Raman Sensor Research Articles

Determination of gas composition in a biogas plant using a Raman-based sensor system

We propose a gas sensor, based on spontaneous Raman scattering, for the compositional analysis of typical biogas mixtures and present a description of the sensor, as well as of the calibration procedure, which allows the quantification of condensable gases. Moreover, we carry out a comprehensive characterization of the system, in order to determine the measurement uncertainty, as well as influences of temperature and pressure fluctuation. Finally, the sensor is applied at different locations inside a plant in which biogas is produced from renewable raw materials. The composition is monitored after fermenting, after purification and after the final conditioning, where natural gas is added. The Raman sensor is able to detect all the relevant gas components, i.e. CH4, CO2, N2 and H2O, and report their individual concentrations over time. The results were compared to reference data from a conventional gas analyzer and good agreement was obtained.

An acoustically enhanced gold film Raman sensor on a lithium niobate substrate

The surface enhanced Raman scattering effect has shown immense potential for detecting trace amounts of explosive vapor molecules. To date, efforts to produce a commercially available, reliable SERS sensor have been impeded by an inability to separate the electromagnetic enhancement produced by the metallic nanostructure from other signal enhancing effects. Here, we show a new Raman sensor that uses surface acoustic waves (SAWs) to produce controllable surface structures on gold films deposited on LiNbO3 substrates that modulate the Raman signal of a target compound (thiophenol) adsorbed on the films. We demonstrate that this sensor can dynamically control the Raman signal simply by changing the SAW's amplitude, allowing the Raman signal enhancement factor to be directly measured with no variation in the concentration of the target compound. The physically adsorbed molecules can be removed from the sensor without physical cleaning or damage, making it possible to reuse it for real‐time Raman detection. Copyright © 2014 John Wiley & Sons, Ltd.

Nanostructured Au film produced by pulsed laser deposition in air at atmospheric pressure

Abstract This work presents results on direct nanostructured film fabrication by pulsed laser deposition (PLD) of gold in air at atmospheric pressure. Due to specific features of the laser-induced plume evolution at these conditions, the deposited film has a porous structure composed of well defined nanoparticles aggregates. The study based on scanning and transmission electron microscopy images of the deposited material at different processing conditions reveals that these nanoparticle aggregates are formed into the ablated plume due to intensive collisions. The obtained structures show characteristic optical spectra related to excitation of plasmons and can be directly used in practical applications as surface enhanced Raman spectroscopy (SERS) and sensors devices.

Porous Gold Films-A Short Review on Recent Progress.

Porous gold films have attracted increasing interest over the last ten years due to the unique properties of high specific surface area and electrical conductivity combined with chemical stability and ability to alter the surface chemistry. Several methods have been developed to synthesize porous gold films such as de-alloying, templating, electrochemical, and self-assembling. These porous gold films are used in diverse fields, for example, as electrochemical and Raman sensors or for chemical catalysis. Here, we provide a short review on the progress of porous gold films over the past ten years, including the synthesis and applications of such films.

Field test of optical and electrical fire detectors in simulated fire scenes in a cable tunnel

This paper presents the testing results of three types of fire detectors: electrical heat sensing cable, optical fiber Raman temperature sensing detector, and optical fiber Bragg grating (FBG) temperature sensing detector, in two simulated fire scenes in a cable tunnel. In the small-scale fire with limited thermal radiation and no flame, the fire alarm only comes from the heat sensors which directly contact with the heat source. In the large-scale fire with about 5 °C/min temperature rising speed within a 3-m span, the fire alarm response time of the fiber Raman sensor and FBG sensors was about 30 seconds. The test results can be further used for formulating regulation for early fire detection in cable tunnels.

Use of Raman spectroscopy for continuous monitoring and control of lignocellulosic biorefinery processes

AbstractThe production of fuels and chemicals from lignocellulosic biomass demands efficient processes to compete with fossil fuel-derived products. Key biorefinery processes, such as enzymatic hydrolysis of cellulose and microbial fermentation, can be monitored by advanced sensors in real time, providing information about reactant and product concentration, contamination, and reaction progress. Spectroscopic techniques such as Raman spectroscopy provide a means of quickly and accurately assessing many types of reaction mixtures non-destructively, in real time, and with no costly sample preparation and analysis time. Raman spectroscopy techniques have been developed to accurately quantify a number of compounds present in lignocellulosic processes, and methods have been developed to overcome the presence of fluorescent compounds that can increase the spectral background. Online Raman sensors also can provide the feedback measurements necessary for advanced process controls (APCs). Specifically, model predictive control, a common APC used extensively throughout similar processing industries, is especially well suited for ensuring optimal production of bio-based chemicals from lignocellulosic material.

Low-cost resonant cavity Raman gas probe for multi-gas detection

Raman based gas sensing can be attractive in several industrial applications, due to its multi-gas sensing capabilities and its ability to detect O2 and N2. In this article, we have built a Raman gas probe, based on low-cost components, which has shown an estimated detection limit of 0.5 % for 30 second measurements of N2 and O2. While this detection limit is higher than that of commercially available equipment, our estimated component cost is approximately one tenth of the price of commercially available equipment. The use of a resonant Fabry-Pérot cavity increases the scattered signal, and hence the sensitivity, by a factor of 50. The cavity is kept in resonance using a piezo-actuated mirror and a photodiode in a feedback loop. The system described in this article was made with minimum-cost components to demonstrate the low-cost principle. However, it is possible to decrease the detection limit using a higher-powered (but still low-cost) laser and improving the collection optics. By applying these improvements, the detection limit and estimated measurement precision will be sufficient for e.g. the monitoring of input gases in combustion processes, such as e.g. (bio-)gas power plants. In these processes, knowledge about gas compositions with 0.1 % (absolute) precision can help regulate and optimize process conditions. The system has the potential to provide a low-cost, industrial Raman sensor that is optimized for specific gas-detection applications.

Alumina-coated Ag nanocrystal monolayers as surfaceenhanced Raman spectroscopy platforms for the direct spectroscopic detection of water splitting reaction intermediates

A novel Ag-alumina hybrid surface-enhanced Raman spectroscopy (SERS) platform has been designed for the spectroscopic detection of surface reactions in the steady state. Single crystalline and faceted silver (Ag) nanoparticles with strong light scattering were prepared in large quantity, which enables their reproducible self-assembly into large scale monolayers of Raman sensor arrays by the Langmuir-Blodgett technique. The close packed sensor film contains high density of sub-nm gaps between sharp edges of Ag nanoparticles, which created large local electromagnetic fields that serve as “hot spots” for SERS enhancement. The SERS substrate was then coated with a thin layer of alumina by atomic layer deposition to prevent charge transfer between Ag and the reaction system. The photocatalytic water splitting reaction on a monolayer of anatase TiO2 nanoplates decorated with Pt co-catalyst nanoparticles was employed as a model reaction system. Reaction intermediates of water photo-oxidation were observed at the TiO2/solution interface under UV irradiation. The surface-enhanced Raman vibrations corresponding to peroxo, hydroperoxo and hydroxo surface intermediate species were observed on the TiO2 surface, suggesting that the photo-oxidation of water on these anatase TiO2 nanosheets may be initiated by a nucleophilic attack mechanism.

Non-invasive quantification of phase equilibria of ternary mixtures composed of carbon dioxide, organic solvent and water

Raman spectra of ternary mixtures of unknown composition are processed to extract the content of the compounds in the mixture. The evaluation method of the ternary mixtures is based on a previous calibration of binary mixtures. The applicability of the method is demonstrated by measuring the vapour liquid equilibria of the ternary system carbon dioxide, ethyl acetate and water at 8.5MPa and 310K and providing them in a triangle diagram. The advantages of the used flexible Raman sensor in comparison to conventional techniques for the determination of phase equilibria are discussed.

Autonomous In-situ Raman Sensor, Suitable for Surface Enhanced Raman Spectroscopy (SERS) for Detection of Chemicals in the Sea

An autonomous in-situ Raman/SERS sensor for the detection of chemicals in seawater has been constructed and successfully tested in the harbor and offshore under harsh field conditions, during October - January 2012-2013. Applying integration time of typically only 10 s, the sensor was able to detect various PAHs in situ, such as fuoranthene, biphenyl, phenanthrene and fluorine in the Mediterranean Sea.

Abilities of Raman sensor to probe pollutants in water

The control of water quality requires rapid and efficient monitoring techniques. A Raman sensor is shown to present interest for the analysis of chemical substances dissolved in water. The identification of chemical pollutants and the determination of their content as well are reliably obtained. The main characteristics and abilities of this multi-component Raman sensor are reported.

A Raman spectroscopy bio‐sensor for tissue discrimination in surgical robotics

We report the development of a fiber-based Raman sensor to be used in tumour margin identification during endoluminal robotic surgery. Although this is a generic platform, the sensor we describe was adapted for the ARAKNES (Array of Robots Augmenting the KiNematics of Endoluminal Surgery) robotic platform. On such a platform, the Raman sensor is intended to identify ambiguous tissue margins during robot-assisted surgeries. To maintain sterility of the probe during surgical intervention, a disposable sleeve was specially designed. A straightforward user-compatible interface was implemented where a supervised multivariate classification algorithm was used to classify different tissue types based on specific Raman fingerprints so that it could be used without prior knowledge of spectroscopic data analysis. The protocol avoids inter-patient variability in data and the sensor system is not restricted for use in the classification of a particular tissue type. Representative tissue classification assessments were performed using this system on excised tissue.

Raman Slow Light in Distributed Raman Fiber Sensors

Distributed Raman sensor offers a number of advantages to the implementation of smart grid, which is aimed to improve reliability and energy efficiency as compared with traditional power grid. However, the fantastic properities of slow light are rarely considered in the former studies on the Raman sensor systems. In this paper, the effects of Raman slow-light on room-temperature single-mode optical fiber sensors are examined by extracting the Raman pulse-delay terms from extended nonlinear Schrodinger equation (NLSE). Numerical study shows that pulse parameters such as pulse position, frequency chirp, and envelope distortion may be greatly affected by slow light. Two important points of pump power are show clearly keeping the Raman pulse zero walk-off or chirp free, respectively. We demonstrate a method based on pump power adjustment for compensating the slow light induced impairment. DOI: http://dx.doi.org/10.11591/telkomnika.v11i5.2472

Optofluidic Raman sensor for simultaneous detection of the toxicity and quality of alcoholic beverages

We report a chemometric prediction of the toxicity and quality of liquor using an optofluidic sensor based upon Waveguide Confined Raman Spectroscopy (WCRS). The WCRS sensor was used to record the Raman spectra, each obtained from a 20 µl sample of a given alcoholic beverage with and acquisition time of 20 s. This was used to predict, simultaneously, both the methanol concentration (toxicity) and ethanol concentration (quality), with an accuracy of 0.1% and 0.7% by volume, respectively, using a Partial Least Squares‐based chemometric model. The model sensor is shown to be capable of identifying toxic liquors, based on the test performed on different types of liquor samples. Copyright © 2013 John Wiley & Sons, Ltd.

Nanoporous Gold Electrodes and Their Applications in Analytical Chemistry

Nanoporous gold prepared by dealloying Au:Ag alloys has recently become an attractive material in the field of analytical chemistry. This conductive material has an open, 3D porous framework consisting of nanosized pores and ligaments with surface areas that are 10s to 100s of times larger than planar gold of an equivalent geometric area. The high surface area coupled with an open pore network makes nanoporous gold an ideal support for the development of chemical sensors. Important attributes include conductivity, high surface area, ease of preparation and modification, tunable pore size, and a bicontinuous open pore network. In this paper, the fabrication, characterization, and applications of nanoporous gold in chemical sensing are reviewed specifically as they relate to the development of immunosensors, enzyme-based biosensors, DNA sensors, Raman sensors, and small molecule sensors.

Plasmonic Nanorice Antenna on Triangle Nanoarray for Surface-Enhanced Raman Scattering Detection of Hepatitis B Virus DNA

The sensitivity and the limit of detection of Raman sensors are limited by the extremely small scattering cross section of Raman labels. Silver nanorice antennae are coupled with a patterned gold triangle nanoarray chip to create spatially broadened plasmonic "hot spots", which enables a large density of Raman labels to experience strong local electromagnetic field. Finite difference time domain simulations have confirmed that the quasi-periodic structure increases the intensity and the area of the surface plasmon resonance (SPR), which enhances the surface-enhanced Raman scattering (SERS) signal significantly. The SERS signal of the nanorice/DNA/nanoarray chip is compared with that of the nanorice/DNA/film chip. The SERS signal is greatly enhanced when the Ag nanorices are coupled to the periodic Au nanoarray instead of the planar film chip. The resulting spatially broadened SPR field enables the SERS biosensor with a limit of detection of 50 aM toward hepatitis B virus DNA with the capability of discriminating a single-base mutant of DNA. This sensing platform can be extended to detect other chemical species and biomolecules such as proteins and small molecules.

Distributed Optical Fiber Raman Signal Noise Cancellation Based on Empirical Mode Decomposition

The distributed optical fiber Raman sensor system was widely used for real-time measurement temperature, but the Anti-Stokes and Stokes scattering Raman signal is very weak. In order to improve measurement accuracy the signal must be denoised before obtaining the temperature. In this paper, a new noise cancellation of empirical mode decomposition is proposed for enhancing signal-to-noise ration of the Anti-Stokes and Stokes scattering Raman signal. The signal-to-noise ratio was enhanced by using this method and it is easy to be realized in computer.

Fabrication and characterization of a nanoantenna-based Raman device for ultrasensitive spectroscopic applications

► Fabrication and characterization of a polarization-selective Raman biosensor. ► Surface Plasmon Resonances in nanoantenna structures enhance the Raman signal. ► Optical transmittance and SERS signal confirm the polarization-dependent response. We report on the fabrication and spectroscopic characterization of a polarization-selective Raman sensor composed of an ordered array of planar nanoantennas. The device shows two distinct plasmon resonances associated with the main axes of the elongated nanostructures and is able to significantly enhance the Raman signal when the excitation wavelength matches one of these resonances.

Surface enhanced Raman scattering in the presence of multilayer dielectric structures

We perform a systematic study of spontaneous Raman scattering in resonant planar structures. We present a semiclassical approach that allows the description of spontaneous Raman scattering in an arbitrary multilayer, providing analytical expressions of the Raman cross sections in terms of the Fresnel coefficients of the structure and taking into account beam size effects. Large enhancements of the Raman cross section are predicted in fully dielectric structures. In particular, given our results, truncated periodic multilayers supporting Bloch surface waves might be of interest for the realization of integrated Raman sensor devices.

Electron Hopping Through Single-to-Few-Layer Graphene Oxide Films. Side-Selective Photocatalytic Deposition of Metal Nanoparticles.

Single- to few-layer graphene oxide (GO) sheets have been successfully anchored onto TiO2 films using electrophoretic deposition. Upon UV illumination of TiO2-GO films, photogenerated electrons from TiO2 are captured by GO. These electrons are initially used in GO's reduction, while additional electron transfer results in storage across its sp(2) network. In the presence of silver ions, deposition of silver nanoparticles (NPs) is accomplished on the GO surface opposite the TiO2, thus confirming the ability of GO to transport electrons through its plane. Illumination-controlled reduction of silver ions allows for simple selection of particle size and loading, making these semiconductor-graphene-metal (SGM) films ideal for custom catalysis and sensor applications. Initial testing of SGM films as surface-enhanced resonance Raman (SERRS) sensors produced significant target molecule signal enhancements, enabling detection of nanomolar concentrations.