Novel SERS Probe Based on Ag Nanobean/Cu Foam for Deep-Sea Extreme Environment Biomolecule Detection.

Here, we report on progress made in coupling advances in surface-enhanced Raman scattering (SERS) techniques with a deep-ocean deployable Raman spectrometer. Our SERS capability is provided by development of a Cu foam-loaded silver-nanobean (Ag/Cu foam) which we have successfully coupled to the tip of a Raman probe head capable of insertion into deep-sea sediments and associated fluids. Our purpose is to expand the range of molecular species which can be detected in deep-sea biogeochemical environments, and our initial targets are a series of amino acids reportedly found in pore waters of seep locations. Our work has progressed to the point of a full dock-based end-to-end test of the essential ship tether-ROV-deep-sea Raman system. We show here the initial results from this test as the essential requirement before at sea full ocean depth deployment. We describe in detail the procedures for preparing the Ag/Cu foam bean and demonstrate in our end-to-end test that this, when coupled to the spectrometer probe tip, yields a SERS signal enhancement of 1.2 × 106 for test molecules and detection of amino acids at 10-6 M levels consistent with reported levels of natural occurrence. Each nanobean unit is for single-use sensing since invasion of the sample fluid into the Ag/Cu foam matrix is not reversible. We describe techniques for bean rotation/replacement at depth to allow for multiple analyses at several locations during each ROV dive.

An intrusion and environmental effects of man-made silver nanoparticles in cold seeps.

Silver nanoparticles (AgNPs) are among the most widely used metal-based engineered nanomaterials in biomedicine and nanotechnology, and account for >50 % of global nanomaterial consumer products. The increasing use of AgNPs potentially causes marine ecosystem changes; however, the environmental impacts of man-made AgNPs are still poorly studied. This study reports for the first time that man-made AgNPs intruded into cold seeps, which are important marine ecosystems where hydrogen sulfide, methane, and other hydrocarbon-rich fluid seepage occur. Using a combination of electron microscopy, geochemical and metagenomic analyses, we found that in the cold seeps with high AgNPs concentrations, the relative abundance of genes associated with anaerobic oxidation of methane (AOM) was lower, while those related to the sulfide oxidizing and sulfate reducing were higher. This suggests that AgNPs can stimulate the proliferation of sulfate-reducing and sulfide-oxidizing bacteria, likely due to the effects of activating repair mechanisms of the cells against the toxicant. A reaction of AgNPs with hydrogen sulfide to form silver sulfide could also effectively reduce the amount of available sulfate in local ecosystems, which is generally used as the AOM oxidant. These novel findings indicate that man-made AgNPs may be involved in the biogeochemical cycles of sulfur and carbon in nature, and their potential effects on the releasing of methane from the marine methane seeps should not be ignored in both scientific and environmental aspects.

Nitrogen and sulfur cycling driven by Campylobacterota in the sediment-water interface of deep-sea cold seep: a case in the South China Sea.

Chemoautotrophs within Campylobacterota, especially Sulfurovum and Sulfurimonas, are abundant in the seawater-sediment interface of the Formosa cold seep in the South China Sea. However, the in situ activity and function of Campylobacterota are unknown. In this study, the geochemical role of Campylobacterota in the Formosa cold seep was investigated with multiple means. Two members of Sulfurovum and Sulfurimonas were isolated for the first time from deep-sea cold seep. These isolates are new chemoautotrophic species that can use molecular hydrogen as an energy source and CO2 as a sole carbon source. Comparative genomics identified an important hydrogen-oxidizing cluster in Sulfurovum and Sulfurimonas. Metatranscriptomic analysis detected high expression of hydrogen-oxidizing gene in the RS, suggesting that H2 was likely an energy source in the cold seep. Genomic analysis indicated that the Sulfurovum and Sulfurimonas isolates possess a truncated sulfur-oxidizing system, and metatranscriptomic analysis revealed that Sulfurovum and Sulfurimonas with this genotype were active in the surface of RS and likely contributed to thiosulfate production. Furthermore, geochemical and in situ analyses revealed sharply decreased nitrate concentration in the sediment-water interface due to microbial consumption. Consistently, the denitrification genes of Sulfurimonas and Sulfurovum were highly expressed, suggesting an important contribution of these bacteria to nitrogen cycling. Overall, this study demonstrated that Campylobacterota played a significant role in the cycling of nitrogen and sulfur in a deep-sea cold seep. IMPORTANCE Chemoautotrophs within Campylobacterota, in particular Sulfurovum and Sulfurimonas, are ubiquitous in deep-sea cold seeps and hydrothermal vents. However, to date, no Sulfurovum or Sulfurimonas has been isolated from cold seeps, and the ecological roles of these bacteria in cold seeps remain to be investigated. In this study, we obtained two isolates of Sulfurovum and Sulfurimonas from Formosa cold seep, South China Sea. Comparative genomics, metatranscriptomics, geochemical analysis, and in situ experimental study indicated collectively that Campylobacterota played a significant part in nitrogen and sulfur cycling in cold seep and was the cause of thiosulfate accumulation and sharp reduction of nitrate level in the sediment-water interface. The findings of this study promoted our understanding of the in situ function and ecological role of deep-sea Campylobacterota.

Study of Microbial Sulfur Metabolism in a Near Real-Time Pathway through Confocal Raman Quantitative 3D Imaging.

As microbial sulfur metabolism significantly contributes to the formation and cycling of deep-sea sulfur, studying their sulfur metabolism is important for understanding the deep-sea sulfur cycle. However, conventional methods are limited in near real-time studies of bacterial metabolism. Recently, Raman spectroscopy has been widely used in studies on biological metabolism due to its low-cost, rapid, label-free, and nondestructive features, providing us with new approaches to solve the above limitation. Here, we used the confocal Raman quantitative 3D imaging method to nondestructively detect the growth and metabolism of Erythrobacter flavus 21-3 in the long term and near real time, which possessed a pathway mediating the formation of elemental sulfur in the deep sea, but the dynamic process was unknown. In this study, its dynamic sulfur metabolism was visualized and quantitatively assessed in near real time using 3D imaging and related calculations. Based on 3D imaging, the growth and metabolism of microbial colonies growing under both hyperoxic and hypoxic conditions were quantified by volume calculation and ratio analysis. Additionally, unprecedented details of growth and metabolism were uncovered by this method. Due to this successful application, this method is potentially significant for analyzing the in situ biological processes of microorganisms in the future. IMPORTANCE Microorganisms contribute significantly to the formation of deep-sea elemental sulfur, so studies on their growth and dynamic sulfur metabolism are important to understand the deep-sea sulfur cycle. However, near real-time in situ nondestructive metabolic studies of microorganisms remain a great challenge due to the limitations of existing methods. We thus used an imaging-related workflow by confocal Raman microscopy. More detailed descriptions of the sulfur metabolism of E. flavus 21-3 were disclosed, which perfectly complemented previous research results. Therefore, this method is potentially significant for analyzing the in-situ biological processes of microorganisms in the future. To our knowledge, this is the first label-free and nondestructive in situ technique that can provide temporally persistent 3D visualization and quantitative information about bacteria.

Rapid identification of fish species by laser-induced breakdown spectroscopy and Raman spectroscopy coupled with machine learning methods.

There has been an increasing demand for the rapid verification of fish authenticity and the detection of adulteration. In this work, we combined LIBS and Raman spectroscopy for the fish species identification for the first time. Two machine learning methods of SVM and CNN are used to establish the classification models based on the LIBS and Raman data obtained from 13 types of fish species. Data fusion strategies including low-level, mid-level and high-level fusions are used for the combination of LIBS and Raman data. It shows that all these data fusion strategies offer a significant improvement in fish classification compared with the individual LIBS or Raman data, and the CNN model works more powerfully than the SVM model. The low-level fusion CNN model provides a best classification accuracy of 98.2%, while the mid-level fusion involved with feature selection improves the computing efficiency and gains the interpretability of CNN.

Neurological safety of spinal surgery for nucleus pulposus removal under spinal endoscopic imaging guided by inter laminar spine.

OBJECTIVE: To explore the technical points, approach selection and short-term clinical efficacy of PELD through the intervertebral foramina or interlaminar approach in the treatment of highly shifted LDH. METHODS: From September 2018 to June 2020, 19 patients with highly shifted LDH were treated with PELD in The First Hospital of Yulin. It included, 10 males and 9 females; aged 34 to 69 years, with an average of 48 years. Thirteen cases were shifted to the caudal side, and six cases were shifted to the head side. The responsible segments included L3/41 cases, L4/511 cases, and L5/S17 cases. All patients had symptoms of low back and leg pain. The Sowerby dysfunction index (ODI) was 63.5%±10.7% before surgery. The visual analogue scale of pain (VAS) was low back pain (5.2±2.1) and leg pain (7.1±2.4). 14 cases used transforaminal approach, and 5 cases used translaminar approach. RESULTS: All cases completed the operation successfully, the operation time was 60~110min, with an average of 70 minutes. The follow-up time ranged from 6 to 42 months, with an average of 20.8 months. At the last follow-up, ODI was 10.8%±6.8%, VAS back pain score (2.1±1.1) and leg pain score (1.8±0.9). Compared with preoperative, ODI and VAS scores were significantly decreased (P<0.05). The results of Mac Nab method were 14 excellent, four good, and one fair. During the follow-up period, one patient's leg pain symptoms recurred seven days after operation. No further hernia was found under intervertebral foramen. The symptoms disappeared after two weeks of symptomatic treatment such as swelling and analgesia, and he was discharged. No perioperative complications such as infection and nerve root injury occurred. CONCLUSION: When PELD is used to treat high-displacement LDH, the choice of transforaminal approach or interlaminar approach needs to be personalized according to the LDH segment and the direction of displacement.

A Piecewise Model for In Situ Raman Measurement of the Chlorinity of Deep-Sea High-Temperature Hydrothermal Fluids.

The chlorinity of deep-sea hydrothermal fluids, representing one of the crucial deep-sea hydrothermal indicators, indicates the degree of deep phase separation of hydrothermal fluids and water/rock reactions. However, accurately measuring the chlorinity of high-temperature hydrothermal fluids is still a significant challenge. In this paper, a piecewise chlorinity model to measure the chlorinity of high-temperature hydrothermal fluids was developed based on the OH stretching band of water, exhibiting an accuracy of 96.20%. The peak position, peak area ratio, and F value were selected to establish the chlorinity piecewise calibration model within the temperature ranges of 0-50 ℃, 50-200 ℃, and 200-300 ℃. Compared with that of the chlorinity calibration model built based on a single parameter, the accuracy of this piecewise model increased by approximately 4.83-12.33%. This chlorinity calibration model was applied to determine the concentrations of Cl for high-temperature hydrothermal fluids in the Okinawa Trough hydrothermal field.

Endosymbionts of Metazoans Dwelling in the PACManus Hydrothermal Vent: Diversity and Potential Adaptive Features Revealed by Genome Analysis.

Deep-sea hydrothermal vent communities are dominated by invertebrates, namely, bathymodiolin mussels, siboglinid tubeworms, and provannid snails. Symbiosis is considered key to successful colonization by these sedentary species in such extreme environments. In the PACManus vent fields, snails, tubeworms, and mussels each colonized a niche with distinct geochemical characteristics. To better understand the metabolic potentials and genomic features contributing to host-environment adaptation, we compared the genomes of the symbionts of Bathymodiolus manusensis, Arcovestia ivanovi, and Alviniconcha boucheti sampled at PACManus, and we discuss their environmentally adaptive features. We found that B. manusensis and A. ivanovi are colonized by Gammaproteobacteria from distinct clades, whereas endosymbionts of B. manusensis feature high intraspecific heterogeneity with differing metabolic potentials. A. boucheti harbored three novel Epsilonproteobacteria symbionts, suggesting potential species-level diversity of snail symbionts. Genome comparisons revealed that the relative abundance of gene families related to low-pH homeostasis, metal resistance, oxidative stress resistance, environmental sensing/responses, and chemotaxis and motility was the highest in A. ivanovi's symbiont, followed by symbionts of the vent-mouth-dwelling snail A. boucheti, and was relatively low in the symbiont of the vent-periphery-dwelling mussel B. manusensis, which is consistent with their environmental adaptations and host-symbiont interactions. Gene families classified as encoding host interaction/attachment, virulence factors/toxins, and eukaryotic-like proteins were most abundant in symbionts of mussels and least abundant in those of snails, indicating that these symbionts may differ in their host colonization strategies. Comparison of Epsilonproteobacteria symbionts to nonsymbionts demonstrated that the expanded gene families in symbionts were related to vitamin B12 synthesis, toxin-antitoxin systems, methylation, and lipopolysaccharide biosynthesis, suggesting that these are vital to symbiont establishment and development in EpsilonproteobacteriaIMPORTANCE Deep-sea hydrothermal vents are dominated by several invertebrate species. The establishment of symbiosis has long been thought to be the key to successful colonization by these sedentary species in such harsh environments. However, the relationships between symbiotic bacteria and their hosts and their role in environmental adaptations generally remain unclear. In this paper, we show that the distribution of three host species showed characteristic niche partitioning in the Manus Basin, giving us the opportunity to understand how they adapt to their particular habitats. This study also revealed three novel genomes of symbionts from the snails of A. boucheti Combined with a data set on other ectosymbiont and free-living bacteria, genome comparisons for the snail endosymbionts pointed to several genetic traits that may have contributed to the lifestyle shift of Epsilonproteobacteria into the epithelial cells. These findings could increase our understanding of invertebrate-endosymbiont relationships in deep-sea ecosystems.

High-Throughput Sequencing Reveals a Potentially Novel Sulfurovum Species Dominating the Microbial Communities of the Seawater-Sediment Interface of a Deep-Sea Cold Seep in South China Sea.

In the Formosa cold seep of the South China Sea (SCS), large amounts of methane and sulfide hydrogen are released from the subseafloor. In this study, we systematically investigated the microbial communities in the seawater-sediment interface of Formosa cold seep using high-throughput sequencing techniques including amplicon sequencing based on next-generation sequencing and Pacbio amplicon sequencing platforms, and metagenomics. We found that Sulfurovum dominated the microbial communities in the sediment-seawater interface, including the seawater close to the seepage, the surface sediments, and the gills of the dominant animal inhabitant (Shinkaia crosnieri). A nearly complete 16S rRNA gene sequence of the dominant operational taxonomic units (OTUs) was obtained from the Pacbio sequencing platforms and classified as OTU-L1, which belonged to Sulfurovum. This OTU was potentially novel as it shared relatively low similarity percentages (<97%) of the gene sequence with its close phylogenetic species. Further, a draft genome of Sulfurovum was assembled using the binning technique based on metagenomic data. Genome analysis suggested that Sulfurovum sp. in this region may fix carbon by the reductive tricarboxylic acid (rTCA) pathway, obtain energy by oxidizing reduced sulfur through sulfur oxidizing (Sox) pathway, and utilize nitrate as electron acceptors. These results demonstrated that Sulfurovum probably plays an important role in the carbon, sulfur, and nitrogen cycles of the Formosa cold seep of the SCS. This study improves our understanding of the diversity, distribution, and function of sulfur-oxidizing bacteria in deep-sea cold seep.

Discovery of supercritical carbon dioxide in a hydrothermal system.

Supercritical CO2 appearing as bubbles in hydrothermal vents was identified in the south part of the Okinawa Trough using in situ Raman spectroscopy. Significantly, the N2 peak in supercritical CO2 is much larger than those in seawater and vent fluids, indicating that supercritical CO2 enriches N2 from the surrounding environment. Considering that the partial pressures of CO2 and N2 in the Earth's proto-atmosphere were ~10-20 MPa, supercritical CO2 with high N2 was likely the dominant CO2 phase near the water-air interface in the early history of the Earth, which promoted the synthesis, pre-enrichment and preservation of amino acids and other organic matters that are essential to the origin of life.

A New Approach to Measuring the Temperature of Fluids Reaching 300 ℃ and 2 mol/kg NaCl Based on the Raman Shift of Water.

The OH stretching band of water is very sensitive to temperature and salinity for the existence of hydrogen bonds between H2O molecules. In this study, the OH stretching band was deconvoluted into two Gaussian peaks, with peak 1 at approximately 3450 cm-1 and peak 2 at approximately 3200 cm-1. The positions of peaks 1 and 2 both shifted to higher wavenumbers with increasing temperature from 50 ℃ to 300 ℃. The effects of salinity in the range of 0-2 mol/kg NaCl on the OH stretching band were also studied. Linearity for the relationship between Raman shift of peak 1 and temperature increased as the salt concentration increased from 0 to 2 mol/kg, while peak 2 displayed an opposing trend. Two temperature calibration models were developed based on the temperature-dependent changes in the Raman frequency shifts of peaks 1 and 2 (precision of 0.9 ℃ and 1.0 ℃, respectively). The calibration models for temperature were successfully applied to determining the temperatures of deep-sea hydrothermal fluids in the Okinawa Trough hydrothermal field. The degree of mixing of hydrothermal fluids and ambient seawater during in situ Raman measurements was estimated by the difference in temperatures determined through these calibration models and those measured through thermocouple sensors.

A Direct Quantitative Raman Method for the Measurement of Dissolved Bisulfate in Acid-Sulfate Fluids.

Raman spectroscopy has been applied to the quantitative analysis of the concentration of bisulfate in acid-sulfate fluids at different temperatures. The quantitative analysis method is based on the peak area ratios of [Formula: see text](ν1) and H2O (ν2), where PA([Formula: see text]/H2O) = [[Formula: see text]] × (0.0066 × T + 1.3070) at a temperature range of 0-100 ℃. We found that the molal scattering coefficient of bisulfate increases slightly at the elevated temperature may be due to the changes of fraction of water molecules that are hydrogen-bonded. The method can also be applied to analyze physicochemical parameters of other acid fluids, such as hydrogen phosphate, bicarbonate, etc., and especially to the in situ detection of deep sea acid-sulfate hydrothermal fluids in the future.

In Situ Raman Spectral Characteristics of Carbon Dioxide in a Deep-Sea Simulator of Extreme Environments Reaching 300 ℃ and 30 MPa.

Deep-sea carbon dioxide (CO2) plays a significant role in the global carbon cycle and directly affects the living environment of marine organisms. In situ Raman detection technology is an effective approach to study the behavior of deep-sea CO2. However, the Raman spectral characteristics of CO2 can be affected by the environment, thus restricting the phase identification and quantitative analysis of CO2. In order to study the Raman spectral characteristics of CO2 in extreme environments (up to 300 ℃ and 30 MPa), which cover most regions of hydrothermal vents and cold seeps around the world, a deep-sea extreme environment simulator was developed. The Raman spectra of CO2 in different phases were obtained with Raman insertion probe (RiP) system, which was also used in in situ Raman detection in the deep sea carried by remotely operated vehicle (ROV) "Faxian". The Raman frequency shifts and bandwidths of gaseous, liquid, solid, and supercritical CO2 and the CO2-H2O system were determined with the simulator. In our experiments (0-300 ℃ and 0-30 MPa), the peak positions of the symmetric stretching modes of gaseous CO2, liquid CO2, and supercritical CO2 shift approximately 0.6 cm-1 (1387.8-1388.4 cm-1), 0.7 cm-1 (1385.5-1386.2 cm-1), and 2.5 cm-1 (1385.7-1388.2 cm-1), and those of the bending modes shift about 1.0 cm-1 (1284.7-1285.7 cm-1), 1.9 cm-1 (1280.1-1282.0 cm-1), and 4.4 cm-1 (1281.0-1285.4 cm-1), respectively. The Raman spectral characteristics of the CO2-H2O system were also studied under the same conditions. The peak positions of dissolved CO2 varied approximately 4.5 cm-1 (1282.5-1287.0 cm-1) and 2.4 cm-1 (1274.4-1276.8 cm-1) for each peak. In comparison with our experiment results, the phases of CO2 in extreme conditions (0-3000 m and 0-300 ℃) can be identified with the Raman spectra collected in situ. This qualitative research on CO2 can also support the further quantitative analysis of dissolved CO2 in extreme conditions.

Identifying the genetic diversity, genetic structure and a core collection of Ziziphus jujuba Mill. var. jujuba accessions using microsatellite markers.

Ziziphus is a genus of spiny shrubs and small trees in the Rhamnaceae family. This group has a controversial taxonomy, with more than 200 species described, including Chinese jujube (Ziziphus jujuba Mill. var. jujuba) and Indian jujube (Z. mauritiana), as well as several other important cultivated fruit crops. Using 24 SSR markers distributed across the Chinese jujube genome, 962 jujube accessions from the two largest germplasm repositories were genotyped with the aim of analyzing the genetic diversity and structure and constructing a core collection that retain high genetic diversity. A molecular profile comparison revealed 622 unique genotypes, among which 123 genotypes were genetically identical to at least one other accessions. STRUCTURE analysis and multivariate analyses (Cluster and PCoA) roughly divided the accessions into three major groups, with some admixture among groups. A simulated annealing algorithm and a heuristic algorithm were chosen to construct the core collection. A final core of 150 accessions was selected, comprising 15.6% of the analyzed accessions and retaining more than 99.5% of the total alleles detected. We found no significant differences in allele frequency distributions or in genetic diversity parameters between the chosen core accessions and the 622 genetically unique accessions. This work contributes to the understanding of Chinese jujube diversification and the protection of important germplasm resources.

[Research on the Quantitative Analysis for In-Situ Detection of Acid Radical Ions Using Laser Raman Spectroscopy].

Laser Raman spectroscopy as an in situ analytical technology can enable detailed investigation of the ocean environment. It is necessary to set up a quantitative analysis method based on laser Raman spectroscopy to understand the marine status in situ. In the laboratory investigations, varied concentration of HCO3(-), SO4(2-) and coastal waters of Qingdao are taken as the samples, operating 532 nm of laser, using fiber optic probes to simulate detection mode in situ. Raman spectra are analyzed using the method of internal standard normalization, multiple linear regression (MLR), general Partial Least Squares (PLS) and PLS based on dominant factor respectively in data processing. It was found that correlation coefficients of calibration curves are not high in internal standard normalization method and predicted relative errors on the prepared samples are much high, so internal standard normalization method cannot be effectively used in the quantitative analysis of HCO3(-), SO4(2-) in the water. And with the multiple linear regression, the analysis accuracy was improved effectively. The calibration curve of PLS based on dominant factor showed that the SO4(2-) and HCO3(-) of pre-made solution with correlation coefficient R2 of 0.990 and 0.916 respectively. The 30 mmol · L(-1) of SO4(2-) and 20 mmol · L(-1) of HCO3(-) in two target samples were determined with the relative errors lower than 3.262% and 5.267% respectively. SO4(2-) in the coastal waters as the research object was analyzed by above-mentioned methods, comparing with 28.01 mmol · L(-1) by ion chromatography. It was demonstrated that PLS based on dominant factor method is superior to the rest of the three analysis methods, which can be used in situ calibration, with the mean relative error about 1.128%. All the results show that analysis accuracy would be improved by the PLS based on dominant factor method to predict concentration of acid radical ions.

[Automatic Recognition of Overlapped Spectral Peaks by Combined Symmetric Zero-Area Conversion and L-M Fitting].

The peaks' overlapping often exists in Raman spectroscopy analysis, because of the low spectral resolution of the spectrograph and the complex sample components. The overlapped peaks lead to the errors in peak parameters extraction easily, and at last lead to the analysis error of sample components, which increases the difficulty in automatic analysis of field spectra. The identification of overlapped peaks is the key difficulty of in-situ spectra analysis. To solve this problem, an automatic method of identifying the overlapped peaks was established basing on an analysis model with multiple Gaussian shape peaks. The peak number and the initial parameters(the peak position, peak height, and width) were obtained by symmetric zero-area transformation firstly, and then the parameters were optimized by Levenberg-Marquardt fitting method eventually. Some algorithm experiments were executed to test the method respectively by simulated data and Raman spectra data, and the former showed that the symmetric zero-area transformation method can extract the initial peak parameters with high accuracy, and then converges fast, and is adaptive to signal with wide dynamic range of SNR, but has false and omissive peaks to low SNR signal. The research results show that the automatic method of identifying the overlapped peaks with symmetric zero-area transformation combined with L-M fitting has a certain practical value.

[Raman Signal Enhancement for Gas Detection Using a Near Concentric Cavity].

The detection of dissolved gases in seawater plays an important role in ocean observation and exploration. Raman spectroscopy has a great advantage in simultaneous multiple species detection and is thus regarded as a favorable choice for ocean application. However, its sensitivity remains insufficient, and a demand in enhancements is called! for before putting Raman spectroscopy to actual use in marine studies In this work, we developed a near-concentric cavity, in which laser beam could be trapped and reflected back and forth, for the purpose of intensifying Raman signals. The factors that would influence Raman signals were taken into account. The result show that the smaller angle between collection direction and optical axis of reflection mirror, the stronger the signal and signal to noise ratio (SNR) is. With a collection angle of 30 degrees, our Near-concentric Cavity System managed to raise the SNR to a figure about 16 times larger than that of common methods applying 90 degrees. Moreover, the alignment pattern in our system made it possible to excel concentric cavity with a 3 times larger SNR. Compared with the single-pass Raman signal, the signal intensity of our near-concentric cavity was up to 70 times enhanced. According to the obtained results of CO2 measurement, it can be seen that the new system provides a limit of detection(LOD) for CO2 about 0.19 mg x L(-1) using 3-σ criterion standard, and the LOD of 11.5 µg x L(-1) for CH4 was evaluated with the theoretical cross section values of CO2 and CH4.

Investigation of two novel approaches for detection of sulfate ion and methane dissolved in sediment pore water using Raman spectroscopy.

The levels of dissolved sulfate and methane are crucial indicators in the geochemical analysis of pore water. Compositional analysis of pore water samples obtained from sea trials was conducted using Raman spectroscopy. It was found that the concentration of SO42- in pore water samples decreases as the depth increases, while the expected Raman signal of methane has not been observed. A possible reason for this is that the methane escaped after sampling and the remaining concentration of methane is too low to be detected. To find more effective ways to analyze the composition of pore water, two novel approaches are proposed. One is based on Liquid Core Optical Fiber (LCOF) for detection of SO42-. The other one is an enrichment process for the detection of CH4. With the aid of LCOF, the Raman signal of SO42- is found to be enhanced over 10 times compared to that obtained by a conventional Raman setup. The enrichment process is also found to be effective in the investigation to the prepared sample of methane dissolved in water. By CCl4 extraction, methane at a concentration below 1.14 mmol/L has been detected by conventional Raman spectroscopy. All the obtained results suggest that the approach proposed in this paper has great potential to be developed as a sensor for SO42- and CH4 detection in pore water.

[The measurement of methane dissolved in water using raman spectroscopy assisted with CCl4 extraction].

While under laboratory conditions, the concentration of methane dissolved in water is too low to be detected because of the low solubility of methane using Raman spectroscopy. In the present paper, a novel approach based on CCl4 extraction was introduced, and used in the measurement of methane dissolved in water using Raman spectroscopy under laboratory conditions. Saturated aqueous solution of CH4, CCl4 solution after extraction of CH4 from the saturated aqueous solution and the saturated CCl4 solution of CH4 were prepared, and the Raman spectra of three samples were obtained. The obtained results show that the CH4 dissolved in saturated aqueous solution(the concentration of CH4 is about 1.14 mmol x L(-1)) can't been detected using Raman spectroscopy under laboratory conditions, but the CH4 Raman peak can be clearly seen in the spectra obtained for CCl4 solution after extraction. All the results demonstrate that the proposed approach can improve the Raman spectroscopy sensitivity of methane detection dissolved in water, and this approach has significant potential to be developed as an effective method for detection of methane dissolved in water.