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 ATRSEIRAS.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 ATRSEIRAS technique with enhanced sensitivity,improved time and spatial resolutions will be prospected.

Spectroscopy system based on a single quantum cascade laser for simultaneous detection of CO and CO_2

A quantum cascade laser（QCL） based system for simultaneous detection of CO and CO_2 is developed.The QCL can scan over two neighboring CO（2055.40 cm^（-1）） and CO_2（2055.16 cm^（-1）） lines with a single current scan.The wavelength modulation spectroscopy（ f = 20 k Hz） is utilized to enhance the signal-to-noise ratio.A white cell with an effective optical path length of 74 m is used.The calibration of the sensor is performed and minimum detection limits of 1.3 ppb（1 × 10^（-9））for CO and 0.44 ppm（1 × 10^（-6）） for CO_2 are achieved.

Synthesis and Characteristics of Diamond-like Carbon Films Deposited on Quartz Substrate

Diamond-like carbon (DLC) films are deposited on quartz substrate using pure CH4 in the surface wave plasma equipment. A direct current negative bias up to -90 V is applied to the substrate to investigate the bias effect on the film characteristics. Deposited films are characterized by Raman spectroscopy, infrared (IR) and ultraviolet-visible absorption techniques. There are two broad Raman peaks around 1340 cm-1 and 1600 cm-1 and the first one has a greater sp3 component with an increased bias. Infrared spectroscopy has three sp3 C-H modes at 2852 cm-1, 2926 cm-1 and 2962 cm-1, respectively and also shows an intensity increase with the negative bias. Optical band gap is calculated from the ultraviolet-visible absorption spectroscopy and the increased values with negative bias and deposition time are obtained. After a thermal anneal at about 500℃ for an hour to the film deposited under the bias of-90 V, we get an almost unchanged Raman spectrum and a peak intensity-reduced IR signal, which indicates a reduced H-content in the film. Meanwhile the optical band gap changed from 0.85 eV to 1.5 eV.

Supported Cu/Ni Bimetallic Cluster Electrocatalysts Boost CO_(2) Reduction

Supported metal clusters with the integrated advantages of single-atom catalysts and conventional nanoparticles held great promise in the electrocatalytic carbon dioxide reduction(ECO_(2)R)operated at low overpotential and high current density.However,its precise synthesis and the understanding of synergisti-cally catalytic effects remain challenging.Herein,we report a facile method to synthesize the bimetallic Cu and Ni clusters anchored on porous carbon(Cu/Ni-NC)and achieve an enhanced ECO_(2)R.The aberration-corrected high-angle annular dark-field scanning transmission electron microscopy and synchrotron X-ray absorption spectroscopy were employed to verify the metal dispersion and the coordination of Cu/Ni clusters on NC.As a result of this route,the target Cu/Ni-NC exhibits excellent electrocatalytic performance including a stable 30 h electrolysis at 200 mA cm^(-2) with carbon monoxide Faradaic efficiency of∼95.1%using a membrane electrode assembly electrolysis cell.Combined with the in situ analysis of the surface-enhanced Fourier transform infrared spectroelectrochemistry,we propose that the synergistic effects between Ni and Cu can effectively promote the H_(2)O dissociation,thereby accelerate the hydrogenation of CO_(2)to*COOH and the overall reaction process.

Cu/Mo2C synthesized through Anderson-type polyoxometalates modulate interfacial water structure to achieve hydrogen evolution at high current density

The development of efficient non-precious metal catalysts is important for the large-scale application of alkaline hydrogen evolution reaction(HER).Here,we synthesized a composite catalyst of Cu and Mo_(2)C(Cu/Mo_(2)C)using Anderson-type polyoxometalates(POMs)synthesized by the facile soaking method as precursors.The electronic interaction between Cu and Mo_(2)C drives the positive charge of Cu,alleviating the strong adsorption of hydrogen at the Mo site by modulating the d-band center of Mo_(2)C.By studying the interfacial water structure using in situ attenuated total reflection surface-enhanced infrared absorption spectroscopy(ATR-SEIRAS),we determined that the positively charged Cu crystals have the function of activating water molecules and optimizing the interfacial water structure.The interfacial water of Cu/Mo_(2)C contains a large amount of free water,which could facilitate the transport of reaction intermediates.Due to activated water molecules and optimized interfacial water structure and hydrogen adsorption energy,the overpotential of Cu/Mo_(2)C is 24 mV at a current density of 10 mA·cm^(-2) and 178 mV at a current density of 1000 mA·cm^(-2).This work improves catalyst performance in terms of interfacial water structure optimization and deepens the understanding of water-mediated catalysis.

Nanoplasmonic mid-infrared biosensor for in vitro protein secondary structure detection

Plasmonic nanoantennas offer new applications in mid-infrared(mid-IR)absorption spectroscopy with ultrasensitive detection of structural signatures of biomolecules,such as proteins,due to their strong resonant near-fields.The amide I fingerprint of a protein contains conformational information that is greatly important for understanding its function in health and disease.Here,we introduce a non-invasive,label-free mid-IR nanoantenna-array sensor for secondary structure identification of nanometer-thin protein layers in aqueous solution by resolving the content of plasmonically enhanced amide I signatures.We successfully detect random coil to crossβ-sheet conformational changes associated withα-synuclein protein aggregation,a detrimental process in many neurodegenerative disorders.Notably,our experimental results demonstrate high conformational sensitivity by differentiating subtle secondary-structural variations in a nativeβ-sheet protein monolayer from those of crossβ-sheets,which are characteristic of pathological aggregates.Our nanoplasmonic biosensor is a highly promising and versatile tool for in vitro structural analysis of thin protein layers.

Boron nitride nanoresonators for phonon-enhanced molecular vibrational spectroscopy at the strong coupling limit

Enhanced light-matter interactions are the basis of surface-enhanced infrared absorption(SEIRA)spectroscopy,and conventionally rely on plasmonic materials and their capability to focus light to nanoscale spot sizes.Phonon polariton nanoresonators made of polar crystals could represent an interesting alternative,since they exhibit large quality factors,which go far beyond those of their plasmonic counterparts.The recent emergence of van der Waals crystals enables the fabrication of highquality nanophotonic resonators based on phonon polaritons,as reported for the prototypical infrared-phononic material hexagonal boron nitride(h-BN).In this work we use,for the first time,phonon-polariton-resonant h-BN ribbons for SEIRA spectroscopy of small amounts of organic molecules in Fourier transform infrared spectroscopy.Strikingly,the interaction between phonon polaritons and molecular vibrations reaches experimentally the onset of the strong coupling regime,while numerical simulations predict that vibrational strong coupling can be fully achieved.Phonon polariton nanoresonators thus could become a viable platform for sensing,local control of chemical reactivity and infrared quantum cavity optics experiments.

Unraveling the interfacial effect of PdBi bimetallic catalysts on promoting CO_(2)electroreduction to formate

Through interface engineering and content control strategy,a PdBi bimetallic interface structure was constructed for the first time to selectively convert CO_(2)to formate with a remarkably high Faraday efficiency(FEformate)of 94%and a partial current density(jformate)of 34 mA·cm^(−2)at−0.8 V vs.reversible hydrogen electrode(RHE)in an H-cell.Moreover,the PdBi interface electrocatalyst even exhibited a high current density of 180 mA·cm^(−2)with formate selectivity up to 92%in a flow cell and could steadily operate for at least 20 h.Electrochemical in-situ attenuated total reflection surface enhanced infrared absorption spectroscopy(ATR-SEIRAS)confirmed that the PdBi interface could greatly weaken the adsorption of*CO intermediates due to electronic and geometric effects.Density functional theory(DFT)calculations also established that the PdBi interface regulated the CO_(2)-to-formate pathway by reducing the energy barrier toward HCOOH and largely weakening the adsorption of*CO intermediates on the catalyst surface.This study reveals that the unique PdBi bimetallic interface can provide a novel platform to study the reaction mechanism through combining in-situ ATR-SEIRAS and DFT calculations.