Weak Raman Signal Research Articles

Eumelanin and pheomelanin are predominant pigments in bumblebee (Apidae: Bombus) pubescence.

BackgroundBumblebees (Hymenoptera: Apidae: Bombus) are well known for their important inter- and intra-specific variation in hair (or pubescence) color patterns, but the chemical nature of the pigments associated with these patterns is not fully understood. For example, though melanization is believed to provide darker colors, it still unknown which types of melanin are responsible for each color, and no conclusive data are available for the lighter colors, including white.MethodsBy using dispersive Raman spectroscopy analysis on 12 species/subspecies of bumblebees from seven subgenera, we tested the hypothesis that eumelanin and pheomelanin, the two main melanin types occurring in animals, are largely responsible for bumblebee pubescence coloration.ResultsEumelanin and pheomelanin occur in bumblebee pubescence. Black pigmentation is due to prevalent eumelanin, with visible signals of additional pheomelanin, while the yellow, orange, red and brown hairs clearly include pheomelanin. On the other hand, white hairs reward very weak Raman signals, suggesting that they are depigmented. Additional non-melanic pigments in yellow hair cannot be excluded but need other techniques to be detected. Raman spectra were more similar across similarly colored hairs, with no apparent effect of phylogeny and both melanin types appeared to be already used at the beginning of bumblebee radiation.DiscussionWe suggest that the two main melanin forms, at variable amounts and/or vibrational states, are sufficient in giving almost the whole color range of bumblebee pubescence, allowing these insects to use a single precursor instead of synthesizing a variety of chemically different pigments. This would agree with commonly seen color interchanges between body segments across Bombus species.

Fructose and Pectin Detection in Fruit-Based Food Products by Surface-Enhanced Raman Spectroscopy.

Surface-Enhanced Raman Spectroscopy (SERS) enables the investigation of samples with weak specific Raman signals, such as opaque samples, including fruit juices and pulp. In this paper, biological apple juices and apple/pear pulp have been studied in order to evidence the presence of fructose and pectin, which are components of great relevance for quality assessment of these kinds of products. In order to perform SERS measurements a low-cost home-made substrate consisting of a glass slide decorated with 30-nm-sized gold nanoparticles has been designed and used. By employing a conventional micro-Raman spectroscopy set-up and a suitable data treatment based on “wavelet” denoising algorithms and background subtraction, spectra of pectin and fructose with clear Raman features have been obtained. The results have confirmed the potential of SERS in the food industry for product characterization, also considering the low-cost and the relative ease of the fabrication process of the employed SERS substrate.

In ovo sexing of chicken eggs by fluorescence spectroscopy.

Culling of day-old male chicks in production of laying hen strains involves several millions of animals every year worldwide and is ethically controversial. In an attempt to provide an alternative, optical spectroscopy was investigated to determine nondestructively in ovo the sex of early embryos of the domestic chicken. The extraembryonic blood circulation system was accessedby producing a window in the egg shell and the flowing blood was illuminated with a near-infrared laser. The strong fluorescence and the weak Raman signals were acquired and spectroscopically analyzed between 800 and 1000nm. The increase of fluorescence intensity between 3.5 and 11.5days of incubation was found to be in agreement with the erythropoietic stages, thus enabling to identify hemoglobin as fluorescence source. Sex-related differences in the fluorescence spectrum were found at day 3.5, and principal component (PC) analysis showed that the blood of males was characterized by a specific fluorescence band located at ∼910nm. Supervised classification of the PC scores enabled the determination of the sex of 380 eggs at day 3.5 of incubation with a correct rate up to 93% by combining the information derived from both fluorescence and Raman scattering. Graphical abstract The fluorescence of blood obtained in ovo by illumination of embryonic vessels with a IR laser displays spectral differences that can be employed for sexing of eggs in early stage of incubation, before onset of embryo sensitivity and without hindering its development into a healthy chick.

A whole spectroscopic mapping approach for studying the spatial distribution of pigments in paintings

We propose a non-invasive approach for the identification and mapping of pigments in paintings. The method is based on three highly complementary imaging spectroscopy techniques, visible multispectral imaging, X-Ray fluorescence mapping and Raman mapping, combined with multivariate data analysis of multidimensional spectroscopic datasets for the extraction of key distribution information in a semi-automatic way. The proposed approach exploits a macro-Raman mapping device, capable of detecting Raman signals from non-perfectly planar surfaces without the need of refocusing. Here, we show that the presence of spatially correlated Raman signals, detected in adjacent points of a painted surface, reinforces the level of confidence for material identification with respect to single-point analysis, even in the presence of very weak and complex Raman signals. The new whole-mapping approach not only provides the identification of inorganic and organic pigments but also gives striking information on the spatial distribution of pigments employed in complex mixtures for achieving different hues. Moreover, we demonstrate how the synergic combination on three spectroscopic methods, characterized by highly different time consumption, yields maximum information.

The Recording and Summing System of Weak Signals in the Fourier Spectrometer

One of the problems in remote monitoring and analysis is to record and analyze accumulation and summation of weak signals, which have intensity at the noise level. Therefore, it becomes necessary to correct accumulation and summation of signal to pull it at the background of noise. In the existing schemes of Fourier spectrometers, which use a white light channel, a recording process of the interferogram in the main channel starts at zero optical path difference (ZPD) of the white light channel, and thus binding to the same absolute scale of the optical path difference. With this construction scheme, there should be a shift of the ZPD of the white light channel with respect to the ZPD of the main channel, using the optical methods, so that we can record a double-sided interferogram. The additional optical elements can lead to the shift of ZPD in the white light channel with respect to the main channel. To solve the given problem we suggest a mechanism of using the white light channel, in which the ZPD positions of both channels match. In this case, the ZPD of the white light forms a mark on the optical path difference scale in the interferogram of the main channel. Further, using this label, the recorded interferograms are shifted and linked to the absolute scale of the optical path difference, after which they are summed-up. To implement this summing mechanism was developed driver of white light label, which allows us to bind a maximum position in the interferogram of the main channel with the maximum in the interferogram of the white light channel. Such construction of the binding system allows us to reduce the size of the entire system and provide more stability to thermal and vibration shocks. The described system of a label driver has found a successful implemented in the layout of the continuous scanning dynamic Fourier spectrometer operating in the Near Infrared spectral range from 800 nm to 1100 nm. The experimental research in recording and accumulating weak Raman signals when exciting by the laser source of 785 nm wavelength used the proposed system. Further comparison of the recovered Raman spectra with reference spectra proved that the proposed interferogram summation system is efficient.

Surface enhanced Raman scattering of melamine on silver substrate: An experimental and DFT study

Surface enhanced Raman spectroscopy (SERS) is a powerful vibrational spectroscopy technique that allows amplifying weak Raman signals by the excitation of localized surface plasmons. In this paper, we used nanoscale roughened silver surface to enhance Raman signals of melamine analyte. Silver nanoparticles were synthesized by wet-chemical method and employed for SERS measurement. Theoretically, optimized geometries and vibrational frequencies of melamine and melamine absorbed on silver-cluster surface were calculated by using the B3LYP/6-31G(d) method. Then, the predicted spectrograms are compared with the experimental Raman spectra. As a result, Raman signals of melamine were dramatically enhanced by using obtained silver nanoparticles as the substrate. Typical peaks of melamine at 676 and 983cm−1 were enhanced and could be obviously observed in experiments. The calculated vibrational frequencies seem to relatively coincide with the experimental values. SERS effect of melamine on nanoscale silver was also explained by analyzing molecular frontier orbitals (HOMO and LUMO) melamine–silver complexes.

Flexible and Transparent Surface-Enhanced Raman Scattering (SERS)-Active Metafilm for Visualizing Trace Molecules via Raman Spectral Mapping.

Raman spectral mapping is a powerful tool for directly visualizing the composition, structure, and distribution of molecules on any surface of interest. However, one major limitation of Raman mapping is its overlong imaging time caused by the intrinsic weak Raman signal. Here, we developed a fast Raman imaging approach based on a flexible and transparent surface-enhanced Raman scattering (SERS)-active metafilm. This particular SERS substrate can be conformably attached to a sample surface to enhance the Raman signal of analytes and the good optical transparency allow excitation and collection of signal from the backside of the substrate. Therefore, by simply attaching it to the surface of interest, a fast Raman imaging can be realized. We noticed that the imaging speed can be increased by several orders of magnitude, compared to a conventional Raman mapping approach. Importantly, the proposed approach required little or no sample preparation and exhibited good generalizability that can be performed perfectly on different surfaces. It is believed that the proposed methodology will provide new trends for chemical imaging using Raman microscopy.

A Method to Create a Universal Calibration Dataset for Raman Reconstruction Based on Wiener Estimation

Raman spectroscopy has been intensively explored in biomedical applications. However, Raman data acquisition is generally slow due to inherently weak Raman signals. Narrow-band Raman measurements can compensate for the weak Raman signal by performing integration in the wavenumber dimension, in which the Raman spectrum with high spectral resolution needs to be reconstructed from the narrow-band measurements. However, this method is limited in the requirement of a calibration dataset, in which the calibration samples have to be similar to test samples in Raman features. Therefore, a new calibration dataset is often needed for every type of samples. We propose a method to create a universal calibration dataset for Raman reconstruction to overcome this limitation. In our method, the Raman spectra measured from each basic biochemical component in samples instead of from actual samples are used in the calibration dataset. In this study, the proposed method was tested on 27 liquid phantoms and 56 cell measurements. The results demonstrated the excellent performance of Raman reconstruction using the universal calibration dataset compared to that using the traditional calibration dataset and the measured Raman spectra.

Noise Removal with Maintained Spatial Resolution in Raman Images of Cells Exposed to Submicron Polystyrene Particles.

The biodistribution of 300 nm polystyrene particles in A549 lung epithelial cells has been studied with confocal Raman spectroscopy. This is a label-free method in which particles and cells can be imaged without using dyes or fluorescent labels. The main drawback with Raman imaging is the comparatively low spatial resolution, which is aggravated in heterogeneous systems such as biological samples, which in addition often require long measurement times because of their weak Raman signal. Long measurement times may however induce laser-induced damage. In this study we use a super-resolution algorithm with Tikhonov regularization, intended to improve the image quality without demanding an increased number of collected pixels. Images of cells exposed to polystyrene particles have been acquired with two different step lengths, i.e., the distance between pixels, and compared to each other and to corresponding images treated with the super-resolution algorithm. It is shown that the resolution after application of super-resolution algorithms is not significantly improved compared to the theoretical limit for optical microscopy. However, to reduce noise and artefacts in the hyperspectral Raman images while maintaining the spatial resolution, we show that it is advantageous to use short mapping step lengths and super-resolution algorithms with appropriate regularization. The proposed methodology should be generally applicable for Raman imaging of biological samples and other photo-sensitive samples.

Modulating the Morphology of Gold Graphitic Nanocapsules for Plasmon Resonance-Enhanced Multimodal Imaging.

With their unique optical properties and distinct Raman signatures, graphitic nanomaterials can serve as substrates for surface-enhanced Raman spectroscopy (SERS) or provide signal amplification for bioanalysis and detection. However, a relatively weak Raman signal has limited further biomedical applications. This has been addressed by encapsulating gold nanorods (AuNRs) in a thin graphitic shell to form gold graphitic nanocapsules. This step improves plasmon resonance, which enhances Raman intensity, and has the potential for integrating two-photon luminescence (TPL) imaging capability. However, changing the morphology of gold graphitic nanocapsules such that high quality and stability are achieved remains a challenge. To address this task, we herein report a confinement chemical vapor deposition (CVD) method to prepare the construction of AuNR-encapsulated graphitic nanocapsules with these properties. Specifically, through morphological modulation, we (1) achieved higher plasmon resonance with near-IR incident light, thus achieving greater Raman intensity, and (2) successfully integrated two-photon luminescence dual-modal (Raman/TPL) bioimaging capabilities. Cancer-cell-specific aptamers were further modified on the AuNR@G graphitic surface through simple, but strong, π-π interactions to achieve imaging selectivity through differential cancer cell recognition.

All-Solution-Processed Wrinkled Gold Nanoparticles As Sensors

Design and Methodology: Materials with feature sizes spanning the nano- and micro-scale range have been sought after by materials scientists and engineers to address specific functional demands unmet by bulk materials, in fields ranging from energy to sensors. Surface-enhanced Raman scattering (SERS) based sensors for molecular detection rely on nano- and micro-structuring of metallic substrates to amplify the intrinsically weak Raman signal, however fabricating SERS substrates can be tedious and time consuming. Our vision was to create a versatile and simple approach to fabricate SERS substrates. Wrinkling of a thin film on a compliant substrate is a rapid and inexpensive fabrication method for controllably creating materials with features covering several lengthscales.[1] Bioprocessing and biosensing devices have been fabricated using wrinkling with sputtered thin films,[2–4]however we sought to develop a method to create tunable wrinkled materials for SERS without the use of complex, vacuum-based deposition systems. First, a layer of gold nanoparticles was formed on an amino-silane treated heat-shrinkable substrate using self-assembly. Then, wrinkling of the nanoparticle layer was induced by heating the coated polymer substrate over its glass transition temperature, causing the footprint of the substrate to be reduced to 16% of the original area, while exerting a compressive force on the gold nanoparticle layer. The mechanical stress was relieved through the buckling of the gold nanoparticle layer on the surface of the substrate. Original Data and Results: The wrinkling behaviour of the gold nanoparticle film was assessed before shrinking, after shrinking uniaxially (by physically constraining two sides of the substrate), and after shrinking biaxially using scanning electron microscopy (SEM), atomic force microscopy (AFM), and transmission electron microscopy (TEM). Well-ordered uniaxial and biaxial nanoparticle wrinkles were produced across the entire surface of the substrate. In order to control the wavelength and amplitude of the resulting wrinkles, nanoparticles of different diameters (~12 nm, ~18 nm, and ~36 nm) were deposited as the film layer. In addition, we assessed the effect of depositing multiple layers of ~12 nm nanoparticles on the resulting wrinkled structures. We observed that by increasing the diameter of the nanoparticles or by increasing the number of deposited nanoparticle layers, the wavelength and amplitude of the wrinkles could be controllably increased (Figure 1). These wrinkle structured nanoparticle surfaces were applied as SERS substrates, using 4-mercaptopyridine as the target analyte. By tuning the wavelength and morphology of the wrinkled structures, using different sized nanoparticles or multiple nanoparticle layers, the enhancement factor of the various SERS substrates was altered and optimized. Conclusions:We have developed a benchtop all-solution-processing method to create wrinkled metallic nano-/microstructures, tunable in size and morphology, on polymer substrates. By altering the nanoparticle diameters and number of deposited layers, we were able to control the amplitude and wavelength of the resulting wrinkled structures. Moreover, using physical constraints during the shrinking/wrinkling process allows for further regulation of the wrinkle morphology. We have demonstrated that these structures can used to create optical sensors as they were successfully applied as tunable SERS substrates to specifically detect a target analyte, and we envision these nanoparticle polymer composites finding other applications in chemical sensors, biosensors, and optoelectronics. [1] A. Schweikart, A. Horn, A. Böker, A. Fery, Adv. Polym. Sci. 2010, 227, 75. [2] S. M. Woo, C. M. Gabardo, L. Soleymani, Anal. Chem. 2014, 86, 12341. [3] C. M. Gabardo, A. M. Kwong, L. Soleymani, Analyst 2015. [4] A. Hosseini, L. Soleymani, Appl. Phys. Lett. 2014, 105, 074102. Figure 1

Analysis of waveguide-coupled directional emission for efficient collection of Fluorescence/Raman light from surface

A theoretical method based on the optical reciprocity theorem combined with the Fresnel theory has been developed for the analysis of waveguide-coupled directional emission technique, which is useful for the surface Fluorescence/Raman spectroscopy. The Kretschmann-type waveguide with a molecular dipole located above or inside the core layer serves as the simulation model. The two-dimensional (2D) pattern of power density for the waveguide-coupled emission from the molecular dipole was calculated using the theoretical method. According to the results, with a given waveguide the 2D pattern of power density is highly dependent on both the orientation and position of the dipole. The maximum fraction of power occupied by the waveguide-coupled emission is 87% with the plasmon waveguide and 95% with the resonant mirror. Compared with the dipole emission in free space, the waveguide-coupled directional emission possesses easy collection, which is benefit for the detection of weak Fluorescence and Raman signals. From this point, the theoretical method used here is helpful for design and optimization of Kretschmann-type waveguide structures for high-sensitivity surface monitoring by Fluorescence/Raman spectroscopy.

SERS study of bacteria using biosynthesized silver nanoparticles as the SERS substrate

Surface-enhanced Raman scattering (SERS) spectroscopy has great advantages as a spectroscopic analytical tool due to the large enhancement of the weak Raman signal and thereby facilitates suitable identification of chemical and biological systems.

Hyperspectral coherent Raman imaging – principle, theory, instrumentation, and applications to life sciences

Coherent Raman scattering microscopy such as coherent anti‐Stokes Raman scattering and stimulated Raman scattering microscopy boosts the weak Raman signal and enables us to perform label‐free visualization of the molecular distribution and its dynamical behavior in living cells and tissues with high speed. In comparison with fluorescence imaging, cells and tissues can be visualized without specifying the target molecule. In this review, we describe the characteristics of a hyperspectral coherent Raman imaging method, which is capable of acquiring both spectra and images simultaneously, and review applications to life sciences. Copyright © 2015 John Wiley & Sons, Ltd.

Identification of Natural Dyes in Ancient Textiles by Time-of-Flight Secondary Ion Mass Spectrometry and Surface-Enhanced Raman Spectroscopy.

The identification of dyes in archaeological remains is a long standing challenge. Major problems include contamination by environmental conditions over long periods of time, small amounts and limited availability of excavated samples, and low concentrations of dyestuff in the obtained samples. To address these issues, highly sensitive and non-destructive techniques are required. In response, in this work, two non-destructive analytical techniques, Time-of-Flight Secondary Ion Mass Spectrometry (TOF-SIMS) and Surface-Enhanced Raman Spectroscopy (SERS), were used for dye detection and the analysis results are compared. TOF-SIMS provides high detection efficiency for the analysis of organic materials whereas SERS is a useful technique for the detection of dyes in ancient textiles. An Ag colloid was employed to surmount the limitations of normal Raman measurement such as background fluorescence and weak Raman signals in small amounts of components. To identify the dyes used in ancient textiles, standard samples prepared using various dyestuffs and historical samples were analyzed with TOF-SIMS and Raman techniques. From the TOF-SIMS and the SERS spectra, dyestuffs such as alizarin, berberine, an indigo were identified in ancient textiles. The results suggest that TOF-SIMS and SERS are efficient non-destructive techniques for the characterization of archaeological textiles.

Raman spectroscopic detection for liquid and solid targets using a spatial heterodyne spectrometer

Spatial heterodyne Raman spectroscopy (SHRS) is a new type of effective method for the analysis of structure and composition of liquid and solid targets with the characteristics of no moving parts, high spectral resolution, high optical throughput and large field of view. The technique is very suitable for detecting the targets from long distances or under the conditions with ambient light, which is essential for the exploration of planetary surface. In order to have a better understanding of the ability of SHRS for the detection of liquid and solid targets, a breadboard was designed, built and calibrated. Signal to noise was estimated at different integration time or laser power for carbon tetrachloride. Pure materials or materials contained in bottles were both tested. The mixture of organic liquids or inorganic solids were tested. In order to test the detection ability for natural targets, some composition-unknown rocks and pebbles were tested. The results have shown that SHRS can meet the requirements for the detection of weak Raman signal scattered from artificial or natural targets. Standoff detection of sulfur from 5-m or 10-m distance without using any telescope or collimation optics was also tried to test the high optical throughput of SHRS. The potential feasibility of standoff detection has been proved. Copyright © 2015 John Wiley & Sons, Ltd.

Optimization of advanced Wiener estimation methods for Raman reconstruction from narrow-band measurements in the presence of fluorescence background.

Raman spectroscopy has shown great potential in biomedical applications. However, intrinsically weak Raman signals cause slow data acquisition especially in Raman imaging. This problem can be overcome by narrow-band Raman imaging followed by spectral reconstruction. Our previous study has shown that Raman spectra free of fluorescence background can be reconstructed from narrow-band Raman measurements using traditional Wiener estimation. However, fluorescence-free Raman spectra are only available from those sophisticated Raman setups capable of fluorescence suppression. The reconstruction of Raman spectra with fluorescence background from narrow-band measurements is much more challenging due to the significant variation in fluorescence background. In this study, two advanced Wiener estimation methods, i.e. modified Wiener estimation and sequential weighted Wiener estimation, were optimized to achieve this goal. Both spontaneous Raman spectra and surface enhanced Raman spectra were evaluated. Compared with traditional Wiener estimation, two advanced methods showed significant improvement in the reconstruction of spontaneous Raman spectra. However, traditional Wiener estimation can work as effectively as the advanced methods for SERS spectra but much faster. The wise selection of these methods would enable accurate Raman reconstruction in a simple Raman setup without the function of fluorescence suppression for fast Raman imaging.

Demonstration of a signal enhanced fast Raman sensor for multi‐species gas analyses at a low pressure range for anesthesia monitoring

The spontaneous Raman scattering technique is an excellent tool for a quantitative analysis of multi‐species gas mixtures. It is a noninvasive optical method for species identification and gas phase concentration measurement of Raman active molecules, since the intensity of the molecule specific Raman signal is linearly dependent on the concentration. Applying a continuous wave (cw) laser it typically takes a few seconds to capture a gas phase Raman spectrum at room temperature. Nevertheless in contrast to these advantages the weak Raman signal intensity is a major drawback. Thus, it is still challenging to detect gas phase Raman spectra in a low‐pressure regime with a temporal resolution of only a few 100 ms. In the presented study a fully functional gas phase Raman system for measurements in the low‐pressure regime (p ≥ 980 hPa (absolute)) is presented; it overcomes the drawback of the weak Raman effect by using a multipass cavity to enhance the Raman signal. The signal amplification of a retro‐reflecting cavity is experimentally compared to a near‐confocal cavity. A description of this sensor setup as well as of the calibration procedure, which also allows the quantification of condensable gases, is presented. Moreover the functionality of the sensor system is demonstrated in a measurement campaign at an anesthesia simulator under clinical relevant conditions and in comparison to a conventional gas monitor. Copyright © 2015 John Wiley & Sons, Ltd.

Three-dimensional surface-enhanced Raman scattering hotspots in spherical colloidal superstructure for identification and detection of drugs in human urine.

Rapid component separation and robust surface-enhanced Raman scattering (SERS) identification of drugs in real human urine remain an attractive challenge because of the sample complexity, low molecular affinity for metal surface, and inefficient use of hotspots in one- or two-dimensional (2D) geometries. Here, we developed a 5 min strategy of cyclohexane (CYH) extraction for separating amphetamines from human urine. Simultaneously, an oil-in-water emulsion method is used to assemble monodisperse Ag nanoparticles in the CYH phase into spherical colloidal superstructures in the aqueous phase. These superstructures create three-dimensional (3D) SERS hotspots which exist between every two adjacent particles in 3D space, break the traditional 2D limitation, and extend the hotspots into the third dimension along the z-axis. In this platform, a conservative estimate of Raman enhancement factor is larger than 10(7), and the same CYH extraction processing results in a high acceptability and enrichment of drug molecules in 3D hotspots which demonstrates excellent stability and reproducibility and is suitable for the quantitative examination of amphetamines in both aqueous and organic phases. Parallel ultraperformance liquid chromatography (UPLC) examinations corroborate an excellent performance of our SERS platform for the quantitative analysis of methamphetamine (MA) in both aqueous solution and real human urine, of which the detection limits reach 1 and 10 ppb, respectively, with tolerable signal-to-noise ratios. Moreover, SERS examinations on different proportions of MA and 3,4-methylenedioxymethamphetamine (MDMA) in human urine demonstrate an excellent capability of multiplex quantification of ultratrace analytes. By virtue of a spectral classification algorithm, we realize the rapid and accurate recognition of weak Raman signals of amphetamines at trace levels and also clearly distinguish various proportions of multiplex components. Our platform for detecting drugs promises to be a great prospect for a rapid, reliable, and on-spot analyzer.

A signal enhanced portable raman probe for anesthetic gas monitoring

The spontaneous Raman scattering technique is an excellent tool for a quantitative analysis of multi-species gas mixtures. It is a noninvasive optical method for species identification and gas phase concentration measurement of all Raman active molecules, since the intensity of the species specific Raman signal is linearly dependent on the concentration. Applying a continuous wave (CW) laser it typically takes a few seconds to capture a gas phase Raman spectrum at room temperature. Nevertheless in contrast to these advantages the weak Raman signal intensity is a major drawback. Thus, it is still challenging to detect gas phase Raman spectra in alow-pressure regime with a temporal resolution of only a few 100 ms. In this work a fully functional gas phase Raman system for measurements in the low-pressure regime (p ≥ 980 hPa (absolute)) is presented. It overcomes the drawback of a weak Raman signal by using a multipass cavity. A description of the sensor setup and of the multipass arrangement will be presented. Moreover the complete functionality of the sensor system will be demonstrated by measurements at an anesthesia simulator under clinical relevant conditions and in comparison to a conventional gas monitor.