry is optimized. We show by systematically examining the important parameters that the slit width has an especially strong influence on the near-field intensity and therefore on the SEIRA signal. Furthermore, the transversal and longitudinal couplings of nanoslits are studied. Compared to nanorod arrays, a stronger influence of the array periodicities on the plasmonic excitations is observed, which indicates coupling via surface plasmon polaritons. So the array periodicity could be further optimized toward higher SE...

Revealing the Nature of Interaction between Graphene Oxide and Lipid Membrane by Surface-Enhanced Infrared Absorption Spectroscopy.

Revealing the nature of interaction between graphene oxide (GO) and lipid membrane is a crucial issue but still remains challenging. Here, we describe our recent effort toward this direction by studying the GO-induced vibrational changes of interfacial water and lipid membrane with surface-enhanced infrared absorption (SEIRA) spectroscopy. The experimental results provide evidence that overcoming the electrostatic repulsion of phosphate group, its hydrogen bonding attraction as well as the electrostatic and hydrophobic interaction of choline group are the driving forces for the effective adsorption of GO on lipid membrane. This work will open exciting new avenues to explore the use of SEIRA spectroscopy technique in probing nanobio interface.

Pt/Ionomer Interface Analyses with the Combination of Voltammetry and Spectroscopy

In catalyst layers of polymer electrolyte fuel cells, a solid polymer electrolyte, called “ionomer” for distinguishing it from the electrolyte membrane, is generally used to form good electrochemical interfaces on catalyst surfaces. However, model experiments using Pt single crystal electrodes covered with ionomer films suggested that sulfonate anion in perfluorinated sulfonic acid polymer (e.g. Nafion, with the side chain of OCF2CF(CF3)O(CF2)2SO3H) blocks active sites on Pt catalyst and therefore, slows down the kinetics of oxygen reduction reaction (ORR) [1]. Recently, the catalyst poisoning was found to be weakened by using an ionomer with different anionic structure (NBC4, having two sulfonimide acid groups in its side chain ended with a perfluorobutane, instead of a sulfonic acid group), as shown by broader and smaller anion-related peaks (0.4 – 0.6 V) in the cyclic voltammogram (CV) of Pt (111) coated with NBC4 (black dashed curve in Fig. 1a) than that with Nafion (gray solid curve in Fig. 1a) [2]. In the present study, we report that the anion adsorptivity can be also controlled even by changing the structures of perfluorinated side chain of sulfonic acid ionomer. In Fig. 1a, the black solid curve is the CV for a sulfonic acid ionomer with short side chains (Aquivion, with the side chain of O(CF2)2SO3H). Although the peaks due to the adsorption and desorption of sulfonate anion are sharp, the peak potentials are higher and the peak intensities are weaker than those for the Nafion-coated Pt. Thus ionomer with the shorter side chain is less adsorptive on Pt surface. Fig. 1b shows the CVs for a bare Pt (111) single crystal electrode in low-molecular-weight perfluoro-sulfonic acids of C4F9SO3H (nonafluorobutane sulfonic acid, NFBSA) and C2F5OC2F4SO3H (Perfluoro (2-ethoxyethane) sulfonic acid, PES). The CVs show reduction current due to residual oxygen and ill-defined features probably due to impurities. The Pt (111)-like Hupd plateaus are, however, seen between 0.07 – 0.4 V and anion-related peaks are observed (dashed circles). The potentials of the anion adsorption/desorption peaks are lower and the peak areas are larger for PES than for NFBSA. In addition, the surface enhanced infrared absorption (SEIRA) spectra for a Pt polycrystalline film in the electrolyte of NFBSA showed the band for adsorbed sulfate anion on Pt at 0.4 – 0.7 V (Fig. 2a, the shaded region at ca. 1100 cm-1) and therefore, the anion adsorption peak in the CV of Pt (111) may be not due to the adsorption of NFBSA anion itself, but due to the adsorption of sulfate anion as impurity, which was found to be contained with non-negligible concentration, <3000 ppm (corresponding to <1 mM for the 0.1 M electrolytes) in these types of chemical. (In this case, the other positive bands at 1066, 1140, 1250 and 1350 cm-1in the SEIRA spectra can be ascribed to the orientations of NFBSA molecules to more IR-active states, not to their adsorptions on the Pt surface.) In contrast, because the SEIRA spectra for PES do not show the clear band due to adsorbed sulfate anion (Fig. 2b), the anion adsorption peak in the CV can be ascribed to the adsorption of PES anion itself. Therefore, presumably, the PES anion is much more adsorptive on Pt than NFBSA anion is, and the presence or absence of the ether group in the perfluoro-sulfonate anions affects the adsorptivity of the anions.

Fabrication of Square-Centimeter Plasmonic Nanoantenna Arrays by Femtosecond Direct Laser Writing Lithography: Effects of Collective Excitations on SEIRA Enhancement

We demonstrate the use of femtosecond direct laser writing lithography for a fast and homogeneous large-area fabrication of plasmonic nanoantennas on a substrate by creating a patterned polymer as an etch mask on a metal layer. Subsequent argon ion beam etching provides plasmonic nanoantennas with feature sizes below the diffraction limit of the laser light. They exhibit tunable high-quality plasmon resonances in the mid-infrared spectral range, which are ideally suited for surface-enhanced infrared absorption (SEIRA). In the present work, we demonstrate reliable, fast, and low-cost fabrication of a wide variety of antenna arrays and examine particularly the influence of plasmonic coupling between neighboring antennas on the SEIRA enhancement effect. Specifically, we measure the enhanced infrared vibrational bands of a 5 nm thick 4,4′-bis(N-carbazolyl)-1,1′-biphenyl layer evaporated on arrays with different longitudinal and transversal spacings between antennas. An optimum SEIRA enhancement per antenna of...

Structure and Dynamics at Ionic Liquid/Electrode Interfaces

Ionic liquids (ILs) are potentially ‘game changing’ electrolytes for energy conversion applications such as capacitors [i] ,[ii] , batteries [iii] ,[iv] , fuel cells [v] ,[vi] , and solar cells. [vii] ,[viii] Significant progress has been made towards utilizing these remarkably adaptable materials for specific applications however, much work remains to generate technologically and economically relevant devices and processes.[ix] Characterizations of interfaces between IL-based electrolyte/electrode systems are crucial to continued development for these enterprises. In specific, detailed descriptions and understanding of structure and dynamics at electrolyte/electrode interfaces are necessary to realize engineered progress because device efficiencies are often largely determined by processes that occur at the interface. [x] ,[xi] Our presentation will focus on initial efforts to employ spectroscopic techniques that characterize interfacial structure and dynamics between ionic liquid media and electrode surfaces during simultaneous electrochemical perturbation. In specific, we will present surface enhanced infrared absorption (SEIRA) spectroscopy data for ILs composed of imidazolium-based cations with bis(trifluoromethylsulfonyl)imide anions at nanostructured noble metal electrodes (i.e, Au). [i]. T. Sato, G. Masuda, K. Takagi, Electrochim. Acta, 2004, 49, 3603-3611. [ii]. A. Orita, K. Kamijima, M. Yoshida, J. Power Sources, 2010, 195, 7471-7479. [iii]. A. S. Best, A. I. Bhatt, A. F. Hollenkamp, J. Electrochem. Soc., 2010, 157, A903-A911. [iv]. J.-K. Kima, A. Matica, J.-H. Ahnb, P. Jacobsson, J. Power Sources, 2010, 195, 7639-7643. [v]. S.-Y. Lee, A. Ogawa, M. Kanno, H. Nakamoto, T. Yasuda, M. Watanabe, J. Am. Chem. Soc., 2010, 132, 9764-9773. [vi]. M. Guo, J. Fang, H. Xu, W. Li, X. Lu, C. Lan, K. Li, J. Membr. Sci., 2010, 362, 97-104. [vii]. P. K. Singh, N. A. Jadhav, S. K. Mishra, U. P. Singh, B. Bhattacharya, Ionics, 2010, 16, 645-648. [viii]. C.-P. Lee, P.-Y. Chen, R. Vittal, K.-C. Ho, J. Mater. Chem., 2010, 20, 2356-2361. [ix]. M. Armand, F. Endres, D. R. MacFarlane, H. Ohno, B. Scrosati, Nature Materials, 2009, 8, 621-629. [x]. A. J. Bard, L. R. Faulkner, Electrochemical Methods: Fundamentals and Applications, 2nd ed., 2002, John Wiley & Sons, Inc., New York, NY. [xi]. M. Yoshida, A. Yamakata, K. Takanabe, J. Kubota, M. Osawa, K. Domen, J. Am. Chem. Soc., 2009, 131, 13218-13219.

Effect of Hydrogen on the Orientation of Cinchonidine Adsorbed on Platinum: An ATR-SEIRAS Study

Abstract The orientation of cinchonidine (CD) adsorbed on a Pt surface, a model system of enantioselective catalysis for hydrogenation reactions, is studied in 1,2-dichloroethane by in situ surface-enhanced infrared absorption spectroscopy in attenuated total reflection configuration. The quinoline (QN) moiety of CD is shown to be reoriented from a π-bonded nearly parallel orientation to an N-bonded upright one by bubbling the solution with H2. The origin of the reorientation is ascribed to the repulsive interaction of a QN π-orbital and the negative surface charge induced by dissociative adsorption of H2 and hydrogenation of the vinyl moiety.

Surface enhanced infrared absorption by nanoantenna on chalcogenide glass substrates

In recent years, nanowires have been proven efficient to enhanced IR absorption of molecules and opened prospects of new ultrasensitive IR sensors. The development of integrated components requires the use of special IR glasses such as chalcogenide or silver halide glasses. In this study, we report the fabrication of a surface enhanced IR absorption substrate composed of nanowires deposited onto a chalcogenide glass slide. It enabled us to detect 4-nitrophenol at the femtomolar level and enhancement factor close to 106 was calculated.

Fan-shaped gold nanoantennas above reflective substrates for surface-enhanced infrared absorption (SEIRA).

Here, we report a new nanoantenna for surface-enhanced infrared absorption (SEIRA) detection, consisting of a fan-shaped Au structure positioned at a well-specified distance above a reflective plane with an intervening silica spacer layer. We examine how to optimize both the antenna dimensions and the spacer layer for optimal SEIRA enhancement of the C-H stretching mode. This tunable 3D geometry yields a theoretical SEIRA enhancement factor of 10(5), corresponding to the experimental detection of 20-200 zeptomoles of octadecanethiol, using a standard commercial FTIR spectrometer. Experimental studies illustrate the sensitivity of the observed SEIRA signal to the gap dimensions. The optimized antenna structure exhibits an order of magnitude greater SEIRA sensitivity than previous record-setting designs.

Controllable Fe3O4/Au substrate for surface-enhanced infrared absorption spectroscopy

In this paper, the Fe3O4/Au nanocomposites were fabricated and employed as surface-enhanced infrared absorption (SEIRA) substrates. The superparamagnetic nature of Fe3O4/Au nanocomposites makes them suitable for controlled magnetic manipulation. The infrared absorption enhancements of Fe3O4/Au composite were improved as the magnetic field intensity increasing both for mercaptobenzoic acid and nitrobenzoic acid probe molecules. When the magnetic field intensities increase to 280 mT, the infrared enhancement could raise up to 3.3 and 10.7 times for -SH and -NO2 groups, respectively. The enhancement is due to the synergy of localized surface plasmon resonance of Au and the magnetism of Fe3O4. Under the strong magnetic field, the superparamagnetic Fe3O4/Au nanoparticles are highly concentrated, leading to the increase number of SEIRA “active sites” and the surface density of Au nanoparticles. The synergistic effects of both Fe3O4 and Au nanoparticles make the composites an excellent SEIRA substrate. In addition, the Fe3O4/Au nanocomposites were also utilized to determine the thiol and thione tautomers in -SH based molecules.

Electron Transfer to Light-Activated Photosynthetic Reaction Centers from Rhodobacter sphaeroides Reconstituted in a Biomimetic Membrane System

Photosynthetic reaction centers (RCs) from Rb. sphaeroides with a genetically engineered 7-his-tag at the C-terminus of the M-subunit are bound to a Ni-NTA-modified gold surface. Subsequently, the bound RCs are subjected to in situ dialysis in the presence of lipid micelles to form a protein-tethered lipid bilayer membrane (ptBLM). Redox properties of the RC thus immobilized are investigated by cyclic voltammetry. Photocurrrents are generated in the range of 10 μA cm–2, however, different from previous studies at potentials of −200 and −300 mV, and without cytochrome c as a mediator. The unexpected behavior is explained in terms of an interprotein reaction between RC molecules promoted by the lipid bilayer, which we had previously detected by surface-enhanced infrared absorption spectroscopy.

Electroless reduction of silver chloride precipitates for the preparation of highly sensitive substrates for surface-enhanced infrared absorption (SEIRA) measurements.

To prepare silver nanoparticles (AgNPs) on infrared-transmitting crystal for surface-enhanced infrared absorption (SEIRA) measurements, a new strategy is proposed and demonstrated using electroless reduction of preformed silver chloride (AgCl) particles. Silver chloride precipitates were formed using an additive of polyvinyl pyrrolidone (PVP) to vary the size and shape of the precipitates. After settling on germanium substrates, the preformed particles of AgCl were reduced electrolessly and spontaneously coagulated to AgNPs. The resulting AgNPs showed a multilayer structure, but the AgNPs were isolated, as shown by the lack of absorption-band distortion in the SEIRA measurements. Hence, the sensitivity and analyte-loading capacity for SEIRA measurements are improved significantly. To optimize the chemical deposition and electroless reduction method, we examined several parameters, including the concentrations of reagents during AgCl precipitation and the reaction time required in the deposition-reduction steps. We used para-nitrobenzoic acid (pNBA) to probe the intensity of the SEIRA effect for the prepared substrates. To better correlate the SEIRA performances with each variable, we examined the prepared substrates using a scanning electron microscope and SEIRA. The results indicate that two major morphologies of AgNPs are observed: nanoparticles and nanorods. The distributions of nanorods we observed were related to the procedures used to prepare the substrates. Based on SEIRA signals, we observed enhancement factors approaching three orders of magnitude compared to conventional transmission measurement. Also, based on the morphologies, the large signals were mainly caused by the formation of multilayers of non-percolated AgNPs.

Qualifying label components for effective biosensing using advanced high-throughput SEIRA methodology.

The need for technological progress in bio-diagnostic assays of high complexity requires both fundamental research and constructing efforts on nano-scaled assay recognition elements that can provide unique selectivity and design-enhanced sensitivity features. Nanoparticle induced sensitivity enhancement and its application related to multiplexed capability Surface-Enhanced InfraRed Absorption (SEIRA) assay formats are well suitable for these purposes. The potential of diverse fluorophore-antibody conjugates, being chemisorbed onto low-cost gold nanoparticulate SEIRA substrates, has been explored with respect to their spectral discriminability. These novel biolabels deliver molecular SEIRA fingerprints that have been successfully analyzed by both uni- and multivariate analyzing tools, to discriminate their multiplexing capabilities. We show that this robust spectral encoding via SEIRA fingerprints opens up new opportunities for a fast, reliable and multiplexed high-end screening in biodiagnostics.

Optimisation of the Detection Sensitivity of Plasmonic Nanoantenna Based Sensors for Mid-infrared Spectroscopy

In this paper we report on the optimisation of the optical characteristics of 2D-arrays of plasmonic gold nanoantennas (NA) that can be used as high sensitivity mid-infrared spectroscopic sensor for the detection of chemical/biological substances by using the Surface Enhanced Infrared Absorption (SEIRA) technique. This approach allows to detect the presence of a substance adsorbed on the NA by measuring its optical absorption under the conditions for which the maximum of the reflectivity response of the 2D-array occurs at the same wavelength of the substance maximum absorption peak. In particular, by acting on the 2D-array periodicity, NA shape, size and thickness, numerical simulations of the 2D-array detection response, based on Finite Element Method (FEM), demonstrate that is possible to obtain an increase in the detection sensitivity of more than three orders of magnitude with respect to that one achievable if the same substance is deposited on an unstructured planar metal surface, independently from the wavelength at which the substance absorption occurs. Moreover, we present the results of an analysis of the dependence of the 2D-array maximum reflectivity and peak wavelength on the geometrical parameters characterising the NA and the 2D-array.

Toxicity mechanism of graphene oxide and nitrogen-doped graphene quantum dots in RBCs revealed by surface-enhanced infrared absorption spectroscopy

GO can extract the lipid bilayer of RBCs membranes, resulting in hemolysis and aberrant forms. In contrast, GQDs just disturb the structure and conformation of the lipid, resulting in only aberrant cells.

Surfactant-assisted electroless deposition of silver nanoparticles on Ge crystal for ultra-sensitive detection by surface-enhanced infrared absorption spectroscopy

Fabrication of highly sensitive substrates for SEIRA measurements via assistance of surfactant to electrolessly deposit silver nanoparticles on Ge crystal.

Surface-enhanced IR absorption spectroscopy of the KcsA potassium channel upon application of an electric field.

Surface-enhanced IR absorption spectroscopy (SEIRAS) is a powerful tool for studying the structure of molecules adsorbed on an electrode surface (ATR-SEIRA). Coupled with an electrochemical system, structural changes induced by changes in the electric field can be detected. All the membrane proteins are subjected to the effect of membrane electric field, but conformational changes at different membrane potentials and their functional relevance have not been studied extensively except for channel proteins. In this contribution, background information of potential-dependent functional and structural changes of a prototypical channel, the KcsA channel, is summarized, and SEIRAS applied to the KcsA channel under the application of the potential is shown. The potassium channels allow K(+) to permeate selectively through the structural part called the selectivity filter, in which dehydrated K(+) ions interact with backbone carbonyls. In the absence of K(+), the selectivity filter undergoes conformational changes to the non-conductive collapsed conformation. To apply the electric field, the KcsA channels were fixed on the gold surface in either upside or reverse orientation. The SEIRA spectrum in K(+) or Na(+) solution revealed both backbone structural changes and local changes in the OCO-carboxylate groups. Upon application of the negative electric field, the spectrum of OCO was enhanced only in the K(+) solution. These results indicate that the negative electric field accumulates local K(+) concentration, which turned the collapsed filter to the conductive conformation. ATR-SEIRA serves as an unprecedented experimental system for examining membrane proteins under an electric field.

Nanogap-enhanced infrared spectroscopy with template-stripped wafer-scale arrays of buried plasmonic cavities.

We have combined atomic layer lithography and template stripping to produce a new class of substrates for surface-enhanced infrared absorption (SEIRA) spectroscopy. Our structure consists of a buried and U-shaped metal-insulator-metal waveguide whose folded vertical arms efficiently couple normally incident light. The insulator is formed by atomic layer deposition (ALD) of Al2O3 and precisely defines the gap size. The buried nanocavities are protected from contamination by a silicon template until ready for use and exposed by template stripping on demand. The exposed nanocavity generates strong infrared resonances, tightly confines infrared radiation into a gap that is as small as 3 nm (λ/3300), and creates a dense array of millimeter-long hotspots. After partial removal of the insulators, the gaps are backfilled with benzenethiol molecules, generating distinct Fano resonances due to strong coupling with gap plasmons, and a SEIRA enhancement factor of 10(5) is observed for a 3 nm gap. Because of the wafer-scale manufacturability, single-digit-nanometer control of the gap size via ALD, and long-term storage enabled by template stripping, our buried plasmonic nanocavity substrates will benefit broad applications in sensing and spectroscopy.

REACTIVITY SINGLE WALLED CARBON NANOTUBES UNDER INTERACTION WITH BIOLOGICAL MOLECULES – DNA AND PROTEINS

Literature review of experimental and calculated data on non-covalent interaction of DNA and proteins with nonfunctional carbon nanotubes was done in the paper. The results on characterization of single walled carbon nanotubes with Raman spectroscopy and conformation analysis of main biological polymers – DNA and protein of bovine serum albumin (BSA) under interaction with single walled carbon nanotubes with SEIRA (surface enhanced infrared absorption) was presented. The experiments give a possibility to conclude about non-covalent interaction in the complex nanotube-biomolecule. Analysis of the experimental data have proved that under DNA interaction with nanotubes, the bounding of DNA occurs at the nanotube surface, forming stable complex with Van-der-Vaalse interaction . In this case, -stacking has a main role with intra H-bond reconstruction biomolecules. We suppose, that albumin adsorption on nanotube surface takes place with participation of conventional cite interaction for BSA, due to hydrophobic interaction and -stacking. Experimental data on structural reconstruction of albumin is an evidence of this fact.

Localized surface plasmon resonances in nanostructures to enhance nonlinear vibrational spectroscopies: towards an astonishing molecular sensitivity.

Vibrational transitions contain some of the richest fingerprints of molecules and materials, providing considerable physicochemical information. Vibrational transitions can be characterized by different spectroscopies, and alternatively by several imaging techniques enabling to reach sub-microscopic spatial resolution. In a quest to always push forward the detection limit and to lower the number of needed vibrational oscillators to get a reliable signal or imaging contrast, surface plasmon resonances (SPR) are extensively used to increase the local field close to the oscillators. Another approach is based on maximizing the collective response of the excited vibrational oscillators through molecular coherence. Both features are often naturally combined in vibrational nonlinear optical techniques. In this frame, this paper reviews the main achievements of the two most common vibrational nonlinear optical spectroscopies, namely surface-enhanced sum-frequency generation (SE-SFG) and surface-enhanced coherent anti-Stokes Raman scattering (SE-CARS). They can be considered as the nonlinear counterpart and/or combination of the linear surface-enhanced infrared absorption (SEIRA) and surface-enhanced Raman scattering (SERS) techniques, respectively, which are themselves a branching of the conventional IR and spontaneous Raman spectroscopies. Compared to their linear equivalent, those nonlinear vibrational spectroscopies have proved to reach higher sensitivity down to the single molecule level, opening the way to astonishing perspectives for molecular analysis.

Biomimetic environment to study E. coli complex I through surface-enhanced IR absorption spectroscopy.

In this study complex I was immobilized in a biomimetic environment on a gold layer deposited on an ATR-crystal in order to functionally probe the enzyme against substrates and inhibitors via surface-enhanced IR absorption spectroscopy (SEIRAS) and cyclic voltammetry (CV). To achieve this immobilization, two methods based on the generation of a high affinity self-assembled monolayer (SAM) were probed. The first made use of the affinity of Ni-NTA toward a hexahistidine tag that was genetically engineered onto complex I and the second exploited the affinity of the enzyme toward its natural substrate NADH. Experiments were also performed with complex I reconstituted in lipids. Both approaches have been found to be successful, and electrochemically induced IR difference spectra of complex I were obtained.