Surface-enhanced Infrared Absorption Effect Research Articles

Surface-Enhanced Infrared Absorption Spectroscopy for Analyzing Nucleophilic Molecules Using Ethylene Glycol Decorated TiO2 Nanosheet.

Surface-enhanced infrared absorption (SEIRA) spectroscopy has been developed for the nondestructive analysis of trace molecules. Herein, we found that ethylene glycol (EG) decorated TiO2 nanosheet exhibits a selective SEIRA effect for molecules with nucleophilic groups, such as -NH2 and -OH. The SEIRA effect was attributed to the chemical mechanism originating from the interactions between the surface EG and the analytes. The enhancement factor was negatively correlated with the electrophilicity index of the analytes (p = 0.004), and the noncovalent bond dominates the interactions between the analytes and EG. The charge distribution analysis revealed that the -CH2 groups of EG exposed on the TiO2 surface are positively charged, attracting the electron-rich groups of the analyte. This attraction concentrates the analyte, redistributes its charge, defines its molecular dipole moment, and thereby enhances the SEIRA effect. The insights gained from this study shed light on developing new SEIRA substrates and emphasized the critical role of surface ligands in SEIRA applications.

On‐chip near‐infrared absorption enhancement of liquid water using chalcogenide waveguide with silver island film

AbstractFor optical waveguide sensor based on evanescent field, the limitation of the light intensity caused by the waveguide loss leads to a short interaction length. Increasing external confinement factor can increase absorbance to overcome this problem. A chalcogenide waveguide was proposed for water absorption measurement, whose core layer was fabricated by lift‐off method. Silver island film was fabricated on the surface of core layer by oblique angle deposition method, which was used to introduce surface‐enhanced infrared absorption (SEIRA) effect. The surface morphology of the metal island structure with different thicknesses were characterized. Liquid water was used as the analyte. The sensor with 1.8 nm thick silver island film had the largest absorbance enhancement factor (>2.1) with an increased waveguide loss of only 1 dB/cm. The SEIRA effect using metal island film can also be used in slot waveguide or suspended waveguide to further achieve better performance.

Infrared Plasmonic Biosensor with Tetrahedral DNA Nanostructure as Carriers for Label-Free and Ultrasensitive Detection of miR-155.

MicroRNAs play an important role in early development, cell proliferation, apoptosis, and cell death, and are aberrantly expressed in many types of cancers. To understand their function and diagnose cancer at an early stage, it is crucial to quantitatively detect microRNA without invasive labels. Here, a plasmonic biosensor based on surface‐enhanced infrared absorption (SEIRA) for rapid, label‐free, and ultrasensitive detection of miR‐155 is reported. This technology leverages metamaterial perfect absorbers stimulating the SEIRA effect to provide up to 1000‐fold near‐field intensity enhancement over the microRNA fingerprint spectral bands. Additionally, it is discovered that the limit of detection (LOD) of the biosensor can be greatly improved by using tetrahedral DNA nanostructure (TDN) as carriers. By using near‐field enhancement of SEIRA and specific binding of TDN, the biosensor achieves label‐free detection of miR‐155 with a high sensitivity of 1.162% pm −1 and an excellent LOD of 100 × 10−15 m. The LOD is about 5000 times lower than that using DNA single strand as probes and about 100 times lower than that of the fluorescence detection method. This work can not only provide a powerful diagnosis tool for the microRNAs detection but also gain new insights into the field of label‐free and ultrasensitive SEIRA‐based biosensing.

Dispersion-based intertwined SEIRA and SPR effect detection of 2,4-dinitrotoluene using a plasmonic metasurface.

Surface enhanced infrared absorption (SEIRA) spectroscopy and surface plasmon resonance (SPR) make possible, thanks to plasmonics nanoantennas, the detection of low quantities of biological and chemical materials. Here, we investigate the infrared response of 2,4-dinitrotoluene deposited on various arrays of closely arranged metal-insulator-metal (MIM) resonators and experimentally show how the natural dispersion of the complex refractive index leads to an intertwined combination of SEIRA and SPR effect that can be leveraged to identify molecules. They are shown to be efficient for SEIRA spectroscopy and allows detecting of the dispersive explosive material, 2,4-dinitrotoluene. By changing the in-plane parameters, a whole spectral range of absorptions of 2,4-DNT is scanned. These results open the way to the design of sensors based on SEIRA and SPR combined effects, without including a spectrometer.

Mid-Infrared Plasmonic Excitation in Indium Tin Oxide Microhole Arrays

Transparent conducting oxides (TCOs) are emerging as possible alternative constituent materials to replace noble metals such as silver and gold for low-loss plasmonic applications in the near-infrared (NIR) and mid-infrared (MIR) regimes. In particular, TCO-based nanostructures are extensively investigated for biospectroscopy exploiting their surface-enhanced infrared absorption (SEIRA). The latter enhances the absorption from vibrational and rotational modes of nearby biomolecules, making TCO nanostructures a promising candidate for IR sensing applications. Nevertheless, in order to produce inexpensive devices for lab-on-a-chip diagnostics, it would be favorable to achieve surface-enhanced infrared absorption with very simple microstructures not requiring nanosize control. In this work, we attempt to demonstrate a SEIRA effect with the least challenging fabrication, μm-scale instead of nm-scale, by tailoring both device design and charge density of the indium tin oxide (ITO) film. We show that microperio...

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.

Enhancement of infrared absorption of biomolecules absorbed on single-wall carbon nanotubes and graphene nanosheets

Surface-enhanced infrared absorption effect was shown for graphene for the first time. Comparative analysis of the effect was carried out for thymine (Thy), one of the bases of DNA, absorbed on single-wall carbon nanotubes (SWCNT) and graphene sheets. The enhancement factor in the case of SWCNT was generally greater in comparison with that obtained for graphene sheets. Its value for SWCNT was up to six and the largest enhancement factors were found for vibrations of CH, C−OH , and C−N bonds. The maximum enhancement factor in the case of graphene sheets equal to 3.7 was found for ring and deformational vibrations of N-H bonds. The obtained experimental data allowed us to suppose that H-bonds influence the interaction between SWCNT and Thy in Thy-SWCNT/Au, while the chemically induced charge transfer is probably dominant in the case of Thy-graphene/Au.

P‐Nitrobenzoic Acid Adsorption on Nanostructured Gold Surfaces Investigated by Combined Experimental and Computational Approaches

Adsorption of guest molecules on host surfaces can lead to dramatic changes in the spectral properties of the guest. One such effect is surface-enhanced infrared absorption (SEIRA), observed when the guest is adsorbed on, for example, thin films, metal surfaces, or nanotubes. p-Nitrobenzoic acid (p-NBA) exhibits a SEIRA effect when adsorbed on Ag and Au. Herein, the IR spectra of p-NBA adsorbed on a homemade rough Au surface, recorded in reflection mode with an angle of incidence of 16.5°, are reported. This SEIRA experiment reveals more bands than found by previous SEIRA studies. The intensities of both symmetric and asymmetric COO(-) and NO(2) stretching, in-plane CH, and C=C ring stretching modes are enhanced. Theoretical models constructed on the basis of density functional theory reveal the binding mode of p-NBA to gold "particles". The p-NBA anion binds to gold much more strongly than the neutral form, and interaction via the carboxylic oxygen atoms is preferred over the nitro group-gold contact. A significant charge transfer during chemisorption is found, which is considered to be crucial in leading to a high SEIRA enhancement factor.

Surface Enhanced Infrared Absorption (SEIRA) Spectroscopy using Gold Nanoparticles on As2S3 Glass

Surface enhanced infrared absorption (SEIRA) spectroscopy was investigated using sputtered gold nanoparticles on the As2S3 chalcogenide glass. Islands films were sputtered on the substrate with various thicknesses from 11.1±0.9nm to 31.4±3.6nm. Infrared transmission spectra of 4-nitrothiophenol adsorbed on gold nanoparticles show that SEIRA effect was dependent of the thickness of discontinuous gold films. Only symmetric NO2 stretch (1336cm-1) was observed and enhanced due to surface selection rules. The best enhancement is one order of magnitude stronger than for a continuous gold film. The corresponding thickness measured by Atomic Force Microscopy is 16.3±0.5nm.

Para-Mercaptobenzoic acid-modified silver nanoparticles as sensing media for the detection of ammonia in air based on infrared surface enhancement effect

To utilize the large signals provided by surface-enhanced infrared absorption (SEIRA) measurements for chemical sensing, a new sensing scheme was proposed and demonstrated for detection of ammonia in air samples. To increase the SEIRA effect, a sensing phase composed of multi-layers of silver nanoparticles (AgNPs) was prepared using a chemically controlled electroless deposition method. para-Mercaptobenzoic acid (pMBA) served as the controlling agent in formation of AgNPs, a surface modification agent of AgNPs for sensing, and a stabilizer to protect the AgNPs from coagulation and oxidation. The sensing approach utilized the interaction between pMBA and ammonia, which involves the formation of carboxylate-ammonium complex. After interaction, the enhanced IR absorption bands of pMBA on AgNPs were significantly changed and able to provide quantitative information on the ammonia concentrations. To optimize the conditions for preparing sensing elements, parameters used to form multi-layers of AgNPs were systematically varied and their corresponding sensitivities in detection of ammonia were recorded. The results indicate that AgNPs with diameters in the range of 100 nm provided the best performance in terms of detecting ammonia via the SEIRA effect. Also, the analytical signal generally increased as the number of layers of AgNPs increased, but was limited to certain layers, depending on the reaction conditions used in preparation of AgNPs. The sensing elements were found to be highly selective to ammonia and the detection limit approached 150 ppb with a linear range up to 25 ppm.

Dynamic Processes in Electrochemical Reactions Studied by Surface-Enhanced Infrared Absorption Spectroscopy (SEIRAS)

Abstract Molecules adsorbed on evaporated thin metal films exhibit enormously strong infrared absorption. The thin metal films that exhibit the surface-enhanced infrared absorption (SEIRA) consist of metal particles much smaller than the wavelength of light. Electric field associated with the incident infrared radiation is enhanced via the excitation of localized plasmon of the particles, yielding the absorption enhancement. Preferential orientation and the change in absorption coefficient of molecules caused by chemisorption onto the metal surface provide additional enhancement. Most characteristic observations in SEIRA experiments are well explained by a simple electromagnetic theory. The infrared spectroscopy utilizing the SEIRA effect is promising as a new surface analytical tool. In particular, it is very useful for in situ studies of electrode/electrolyte interfaces. By the combined use of the attenuated-total-reflection technique, reactions and adsorption/desorption of molecules at the interfaces can be investigated at a high sensitivity without the interference from the bulk solution. The high sensitivity of this technique enables dynamic (or time-resolved) infrared monitoring of reactions and other time-dependent phenomena at the electrochemical interface at time-resolutions ranging from microseconds to milliseconds. Two-dimensional correlation analysis of time-resolved spectra highlights certain useful information that is not clearly seen in the usual one-dimensional spectra.