Rapid and in-situ preparation COFs coated capillary by adsorption method for the separation and determination of phthalate ester using CEC.

As a novel class of stationary phase materials, covalent organic frameworks (COFs) have shown great promise in open-tubular capillary electrochromatography. However, the current preparation of COFs coating capillaries heavily relies on tedious and time-consuming covalent bond methods. In this work, a novel, simple and rapid adsorption method was developed for fabrication of TPB-DMTP COF (fabricated from 1,3,5-tris(4-aminophenyl)benzene (TPB) and 2,5-dimethoxyterephthalaldehyde (DMTP)) coated capillary. Due to the crystallization process of the COF is greatly shortened because pre-modification capillary does not require silane coupling agent, this method enables the rapid preparation of COFs-coated capillaries. The organic molecular building units only need 25 min to form a stable COFs coating on the inner wall of a capillary by this method. To our knowledge, this is the shortest method for preparing COFs coated capillary up to now. The performance of the TPB-DMTP COF coated capillary was evaluated by using phthalate esters as model analytes. The results demonstrated that the TPB-DMTP COF coated capillary has excellent repeatability and stability. The relative standard deviations (RSDs) of the analyte's retention time of intra-day, inter-day and column-to-column were in the range of 0.05 %-0.27 %, 0.31 %-0.63 % and 0.31 %-0.88 %, respectively. And, no significant changes were observed in separation efficiency and retention time after over 200 runs. Finally, the TPB-DMTP COF coated capillary was applied for the determination of phthalates in marketed plastic bag and the recovery ranged from 88.0 % to 114.0 %.

[Recent developments in the application of covalent organic frameworks in capillary electrochromatography].

Capillary electrochromatography (CEC) has received increased attention from the academic community because it combines the excellent selectivity of high performance liquid chromatography (HPLC) and the high efficiency of capillary electrophoresis (CE). Selecting the most appropriate stationary phase material is crucial to achieve better separation effects in CEC. In recent years, a considerable number of materials, such as graphene oxide, proteins, metal organic frameworks, and covalent organic frameworks (COFs), have been widely used as stationary phases in CEC to further improve its separation performance and extend its scope of potential applications. Among these materials, COFs have shown great application prospects in CEC owing to their unique properties, which include high porosity, large surface area, excellent stability, tunable pore size, and high designability of the framework structure. This review systematically summarizes published papers on the development and application of COFs in CEC from 2016 to 2023. First, two COF-based capillary columns (i. e., open-tube CEC columns and monolithic CEC columns) and their preparation methods are introduced. Second, the applications of CEC based on COF stationary phases in the separation of environmental endocrine disruptors, pesticides, aromatic compounds, amino acids, and drugs, particularly chiral drugs, are systematically summarized. The separation mechanism of CEC based on COF stationary phases is also introduced. At present, the good separation ability of COF-based CEC is mainly attributed to two factors: 1) The size exclusion effect of the pores of the COF stationary phase. Because of differences in the sizes of their organic molecular building units and side chains, COFs have varying pore sizes and topological structures. Thus, target analytes smaller than the pores of the COFs can enter the frameworks and interact with them during separation. On the other hand, target analytes larger than the pores of the COFs cannot enter the frameworks and interact with them during separation; thus, they can be separated. 2) The interactions between the target analytes and side chains (e. g., hydrophobic interactions, hydrogen bonding, π-π interactions, etc.) of the COFs. Since COFs usually contain alkyl side chains, aromatic structures, and oxygen and/or nitrogen atoms with high electronegativity, various interactions could occur between the COFs and target analytes. Finally, directions for the future development and strategic application of CEC based on COF stationary phases are proposed. We believe that future research in CEC based on COF stationary phases should focus on the following aspects: 1) The use of cheminformatics to design and construct COFs to improve the efficiency of COF capillary column preparation; 2) the development of milder methods to synthesize COFs that can meet the requirements of high performance COF capillary columns; and 3) in-depth research to explore the separation mechanism of CEC based on COF stationary phases to provide theoretical guidance for developing CEC methods suitable for the separation and analysis of complex samples.

Study of the separation ability differences of three covalent organic frameworks as coated materials in capillary electrochromatography.

Covalent organic frameworks (COFs) have great potential applications in chromatographic separation. So it is crucial to understand the relationship between the separation ability of COFs and their structures. Here we report a strategy to evaluate the separation ability of three 2D COFs and explore the relationship between separation ability and their molecular structures. The three 2D COFs (COF-LZU1, COF-42 and COF-LZU8) have one same building unit 1,3,5-triformylbenzene, while varied from the conjugated linking units and functional side-chains. They were used to construct coated capillary column for capillary electrochromatographic separation of same groups of phthalates. They exhibited different separation efficiencies. COF-42 and COF-LZU8 coated capillary columns provided good signal resolutions and high column efficiencies with high theoretical plate numbers. It is demonstrated that COFs with hydrazone unit and longer side-chains provided higher selectivity and resolutions for the phthalates separation. Molecular simulations and DFT calculations were further proceeded to explore the deep reason why the three COFs coated CEC displayed different separation ability based on the host-guest interactions on molecular level. This work highlights a new opportunity to select or design functional COFs and improve their efficiency in chromatographic separation based on host-guest chemistry.

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.

Synthesis of Silicon Nanoparticles Emitting Yellow-Green Fluorescence for Visualization of pH Change and Determination of Intracellular pH of Living Cells.

In order to understand related pathogenesis of some diseases and design new intracellular drug delivery systems, investigation of pH change in living cells in real time is important. In this paper, a new style of fluorescent silicon nanoparticles (SiNPs) as a pH-sensitive probe and for the visualization of the pH changes in cells was designed and prepared using 4-aminophenol as a reducing agent and N-aminoethyl-γ-aminopropyltrimethyl as a silicon source by a one-pot hydrothermal method. It was particularly noteworthy that the fluorescence intensity emitted from the SiNPs positively correlated with the pH value of solutions, making the SiNPs a viable probe used for sensitive sensing of pH. At the same time, a response of the probe to the pH was found in 5.0-10.0, and the SiNPs have an excellent biocompatibility (e.g., ∼74% of cell viability was remained after treatment for 24 h at 500 µg/mL of the SiNPs). The proposed method that could display the change in pH of live cells provided an effective means for visually diagnosing diseases related to intracellular pH.

Determination of potassium ferrocyanide in table salt and salted food using a water-soluble fluorescent silicon quantum dots.

The addition of potassium ferrocyanide (K4[Fe(CN)6]) in table salt as anti-caking agent has a crucial role in preventing the formation of lumps. However, the excess of K4[Fe(CN)6] and its decomposers are harmful to both human health and environment. To date, there are still lack of suitable methods for simple and rapid analysis of K4[Fe(CN)6] in table salt and salted food. Herein, a novel fluorescent Si QDs probe for sensitive, selective and rapid detection of K4[Fe(CN)6] was synthesized by facile one-step strategy. Notably, the fluorescence of Si QDs could be remarkably quenched by K4[Fe(CN)6] via electrostatic interaction. Based on this phenomenon, a new method of determination of K4[Fe(CN)6] was established. A wide linear range was obtained from 0.05 to 8.0 µg/mL with a detection limit of 30 ng/mL. The established fluorescent new method was suitable for detecting K4[Fe(CN)6] in table salt and salted food samples with satisfactory results.

Modification-Free Fabricating Ratiometric Nanoprobe Based on Dual-Emissive Carbon Dots for Nitrite Determination in Food Samples.

Great challenges still exist for facilely fabricating ratiometric fluorescent nanoprobes. Fortunately, the appearance of dual-emissive carbon dots (CDs) offers a glimmer of hope for the fabrication of modification-free ratiometric nanoprobe. The chemical and electronic structure characteristics of the dual-emissive CDs might be modulated by conjugated structures of carbon sources and the doped nitrogen and sulfur atoms, and the surface state also contributed to the fluorescence properties via surface functional groups. Herein, we report a one-pot strategy for simultaneous preparation of two kinds of CDs named RYDE CDs and RODE CDs, showing dual-emissive fluorescent peaks with long wavelength by 2,3-diaminobenzoic acid hydrochloride for the first time. Notably, trace nitrite determination with high sensitivity and selectivity was realized for the first time based on the modification-free ratiometric fluorescent nanoprobe fabricated rapidly and directly by the as-prepared RYDE CDs at constant room temperature (20 °C). Under the optimal conditions, the limit of detection for nitrite was 31.61 nM, with a wide concentration linear range of 0.1-100 µM. Furthermore, this ratiometric nanoprobe was successfully applied for nitrite analysis in bacon, sausage, pickle, and milk samples. Additionally, the nanoprobe was also capable of visually monitoring temperature fluctuations and cell imaging.

A new double-emission fluorescent probe for fast detection of thiophenols in aqueous solution and living cells.

A new fluorescent probe was designed and synthesized according to the photo-induced electron transfer theory (PET) and the results of density functional theory calculation. The synthesized probe had a larger Stokes shift (130 nm) and double emission peak in response to highly toxic thiophenols, which could be applied in rapid and high sensitive detection of thiophenol in aqueous solution. A 25-fold fluorescence intensity enhancement was achieved and the fluorescent intensity at 460 nm had a linear relationship to the thiophenol in concentration range of 0-2.0 µM. Furthermore, a remarkable detection limit (6 nM) could be achieved. 50-fold other species have no interference to the detection. The practical utility of the probe was demonstrated by live HeLa cells imaging and thiophenol detection in real water samples. In linear range of 0-2.0 µM, the probe showed good recoveries (from 95% to 108%) for thiophenol detection in natural water samples. This method possesses high sensitivity, lower detection limit and fast response (i.e., 10 min, which is shorter than the average time response of other reported methods), indicating that the synthesized probe would be promising for real-time detection of thiophenols.

Investigation of nitrogen content effect in reducing agent to prepare wavelength controllable fluorescent silicon nanoparticles and its application in detection of 2-nitrophenol.

Fluorescent silicon nanoparticles (SiNPs) displayed different emission wavelengths have been synthesized, but it has not been reported that the preparation of wavelength controllable SiNPs by adjusting the nitrogen content of reducing agents. In this paper, the wavelength-controlled fluorescent SiNPs were prepared by selecting the dopamine (DA) with nitrogen content between catechol and 2-aminophenol as the reducing agent and N-[3-(trimethoxysilyl) propyl]-ethylenediamine (DAMO) as the silicon source via one-step hydrothermal method. The emission wavelength of the prepared SiNPs was in direct proportion to the nitrogen content in the reducing agent. To the best of our knowledge, this is the first time for exploring the nitrogen content in reducing agents could affect the optical properties of SiNPs so far. In addition, the obtained SiNPs could be applied to determinate 2-nitrophenol (2-NP). Based on the combination action of inner filter effect (IFE) and static quenching effect (SQE) mechanism, a wide linear range was obtained from 0.1 to 500 µM, and the limit of detection was 0.029 µM for 2-NP, which was comparable to or even lower than some previous reports. This SiNPs probe was also successfully employed for sensing of 2-NP in industrial effluent with satisfactory results (98.6%-103.4%).

Fabrication of Co3O4 NPs-graphene oxide nanocomposites as an efficient catalyst towards oxygen reduction and its catalytic applications.

Co3O4 nanoparticles-graphene oxide (Co3O4 NPs-GO) nanocomposites with good solubility were successfully synthesized and well characterized. As a nanocatalyst with oxidase-mimicking activity, the nanocomposites can catalyze the oxidation of 3',5,5'-tetramethylbenzidine (TMB) with high efficiency. The catalyzing reaction was rapid and no extra H2O2 was needed compared with other similar TMB oxidation reactions. The catalyzing reaction mechanism of the system was investigated in detail. And it was demonstrated that the oxygen involved in the reaction came from the oxygen absorbed on the nanocomposites which oxidized TMB. Based on this reaction, a colorimetric system for vitamin C detection in vegetable and fruits was established. Under the optimum conditions, the detection can be achieved within 10 min and a linear relationship in concentration range of 2.5 × 10-6 to 1.8 × 10-5 M and 3.4 × 10-5 to 1.7 × 10-4 M was obtained with a detection limit of 7.0 × 10-7 M. The colorimetric system exhibited good selectivity, sensitivity and satisfactory recoveries ranged from 93.1% to 101.1%.

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.

Ratiometric fluorescent detection of chromium(VI) in real samples based on dual emissive carbon dots.

As we know, hexavalent chromium (Cr(VI)) was usually used as an additive to improve the color fastness during the printing and dyeing process, and thus posing tremendous threat to our health and living quality. In this work, the dual emissive carbon dots (DECDs) were synthesized through hydrothermal treatment of m-aminophenol and oxalic acid. The obtained DECDs not only exhibited dual emission fluorescence peaks (430 nm, 510 nm) under the single excitation wavelength of 380 nm, but also possessed good water solubility and excellent fluorescence stability. A ratiometric fluorescent method for the determination of Cr(VI) was developed using the DECDs as a probe. Under the optimal conditions, a linear range was obtained from 2 to 300 µM with a limit of detection of 0.4 µM. Furthermore, the proposed ratiometric fluorescent method was applied to the analysis of Cr(VI) in textile, steel, industrial wastewater and chromium residue samples with satisfactory recoveries (88.4-106.8%).

Ratiometric Detection of Intracellular Lysine and pH with One-Pot Synthesized Dual Emissive Carbon Dots.

Recently, the development of new fluorescent probes for the ratiometric detection of target objects inside living cells has received great attention. Normally, the preparation, modification as well as conjugation procedures of these probes are complicated. On this basis, great efforts have been paid to establish convenient method for the preparation of dual emissive nanosensor. In this work, a functional dual emissive carbon dots (dCDs) was prepared by a one-pot hydrothermal carbonization method. The dCDs exhibits two distinctive fluorescence emission peaks at 440 and 624 nm with the excitation at 380 nm. Different from the commonly reported dCDs, this probe exhibited an interesting wavelength dependent dual responsive functionality toward lysine (440 nm) and pH (624 nm), enabling the ratiometric detection of these two targets. The quantitative analysis displayed that a linear range of 0.5-260 µM with a detection limit of 94 nM toward lysine and the differentiation of pH variation from 1.5 to 5.0 could be readily realized in a ratiometric strategy, which was not reported before with other carbon dots (CDs) as the probe. Furthermore, because of the low cytotoxicity, good optical and colloidal stability, and excellent wavelength dependent sensitivity and selectivity toward lysine and pH, this probe was successfully applied to monitor the dynamic variation of lysine and pH in cellular systems, demonstrating the promising applicability for biosensing in the future.

One-Pot Synthesis of Fluorescent Silicon Nanoparticles for Sensitive and Selective Determination of 2,4,6-Trinitrophenol in Aqueous Solution.

Because 2,4,6-trinitrophenol (TNP) and its analogues such as 2,4,6-trinitrotoluene (TNT) possess similar chemical structures and properties, the reliable and accurate detection of TNP from its analogues still remains a challenging task. In the present work, a selective and sensitive method based on the water-soluble silicon nanoparticles (SiNPs) for the determination of TNP was established. The SiNPs with good thermostability and excellent antiphotobleaching capability were prepared via a simple one-pot method. Compared with the synthesized time of other nanomaterials with respect to the detection of TNP, this method avoided a multistep and time-consuming synthesis procedure. Significantly, the fluorescence of the SiNPs could be remarkably quenched by TNP via an inner filter effect. A wide linear range was obtained from 0.02 to 120 µg/mL with a limit of detection of 6.7 ng/mL. The method displayed excellent selectivity toward TNP over other nitroaromatic explosives. The proposed fluorescent method was successfully applied to the analysis of TNP. Moreover, a straightforward and convenient fluorescent filter paper sensor was developed for the detection of TNP, providing a valuable platform for TNP sensing in public safety and security.

pH-Regulated Synthesis of Trypsin-Templated Copper Nanoclusters with Blue and Yellow Fluorescent Emission.

In this article, a simple protocol to prepare water-soluble fluorescent copper nanoclusters (CuNCs) using trypsin as a stabilizer and hydrazine hydrate as a reducing agent was reported. It was found that the pH of the reaction solution was critical in determining the fluorescence of CuNCs. CuNCs with blue and yellow fluorescent emission were obtained under basic and acidic conditions, respectively. Although the detailed formation mechanisms of these CuNCs required further analysis, the synthetic route was promising for preparing different fluorescent metal NCs for applications. With good water solubility and excellent photostability, the yellow-emitting CuNCs could serve as a fluorescence probe for detection of Hg2+ based on the aggregation-induced quenching mechanism. The fluorescence quenching efficiency had fantastic linearity to Hg2+ concentrations in the range of 0.1-100 µM, with a limit of detection of 30 nM. Additionally, the yellow-emitting CuNCs exhibited negligible cytotoxicity and were successfully applied to bioimaging of HeLa cells.

One-Step Synthesis of Water-Dispersible and Biocompatible Silicon Nanoparticles for Selective Heparin Sensing and Cell Imaging.

A sensitive and selective fluorescence "turn-off" sensor to detect heparin using water-soluble silicon nanoparticles (Si NPs) was developed for the first time. The Si NPs were synthesized by a simple one-step procedure, which did not need high-temperature and complex modification. The as-prepared Si NPs featured strong fluorescence, favorable biocompatibility, and robust photo- and pH stability. Significantly, the Si NPs were induced to assemble or aggregate via hydrogen bonding, which resulted in the fluorescence of Si NPs quenched. Under the optimized conditions, the linear range was obtained from 0.02 to 2.0 µg/mL, with a limit of detection of 18 ng/mL (equal to 0.004 U/mL). It was lower than the proper therapeutic level of heparin during cardiovascular surgery and long-term therapy. This proposed method was relatively free of interference from heparin analogues, which commonly existed in heparin samples and could possibly affect heparin detection. Moreover, it did not need to introduce any control medium. As expected, the method was successfully applied to detect heparin in human serum samples with satisfactory recovery ranging from 98.8 to 102.5%. The Si NPs were superbly suitable for cell imaging owing to the negligible cytotoxicity and excellent biocompatibility.

Fluorescent carbon nanoparticles: A low-temperature trypsin-assisted preparation and Fe(3+) sensing.

In recent years, extensive researches are focused on the fluorescent carbon nanoparticles (CNPs) due to their excellent photochemical, biocompatible and water-soluble properties. However, these synthesis methods are generally suffered from tedious processes. In this paper, fluorescent carbon nanoparticles are synthesized by a facile, one-pot, low-temperature method with trypsin and dopamine as precursors. The synthesis process avoids any heating operation and organic solvent, which provides a "green" and effective preparation route. The obtained CNPs exhibit excellent water-solubility, salt-tolerance and photostability. Based on the synergistic action of the inner filter effect and static quenching mechanism, the CNPs are exploited as a "turn-off" fluorescence sensor for sensitive and selective detection of Fe(3+) ions. The probe shows a wide linear range from 0.1 to 500 µM, with a limit of detection of 30 nM. Furthermore, the as-fabricated fluorescent sensing system is successfully applied to the analysis of Fe(3+) in biological samples such as human urine and serum samples with satisfactory recoveries (92.8-113.3%).

"Switch-On" Fluorescent Sensing of Ascorbic Acid in Food Samples Based on Carbon Quantum Dots-MnO2 Probe.

This work describes a "switch-on" fluorescence approach for sensing of ascorbic acid (AA) in food samples. In the present method, the fluorescence intensity (FL) of carbon quantum dots (CQDs) was first quenched by addition of MnO2 nanosheets through an inner filter effect to form a CQDs-MnO2 probe. When reductive AA was introduced into the quenched CQDs solution, the added MnO2 was destroyed due to the redox reaction between AA and MnO2 nanosheets, and the FL of the system was recovered. Under the optimal conditions, the limit of detection for AA was 42 nM, with a wide concentration linear range of 0.18-90 µM. Furthermore, the as-fabricated fluorescent sensing system was successfully applied to the analysis of AA in fresh fruits, vegetables, and commercial fruit juices samples with satisfactory results.

Fluorescence resonance energy transfer-based ratiometric fluorescent assay for highly sensitive and selective determination of sulfide anions.

A novel and effective ratiometric fluorescence strategy was developed for rapidly, sensitively and selectively probing sulfide anions (S(2-)). A dual-emission nanosensor was prepared by covalently attaching fluorescent carbon nanoparticles (CNPs) to gold nanoclusters (Au NCs), triggering the sensing mechanism of fluorescence resonance energy transfer (FRET) from CNPs (donor) to Au NCs (acceptor). Once S(2-) was added, considerable fluorescence recovery of CNPs and quenching of Au NCs were observed due to the inhibition of FRET progress via the formation of Au2S. The ratiometric probe showed good, specific S(2-) sensing behavior and high sensitivity with a detection limit of 18 nM. Significantly, the assay was successfully employed to determine the S(2-) content in biological and water samples, presenting immense promise in the biological and environmental fields.

Solid-phase synthesis of highly fluorescent nitrogen-doped carbon dots for sensitive and selective probing ferric ions in living cells.

Carbon quantum dots (C-Dots) have drawn extensive attention in recent years due to their stable physicochemical and photochemical properties. However, the development of nitrogen-doped carbon quantum dots (N-doped C-Dots) is still on its early stage. In this paper, a facile and high-output solid-phase synthesis approach was proposed for the fabrication of N-doped, highly fluorescent carbon quantum dots. The obtained N-doped C-Dots exhibited a strong blue emission with an absolute quantum yield (QY) of up to 31%, owing to fluorescence enhancement effect of introduced N atoms into carbon dots. The strong coordination of oxygen-rich groups on N-doped C-Dots to Fe(3+) caused fluorescence quenching via nonradiative electron-transfer, leading to the quantitative detection of Fe(3+). The probe exhibited a wide linear response concentration range (0.01-500 µM) to Fe(3+) with a detection limit of 2.5 nM. Significantly, the N-doped C-Dots possess negligible cytotoxicity, excellent biocompatibility, and high photostability. All these features are favorable for label-free monitoring of Fe(3+) in complex biological samples. It was then successfully applied for the fluorescence imaging of intracellular Fe(3+). As an efficient chemosensor, the N-doped C-Dots hold great promise to broaden applications in biological systems.