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In this work, a hyphenated technique of dual ultrasound-assisted dispersive liquid-liquid microextraction combined with microwave-assisted derivatization followed by ultra high performance liquid chromatography tandem mass spectrometry has been developed for the determination of phytosterols in functional foods and medicinal herbs. Multiple reaction monitoring mode was used for the tandem mass spectrometry detection. A mass spectrometry sensitive reagent, 4′-carboxy-substituted rosamine, has been used as the derivatization reagent for five phytosterols, and internal standard diosgenin was used for the first time. Parameters for the dual microextraction, microwave-assisted derivatization, and ultra high performance liquid chromatography tandem mass spectrometry were all optimized in detail. Satisfactory linearity, recovery, repeatability, accuracy and precision, absence of matrix effect, extremely low limits of detection (0.005-0.015 ng/mL) and limits of quantification (0.030-0.10 ng/mL) were achieved. The proposed method was compared with previously reported methods. It showed better sensitivity, selectivity, and accuracy. The matrix effect was also significantly reduced. The proposed method was successfully applied to the determination of five phytosterols in vegetable oil (sunflower oil, olive oil, corn oil, peanut oil), milk and orange juice (soymilk, peanut milk, orange juice), and medicinal herbs (Ginseng, Ganoderma lucidum, Cordyceps, Polygonum multiflorum) for the quality control of functional foods and medicinal herbs. [ABSTRACT FROM AUTHOR]

We report a simple method for the direct and quantitative determination of L-tryptophan (Trp) and L-tyrosine (Tyr) using a glassy carbon electrode (GCE) modified with single-walled carbon nanohorns (SWCNHs). The SWCNH modified GCE exhibits high electrocatalytic activity towards the oxidation of both Trp and Tyr. It shows a linear response to Trp between 0.5 and 50 μM and to Tyr between 2 and 30 μM. The detection limits for Trp and Tyr are 50 nM and 400 nM, respectively. In addition, the modified GCE displays good selectivity and good sensitivity, thus making it suitable for the determination of Trp and Tyr in spiked serum samples. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

DNA-templated silver nanoclusters (DNA/AgNCs) serve as a useful electrochemical sensing nanomaterial characterized by excellent electroactivity and good stability, while the effect of surrounding nucleotides on their electroactivity has not been studied. Herein, we validated a nucleotide-assisted enhancement mechanism of the DNA/AgNCs electroactivity caused by T-rich nucleic acid sequences in the vicinity of AgNCs. Based on the T-rich nucleic acid-enhanced AgNCs (NAE-AgNCs) combined with hybrid chain reaction (HCR), a novel signal-enhanced electrochemical biosensing platform was established for the ultrasensitive detection of miRNA. In the presence of target miRNA-155, HCR could be triggered to generate duplex strands containing both numerous AgNC synthesis sites and T-rich overhang strands upon the electrode. With the electrodeposition of adjacent AgNCs on the electrode, the larger oxidation potential of T-rich nucleic acid leaded to stronger electron-accepting capacity, which could contribute to increased current responses. The T-rich NAE HCR electrochemical strategy resulted in a detection limit of 0.39 fM for miRNA-155 detection, one order of magnitude lower than conventional HCR-based electrochemical sensors. This T-rich nucleic acid-assisted enhancement mechanism provided a new direction to construct highly sensitive, label-free, low-cost, and simple sensing platforms for applications in biomarker assays and clinic diagnosis. [Display omitted] [ABSTRACT FROM AUTHOR]

The incorporation of waste eggshells as fillers in construction materials is currently constrained by factors such as shell-membrane separation, particle size, and proportion of incorporation. This study aims to assess the feasibility of utilizing non-calcined eggshell particles (EPs) in alkali-activated solid waste-based materials. Initially, the micro characteristics of water-treated and alkali-treated eggshells were evaluated. Subsequently, nine groups of alkali-activated slag-based paste samples were prepared by using EPs as fillers, and the influence of the particles on the physical and mechanical properties of the materials was assessed based on flowability, density, and compressive strength. Furthermore, the impact of shell-membrane separation and particle size on the microstructure and composition of the alkali-activated materials (AAMs) was characterized by using a combination of SEM-EDS, XRD, FTIR, and TG-DSC techniques. Finally, six groups of alkali-activated slag-red mud-fly ash-based mortar samples were prepared with EPs as fillers, which demonstrates the feasibility of EPs in multi-waste-based materials and expands the application range of non-calcined eggshells. The results show that water treatment and alkali treatment of EPs provide viable methods for shell-membrane separation, albeit with some loss of fine particles. The physical filling of membranes in AAMs does not affect the chemical composition. The EPs (with a particle size less than 0.5 mm) can be used as fillers in AAMs without shell-membrane separation. Moreover, when the EPs content is increased to 33%, the 90-d flexural strength of the AAMs increases by 60% compared to the control group (without EPs), while the compressive strength remains unchanged. Thus, it is feasible to directly crush and sieve non-calcined eggshells for use as fillers in alkali-activated waste-based cementitious materials without the need for shell-membrane separation, and this method does not produce any negative impact. The findings of this research provide an effective technical approach for the application of waste eggshells in eco-friendly construction materials. • Waste eggshells were recycled as fillers to prepare alkali-activated solid waste-based materials. • Ground eggshell particles with a maximum particle size of 0.5 mm were recommended without shell-membrane separation. • Role of eggshell particles was physical and not chemical in structures of alkali-activated materials. • Eggshell particles content was increased to 33% without reducing flexural and compressive strengths. [ABSTRACT FROM AUTHOR]

Endocrine disrupting chemicals (EDCs), belonging to the category of emerging contaminants, are a class of highly heterogeneous persistent pollutants that can seriously interfere with the function of human endocrine system. Human matrices are extremely complex, and EDCs are usually present in trace concentrations and are often accompanied with analysis challenge due to their physical and chemical structure and properties. Therefore, sample preparation and analytical techniques are the key steps in the identification and quantitation of EDCs in human matrices. Mass spectrometry (MS) technique has powerful analytical performance, and is one of the preferred choices for EDCs. This review focused on 11 types of EDCs, including bisphenols, alkylphenols, phthalates, parabens, perfluorinated compounds, flame retardants, organic UV-filters, polycyclic aromatic hydrocarbons, pesticides, heavy metals, and some other concerned endocrine disruptors. The research progresses, advantages, disadvantages, and trends of sample preparation techniques and MS-based analytical methods for EDCs in human matrices were reviewed. This review focuses on recent advances of MS-based analytical methods for 11 types of EDCs in human matrices. Their sources, characteristics and exposure routes were summarized, and the health risks caused by EDCs exposure were expounded from the perspective of toxicology. The research progresses, advantages, disadvantages, and trends of preparation techniques and MS analytical methods for EDCs since 2010 were reviewed critically. [Display omitted] • Exposure to EDCs can lead to serious human health risks. • The source, characteristics, exposure routes and health risks of EDCs were reviewed. • Mass spectrometry is the preferred choice for the measurement of trace EDCs. • Highlights the discussions of preparation techniques and analytical methods. • Analysis of EDCs in human matrices will help to assess and prevent health effects. [ABSTRACT FROM AUTHOR]

In this work, we proposed a convenient fluorescent assay for the detection of quinolones based on their inhibition towards the oxidation of o-phenylenediamine (OPD) by copper ions (Cu2+). Free Cu2+ can oxidize OPD into fluorescent 2,3-diaminophenzine followed by the formation of copper nanoparticles (CuNPs), which would further catalyze the oxidation of OPD. When quinolones were added, their strong binding affinity to Cu2+ inhibited the oxidase-like activity of Cu2+. So, the fluorescence intensity of the Cu2+–OPD system decreased obviously. The determination of quinolones can be achieved by using this fluorimetric assay without the use of complicated instruments and protocols. As demonstrated, this assay offered a highly sensitive readout for quinolones including nalidixic acid, cinoxacin, ciprofloxacin, and moxifloxacin in the linear ranges of 1.0–100 nM, 0.5–100 nM, 1.0–100 nM, and 0.1–100 nM, respectively. In addition, the developed assay was successfully applied to the direct analysis of quinolones in real amples. [ABSTRACT FROM AUTHOR]

A ratiometric fluorescence strategy has been designed for the detection of sulfide ions with fluorescent MOF-based nanozyme, which acts as fluorescence reporter as well as biomimetic oxidase. [Display omitted] • A ratiometric nanosensor for S2- based on multifunctional MOF was established for the first time. • NH 2 -Cu-MOF exhibits biomimetic oxidase activity besides its intrinsic fluorescence. • The presence of S2- inhibits the oxidase-like activity of MOF due to the formation of CuS. • The in situ-formed fluorophore can avoid additional synthesis of another probe. A novel ratiometric fluorescence strategy for sulfide ions (S2-) analysis has been developed using metal–organic framework (MOF)-based nanozyme. NH 2 -Cu-MOF displays blue fluorescence (λem = 435 nm) originating from 2-amino-1,4-benzenedicarboxylic acid ligand. Besides, it possesses oxidase-like activity due to Cu2+ node, which can trigger chromogenic reaction. o -Phenylenediamine (OPD), as a common enzyme substrate, can be oxidized by NH 2 -Cu-MOF to form luminescent products (oxOPD) (λem = 570 nm). Inner filter effect occurs between oxOPD and MOF. Upon exposure to S2-, oxidase-like activity of MOF is depressed significantly because of the generation of CuS. On one hand, the amount of free Cu2+ decreases, affecting the yielding of oxOPD. On the other hand, CuNPs with larger size are obtained during the oxidation–reduction reaction between Cu2+ and OPD, which show weaker autocatalytic ability for OPD oxidation. These result in the decrease and increase of intensities at 570 and 435 nm, respectively. This method exhibits sensitive and selective responses towards S2- with LOD of 0.1 μM. Furthermore, such ratiometric strategy has been applied to detect S2- in food samples. [ABSTRACT FROM AUTHOR]

Metabolomics and exposomics are important in the studies of human health and diseases. Chemical isotope labeling (CIL) combined with mass spectrometry (MS) can not only improve sensitivity but also bring significant benefits for selectivity, accuracy, omics coverage, and analysis throughput. Therefore, MS-based CIL techniques have been increasingly used in metabolome and exposome analysis. In this review, we summarize the advantages of MS-based CIL techniques in sensitivity, accuracy, selectivity, stability, analysis throughput, and applicability, and also discuss the potential shortcomings. Moreover, based on five subgroups of representative metabolites and xenobiotics containing amino, carboxyl, carbonyl, hydroxyl and sulfhydryl groups, we review the advances of MS-based CIL techniques in targeted and not-targeted analysis. Notably, some novel CIL techniques emerged in the structural design of CIL reagents has also discussed. Finally, we give our perspective on the future of MS-based CIL techniques in this field, especially on the structural design of ideal CIL reagents. This review focuses on recent advances of CIL-MS strategies in targeted and non-targeted analysis of metabolome and exposome based on five subgroups of representative metabolites and xenobiotics, including amino, carboxyl, carbonyl, hydroxyl and thiol groups. The future perspective of MS-based CIL technique in this field, especially on the structural design of ideal CIL reagents, have also been discussed. [Display omitted] • CIL-MS strategy is powerful for targeted and non-targeted analysis. • Methodological considerations of CIL-MS analysis are discussed in details. • Current CIL techniques for the MS analysis of metabolome and exposome are reviewed. • Two emerging CIL techniques are summarized and prospected in details. • Potential disadvantages and perspectives of CIL-MS strategy are discussed. [ABSTRACT FROM AUTHOR]

• A group of MSIMTs were synthesized to perform multiplexed derivatization of SchA. • A magnetic MIPs was prepared using MSIMT-375-SchA as dummy template. • All 10-plexed MSIMTs-SchA derivatives can be purified by MDSPE before UHPLC-MS/MS. • MSIMT-346-SchA standard derivative was used as internal standard in all procedure. • It was applied for comparative pharmacokinetics of SchA in rat brain and blood. Schisandrol A (SchA) is the main active ingredient of Schisandra chinensis (Turcz.) Baill., which is a famous traditional Chinese herbal medicine. SchA can penetrate the blood-brain barrier and has a significant neuroprotective effect. A group of multiplexed stable isotope mass tags (MSIMTs, m/z 332, 338, 346, 349, 351, 354, 360, 363, 374 and 377) were synthesized to perform multiplexed stable isotope labeling derivatization (MSILD) of SchA in rat microdialysates and standards. A new magnetic molecularly imprinted polymer was prepared using MSIMT-375-SchA as dummy template. All the 10-plexed derivatives of MSIMTs-SchA can be efficiently and selectively enriched and purified using this adsorbent by magnetic dispersive solid phase extraction (MDSPE) before ultra high performance liquid chromatography tandem mass spectrometry (UHPLC-MS/MS) analysis. It should be pointed out that the MSIMT-346-SchA standard derivative was used as internal standard in the process of MDSPE and UHPLC-MS/MS. On these bases, 9 different rat microdialysate samples can be determined by UHPLC-MS/MS in a single run. The utilization of MSIMTs significantly increased the sensitivity, accuracy, selectivity and analysis throughput. Under the optimized conditions, satisfactory linearity (R2> 0.987), limit of detection (LODs, 0.15–0.26 pg/mL) and lower limit of quantitative (LLOQ, 0.8–2.0 pg/mL) were obtained. Intra- and inter-day precisions were in the range of 2.2% -12.5%, and recoveries 94.2% -106.2%. The matrix effects were very low, and the average derivatization efficiency of 10-plex MSIMTs to SchA was as high as 97.8%. Using the developed dual-probe in vivo microdialysis sampling technique, the proposed analytical method has been applied for comparative pharmacokinetics of SchA in the brain and blood of control and Parkinson's disease (PD) rats. [ABSTRACT FROM AUTHOR]

A ratiometric fluorescence strategy has been designed for the first time to detect artemisinin by employing photoluminescent Zn-MOF as reference combined with the catalyzation reaction of hemin towards artemisinin. [Display omitted] • A ratiometric fluorescence method for the detection of artemisinin has been developed for the first time. • Zn-MOF was firstly used to construct sensing platform for artemisinin. • Hemin can catalyze artemisinin to generate oxygen species, which induces chromogenic reaction. • The in situ-formed fluorophore can avoid additional synthesis of another probe. Artemisinin (ART) is a type of frontline drug to treat drug-resistant falciparum malaria. Simple, accurate and selective determination of ART is significant to monitor its clinical pharmaceutical efficacy. Herein, a new ratiometric fluorescence method has been designed for the determination of ART with Zn-MOF as fluorescence reference and hemin as catalyst, respectively. Zn-MOF possesses intrinsic fluorescence at 443 nm owing to 2-aminoterephthalic acid ligand. When o -phenylenediamine (OPD) is mixed with hemin, a weak fluorescent signal at 570 nm ascribed to oxidized product of OPD (oxOPD) is observed. In the presence of ART, hemin can catalyze ART to break its peroxide bridge and release a large number of reactive oxygen species, which effectively oxidize OPD into luminescent oxOPD. Therefore, the fluorescence at 570 nm is enhanced significantly while the fluorescence of Zn-MOF remains basically unchanged. Thus, a ratiometric fluorescence sensing platform has been constructed for the detection of ART. This method exhibits wider linear range (0.15 μM-150 μM) with detection limit of 50 nM. This novel and selective method has been used to detect ART in compound naphthoquinone phosphate tablets. [ABSTRACT FROM AUTHOR]

Exposure to environmental pollutants poses a great threat to human health. Oxidative stress is one of the widely accepted toxicity mechanisms of pollutants, and oxidative stress biomarkers provide tools for tracing the adverse effects of pollutant exposure. In this review, we focus on five kinds of typical oxidative stress biomarkers induced by pollutant exposure, including ROS, antioxidants, oxidative DNA damages, oxidative protein damages and oxidative lipid damages. We will summarize and review the application progress of various analytical methods mainly in the past decade. We also comprehensively discuss and compare their advantages and potential disadvantages. In addition, several novel analytical techniques, such as DNA damage sequencing, chemical isotope labeling, and mass spectrometry imaging, have been applied to the analysis of the biomarkers with different degrees of success. Therefore, a broader prospect is anticipated for oxidative stress biomarkers in the field of health risk assessment of pollutants. [Display omitted] • Oxidative stress is one of the important toxic mechanisms of environmental pollutant. • Pollutant exposure and health risks can be associated and assessed via oxidative stress. • Analytical methods of oxidative stress biomarker from pollutant exposure are reviewed. • The advantages, disadvantages and applicability of analytical methods are discussed. • Innovative analytical methods are urgently needed for environmental health research. [ABSTRACT FROM AUTHOR]

A novel and sensitive IFE-based fluorescence assay for isoniazid has been developed with manganese dioxide nanosheets (MnO 2) and gold nanoparticles (AuNPs) as dual nanoquenchers in combination of analyte-triggered cascade reactions for the first time. [Display omitted] A sensitive fluorescence sensing platform consisting of manganese dioxide nanosheets (MnO 2) and gold nanoparticles (AuNPs) as dual nanoquenchers has been constructed to detect isoniazid combined with analyte-triggered cascade reactions. The fluorescence of 2,3-diaminophenazine (DAP) is quenched simultaneously by MnO 2 and AuNPs via inner filter effect. MnO 2 is decomposed by isoniazid to generate Mn2+, which makes AuNPs aggregated. The quenching abilities of both the decomposed MnO 2 and aggregated AuNPs are inhibited, causing remarkable fluorescence recovery. The usage of dual nanoquenchers enhances the quenching efficiency and reduces the fluorescence background. Moreover, the isoniazid-triggered cascade reaction further amplifies the readout signal. Thus, this strategy exhibits higher sensitivity towards the detection of isoniazid. Compared with MnO 2 -based fluorescence assay, this strategy possesses lower limit of detection. This strategy has been successfully used to detect isoniazid in pharmaceutical preparations, which is of great significance for drug analysis. [ABSTRACT FROM AUTHOR]

[Display omitted] • It is firstly discovered that the Tb-MCs have the property of AIE in water. • The morphological change of Tb-MCs in water/methanol mixtures is firstly reported. • The application of Tb-MCs with AIE feature to detect biomolecule is first studied. The Metallacrowns (MCs) composed of repeated [Metal-N-O] subunits are a type of new material, but the MCs have not been developed and utilized in analytical applications. This essay reports on a new kind of terbium(III)-based Metallacrowns (Tb-MCs) with aggregation-induced emission (AIE) feature to build a sensing platform. It is first time that Tb-MCs are able to aggregate to larger aggregates in water along with a bright green emission, so that the property makes it possible to apply in biosensing. Thereafter, the AIE of Tb-MCs can be quenched effectively by Cu2+. Based on the high affinity of thiol to Cu2+, cysteine (Cys) recovers the fluorescence of Tb-MCs in the presence of Cu2+. There is a good linear range varying from 0.02 to 20 μM with a low limit of detection (LOD) 9.67 nM of Cys. In the end, this novel probe is also successfully applied to the determination of Cys in human serum with satisfactory results. [ABSTRACT FROM AUTHOR]

Herein, a novel peptidyl probe is first synthesized by the amide reaction between glutathione-capped gold nanoclusters (GSH-AuNCs) and positive charged arginine-rich peptide (Arg 9), and it is called Arg 9 -GSH-AuNCs. Polyuridylic acid (polyU), as a polyanion, is firstly used to induce the aggregation-induced emission enhancement (AEE) of positive charged Arg 9 -GSH-AuNCs through electrostatic attraction. The peptide bond on the carboxyl terminal of the arginine residues can be recognized and cleaved by trypsin. Hence, polyU is hard to induce the aggregation of peptidyl probe again, and the AEE from GSH-AuNCs becomes weak. It is an ideal platform to detect trypsin and screen trypsin inhibitors. The fluorescent peptidyl probe exhibits excellent sensitivity for trypsin. A good linear range of trypsin is obtained from 1 to 50 ng·mL−1 with the limit of detection (LOD) 0.31 ng·mL−1, which is lower than those of most reported works. Furthermore, the inhibitory effects of the extracts from foods (i.e., soybean seed flour, black soybean seed flour, mung bean seed flour, and azuki bean seed flour) on the trypsin activity have been studied. The half maximal inhibitory concentration (IC 50) values of extracts from soybean seed flour, black soybean seed flour, mung bean seed flour, and azuki bean seed flour are 4.5, 9.3, 11.6, 20.9 μg·mL−1, respectively. The screening results show that these extracts from foods all have inhibitory effects on trypsin. Among them, the extract from soybean seed flour exhibits significant inhibitory effect. [Display omitted] • A novel peptidyl probe is synthesized by linking GSH-AuNCs with peptide. • The method is universal for diverse targets by replacing substrate peptide sequence. • PolyU is found to be a novel trigger to induce the AEE of peptidyl probe. • Trypsin is detected sensitively with LOD as low as 0.31 ng·mL−1. • This strategy is successfully applied to screening trypsin inhibitors from foods. [ABSTRACT FROM AUTHOR]

[Display omitted] • Aggregation induced emission of GSH-AuNCs is induced by peptide self-assembly. • Diphenylalanine peptide is a novel substrate for chymotrypsin. • The strategy is universal for other targets by replacing substrate peptide sequence. • A new platform is developed to monitor enzyme activity and screen its inhibitors. Herein, a new strategy is developed to induce the aggregation of glutathione-capped gold nanoclusters (GSH-AuNCs) by self-assembly of peptide. The diphenylalanine peptide (L-Phe- l -Phe, FF) self-assembles in aqueous solution into the nano-net structure (FF-Nanonet, FF N). With self-assembly of FF, GSH-AuNCs aggregate in the network of FF N to form a dual-emission probe, called FF-N@GSH-AuNCs. One emission is from the self-assembled FF N at 470 nm, and the other one is the aggregation-induced enhanced emission (AIEE) of the GSH-AuNCs at 575 nm. Due to the hydrolysis of FF by chymotrypsin (CHT), the peptide bond on the carboxyl side of the phenylalanine is cleaved and the AIEE from GSH-AuNCs becomes faint because the released nanoclusters are dispersed in the solution again. Therefore, FF-N@GSH-AuNCs can be applied to screen and evaluate the CHT inhibitors. The inhibitory effects of four ingredients from natural products (i.e. epigallocatechin gallate (EGCG), tannic acid, oleanolic acid, and ursolic acid) on CHT activity have been studied. Oleanolic acid and ursolic acid are invalid. The half maximal inhibitory concentration (IC 50) values of EGCG and tannic acid are 13.9 and 19.2 μM, respectively. The screening results show that these two compounds have significant inhibitory effects on CHT. [ABSTRACT FROM AUTHOR]

[Display omitted] • Perovskites with aggregation-induced emission feature are used for biosensing. • The morphological change of perovskites in DMF/water mixtures is firstly reported. • A few pM of gold nanoparticles effectively quench the fluorescence of perovskites. A new kind of lead halide perovskites (LHPs) with aggregation induced emission (AIE) feature is developed. These LHPs are nonemissive when they disperse in good solvent (DMF), but show high brightness when they aggregate in water. The morphology of LHPs changes from nanometer-sized irregular shape to micrometer-sized needle-like, and then to stick-like with increasing water fraction. However, their AIE is quenched by only a few pM of dispersed gold nanoparticles (AuNPs). Dopamine (DA) induces aggregation of AuNPs, resulting in AIE recovery of LHPs. A good linear range of DA is obtained from 0.5 to 50 μM with the limit of detection (LOD) 0.12 μM. In the catalysis of tyrosinase (TYR), DA is oxidized to dopaquinone, resulting in the fluorescence quenching of LHPs again. Therefore, this system is further used for monitoring TYR activity and evaluating inhibitor of TYR. Finally, this method is successfully applied to detecting DA in urine samples. [ABSTRACT FROM AUTHOR]

A ratiometric fluorescence sensing platform for BLM has been designed based on chameleon DNA-AgNCs with dual fluorescence for the first time. [Display omitted] • Chameleon DNA-AgNCs were designed and applied for ratiometric fluorescence detection of BLM for the first time. • The presence of BLM-Fe(II) complex induces the fluorescence discoloration of DNA-AgNCs from orange to yellow. • This ratiometric assay exhibits a high sensitivity towards BLM with a detection limit of 67 pM. • The ratiometric nanoprobe is one single fluorophore with dual fluorescence and thus is simpler and cost-effective. The authors design dual-emissive DNA-templated silver nanoclusters (DNA-AgNCs) for ratiometric fluorescence sensing bleomycin (BLM) for the first time. A hairpin probe containing two different C-rich DNA templates at two terminals is used to synthesize chameleon DNA-AgNCs, which possess two emission peaks when they are in close proximity. A strong emission is founded at 622 nm (λex = 570 nm) while a weak one is located at 572 nm (λex = 504 nm). Meanwhile, the loop of this probe contains the scission site (5′-GC-3′) of BLM. The loop can be cleaved into two parts by BLM-Fe(II) complex, inducing the two DNA-AgNCs away from each other. The fluorescence intensity at 572 nm and 622 nm increases and decreases, respectively. Such chameleon DNA-AgNCs exhibit an obvious fluorescence discoloration from orange to yellow. Therefore, a sensitive ratiometric fluorescent strategy for BLM detection has been proposed with the detection limit of 67 pM. Finally, this ratiometric method is used to detect BLM in serum samples. [ABSTRACT FROM AUTHOR]

A ratiometric fluorescence assay for alendronate has been developed with Ce4+-triggered cascade chromogenic reaction in combination of the oxidase-like activity of Ce4+ for the first time. • Ce4+ oxidizes AA into DHAA, which condenses with OPD to generate fluorescent DFQ. • Ce4+ mimicked the function of oxidase to catalyze the oxidation of OPD to DAP. • A ratiometric assay for ALDS is developed based on DFQ and DAP for the first time. • This approach offers a convenient and effective "mix-then-test" way for detection. A ratiometric fluorescence assay for alendronate (ALDS) has been designed with Ce4+-triggered cascade chromogenic reaction. This strategy involves three processes: (1) Ce4+ oxidizes ascorbic acid (AA) into dehydroascorbic acid (DHAA), which then condenses with o -phenlenediamine (OPD) to generate fluorescent 3-(dihydroxyethyl)furo[3,4- b quinoxaline-1-one (DFQ), presenting the maximum emission at 434 nm; (2) As oxidase-mimics, Ce4+ can oxidize OPD into fluorescent 2,3-diaminophenazine (DAP) which shows a strong emission at 568 nm; (3) ALDS inhibits the oxidation ability of Ce4+ towards OPD, thus inhibiting the generation of DAP. Accordingly, a homogeneous ratiometric fluorescence system with dual emission comes into being and the presence of ALDS can change the fluorescence intensity ratio obviously. With F 434 / F 568 as readout, ALDS can be detected sensitively with the detection limit of 30 nM. Moreover, this ratiometric method was used to analyze ALDS in both human serum and pharmaceutical samples. [ABSTRACT FROM AUTHOR]

Electrochemical nitrate (NO 3 - ) reduction emerges as a promising strategy to maintain the balance of the global nitrogen cycle and an alternative to nitrogen electroreduction for ambient ammonia (NH 3 ) synthesis. However, the complicated multiple-electron transfer process of NO 3 - -to-NH 3 conversion demands catalysts with high selectivity for NH 3 production. Herein, CoS 2 nanoparticle decorated TiO 2 nanobelt array on a titanium plate (CoS 2 @TiO 2 /TP) is reported as a superb electrocatalyst for the NO 3 - reduction reaction. In 0.1 M NaOH containing 0.1 M NO 3 - , CoS 2 @TiO 2 /TP offers a large NH 3 yield of 538.21 μmol h -1 cm -2 at -0.7 V vs. reversible hydrogen electrode (RHE) and a high faradaic efficiency of 92.80% at -0.5 V vs. RHE. Additionally, it also shows strong stability for the 20 h electrolysis test.

Human exposure to chemical pollutants in the environment can cause a variety of diseases, including cancer, diabetes, cardiovascular disease, and neurodegenerative diseases (Alzheimer's disease, Parkinson's disease, etc.). Exogenous and environmental pollutant exposure-induced endogenous aldehydes are highly reactive electrophilic compounds that can form covalently modified products with a variety of important biological molecules in the human body, thus inducing toxic effects. Exposome research has become a hotspot since it was first proposed in 2005. Exposure studies can map the complex relationships between biomarkers and disease risk. Therefore, the measurable and characteristic changes of all biomarkers together constitute a key basis for exposome research. Aldehydes are among the main components of chemical exposure. Because of the physical and chemical properties of aldehydes and the existence of multiple matrix interferences in the samples, it is particularly difficult to analyze and characterize them. The analysis and detection methods for aldehydes mainly include sensing analysis, electrochemical methods, fluorescence imaging, chromatography, mass spectrometry (MS), and chromatography-MS. Analytical techniques based on gas chromatography-MS (GC-MS) and liquid chromatography-MS (LC-MS) have emerged as the main methods for chemical exposome research. Chemical derivatization, especially stable isotope labeling derivatization (also known as chemical isotope labeling) combined with LC-MS analytical techniques, can help circumvent the problems encountered in targeted and non-targeted metabolome and exposome analysis. The combination of chemical derivatization with chromatography-MS is one of the most important solutions for the accurate analysis of aldehydes in complex samples. Over the past five years, the development and application of chromatography-MS analytical methods based on chemical derivatization have become key topics in aldehyde analysis. This paper summarizes and reviews the latest progress in GC-MS and LC-MS methods based on chemical derivatization (2015-2020). The review focuses on analytical method development for aldehyde exposure biomarkers in bio-matrices (blood, urine, saliva, biological tissue, etc.). Various derivatization reagents for labeling small-molecule aldehydes, qualitative/quantitative analytical methods and their application value, advantages/disadvantages of different analytical methods for aldehyde exposure biomarkers, and future development trends are also included. The manuscript contents may aid the integrated development of exposome, metabolomics, and lipidomics, as well as research on the environment, ecology, and health. To clarify the complex actions of exogenous and endogenous aldehydes in physiological and pathological events, it is necessary to improve the analysis and characterization techniques and tools for studying the "aldehydome." With the development and application of sophisticated mass spectrometers, advances in high-performance chromatographic separation and bioinformatics, and advent of single-cell analysis and MS imaging, future aldehyde exposome analytical methods will have higher sensitivity and throughput. This in turn would be more useful for screening and identifying unknown aldehyde compounds and discovering new exposome biomarkers.

In this work, through the in situ growth of MnO 2 nanosheets on the surface of terbium metal-organic frameworks (Tb-MOFs), MOF@MnO 2 nanocomposites are prepared and the fluorescence of Tb-MOFs is quenched significantly by MnO 2 . Additionally, the hybrid nanoflowers are self-assembled by cholesterol oxidase (ChOx) and copper phosphate (Cu 3 (PO 4 ) 2 ·3H 2 O). Then a new strategy for cholesterol determination is developed based on MOF@MnO 2 nanocomposites and hybrid nanoflowers. Cholesterol is oxidized under the catalysis of hybrid nanoflowers to yield H 2 O 2 , which further reduces MnO 2 nanosheets into Mn 2+ . Hence, the fluorescence recovery of Tb-MOFs is positively correlated to the concentration of cholesterol in the range of 10 to 360 μ M. The limit of detection (LOD) of cholesterol is 1.57 μ M. On the other hand, the hierarchical and confined structure of ChOx-inorganic hybrid nanoflowers greatly improve the stability of the enzyme. The activity of hybrid nanoflowers remains at a high level for one week when stored at room temperature. Moreover, the hybrid nanoflowers can be collected by centrifugation and reused. The activity of hybrid nanoflowers can continue at a high level for five cycles of determination. Therefore, it can be concluded that the hybrid nanoflowers are more stable and more economic than free enzymes, and they show a similar sensitivity and specificity to cholesterol compared with free ChOx. Finally, this strategy has been further validated for the determination of cholesterol in serum samples with satisfactory recoveries., (© 2021 IOP Publishing Ltd.)

The sensitive detection method of levodopa (L-DOPA) and dopamine (DA) in rat brain microdialysate of Parkinson's disease (PD) is an essential tool for the clinical study and attenuated synergistic drug screening for L-DOPA from traditional Chinese medicines. Using d0/d3-10-methyl-acridone-2-sulfonyl chloride (d0/d3-MASC) as stable isotope derivatization reagent, a novel ultra high performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS) method was developed and validated for L-DOPA and DA by stable isotope- coded derivatization coupled with ultrasonic-assisted dispersive liquid-liquid microextraction (UA-DLLME). d3-MASC (light) and d3-MASC (heavy) were used as derivatization reagents for microdialysate samples and standards, respectively. Mixtures of the two solutions were prepared by UA-DLLME for UHPLC-MS/MS analysis with multiple reaction monitoring (MRM) mode. With d3-MASC heavy derivatives as internal standards for corresponding light derivatives from samples, the stable isotope internal standard quantification for L-DOPA and DA was carried out. The stable derivatives were obtained in aqueous acetonitrile (pH 10.8 sodium carbonate-sodium bicarbonate buffer) at 37 °C for 3.0 min, and then were separated within 2.0 min using gradient elution. Linear range was 0.20-1500.0 nmol/L (R > 0.994). LODs were 0.005 and 0.009 nmol/L for DA and L-DOPA (S/N = 3), respectively. This method was validated, and it showed obvious advantages in comparing with the reported methods in terms of sensitivity, analysis speed and anti-matrix interference. This method has been successfully applied to the study of effect of Shouwu Fang on L-DOPA and DA concentration fluctuations in PD rat brain microdialysate.