Rapidly determining the 3D structure of proteins by surface-enhanced Raman spectroscopy.

Despite great advances in protein structure analysis, label-free and ultrasensitive methods to obtain the natural and dynamic three-dimensional (3D) structures are still urgently needed. Surface-enhanced Raman spectroscopy (SERS) can be a good candidate, whereas the complexity originated from the interactions between the protein and the gradient surface electric field makes it extremely challenging to determine the protein structure. Here, we propose a deciphering strategy for accurate determination of 3D protein structure from experimental SERS spectra in seconds by simply summing SERS spectra of isolated amino acids in electric fields of different strength with their orientations in protein. The 3D protein structure can be reconstructed by comparing the experimental spectra obtained in a well-defined gap-mode SERS configuration with the simulated spectra. The gradient electric field endows SERS with a unique advantage to section biomolecules with atomic precision, which makes SERS a competent tool for monitoring biomolecular events under physiological conditions.

Correlation coefficient-directed label-free characterization of native proteins by surface-enhanced Raman spectroscopy.

Investigation of proteins in their native state is the core of proteomics towards better understanding of their structures and functions. Surface-enhanced Raman spectroscopy (SERS) has shown its unique advantages in protein characterization with fingerprint information and high sensitivity, which makes it a promising tool for proteomics. It is still challenging to obtain SERS spectra of proteins in the native state and evaluate the native degree. Here, we constructed 3D physiological hotspots for a label-free dynamic SERS characterization of a native protein with iodide-modified 140 nm Au nanoparticles. We further introduced the correlation coefficient to quantitatively evaluate the variation of the native degree, whose quantitative nature allows us to explicitly investigate the Hofmeister effect on the protein structure. We realized the classification of a protein of SARS-CoV-2 variants in 15 min, which has not been achieved before. This study offers an effective tool for tracking the dynamic structure of proteins and biomedical research.

Simultaneous determination of 31 endocrine disrupting chemicals in fish plasma by solid-phase extraction coupled with ultra-performance liquid chromatography-tandem mass spectrometry.

Solid phase extraction combined with ultra-performance liquid chromatography-tandem mass spectrometry was developed for the simultaneous determination of 31 endocrine-disrupting chemicals in fish plasma. The strong anion exchange/primary-secondary amine cartridge and the mixed cation exchange cartridge were used in tandem instead of using a single mixed cation exchange cartridge for sample purification. Suitable eluents were selected for each of the two cartridges: 4.5% ammonia/acetonitrile solution for cartridges in tandem and acetone:n-hexane (V:V = 3:7) for the strong anion exchange/primary-secondary amine cartridge alone. With this optimized Solid phase extraction method, the recoveries of 31 endocrine disrupting chemicals were between 43.0% and 131.3%, the method detection limits were 0.45 to 1.35 ng/ml, and the limits of quantitation were 1.50-4.50 ng/ml. The innovative pretreatment method that connects two cartridges in tandem is well positioned to mitigate the matrix effects of fish plasma, thereby improving the accuracy of multiclass endocrine-disrupting chemicals determination. The significance of this method is to facilitate the application of the fish plasma model for the environmental risk assessment of endocrine-disrupting chemicals.

Quantitatively Deciphering Electronic Properties of Defects at Atomically Thin Transition-Metal Dichalcogenides.

Defects can locally tailor the electronic properties of 2D materials, including the band gap and electron density, and possess the merit for optical and electronic applications. However, it is still a great challenge to realize rational defect engineering, which requires quantitative study of the effect of defects on electronic properties under ambient conditions. In this work, we employed tip-enhanced photoluminescence (TEPL) spectroscopy to obtain the PL spectra of different defects (wrinkle and edge) in mechanically exfoliated thin-layer transition metal dichalcogenides (TMDCs) with nanometer spatial resolution. We quantitatively obtained the band gap and electron density at defects by analyzing the wavelength and intensity ratio of excitons and trions. We further visualized the strain distribution across a wrinkle and the edge-induced reconstructive regions of the band gap and electron density by TEPL line scans. The doping effect on the Fermi level and optical performance was unveiled through comparative studies of edges on TMDC monolayers of different doping types. These quantitative results are vital to guide defect engineering and design and fabrication of TMDC-based optoelectronics devices.

Electrochemical Tip-Enhanced Raman Spectroscopy: An In Situ Nanospectroscopy for Electrochemistry.

Revealing the intrinsic relationships between the structure, properties, and performance of the electrochemical interface is a long-term goal in the electrochemistry and surface science communities because it could facilitate the rational design of electrochemical devices. Achieving this goal requires in situ characterization techniques that provide rich chemical information and high spatial resolution. Electrochemical tip-enhanced Raman spectroscopy (EC-TERS), which provides molecular fingerprint information with nanometer-scale spatial resolution, is a promising technique for achieving this goal. Since the first demonstration of this technique in 2015, EC-TERS has been developed for characterizing various electrochemical processes at the nanoscale and molecular level. Here, we review the development of EC-TERS over the past 5 years. We discuss progress in addressing the technical challenges, including optimizing the EC-TERS setup and solving tip-related issues, and provide experimental guidelines. We also survey the important applications of EC-TERS for probing molecular protonation, molecular adsorption, electrochemical reactions, and photoelectrochemical reactions. Finally, we discuss the opportunities and challenges in the future development of this young technique.

Atomic Force Microscopy Based Top-Illumination Electrochemical Tip-Enhanced Raman Spectroscopy.

Electrochemical tip-enhanced Raman spectroscopy (EC-TERS) is a powerful technique for the in situ study of the physiochemical properties of the electrochemical solid/liquid interface at the nanoscale and molecular level. To further broaden the potential window of EC-TERS while extending its application to opaque samples, here, we develop a top-illumination atomic force microscopy (AFM) based EC-TERStechnique by using a water-immersion objective of a high numerical aperture to introduce the excitation laser and collect the signal. This technique not only extends the application of EC-TERS but also has a high detection sensitivity and experimental efficiency. We coat a SiO2 protection layer over the AFM-TERS tip to improve both the mechanical and chemical stability of the tip in a liquid TERS experiment. We investigate the influence of liquid on the tip-sample distance to obtain the highest TERS enhancement. We further evaluate the reliability of the as-developed EC-AFM-TERS technique by studying the electrochemical redox reaction of polyaniline. The top-illumination EC-AFM-TERS is promising for broadening the application of EC-TERS to more practical systems, including energy storage and (photo)electrocatalysis.

Probing the edge-related properties of atomically thin MoS2 at nanoscale.

Defects can induce drastic changes of the electronic properties of two-dimensional transition metal dichalcogenides and influence their applications. It is still a great challenge to characterize small defects and correlate their structures with properties. Here, we show that tip-enhanced Raman spectroscopy (TERS) can obtain distinctly different Raman features of edge defects in atomically thin MoS2, which allows us to probe their unique electronic properties and identify defect types (e.g., armchair and zigzag edges) in ambient. We observed an edge-induced Raman peak (396 cm-1) activated by the double resonance Raman scattering (DRRS) process and revealed electron-phonon interaction in edges. We further visualize the edge-induced band bending region by using this DRRS peak and electronic transition region using the electron density-sensitive Raman peak at 406 cm-1. The power of TERS demonstrated in MoS2 can also be extended to other 2D materials, which may guide the defect engineering for desired properties.

The Beneficial Effects of a Polysaccharide from Moringa oleifera Leaf on Gut Microecology in Mice.

Moringa oleifera is a natural plant with high nutritional and pharmacological value. Leaves of M. oleifera contain a variety of active substances. In our previous research, we had obtained a polysaccharide separated from M. oleifera leaf, namely MOs-2-a (1.35 × 104 Da). In this study, this polysaccharide was administrated daily to 6 week-old ICR mice for 4 weeks. Then, the body weight, immunity, intestinal digestion, and intestinal microenvironment of Institute of Cancer Research (ICR) mice were investigated. After 4 weeks of feeding intervention with the polysaccharide, the immune and intestinal digestive ability of the ICR mice were significant as shown by the organ index, digestive enzymes, and reduction of serum tumor necrosis factor-alpha and diamine oxidase levels. The polysaccharide could regulate the microbial composition of the intestinal tract in mice by increasing the bacteria that have been reported for antiobesity effects, short chain fatty acid production, and lactic acid production. These findings indicate that the polysaccharide of M. oleifera leaf might be a promising prebiotic that exhibits health promotion effects.

Correction to: Occurrence of 25 pharmaceuticals in Taihu Lake and their removal from two urban drinking water treatment plants and a constructed wetland.

The article Occurrence of 25 pharmaceuticals in Taihu Lake and their removal from two urban drinking water treatment plants and a constructed wetland, written by Xia-Lin Hu, Yi-Fan Bao, Jun-Jian Hu, You-Yu Liu and Da-Qiang Yin, was originally published electronically on the publisher's internet portal.

Simultaneous determination of 29 pharmaceuticals in fish muscle and plasma by ultrasonic extraction followed by SPE-UHPLC-MS/MS.

A confirmatory method for the simultaneous detection of 29 pharmaceuticals in fish muscle and plasma was developed by using solid-phase extraction combined with ultra-high performance liquid chromatography and tandem mass spectrometry. Fish samples were extracted with methanol and enriched using Oasis HLB solid-phase extraction columns in one step. Twenty-nine target pharmaceuticals were quantified by the internal standard method and the calibration curves showed good linearity in a wide range with determination coefficients of greater than 0.913. The detection limits of the pharmaceuticals ranged from 0.01 to 2.00 µg/kg (µg/L). The applicability of the method was checked by precision and recovery experiments. The average recoveries of the 29 pharmaceuticals were between 61 and 111%, and all the relative standard deviations were below 25%. Our reported method has been demonstrated to be sensitive, convenient, rapid, and reliable for the simultaneous determination of 29 pharmaceuticals in fish muscle and plasma. Real sample determination showed that 25 and 9 of the 29 compounds were detected in fish muscle and plasma, respectively.

Occurrence of 25 pharmaceuticals in Taihu Lake and their removal from two urban drinking water treatment plants and a constructed wetland.

Pharmaceuticals in drinking water sources have raised significant concerns due to their persistent input and potential human health risks. The seasonal occurrence of 25 pharmaceuticals including 23 antibiotics, paracetamol (PAR), and carbamazepine (CMZ) in Taihu Lake was investigated; meanwhile, the distribution and removal of these pharmaceuticals in two drinking water treatment plants (DWTPs) and a constructed wetland were evaluated. A high detection frequency (>70%) in the Taihu Lake was observed for nearly all the 25 pharmaceutics. Chlortetracycline (234.7 ng L-1), chloramphenicol (27.1 ng L-1), erythromycin (72.6 ng L-1), PAR (71.7 ng L-1), and CMZP (23.6 ng L-1) are compounds with both a high detection frequency (100%) and the highest concentrations, suggesting their wide use in the Taihu Basin. Higher concentrations of chloramphenicols, macrolides, PAR, and CMZP were observed in dry season than in wet season, probably due to the low flow conditions of the lake in winter and the properties of pharmaceuticals. The overall contamination levels of antibiotic pharmaceutics (0.2-74.9 ng L-1) in the Taihu Lake were lower than or comparable to those reported worldwide. However, for nonantibiotic pharmaceutics, PAR (45.0 ng L-1) and CMZP (14.5 ng L-1), significantly higher concentrations were observed in the Taihu Lake than at a global scale. High detection frequencies of 25 pharmaceuticals were observed in both the two DWTPs (100%) and the wetland (>60%) except for florfenicol and sulfapyridine. The removal efficacies of the studied pharmaceuticals in DWTP B with advanced treatment processes including ozonation and granular activated carbon filtration (16.7-100%) were superior to DWTP A with conventional treatment processes (2.9-100%), except for sulfonamides. Wetland C with the constructed root channel technology was efficient (24.2-100%) for removing most pharmaceuticals. This work suggests that the application of cost-effective technologies such as constructed wetlands should be considered as an efficient alternative for removing pharmaceuticals from water supply sources.

Ameliorative effects of tannic acid on carbon tetrachloride-induced liver fibrosis in vivo and in vitro.

We investigated the ameliorative effects and potential mechanisms of tannic acid (TA) in carbon tetrachloride (CCl4)-intoxicated mice and hepatic stellate cells (HSCs). Liver fibrosis was observed in CCl4 (800 ml/kg)-induced mice, and high viability was observed in CCl4 (10 mM)-intoxicated HSCs. Pre-treatment of mice with TA (25 or 50 g/kg/day) significantly ameliorated hepatic morphology and coefficient values and reduced the activities of aspartate aminotransferase (AST) and alanine aminotransferase (ALT), the concentrations of malondialdehyde (MDA) and serum levels of endothelin-1 (ET-1). In addition, TA increased the activities of superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GSH-Px), and endothelial nitric oxide synthase (eNOS) and the serum level of NO. Moreover, TA reduced the expression of angiotensin II receptor-1 (ATR-1), interleukin-1ß (IL-1ß), tumor necrosis factor-α (TNF-α), transforming growth factor-ß (TGF-ß), caspase-3, c-fos, c-jun, the ratio of Bax/bcl-2, tissue inhibitor of metalloproteinase-1 (TIMP-1) and TA increased matrix metal proteinase-9 (MMP-9), matrix metalloproteinase-1 (MMP-1). Furthermore, TA (0.01 µM, 0.1 µM or 1 µM) decreased the TIMP-1/MMP-1 ratio and reduced the viability of HSCs. These results indicated that TA exerts significant liver-protective effects in mice with CCl4-induced liver fibrosis. The potential mechanism may rely on the inhibition of collagen accumulation, oxidative stress, inflammation and apoptosis.