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Herein, a novel chiral covalent organic framework, DA-TD COF, with good chemical/thermal stability was synthesized and used as a chiral stationary phase for open-tubular capillary electrochromatography enantioseparation. The DA-TD COF coated capillary exhibited excellent enantioseparation efficiency and its separation efficiency did not show an obvious decrease over 200 runs. Furthermore, the enantioseparation mechanism was studied.

In this study, a colorimetric and fluorescent dual-mode probe based on water-dispersible silicon nanoparticles (SiNPs) was fabricated via a one-step hydrothermal method by using (3-aminopropyl)triethoxysilane (APTES) as the silicon source and ferulic acid as the reducing agent. The as-prepared SiNPs exhibited good thermostability, high salt-tolerance and excellent photo-stability properties. The blue-green fluorescence of the SiNPs could be rapidly and selectively quenched by emodin, and meanwhile the colorimetric response from the original pale yellow color to reddish brown was also visible to the naked eye. Based on the above phenomenon, the quantitative detection of emodin could be achieved through both fluorescence and colorimetric methods. In the fluorescence method, a good linear relationship was obtained in the range of 0.05 to 50 μM with a detection limit of 5.77 nM. In the colorimetric method, comparable sensitivity was also achieved with a detection limit of 9.28 nM. The proposed method was successfully applied to the detection of emodin in traditional Chinese herbs Polygonum cuspidatum and Rheum officinale. Moreover, a SiNP based dual-mode paper sensor was also developed for the visual detection of emodin according to the color change and fluorescence quenching, providing a convenient strategy for emodin sensing.

Chromium (Cr(vi)), a highly toxic metal-oxyanion which is carcinogenic and mutagenic to humans, is a severe environmental pollutant. Developing simple methods for sensitive and selective detection of Cr(vi) is of great significance. In this work, fluorescent silicon nanoparticles (SiNPs) with good water solubility were facilely synthesized via a one-step hydrothermal method by using (3-aminopropyl)triethoxysilane (APTES) as the silicon source and natural antioxidant quercetin as the reducing agent. The obtained SiNPs displayed good thermostability, salt-tolerance and photo-stability. The as-prepared SiNPs exhibited bright blue emission at 437 nm under excitation at 362 nm, allowing them to be developed as a fluorescent probe for detection of Cr2O72-. Significantly, the fluorescence of the SiNPs could be remarkably quenched by Cr2O72-via the internal filtering effect (IFE). Based on this phenomenon, a novel fluorescence method for detection of Cr2O72- was established. A good linear relationship was obtained from 0.5 to 100 μM with a limit of detection (based on 3 s/k, LOD) of 180 nM. The proposed fluorescence method was successfully applied to the detection of Cr2O72- in tap water. Moreover, a fluorescent filter paper sensor was developed for the visual detection of Cr2O72-, providing a valuable platform for Cr2O72- sensing in a convenient way.

Curcumin, an active ingredient in Curcuma longa, which possesses good biological and pharmacological activities, is effective in treating many diseases. Developing simple and sensitive methods for the detection of curcumin is of great significance. In this study, novel water-dispersible silicon quantum dots (SiQDs), which can sensitively respond to curcumin through fluorescent and colorimetric dual modes were synthesized via a one-step hydrothermal treatment of N-[3-(trimethoxysilyl) propyl]-ethylenediamine (DAMO) and p-phenylenediamine. The fluorescence of SiQDs could be remarkably quenched by curcumin via the inner filter effect (IFE) and static quenching effect (SQE). A good linear relationship was obtained in the range of 0.25-75 μM with a detection limit of 91 nM. More interestingly, curcumin could also be visually detected using SiQDs via an obvious color change of the solution from pale yellow to orange-red, which allows the establishment of a sensitive colorimetric method for curcumin detection in the linear range of 0.05-57.5 μM with a detection limit of 32 nM. The proposed method was successfully applied to detect curcumin in health care products and spices. Notably, to realize rapid and convenient visual detection of curcumin, a paper sensor was also fabricated.

Levodopa (L-DOPA) is promising as chiral stationary phase for open tubular capillary electrochromatography (OT-CEC) enantioseparation owing to its self-polymerization adhesive property and chiral recognition potential. In this work, CuSO4/H2O2 was used as a trigger agent to accelerate the polymerization process of L-DOPA and the poly-levodopa (poly-(L-DOPA)) coated column was successfully prepared for the first time by depositing it on the inner wall of fused silica capillary via the rapid and in-situ approach at room temperature. The performance of the poly-(L-DOPA) coated capillary was validated by the separation of different chiral analytes, including chiral amine drugs, neurotransmitters and amino acids, and the good enantioseparation efficiencies were achieved. For five consecutive runs, the relative standard deviations (RSDs) for the migration time of the analytes for intra-day, inter-day and column-to-column were in the range of 0.19-1.33%, 0.96-4.47%, and 2.21-7.79%, respectively. Additionally, the poly-(L-DOPA) coated capillary column could be successively used over 250 runs without observable change in the separation efficiency.

An ingenious and viable method for preparing heterogeneous Co3O4 dodecahedrons that contain carbon and encapsulated Au nanoparticles (Au@C-Co3O4) was proposed via pyrolysis of Au nanoparticle-encapsulated zeolitic imidazolate framework-67 (Au@ZIF-67). The obtained Au@C-Co3O4 possessed hierarchically porous structure, abundant active sites, excellent conductivity, and durability, all of which can significantly improve the analysis performance of the biosensor. Meanwhile, the fabricated electrode based on the porous Au@C-Co3O4 showed remarkable electrocatalytic performance towards H2O2 with a limit of detection of 19 nM and ultra-high sensitivity of 7553 μA mM−1 cm−2, even when the Au content in the composite was as low as 0.85 wt%. This novel biosensor was successfully used to monitor H2O2 concentration released from living cells, and the results can be used to identify cancer cells, thus advancing the use of transition metal oxides in the field of biosensing.

In this work, we report a durable and sensitive H2O2 biosensor based on boronic acid functionalized metal-organic frameworks (denoted as MIL-100(Cr)-B) as an efficient immobilization matrix of horseradish peroxidase (HRP). MIL-100(Cr)-B features a hierarchical porous structure, extremely high surface area, and sufficient recognition sites, which can significantly increase HRP loading and prevent them from leakage and deactivation. The H2O2 biosensor can be easily achieved without any complex processing. Meanwhile, the immobilized HRP exhibited enhanced stability and remarkable catalytic activity towards H2O2 reduction. Under optimal conditions, the biosensor showed a fast response time (less than 4s) to H2O2 in a wide linear range of 0.5-3000μM with a low detection limit of 0.1μM, as well as good anti-interference ability and long-term storage stability. These excellent performances substantially enable the proposed biosensor to be used for the real-time detection of H2O2 released from living cells with satisfactory results, thus showing the potential application in the study of H2O2-involved dynamic pathological and physiological process.

Developing simple methods for separation of analytes that belong to different classes is of great importance. Herein, we developed a simple one-dimensional (1-D) capillary electrochromatography method to demonstrate the simultaneous separation of target fractions that belong to two different classes (i.e., cationic and neutral analytes) without switching buffer solution by a zeolitic imidazolate framework ZIF-8 coated capillary column. Owing to the difference of charge-to-mass ratio of the cationic analytes, the interaction of the cationic analytes and coating material ZIF-8 and the hydrophobic interactions between the neutral analytes and the microporous framework of ZIF-8, six cationic analytes and four neutral analytes were simultaneously separated in a single run by 1-D capillary electrochromatography. The relative standard deviations (RSDs) of the analytes migration time for intra-day, inter-day and column-to-column were in the range of 0.11-0.87%, 0.54-2.04% and 2.00-6.89% and the RSDs of the analytes peak area for intra-day, inter-day and column-to-column were in the range of 0.70-4.45%, 1.33-6.20% and 2.27-11.88%. Additionally, the developed method was employed in the analysis of urine samples with satisfactory recoveries.

In recent years, covalent organic frameworks (COFs) play an important role in the field of chromatographic separation. However, COFs are used rarely in open-tubular capillary electrochromatography (OT-CEC) so far, and the reported methods have not been applied to actual sample analysis. Herein, a novel azine-linked COF (N0-COF) coated capillary was prepared as OT-CEC separation channel and a new method for separation and detection of environmental endocrine disruptors, i.e., bisphenol A (BPA) and its analogues was established. Under optimal separation conditions, the analytes were baseline separated by the N0-COF coated capillary with 20 min. The intra-day, inter-day and column-to-column relative standard deviations were 0.07–2.99%, 1.05–3.20% and 1.31–5.83% for the migration time; 1.68–5.50%, 1.52–9.24% and 4.04–9.14% for the peak area. The method was further applied to separate and determine BPA and its analogues in beverage samples, and the recovery ranged from 91.0–112.0%.

Exploration of the simple and stable coating methods is of great significance in capillary electrochromatography (CEC). In this work, a lysozyme assemble supramolecular membrane coated capillary column was developed for CEC chiral separation. Taking advantage of phase transformation of lysozyme, the coating process was achieved within 1.0 h thus to a large extent reduced the capillary preparation time and simplified the coating procedure. The successful fabrication of the supramolecular membrane coated capillary was verified by scanning electron microscopy (SEM), Fourier transform-infrared spectroscopy (FT-IR), fluorescence imaging, and electroosmotic flow (EOF). The separation capacity of the coated capillary was evaluated by analysis of different chiral analytes, including chiral amine drug and neurotransmitters, and good enantioseparation efficiency was achieved for the three pairs of enantiomers. For three consecutive runs, the relative standard deviations (RSD) for the migration time of the analytes for intra-day (n = 3), inter-day (n = 3) and column-to-column (n = 3) were in the range of 0.7–1.5%, 2.7–3.6%, and 4.5–5.8%, respectively. Additionally, the supramolecular membrane coated capillary column could run consecutively 100 times without observable change in the separation efficiency, proving the feasibility of the coating method based on the adhesion of the protein-based supramolecular membrane.

In recent years, artificial materials with double helix structure have attracted widespread attention due to their unique properties such as the DNA like double-helicity, intrinsic chirality and diverse functional groups. Developing novel chiral stationary phases (CSPs) for capillary electrochromatography enantioseparation is of intriguing interest. Herein, a novel homochiral zeolite-like metal-organic framework (ZMOF) JLU-Liu23 with unique DNA like double-helicity structure was firstly utilized as the CSP in open tubular capillary electrochromatography (OT-CEC) for enantioseparation of chiral monoamine neurotransmitters and analogues. Owing to the unique DNA like double-helicity structure of the homochiral ZMOF JLU-Liu23, the good enantioseparation of four monoamine neurotransmitters and analogues was achieved on the prepared homochiral ZMOF JLU-Liu23 coated capillary column. The relative standard deviations (RSDs) of the analytes migration time for intra-day, inter-day and column-to-column were in the range of 0.3-0.6%, 0.8-2.2% and 3.5-6.5%, respectively.

Inspired by the chiral recognition ability of β-cyclodextrin and the natural adhesive properties of polydopamine under alkaline conditions, in this study, a rapid and in situ modification strategy was developed to fabricate β-cyclodextrin/polydopamine composite material coated-capillary columns for open tubular capillary electrochromatography. The results of scanning electron microscopy, FTIR spectroscopy, streaming potential and electro-osmotic flow studies indicated that β-cyclodextrin/polydopamine was successfully fixed on the inner wall of the capillary column. This coating can be achieved within 1 h affording a greatly reduced capillary preparation time. The performance of the β-cyclodextrin/polydopamine-coated capillary was validated by the analysis of seven pairs of chiral analytes, namely epinephrine, norepinephrine, isoprenaline, terbutaline, verapamil, tryptophane, carvedilol. Good enantioseparation efficiencies were achieved for all. For three consecutive runs, the relative standard deviations for the migration times of the analytes for intra-day, inter-day and column-to-column repeatability were in the range of 0.41–1.74%, 1.03–4.18%, and 1.66–8.24%, respectively. Moreover, the separation efficiency of the β-cyclodextrin/polydopamine-coated capillary column did not decrease obviously over 90 runs. The strategy should also be feasible to introduce and immobilize other chiral selectors on the inner walls surface of capillary columns. This article is protected by copyright. All rights reserved

As the two enantiomers of chiral compounds have different chemical and physiologic properties, the enantioseparation of chiral compounds is of great significance in the fields such as medicine, biology, food and environment. Hence, the enantioseparation of different types of chiral compounds has become one of the hottest research topics in recent years. Capillary electrophoresis, owing to its unique advantages, has a wide application in the enantioseparation field recently. In this review, the latest research progresses in capillary electrophoresis enantioseparation are summarized from 2013 to 2015, and the future developments in this field is also prospected.

Fabricating metal-organic frameworks (MOFs) with the use of nucleating agents in the microenvironment have attracted increasing attention recently. Herein, a simple and rapid synthesis method was developed to in situ fabricate homochiral MOF [Zn(s-nip)2]n in the capillary inner wall by using ZnO nanoparticles as efficient nucleating agents for open tubular capillary electrochromatography (OT-CEC) separation of monoamine neurotransmitters enantiomers of epinephrine, isoprenaline and synephrine, the diastereoisomers of ephedrine and pseudoephedrine, the isomers of nitrophenols and analogues of bisphenols with good resolution. The relative standard deviations (RSDs) for the analytes migration time of intra-day, inter-day and column-to-column were in the range of 0.8-2.1% (n=10), 0.3-3.2% (n=3) and 3.2-9.3% (n=3), respectively. Additionally, the homochiral MOF [Zn(s-nip)2]n coated capillary column could be successively used over 260 runs without observable change in the separation efficiency.

Homochiral metal-organic frameworks (MOFs) are promising as porous stationary phase for open-tubular capillary electrochromatography (OT-CEC) enantioseparation owing to their fine-tuned pore sizes and large surface areas. In this work, the homochiral MOF AlaZnCl was successfully coated on the inner wall of fused silica capillary by an in situ, layer-by-layer self-assembly approach at room temperature. The results of scanning electron microscopy (SEM), X-ray diffraction (XRD), streaming potential (SP) and Fourier-transform infrared spectroscopy (FT-IR) indicated that the homochiral MOF AlaZnCl was successfully coated on the capillary inner wall. To evaluate the performance of the homochiral MOF AlaZnCl coated capillary column, the enantioseparation was carried out by using six amine drugs and monoamine neurotransmitters as model analytes and excellent enantioseparation efficiency was achieved. Run-to-run, day-to-day, and column-to-column relative standard deviations (RSDs) were all less than 5%. Moreover, the separation efficiency of the homochiral MOF AlaZnCl coated capillary column did not decrease obviously over 100 runs.