A Dual Emission Fluorescence Probe Based on Silicon Nanoparticles and Rhodamine B for Ratiometric Detection of Kaempferol.

In this paper, blue fluorescent silicon nanoparticles (SiNPs) with outstanding optical properties and robust stability were synthesized by a simple one-step hydrothermal method. By introducing red emissive rhodamine B (RhB) into SiNPs solution, a dual emission nanoprobe (SiNPs@RhB) was constructed, which showed excellent pH stability, salt resistance and photobleaching resistance. The SiNPs@RhB probe could emit two peaks at 444 nm and 583 nm under 365 nm excitation. It was found that the fluorescence intensity of the two emission peaks decreased in different degrees with the addition of different concentrations of kaempferol (Kae). According to this phenomenon, a novel ratiometric fluorescence method was established for the detection of Kae via utilizing SiNPs@RhB as nanoprobe. The detection range and limit of detection (LOD) were 0.5 ~ 150 µM and 0.24 µM, respectively. The ratiometric fluorescence method exhibited the superiority of rapid detection, excellent stability, wide linear range and high sensitivity. The detection mechanism was studied by ultraviolet visible absorption spectra, fluorescence spectra and fluorescence lifetime. Furthermore, the method was applied to the detection of Kae in real samples (kaempferia powder, sea buckthorn granules and sea buckthorn dry emulsion).

Characterization of the Ligand Exchange Reactions on CdSe/ZnS QDs by Capillary Electrophoresis.

The continuous development of semiconductor quantum dots (QDs) in biochemical research has attracted special attention, and surface functionalizing becomes more important to optimize their performance. Ligand exchange reactions are commonly used to modify the surface of QDs for their biomedical applications. However, the kinetics of ligand exchange for semiconductor QDs remain fully unexplored. Here, we describe a simple and rapid method to characterize the ligand exchange reactions on CdSe/ZnS QDs by capillary electrophoresis (CE). The results of ultraviolet-visible absorption spectra, fluorescence spectra, and Fourier transform infrared spectroscopy indicated the successful implementation of the ligand exchange process. The dynamics of ligand exchange of OA-coated CdSe/ZnS QDs with 4-mercaptobenzoic acid was monitored by CE, and the observed ligand exchange trends were fitted with logistic functions. When the ligand exchange reactions reached equilibrium, the ligand density of QDs can be quantified by CE. It is anticipated that CE will be a new powerful technique for quantitative analysis of the ligand exchange reactions on the surface of QDs.

A novel in situ strategy for the preparation of a ß-cyclodextrin/polydopamine-coated capillary column for capillary electrochromatography enantioseparations.

Inspired by the chiral recognition ability of ß-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 ß-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 ß-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 ß-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 intraday, interday, 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 ß-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.

Silicon Nanoparticle-Based Ratiometric Fluorescence Probes for Highly Sensitive and Visual Detection of VB2.

In this work, blue fluorescent silicon nanoparticles (SiNPs) were prepared by a simple one-step hydrothermal method using (3-aminopropyl) triethoxy silane (APTES) and eriochrome black T as raw materials. The SiNPs showed favorable water solubility, thermal stability, pH stability, salt tolerance, and photobleaching resistance. At an excitation wavelength of 376 nm, the SiNPs emitted bright blue fluorescence at 460 nm. In the presence of vitamin B2 (VB2), the fluorescence intensity (FL intensity) of the SiNPs at 460 nm decreased obviously, and a new peak appeared at 521 nm. Based on this, a novel ratiometric fluorescence method was established for VB2 detection. There was a good linear relationship between the fluorescence intensity ratio (F 521/F 460) and VB2 concentration from 0.5 to 60 µM with a detection limit of 135 nM. This method was successfully applied to detect VB2 content in the samples of vitamin B2 drugs and beverages. Additionally, a simple paper sensor based on the SiNPs was designed to visualize detection of VB2. With the support of color recognition software on a smartphone, the visual quantitative analysis of VB2 was realized, ranging from 40 to 800 µM.

Green synthesis of yellow-green emissive silicon nanoparticles and their application for the sensitive fluorescence detection of bilirubin.

Bilirubin, a tetrapyrrole compound metabolized by heme, is an important biomarker for diagnosis and prognosis of patients with liver diseases. Highly sensitive detection of bilirubin is essential for disease prevention and treatment. In recent years, silicon nanoparticles (SiNPs) have received intense attention due to their excellent optical properties and environmental friendliness. In this paper, water-soluble yellow-green fluorescent SiNPs were synthesized by a mild water bath method using 2-aminophenylboronic acid hydrochloride as the reducing agent and 3-[2-(2-aminoethylamino)ethylamino]propyl-trimethoxysilane (AEEA) as the silicon source. The preparation process does not require high temperature, high pressure and complex modifications. The SiNPs possessed excellent photostability and good water dispersibility. It was found that the fluorescence of SiNPs at 536 nm could be significantly quenched by bilirubin. By using SiNPs as a fluorescent probe, a novel fluorescence method for sensitive detection of bilirubin was established with a wide linear range of 0.05-75 µM and a limit of detection (LOD) of 16.67 nM. The detection mechanism was mainly due to the internal filtration effect (IFE). More significantly, the established method could successfully determine the contents of bilirubin in biological samples with good recoveries.

Water Soluble Silicon Nanoparticles as a Fluorescent Probe for Highly Sensitive Detection of Rutin.

In this work, water-soluble fluorescent silicon nanoparticles (SiNPs) were prepared by one-pot hydrothermal method using 3-(2-aminoethylamino)propyldimethoxymethylsilane (AEAPDMMS) as a silicon source and amidol as a reducing agent. The prepared SiNPs showed bright green fluorescence, excellent stability against photobleaching, salt tolerance, temperature stability, and good water solubility. Due to the internal filtration effect (IFE), rutin could selectively quench the fluorescence of the SiNPs. Based on such phenomena, a highly sensitive fluorescence method was established for rutin detection. The linear range and limit of detection (LOD) were 0.05-400 µM and 15.2 nM, respectively. This method was successfully applied to detect rutin in the samples of rutin tablets, Sophora japonica, fry Sophora japonica, and S. japonica carbon with satisfactory recovery.

Synthesis of a novel chiral DA-TD covalent organic framework for open-tubular capillary electrochromatography enantioseparation.

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.

Enantioseparation in capillary eletrochromatography by covalent organic framework coating prepared in situ.

Chiral covalent organic frameworks (CCOFs) have recently exhibited particularly promising potential as effective chiral stationary phases (CSPs) for open tubular capillary electrochromatography (OT-CEC) enantioseparation. However, it remains difficult to synthesis of CCOFs and preparation of CCOFs coated capillary under mild reaction conditions. In this work, we designed and fabricated a CCOF (CB-DA-COF) with high chemical stability and high specific surface area at room temperature. Then, through one-step in situ growth method, the chiral CB-DA-COF coated capillary was fabricated at room temperature for the first time. This method requires neither pre-modification to the capillary by organic molecular building units nor harsh reaction conditions, and the preparation time of the CCOF coating was significantly shortened (within 2 h). This chiral CB-DA-COF coated capillary showed excellent enantioseparation ability and stability. Under optimal conditions, rapid enantioseparation (within 5 min) could be achieved for six enantiomers including terbutaline, propranolol, phenylephrine, verapamil, norepinephrine and isoprenaline. And, no significant change was observed in enantioseparation efficiency after over 200 runs. The relative standard deviations (RSDs) of the analyte's migration time for intra-day, inter-day and column-to-column were within the range of 0.8-3.5% (n = 5), 1.5-4.7% (n = 3) and 4.3-8.3% (n = 3), respectively. In addition, the enantioseparation mechanism was studied, which indicated that binding energy between of enantiomers and chiral site were the main factors for enantioseparation.

Green-emissive water-dispersible silicon quantum dots for the fluorescent and colorimetric dual mode sensing of curcumin.

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.

One-pot synthesis of novel water-dispersible fluorescent silicon nanoparticles for selective Cr2O72- 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.

[Preparation of a two-dimensional azine-linked covalent organic framework-coated capillary and its application to the separation of nitrophenol environmental endocrine disruptors by open-tubular capillary electrochromatography].

As a class of new porous crystalline materials, covalent organic frameworks (COFs) are attracting the attention of a large number of scientists. Because of their large specific surface area, low density, high stability, and tunable pore size, COFs have been widely applied in many fields, including analytical chemistry. Open-tubular capillary electrochromatography (OT-CEC) is a mode of capillary electrochromatography. In recent years, a variety of materials such as porous organic frameworks have been used as the stationary phase for OT-CEC to overcome the disadvantages of low phase ratio and column capacity, thereby improving the separation efficiency. However, there are a few reports on the use of COFs as the stationary phase to improve the separation efficiency of OT-CEC. Environmental endocrine disruptors (EEDs) are a large class of exogenous chemicals that can disturb the effect of the normal endocrine substances and adversely affect the endocrine and reproductive systems of human beings. Considering the widespread existence of EEDs and the disadvantages of existing detection methods (e. g., gas chromatography-mass spectrometry and high performance liquid chromatography-mass spectrometry), such as complicated operation and large sample consumption, it is necessary to develop new methods for the separation and determination of EEDs in complex samples. OT-CEC is a good choice in this regard because of its low sample dosage, simple operation, and high analytical speed. Accordingly, a two-dimensional azine-linked covalent organic framework (ACOF-1) with a large surface area and small pore size was synthesized according to the reference method. Then, an ACOF-1-coated capillary was fabricated using ACOF-1 as the stationary phase, via covalent bonding, and used as the separation channel to establish a new OT-CEC method for the separation and detection of nitrophenol EEDs. X-ray powder diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), and scanning electron microscopy (SEM) were used to characterize the synthesized ACOF-1 and the ACOF-1-coated capillary. The peak pattern in the XRD spectrum confirmed the successful synthesis of ACOF-1. The absorption peaks in the FT-IR spectrum and the morphology of the inner wall seen in the SEM images also demonstrated that the ACOF-1-coated capillary was fabricated successfully. A series of experiments were carried out to investigate the effects of the organic additive (methanol) content, pH, and concentration of the borate buffer on the resolution, migration time, and peak shape. Based on the results, the optimal separation conditions for the four nitrophenol analytes were 15 mmol/L borate (pH 9.20) with 10% (v/v) methanol. Under the optimum conditions, 2-nitrophenol (2-NP), 4-nitrophenol (4-NP), 2,4-dinitrophenol (DNP), and 2,4,6-trinitrophenol (TNP) could be baseline separated within 20 min by the established OT-CEC method. The linear range for 2-NP and 4-NP was 10-500 mg/L, while that for DNP and TNP was 20-1000 mg/L. The determination coefficients (R2) were greater than 0.99. For the four analytes, the limits of detection and limits of quantitation were in the ranges of 0.13-0.23 mg/L and 0.45-0.60 mg/L, respectively. The intraday, interday, and column-to-column relative standard deviations (RSDs) of the migration time and peak area were less than 9.4%. These results revealed that the established method has good repeatability and high stability, thus being suitable for the separation and detection of nitrophenol EEDs. The mechanism studies revealed that the pore size of ACOF-1 was the main factor influencing the separation behavior of each analyte. This work demonstrated the feasibility of using capillary electrochromatography with COFs as the stationary phase for the separation and detection of EEDs. Future research will continue to focus on the preparation of COF-coated capillaries and their application to OT-CEC separation and determination of EEDs.

An azine-linked covalent organic framework as stationary phase for separation of environmental endocrine disruptors by open-tubular capillary electrochromatography.

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%.

Rapid and mild fabrication of protein membrane coated capillary based on supramolecular assemble for chiral separation in capillary electrochromatography.

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.

High-performance electrochemical biosensor for nonenzymatic H2O2 sensing based on Au@C-Co3O4 heterostructures.

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.

Homochiral zeolite-like metal-organic framework with DNA like double-helicity structure as stationary phase for capillary electrochromatography enantioseparation.

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.

The preparation of poly-levodopa coated capillary column for capillary electrochromatography enantioseparation.

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.

Simultaneous separation of neutral and cationic analytes by one dimensional open tubular capillary electrochromatography using zeolitic imidazolate framework-8 as stationary phase.

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.

A novel biosensor based on boronic acid functionalized metal-organic frameworks for the determination of hydrogen peroxide released from living cells.

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.

In situ rapid preparation of homochiral metal-organic framework coated column for open tubular capillary electrochromatography.

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.

[Recent developments of chiral separation by capillary electrophoresis].

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.