In situ detection and identification of PAHs, a group of well-known persistent organic pollutants, presents a great challenge to environmental researchers. This work developed a novel substrate based ...on thiol-functionalized Fe3O4@Ag core–shell magnetic nanoparticles for surface enhanced Raman scattering (SERS) sensing of PAHs. The surface morphology, structure, and magnetic properties of the substrate were characterized using multiple complementary techniques including transmission electron microscopy, energy-dispersive X-ray spectroscopy, vibrating sample magnetometry analysis, and extended X-ray absorption fine structure spectroscopy. The high saturation magnetization at 48.35 emu g–1 enabled the complete and rapid separation of the substrate from the PAH solution. Benzene, naphthalene, anthracene, phenanthrene, fluorene, pyrene, perylene, and BaP were chosen as probe molecules. Qualitative and quantitative determination of PAHs was achieved using a portable Raman spectrometer. The SERS sensitivity was positively correlated with the hydrophobic nature of PAHs. The SERS response exhibited a linear dependence on the PAHs concentration between 1 to 50 mg/L, and the detection limit in the order 10–5 to 10–7 M was obtained. The SERS platform with magnetic substrate provides a new way for in situ PAH monitoring.
A novel sensitive and recyclable SERS substrate which can actively concentrate chromate (Cr(VI)) in water and substantially enhance Raman signal was synthesized as uniform Fe₃O₄@Ag nanoparticles. The ...surface morphology, structure, and magnetic properties were characterized using transmission electron microscopy, atomic force microscopy, X-ray powder diffraction, X-ray photoelectron spectroscopy, and vibrating sample magnetometry analysis. The closely spaced Fe₃O₄@Ag substrate with a core–shell structure exhibited a 25nm surface roughness. The high saturation magnetization at 48.35emug⁻¹ enabled the complete and rapid separation of the substrate from the solution. The sensitivity and reproducibility of the substrate were confirmed using a common SERS probe molecule, rhodamine 6G. SERS spectra of Cr(VI) in simulated and real contaminated water showed that the symmetric stretching vibrations of Cr–O occurred at 796cm⁻¹. This SERS peak area exhibited a linear dependence (R²=0.9992) on the Cr(VI) concentration between 5 and 100μgL⁻¹. Coexisting anions such as sulfate, nitrate, chloride, carbonate, and humic acid could decrease the sensitivity of the SERS analysis. However, the adverse effect of the competing ions may be eliminated by proper dilution of the raw sample. This study provides a reliable method for qualitative and quantitative analysis of Cr(VI).
In this study, the effect of COD/N ratio on completely autotrophic nitrogen removal over nitrite (CANON) process was investigated in five identical membrane bioreactors. The five reactors were ...simultaneously seeded for 1L CANON sludge and be operated for more than two months under same conditions, with influent COD/N ratio of 0, 0.5, 1, 2 and 4, respectively. DGGE was used to analyze the microbial communities of aerobic ammonia-oxidizing bacteria (AOB) and anaerobic ammonia-oxidizing bacteria (AAOB) in five reactors. Results revealed the harmonious work of CANON and denitrification with low COD concentration, whereas too high COD concentration suppressed both AOB and AAOB. AOB and AAOB biodiversity both decreased with COD increasing, which then led to worse nitrogen removal. The suppressing threshold of COD/N ratio for CANON was 1.7. CANON was feasible for treating low COD/N sewage, while the high sewage should be converted by anaerobic biogas producing process in advance.
Obtaining detailed information on sulfate–nitrate–ammonium (SNA) is fundamentally important to explain the formation of haze in China, since it is a dominant component of fine particulate matter ...(PM2.5) and plays a critical role in the deterioration of air quality. Several single-particle analysis methods have been applied to study and explain SNA formation; however, determining its mixture state remains a challenge. This study describes a direct observation of the SNA components in atmospheric particles on a single-particle scale, and details the first use of a non-destructive surface-enhanced Raman scattering (SERS) technique for SNA analysis. We studied PM2.5 collected at a site on the premises of Tsinghua University in Beijing, China, during a winter haze episode (12.15.2016–12.23.2016). The on-line data show that the SNA component accounted for 9.4% to 68.2% of the total mass of PM2.5, becoming dominant on heavy haze days, and the sulfate concentration increased with the nitrate concentration (R2 = 0.72). Furthermore, the off-line SERS and scanning electron microscopy-energy dispersive X ray analysis (SEM-EDS) results for the single particles collected also indicated that SNA increase with increasing haze pollution. The existing state of the SNA component on each haze day was observed directly in a non-destructive manner mainly in the form of double salts such as 3(NH4NO3)·(NH4)2SO4 and 2(NH4NO3)·(NH4)2SO4. A Raman mapping experiment further confirmed that the SNA was internally mixed. Our data also show that SNA can evaporate under high-vacuum scanning electron microscopy conditions, suggesting that SERS is an effective method to directly observe SNA without sample loss and may represent a promising single-particle technique to supplement traditional electron microscopy methods. This work will provide evidence for the SNA formation, particularly during haze events.
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•Identifying the real status of sulfate-nitrate-ammonium (SNA) particles is difficult.•Surface-enhanced Raman scattering (SERS) is a single-molecule spectroscopy method.•SERS allows effective observation of SNA without sample loss.•SNA exists in haze as double salts mixed internally on a single-particle scale.
Subcellular Raman analysis is a promising clinic tool for cancer diagnosis, but constrained by the difficulty of deciphering subcellular spectra in actual human tissues. We report a label-free ...subcellular Raman analysis for use in cancer diagnosis that integrates subcellular signature spectra by subtracting cytoplasm from nucleus spectra (Nuc.-Cyt.) with a partial least squares-discriminant analysis (PLS-DA) model. Raman mapping with the classical least-squares (CLS) model allowed direct visualization of the distribution of the cytoplasm and nucleus. The PLS-DA model was employed to evaluate the diagnostic performance of five types of spectral datasets, including non-selective, nucleus, cytoplasm, ratio of nucleus to cytoplasm (Nuc./Cyt.), and nucleus minus cytoplasm (Nuc.-Cyt.), resulting in diagnostic sensitivity of 88.3%, 84.0%, 98.4%, 84.5%, and 98.9%, respectively. Discriminating between normal and cancerous cells of actual human tissues through subcellular Raman markers is feasible, especially when using the nucleus-cytoplasm difference spectra. The subcellular Raman approach had good stability, and had excellent diagnostic performance for rectal as well as colon tissues. The insights gained from this study shed new light on the general applicability of subcellular Raman analysis in clinical trials.
•Proposed subcellular Raman approach was applied in actual human tissues diagnosis.•Subcellular Raman analysis significantly enhanced the sensitivity and specificity of colon cancer diagnosis.•The approach has good stability and excellent diagnostic performance in other tissues diagnosis such as rectum.
Concerns over exposure to mercury have motivated the exploration of cost-effective,rapid,and reliable method for monitoring Hg^2＋ in the environment.Recently,surface-enhanced Raman scattering（SERS） ...has become a promising alternative method for Hg^2＋ analysis.SERS is a spectroscopic technique which combines modern laser spectroscopy with the optical properties of nano-sized noble metal structures,resulting in substantially increased Raman signals.When Hg^2＋ is in a close contact with metallic nanostructures,the SERS effect provides unique structural information together with ultrasensitive detection limits.This review introduces the principles and contemporary approaches of SERS-based Hg^2＋detection.In addition,the perspective and challenges are briefly discussed.
Surface-enhanced Raman scattering (SERS) analysis of environmental hydrophobic pollutants without chemical functionalization of a bare nanoparticle (NP) substrate presents a challenge. The motivation ...for our study is to develop a highly reproducible and robust portable SERS sensor for detection and identification of polycyclic aromatic hydrocarbons (PAHs) using bare Au NPs. Our hypothesis is that the coffee ring effect could separate PAHs from the bulk solution and concentrate them on the closely packed Au NP ring, consequently enhancing their Raman scattering. This premise was confirmed with the commonly used citrate-reduced Au NPs in 20 nm, having no structural uniqueness. Because of the coffee ring effect, however, closely packed but not aggregated Au NP arrays were formed and, consequently, facilitated the separation and concentration of hydrophobic PAHs. As a result, a prominent SERS enhancement can be obtained on the ring because of the electromagnetic mechanism. A mixture of six PAHs with different numbers of benzene rings, namely, naphthalene, anthracene, pyrene, benzoapyrene, benzog,h,iperylene, and indeno1,2,3-cdpyrene, could be readily identified in river water. This portable SERS sensor based on the coffee ring effect provides a robust and versatile approach in PAH detection without the need for stringent structural requirements for Au NPs.
Atmosphere aerosols have significant impact on human health and the environment. Aerosol particles have a number of characteristics that influence their health and environmental effects, including ...their size, shape, and chemical composition. A great deal of difficulty is associated with quantifying and identifying atmospheric aerosols because these parameters are highly variable on a spatial and temporal scale. An important component of understanding aerosol fate is Raman Spectroscopy (RS), which is capable of resolving chemical compositions of individual particles. This review presented strategic techniques, especially RS methods for characterizing atmospheric aerosols. The nature and properties of atmospheric aerosols and their influence on environment and human health were briefly described. Analytical methodologies that offer insight into the chemistry and multidimensional properties of aerosols were discussed. In addition, perspectives for practical applications of atmospheric aerosols using RS are featured.
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•Advances in Raman spectroscopy for spectroscopic and microscopic characterizing of atmospheric aerosols have been reviewed.•Technique for evaluating the chemical and physical properties of atmospheric aerosol particles have been described.•Efficient analysis of single aerosol particle in optical or electrodynamic traps have been reviewed from recent studies.
Single-axis rotational inertial navigation systems (single-axis RINSs) are widely used in high-accuracy navigation because of their ability to restrain the horizontal axis errors of the inertial ...measurement unit (IMU). The IMU errors, especially the biases, should be constant during each rotation cycle that is to be modulated and restrained. However, the temperature field, consisting of the environment temperature and the power heating of single-axis RINS, affects the IMU performance and changes the biases over time. To improve the precision of single-axis RINS, the change of IMU biases caused by the temperature should be calibrated accurately. The traditional thermal calibration model consists of the temperature and temperature change rate, which does not reflect the complex temperature field of single-axis RINS. This paper proposed a multiple regression method with a temperature gradient in the model, and in order to describe the complex temperature field thoroughly, a BP neural network method is proposed with consideration of the coupled items of the temperature variables. Experiments show that the proposed methods outperform the traditional calibration method. The navigation accuracy of single-axis RINS can be improved by up to 47.41% in lab conditions and 65.11% in the moving vehicle experiment, respectively.
A 1/δ gap metric based weighting method is proposed for multilinear model control of nonlinear systems, in which the gap metric is employed to formulate weighting functions for local controller ...combination. Comparisons between the proposed weighting method and another 1-δ gap metric based weighting method have been made. A CSTR system is studied to demonstrate the effectiveness of the proposed weighting method. Simulations demonstrate that the proposed weighting method has all the advantages of the 1-δ weighting method. But it is more effective than the 1-δ gap weighting method, and more sensitive to the tuning parameters, making it much easier to apply.
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