High-sensitivity Spectroscopy Research Articles

Spectrum Broadening Due to Nonselective Linear Absorption

The position and linewidth of an emission spectrum reflect the physical properties of the luminophor. So, keeping the spectrum from distortion is very important in its measurement. However, we find that the spectrum linewidth will be broadened when the near-infrared radiation from a sodium lamp passes through a nonselective linear absorbing filter. This counterintuitive linewidth-broadening phenomenon is obvious when the residual light power after the filter is low enough, typically lower than 2.48×10−4 μW. This novel linewidth-broadening effect is different from the well-known Lorentzian, Doppler, and Voigt broadening, and is likely to be more independent evidence of the discrete wavelet structure of classical plane light waves. The effect is significant in high-sensitivity spectroscopy measurements, for example streak camera spectroscopy and Raman spectroscopy experiments. In addition, this effect may also be significant for cosmological research.

Rapid Sample Pretreatment Facilitating SERS Detection of Trace Weak Organic Acids/Bases in Complex Matrices.

Fast and efficient sample pretreatment is the prerequisite for realizing surface-enhanced Raman spectroscopy (SERS) detection of trace targets in complex matrices, which is still a big issue for the practical application of SERS. Recently, we have proposed a highly performed liquid-liquid extraction (LLE)-back extraction (BE) for weak acids/bases extraction in drinking water and beverage samples. However, the performance efficiency decreased drastically on facing matrices like food and biological blood. Based on the total interaction energies among target, interferent, and extractant molecules, solid-phase extraction (SPE) with a higher selectivity was introduced in advance of LLE-BE, which enabled the sensitive (μg L-1 level) and rapid (within 10 min) SERS detection of both koumine (a weak base) and celastrol (a weak acid) in different food and biological samples. Further, the high SERS sensitivity was determined unmanned by Vis-CAD (a machine learning algorithm), instead of the highly demanded expert recognition. The generality of SPE-LLE-BE for various weak acids/bases (2 < pKa < 12), accompanied by the high efficiency, easy operation, and low cost, offers SERS as a powerful on-site and efficient inspection tool in food safety and forensics.

High sensitivity and stability cavity-enhanced photoacoustic spectroscopy with dual-locking scheme

We present a high sensitivity and long-term stability cavity-enhanced photoacoustic spectroscopy (CE-PAS) system with optical cavity and acoustic frequency dual-locking scheme for trace acetylene (C2H2) detection. The first mechanism involves locking the optical wavelength to the cavity resonance by comparing the phase-sensitive component of the reflected light with a reference signal in a feedback loop. The second locking mechanism controls the gas proportion inside the photoacoustic cell to lock the acoustic frequency, suppressing the drift caused by environmental temperature variation. By minimizing amplitude fluctuations through dual-locking, the sensor achieves improved stability with reduced fluctuations from ±10.12 % to ±1.16 %. The linear responsivity and excellent linearity of the sensor are demonstrated over a concentration variation spanning four orders of magnitude. Experimental results showcase a minimum detection limit of 1.2 parts-per-billion (ppb) at an integration time of 400 s, corresponding to a normalized noise equivalent absorption (NNEA) coefficient of 1.37×10−11 cm−1·W· Hz−1/2 for C2H2 detection. Long-term stability is within ±2 % over a 15-day period. The combination of high sensitivity and long-term stability make this CE-PAS sensor suitable for a wide range of applications in environmental monitoring, industrial process control, and gas leak detection.

Design superhydrophobic no-noble metal substrates for highly sensitive and signal stable SERS sensing

Surface-enhanced Raman spectroscopy (SERS) is an analytical technique with a broad range of potential applications in fields such as biomedicine, electrochemistry, and hazardous chemicals. However, it is challenging to develop SERS substrates that are both good sensitive and signal stable. Here we designed a superhydrophobic Nd doped MoS2 uniformly assembled on the activated carbon fiber cloth (CFC) to avoid the coffee ring effect and enrich the analyte, improving the enhancement factor (EF) to 3.9 × 109 and pesticide endosulfan (<10−10) analyte detection. We demonstrate our strategy by density-functional theory (DFT) calculations confirming that both adsorption energy and density of states are enhanced after doping Nd leading to SERS enhancement. Beside DFT calculations, our experiments also provide an effective means to demonstrate that the high SERS sensitivity is based on multiple charge transfer processes combined with the activated carbon cloth. Our results address the limitations of low sensitivity and limit of detection (LOD) of semiconductor SERS substrates for trace analysis and are a step towards practical applications.

High sensitivity and ultra-low concentration range photoacoustic spectroscopy based on trapezoid compound ellipsoid resonant photoacoustic cell and partial least square

A high sensitivity and ultra-low concentration range photoacoustic spectroscopy (PAS) gas detection system, which was based on a novel trapezoid compound ellipsoid resonant photoacoustic cell (TCER-PAC) and partial least square (PLS), was proposed to detect acetylene (C2H2) gas. In the concentration range of 0.5 ppm ∼ 10.0 ppm, the limit of detection (LOD) values of TCER-PAC-based PAS system without data processing was 66.4 ppb, which was lower than that of the traditional trapezoid compound cylindrical resonant photoacoustic cell (TCCR-PAC). The experimental results indicated that the TCER-PAC had higher sensitivity than of TCCR-PAC. Within the concentration range of 12.5 ppb ∼ 125.0 ppb, the LOD and limit of quantification (LOQ) of TCER-PAC-based PAS system combined with PLS regression algorithm were 1.1 ppb and 3.7 ppb, respectively. The results showed that higher detection sensitivity and lower LOD were obtained by PAS system with TCER-PAC and PLS than that of TCCR-PAC-based PAS system.

A comparison of methods of analysis of heavy metals in soil samples of Mitrovica environment, Republic of Kosovo

In this work, the distribution of heavy metals in surface soil samples (0-5 cm) from the MitrovicaRegion, was studied. The investigated region (301.5 km2) is covered by a sampling grid of 1.4×1.4 km. Intotal 156 soil samples from 149 locations were collected. Digestion methods, including Aqua RegiaDigestion (mixture of HNO3 and HCl and water at 95ºC - the 1DX1 method) and acid digestion: use ofconcentrated acids such as hydrofluoric acid (HF), hydrochloric acid (HCl), nitric acid (HNO3) andperchloric acid (HClO4) (ISO 14869- 1:2001(E) method), are used to prepare samples for spectroscopicanalysis. High-sensitivity spectroscopy techniques such as inductively coupled plasma emissionspectrometry (ICP-AES) and inductively coupled plasma mass spectrometry (ICP-MS) were applied tomeasure the concentration of Ni and Co in soil samples. Data analysis and construction of the map wereperformed using the Statistica (ver. 9), AutoDesk Map (ver. 2008) and Surfer (ver. 9) software. It was foundthat the average content of Ni and Co in the surface soil for the entire study area is 96 mg/kg (with a rangeof 7.6-2600 mg/kg) and 22 mg/kg (with a range of 2.7-1600 mg/kg), respectively. The obtained averageand median values obtained by ICP-MS are very similar to those obtained by ICP-AES. Namely, thecorrelation factor for Co and Ni between the results from both methods are 0.92 (for normal distribution),0.93 (for logarithmic) and 0.94 (for rank), and 0.86 (for normal distribution), 0.94 (for logarithmic) and0.96 (for rank), respectively. The obtained results show that the high concentrations of Ni and Co in thesurface soil samples may originate from similar sources and their distribution follows the lithology of thestudy area.

Evidence for intrinsic defects and nanopores as hotspots in 2D PdSe2 dendrites for plasmon-free SERS substrate with a high enhancement factor

Surface-enhanced Raman spectroscopy (SERS), a very powerful tool for the identification of molecular species, has relied mostly on noble metal-based substrates to obtain a high enhancement factor. In this work, we demonstrate that self-driven intrinsic defects in 2D palladium di-selenide (PdSe2) dendrites grown at low temperature (280 °C) act as hotspots for high SERS enhancement. We grow 2D dendritic PdSe2 with ample intrinsic defects to exploit it for SERS application. X-ray electron spectroscopy (XPS) analysis reveals 9.3% outer layer and 4.7% interior Se vacancies. A detailed examination of atomic-scale defects revealed Se vacancy (VSe) coupled with Se–Pd–Se vacancy (VSe-Pd-Se) in monolayer PdSe2, and an array of line defects (Se vacancies) and nanopores in bilayer PdSe2 dendrites. Interestingly, our studies reveal that Se vacancy-rich PdSe2 gives rise to line defects that act like hotspots for SERS enhancement. Remarkably, the vacancy-rich dendritic PdSe2 shows a SERS enhancement factor >105 and can detect RhB at a concentration down to 10−8 M. We speculate that the topological line defects and the edge construction in PdSe2 dendrites act as metallic wire or edge, which is partly responsible for the high enhancement in the SERS signal. The high SERS sensitivity is explained on the basis of multiple charge transfer processes combined with the predicted metal-like behavior of the defected 2D PdSe2. Our conclusions are fully supported by the density functional theory calculation of the electronic density of states of the defective bilayer (2L) PdSe2, which remarkably exhibits metallic character. Being a defect-enabled SERS substrate, dendritic 2D PdSe2 fills the gap between conventional plasmonic SERS substrate and plasmon-free SERS substrate.

A comparison of methods of analysis of heavy metals in soil samples of Mitrovica environment, Republic of Kosovo

In this work, the distribution of heavy metals in surface soil samples (0-5 cm) from the Mitrovica Region, was studied. The investigated region (301.5 km2) is covered by a sampling grid of 1.4×1.4 km. In total 156 soil samples from 149 locations were collected. Digestion methods, including Aqua Regia Digestion (mixture of HNO3 and HCl and water at 95ºC- the 1DX1 method) and acid digestion: use of concentrated acids such as hydrofluoric acid (HF), hydrochloric acid (HCl), nitric acid (HNO3) and perchloric acid (HClO4) (ISO 14869- 1:2001(E) method), are used to prepare samples for spectroscopic analysis. High-sensitivity spectroscopy techniques such as inductively coupled plasma emission spectrometry (ICP-AES) and inductively coupled plasma mass spectrometry (ICP-MS) were applied to measure the concentration of Ni and Co in soil samples. Data analysis and construction of the map were performed using the Statistica (ver. 9), AutoDesk Map (ver. 2008) and Surfer (ver. 9) software. It was found that the average content of Ni and Co in the surface soil for the entire study area is 96 mg/kg (with a range of 7.6-2600 mg/kg) and 22 mg/kg (with a range of 2.7-1600 mg/kg), respectively. The obtained average and median values obtained by ICP-MS are very similar with those obtained by ICP-AES. Namely, the correlation factor for Co and Ni between the results from both methods are 0.92 (for normal distribution), 0.93 (for logarithmic) and 0.94 (for rank), and 0.86 (for normal distribution), 0.94 (for logarithmic) and 0.96 (for rank), respectively. The obtained results show that the high concentrations of the Ni and Co in the surface soil samples may originate from similar sources and their distribution follows the lithology of the study area.

Metal–Organic Framework Nanoparticle Films for Surface-Enhanced Raman Spectroscopy-Based Autograding in the Odor Intensity of Gas Mixture Generated from Kitchen Waste

As few odorous molecules in a gas mixture make a great contribution to its odor intensity, autograding in odor intensity is the key process and of great challenge in the prevention of odor pollution. In this work, the surface-enhanced Raman spectroscopy (SERS) spectra of a gas mixture from kitchen waste are detected on plasmonic MOF nanoparticle (NP) films for autograding in odor intensity. To obtain plasmonic MOF NP films with high SERS sensitivity, AgNP@ZIF-8 NPs with different shell thicknesses and adsorbing times are investigated, which is further confirmed by the simulation of electric field distribution and airflow distribution. Then, a 45 nm shell thickness and 3H adsorbing time are selected to collect the SERS spectra of the gas mixture from kitchen waste with different odor intensities. These SERS spectra point out that the odorous molecules generated from the different statuses of kitchen waste dominate the odor intensity of the gas mixture. Furthermore, autograding in odor intensities with four levels based on deep learning (DL) is achieved here. The results exhibit excellent diagnostic accuracy (93.3%) for the external held-out overall dataset, which indicates that a high-throughput, rapid, and label-free tool for screening odor intensities could be developed. Our work not only enriches the research of gas detection by SERS spectra but also improves the prevention technique of odor pollution.

All-optical thermometry using a single multimode fiber endoscope and diamond nanoparticles containing nitrogen vacancy centers.

Photoluminescence (PL) spectra from diamond nanoparticles containing negative nitrogen vacancy centers were measured by using a single multimode fiber endoscope combined with a high-sensitivity spectroscopy system. A laser light spot was produced at the distal end of the endoscope and the PL spectra from a temperature-controlled ensemble of diamond nanoparticles were measured. After calibrating the sensitivity and wavelength of the spectroscopy system, the temperature dependence of the zero-phonon line peak wavelength similar to those previously reported was obtained.

Measurement Technique of Oxygen Concentration in Narrow Channels of PEFCs Based on Transmission Laser Absorption Spectroscopy

Oxygen transport at cathodes of polymer electrolyte fuel cells (PEFCs) is one of the key factors for determining their power generation performance. To maintain their stable operations, it’s necessary to establish a technique for real-time monitoring of oxygen concentration inside cathode channels of operational cells. In the previous works, the measurements of oxygen distribution within gas channels of operating PEFCs have been conducted using gas chromatograph (GC) [1], oxygen-quenching of fluorescence and phosphorescence [2], and tunable diode laser absorption spectroscopy (TDLAS) [3]. GC techniques provide better accuracy for gas detection in flow channels, however, it takes a long time (at least a few minutes) to collect a gas sample and identify a species. On the other hand, TDLAS enables the non-invasive in-situ monitoring of chemical species inside cells with a high time resolution of 100 milliseconds. Fujii et al. [3] applied the single-ended TDLAS sensor to measure the oxygen concentration in a PEFC channel. In their experiments, since the laser beam is injected perpendicular to the flow direction, the optical path length is extremely short and the sensitivity is insufficient. The detection sensitivity of oxygen is relatively low due to the weak infrared absorption. Therefore, the optical path needs to be lengthened to measure its concentration with high accuracy. In this study, to solve the above-mentioned problem, we developed the fiber-optic transmission TDLAS system and applied it to the quantitative measurement of oxygen concentration in the narrow channel of a simulated cell.Fig. 1 shows the experimental apparatus for measuring the oxygen concentration in a simulated flow cell using the fiber-optic transmission TDLAS system. TDLAS is one of the high sensitive absorption spectroscopy techniques which measure the absorbance of a chemical species and identify its concentration using infrared diode laser. The triangular modulated beam emitted from a DFB laser diode (wavelength: 764 nm) is directly injected into the straight narrow channel (width and depth: 1.0 or 1.5 mm, length: 50 mm) through the single-mode optical fiber. To collimate the laser beam at the channel inlet, a GRIN lens is attached at the top of the pitch fiber. The injected beam passes one or two channels along the flow direction. In the case of passing two channels, the beam transmitted through the first channel is turned 180 degrees by a triangular prism at the bend section (length: 5 mm). The returned beam is passed through the second channel and detected at a photodiode. The output signal is transmitted to a lock-in amplifier, and then the second harmonic (2f) absorption spectrum can be obtained by phase-sensitive detection. In the experiments, the mixed gas of oxygen and nitrogen was supplied to the channel at 100 ml/min. The oxygen concentration in the channels was adjusted to 0 to 100% by controlling each gas flow rate. This measurement was performed at 25 oC and 1 atm.Fig. 2 presents the 2f absorption signals of oxygen in the narrow channel of the simulated flow cell. The incident laser beam passed two straight channels (channel width and depth: 1.5 mm, optical path: 105 mm). The oxygen mole fraction was varied from 0 to 100%. Although the TDLAS measurements were performed inside the narrow channels, the optical fringe noise was hardly observed and the 2f spectra were clearly obtained. It was also noted that the peak-valley height of 2f spectrum increased with an increase in oxygen mole fraction. The oxygen concentration in fuel cell channels can be quantitatively estimated from only the 2f spectrum data using the fiber-optic transmission TDLAS technique.

Fabrication of spectroscopic characterization techniques using an optical fiber-based spectrometer.

High-sensitive spectroscopy instruments have been developed to measure thermoluminescence emission (TLE), diffuse reflectance, and photoluminescence (PL). The key features of these instruments are low cost, high resolution, and compact size. For TLE measurement, A Kanthal resistive heating strip with a linear heating rate and Ocean Optics spectra suite software were used. Thermally stimulated emission of light was recorded using a USB4000+ES spectrophotometer in the UV-Vis region. In the TLE spectra, intensity vs wavelength was recorded as a function of temperature. In the high instance TLE spectrum of Al2O3, Tm3+ measured at 458K shows peaks at 298, 355, 394, 466, 526, 658, 672, 696, and 713nm. The UV-Vis DRS spectrum of the ZnO powder sample was measured at room temperature in the wavelength range 230-750nm. The optical bandgap of ZnO was determined using Kubelka-Munk theory and found to be 3.22eV. In the PL setup, a xenon lamp as the excitation source, direct-attach cuvette holder, visible light filter, IR filter, and adjustable UV bandpass linear variable filter were used. The excitation wavelength was fixed using a filter, and the emission spectra of samples were recorded. In the PL emission spectrum of Al2O3, Tb3+ shows bands at 382, 420, 438, 462, 487, 543, 586, and 623nm, which are characteristic of Tb3+ ions. The obtained PL results are compared with data acquired using the Hitachi (F-2700) fluorescence spectrometer. This cost-effective spectroscopy instrument will be beneficial in materials science research in order to investigate the optical properties of the materials by study of TLE, PL, and diffuse reflectance.

Electric quadrupole transitions in carbon dioxide.

Recent advances in high sensitivity spectroscopy have made it possible, in combination with accurate theoretical predictions, to observe, for the first time, very weak electric quadrupole transitions in a polar polyatomic molecule of water. Here, we present accurate theoretical predictions of the complete quadrupole rovibrational spectrum of a non-polar molecule CO2, important in atmospheric and astrophysical applications. Our predictions are validated by recent cavity enhanced absorption spectroscopy measurements and are used to assign few weak features in the recent ExoMars Atmospheric Chemistry Suite mid-infrared spectroscopic observations of the Martian atmosphere. Predicted quadrupole transitions appear in some of the mid-infrared CO2 and water vapor transparency regions, making them important for detection and characterization of the minor absorbers in water- and CO2-rich environments, such as those present in the atmospheres of Earth, Venus, and Mars.

SERS Approach to Probe the Adsorption Process of Trace Volatile Benzaldehyde on Layered Double Hydroxide Material.

The study of the physicochemical process of volatile organic compound (VOC) adsorption on porous materials is significant for design and screening of adsorbent materials and treatment of VOCs. Traditional measurement methods for studying the adsorption process require lots of adsorbates and adsorbents and are time-consuming. We proposed a facile strategy to study the adsorption process of trace gaseous aldehydes on layered double hydroxide (LDH) using surface-enhanced Raman spectroscopy (SERS). We prepared a composite of Ag nanocubes@hollow Co-Ni LDH (AgNCs@Co-Ni LDH) with a strong adsorption capability and high SERS sensitivity. The adsorption properties of LDH for benzaldehyde in terms of general kinetics and isotherms were investigated. The kinetic adsorption process could be fitted better by the pseudo-first-order kinetics with a higher correlation coefficient than by the pseudo-second-order model, and the adsorption rate of 0.0308 min-1 was obtained from the fitting curve. The isotherm adsorption fits the Langmuir isotherm model, and its adsorption constant is 6.25 × 106 L/mol. Taking advantage of the excellent adsorptive performance and SERS activity, the AgNCs@Co-Ni LDH composite can be used as an effective SERS probe to detect gaseous aldehydes, and it shows a linear dynamic range (5-100 ppb) with a limit of detection reaching 1.83 ppb for benzaldehyde, better than that achieved by previous studies. Therefore, this work has not only established a new measurement method for probing the adsorption process with extremely low consumption of both adsorbates and adsorbents, but also may lay the groundwork for the construction of rapid and ultra-sensitive SERS sensors for probing VOCs in the future.

Beta-delayed charged-particle spectroscopy using TexAT

β-delayed charged-particle emission is a sensitive probe of three-body decays in light nuclei. Time Projection Chambers (TPCs) offer a significant advantage over traditional charged-particle spectroscopy techniques due to a low-energy threshold and a high-geometric efficiency (≈4π) which are essential for use with radioactive ion beams where the beam intensities are limited. The technique for high-sensitivity spectroscopy of β-delayed charged-particle emission is shown to be possible using the Texas Active Target (TexAT) TPC in conjunction with the General Electronics for TPCs (GET) system. The benchmark case studied was that of 12Nβ-decay to the first α-unbound state in 12C, the Hoyle state. Half-life and branching ratio measurements are presented and are in good agreement with previous studies. The efficacy of using TPCs to study such a near-threshold state and disentangle the three-body dynamics of the decay products is demonstrated.

Improving the analysis accuracy of components in blood by SSP-MCSD and multi-mode spectral data fusion.

In recent years, spectral quantitative analysis for blood components has been a research hotspot in biomedical engineering. But researches have been limited to the application of high-sensitivity spectroscopy instruments and the complexity of blood components-the overlapping of absorption curves for many components is severe. This has led to the difficulty in achieving satisfactory results when using spectroscopy to quantify components in blood. In order to enhance the model robustness and improve the model performance, this paper proposed a sample set partitioning strategy based on multi-component spatial distance (SSP-MCSD). Different from the other sample set partitioning strategies, which only consider the uniformity of the concentration distribution of the target component, this strategy also concerns to the concentration distribution of non-target components. The concentration of the target component and non-target components are used to construct a multi-dimensional space, and the Euclidean Distance of sample points in this space is used as the criterion to partition the sample set. At the same time, the spectra collected in multi-modes are fused for increasing the amount of information. So as to enhance the model robustness and to improve the analysis accuracy of the target components. In order to verify the effectiveness of this strategy, the serum of 101 volunteers was analyzed. Taking total protein in serum as the non-target component, the regression model for bilirubin concentration was established by transmission spectra, fluorescence spectra, and the joint spectra after fusion of the above two spectra, respectively. The experimental results showed that the prediction accuracy of the model established by SSP-MCSD combined with multi-mode spectral fusion is obviously higher than that of other methods. It can effectively improve the analysis accuracy of blood components.

Surface-Enhanced Raman Spectroscopy of 2D Organic Semiconductor Crystals

Recently developed ultrathin two-dimensional (2D) organic semiconductor crystals are a promising platform for advanced organic electronic devices. Remarkable quality of such crystals results in charge-carrier mobilities comparable to those of bulk crystals, but their structure and orientation are hard to study because of their extremely small thickness. Here, we applied surface-enhanced Raman spectroscopy (SERS) to investigate the structure of the thinnest 2D single crystals—monolayers, which are based on thiophene-phenylene co-oligomers: 1,4-bis(5′-decyl-2,2′-bithiene-5-yl)benzene and 1,4-bis(5′-hexyl-2,2′-bithiene-5-yl)benzene. Their Raman spectra were calculated as a function of the molecule orientation and SERS microscopy maps were acquired. High sensitivity of SERS allowed us to study monolayer single-crystal domains with the optical spatial resolution. Raman anisotropy was used to probe the orientations of single-crystal domains and the molecule orientation within them. Notably, the SERS microscopy ...

Wafer‐Scale Polymer‐Based Transparent Nanocorals with Excellent Nanoplasmonic Photothermal Stability for High‐Power and Superfast SERS Imaging

AbstractPolymer‐based surface‐enhanced Raman spectroscopy (SERS) substrates offer distinctive advantages such as low‐cost and high optical transparency which allows direct detection of trace chemicals on target surfaces and easy microfluidic integration. However, incident‐laser‐induced localized surface plasmon resonances can generate heat that deform the polymer and significantly reduce the intensities of recorded SERS signals. Herein, a novel wafer‐scale polymer‐based transparent nanocoral (WTNC) SERS substrate with 3D electromagnetic “hotspots” is presented. Its fabrication is simple and lithography‐free. The novel SERS substrate demonstrates excellent nanoplasmonic heat resistance, high SERS sensitivity, and unmatched SERS signal uniformity with a relative standard deviation of ≈6% across 80 mm. Excellent photothermal stability is achieved by highly crosslinking SU‐8, a negative epoxy photoresist, raising its initial degradation temperature to ≈230 °C, much higher than the glass transition temperature of state‐of‐the‐art thermalplasts used in SERS substrates, including polyethylene terephthalate and poly(methyl methacrylate). The WTNC substrate can withstand very high laser irradiance of up to 300 kW cm−2, enabling superfast SERS imaging of analytes in extremely small quantities. A high resolution SERS image containing 10 201 spectra of ≈44 amol trans‐1,2‐bis(4‐pyridyl)ethylene is obtainable in &lt;5 min. The WTNC substrate pushes the state‐of‐the‐art in polymer‐based SERS substrates and has great potential for rapid routine analyses.

Sideband amplitude modulation absorption spectroscopy of CH4 at 1170 nm.

We report on the method of the sideband amplitude modulation (SAM) to achieve high-sensitivity spectroscopy with a fiber electro-optic modulator (fiber-EOM). This method increases the signal to noise ratio (SNR) by a factor of forty, comparing with conventional absorption spectroscopy. It is a temporal balanced detection to eliminate the intensity noise of the light source, and capable of preserving an undistorted Doppler profile for further quantitative analysis. Taking advantage of the newly developed fiber-EOM, SAM is applicable for various spectroscopies with a simple experimental setup. We performed SAM on CH43ν3 overtone band at 1170 nm using an external cavity Quantum dot laser. We demonstrated that one of the absorption lines buried in the other ten times stronger nearby lines was clearly extracted. SAM shows great potential on the molecular spectroscopy, where the spectrum is complicated and quantitative analysis is required.

Application of High-Sensitivity UV photoemission Spectroscopy to Examine the Electronic Structure of Thermophilic Rhodopsin

The electronic structures of materials such as HOMO and LUMO are essential information to understand their functions. Photoemission spectroscopy, which is the most standard technique to examine the electronic structures of various materials, has been not well applied to biomolecules mostly due to sample charging and poor sensitivity. Very recently, we have developed high-sensitivity photoemission spectroscopy (HS-PES) using low photon energy. In this study, HS-PES has been successfully applied to a thermophilic rhodopsin (TR) film. The high sensitivity of our technique enabled to observe the HOMO region of retinal part in TR without any problem due to sample charging. This technique is expected to explore the electronic structures of various proteins.