•Confocal laser-induced fluorescence detector for submicron capillary system.•Laser-induced fluorescence detector with yoctomole detection limit.•2-μm-tubing flow injection system capable of detecting 1.4 zeptomole fluorescein.Laser-induced fluorescence (LIF) detectors for low-micrometer and sub-micrometer capillary on-column detection are not commercially available. In this paper, we describe in details how to construct a confocal LIF detector to address this issue. We characterize the detector by determining its limit of detection (LOD), linear dynamic range (LDR) and background signal drift; a very low LOD (~70 fluorescein molecules or 12 yoctomole fluorescein), a wide LDR (greater than 3 orders of magnitude) and a small background signal drift (~1.2-fold of the root mean square noise) are obtained. For detecting analytes inside a low-micrometer and sub-micrometer capillary, proper alignment is essential. We present a simple protocol to align the capillary with the optical system and use the position-lock capability of a translation stage to fix the capillary in position during the experiment. To demonstrate the feasibility of using this detector for narrow capillary systems, we build a 2-μm-i.d. capillary flow injection analysis (FIA) system using the newly developed LIF prototype as a detector and obtain an FIA LOD of 14 zeptomole fluorescein. We also separate a DNA ladder sample by bare narrow capillary – hydrodynamic chromatography and use the LIF prototype to monitor the resolved DNA fragments. We obtain not only well-resolved peaks but also the quantitative information of all DNA fragments.

•A highly fluorescent molecule TPCA was synthesized by a one-step green route.•TPCA crystal was obtained without further treatment.•In-situ formation of AgNPs from TPCA-Ag+ was used for dopamine sensing.•The probe showed high sensitivity and selectivity for dopamine.Carbon dots derived from citric acid and amines have been gaining considerable attention due to their high quantum efficiency, but there are researches proven the presence of small fluorescent molecules in those materials. In this work, with proper control of the synthetic conditions, highly fluorescent 5-oxo-3,5-dihydro-2H-thiazolo[3,2-a]pyridine-7-carboxylic acid (TPCA) as nice needle-like crystals were harvested by a simple one-step hydrothermal method directly based on the reaction of citric acid and cysteamine hydrochloride. The proposed synthesis route does not need extra complicated purification process. The yield of TPCA was 46.9% and the quantum yield was as high as 83.2%. Experimental results confirmed that TPCA possesses all advantages of carbon dots reported previously with similar starting materials. In addition, a novel and effective fluorescent probe, TPCA-Ag+, was designed for sensitive and selective sensing of dopamine (DA) based on in-situ formation of sliver nanoparticles. The calibration curve for DA was linear up to 0.4 μmol/L, and a detection limit of 0.75 nmol/L was attained. The method was successfully applied to the determination of DA in dopamine hydrochloride injection and urine samples and the standard addition recoveries were in a range of 87.2–102.8%.

•Gold nanoparticles with self-assembled rhodanine were used as a sensor for Hg2+.•The sensor is simple, cost-effective and sensitive with an LOD of 6 nM.•0.1 μM of Hg2+ could be detected with the naked eye based on the color change.Self-assembling of rhodanine (R) on gold nanoparticles was used to construct a colorimetric sensor for detecting Hg2+ in aqueous media. Gold nanoparticles capped with R (AuNPs@R) were well dispersed in phosphate buffer (NaH2PO4-Na2HPO4) as clear wine red solutions. The presence of Hg2+ induced aggregation of AuNPs@R and resulted in a color change from wine red to blue. The experimental results indicated that formation of rhodanine-Hg2+-rhodanine (R-Hg2+-R) structure was the initial driving force of the aggregation, without the use of expensive DNA and complicated functionalization of AuNPs. This aggregation phenomenon is similar to that used for the determination of Hg2+ by thymine. The color change was successfully used for the determination of Hg2+. Under the optimum conditions, the linear relationship between the absorbance ratio A650/A520 and Hg2+ concentration was in a range of 0.02–0.5 μM, and the limit of the detection (LOD) was 6.0 nM. The color change was evident and it is possible to recognize the presence of Hg2+ as low as 0.1 μM by the naked eye. The method avoids complicated surface modifications and tedious separation processes. Its applicability was verified by analysis of Hg2+ in tap water and lake water with the quantitative spike recoveries ranging from 94.8 to 110%.Simple, cost-effective and sensitive detection of mercury (II) based on rhodanine stabilized gold nanoparticles.Download high-res image (206KB)Download full-size image

The deposition kinetics of graphene oxide (GO) onto poly(ethylene imine) (PEI) layer was characterized in situ with pulsed streaming potential (SP) measurement, and it was found that the initial rate constant (ki) was dependent on the size of GO with same surface charge density at a fixed concentration under controlled experimental conditions. Assuming the deposition was controlled by diffusion at the initial stage, ki is proportional to Rh–2/3, where Rh is the hydrodynamic radius. By flushing a GO solution through a capillary coated with PEI, the initial change rate of relative SP (dEr/dt) was obtained in 20 s and ki was measured with five different concentrations in about 2 min. Three GO samples of different sizes obtained from the same batch of raw material were characterized with pulsed SP to get ki values, and their sizes were verified with atomic force microscopy and dynamic light scattering. The experimental results are consistent with the predicted effects of the size of NPs on their deposition kinetics.

•High content methanol was used for better separation of easily adsorbed dyes in MCE.•Polyacrylic acid was used to ensure the separation efficiency and repeatability.•Two rhodamine dyes were well-resolved with a BGE containing 80% methanol.•Theoretical plate number of 7.0 × 105 was achieved.•Food samples and cosmetic products were analyzed with simple pre-treatment.Plastic microchips can significantly reduce the fabrication cost but the adsorption of some analytes limits their application. In this work, background electrolyte containing ionic polymer and high content of organic solvent was adopted to eliminate the analyte adsorption and achieve highly efficient separation in microchip electrophoresis. Two dyes, rhodamine 6G (Rh6G) and rhodamine B (RhB) were used as the model analytes. By using methanol as the organic solvent and polyacrylic acid (PAA) as a multifunctional additive, successful separation of the two dyes within 75 μm id. microchannels was realized. The role of PAA is multiple, including viscosity regulator, selectivity modifier and active additive for counteracting analyte adsorption on the microchannel surface. The number of theoretical plate of 7.0 × 105/m was attained within an effective separation distance of 2 cm using background electrolyte consisting 80% methanol, 0.36% PAA and 30 mmol/L phosphate at pH 5.0. Under optimized conditions, relative standard deviations of Rh6G and RhB detection (n = 5) were no more than 1.5% for migration time and 2.0% for peak area, respectively. The limit of detection (S/N = 3) was 0.1 nmol/L for Rh6G. The proposed technique was applied in the determination of both Rh6G and RhB in chilli powder and lipstick samples with satisfactory recoveries of 81.3–103.7%.

•PGEs have high capacity of DNA immobilization compared with traditional gold electrodes.•Unique surface feature containing nano-scale structure was observed on PGEs.•A probable mechanism of carboxylic acid produced on polystyrene substrate was proposed.In the past decades, many efforts have been made to improve the sensitivity and specificity of electrochemical DNA biosensors. However, it is still strongly required to develop disposable and reliable DNA biosensors for wide and practical application. In this article, we reported superior electrochemical properties of an integrated plastic-gold electrode (PGE) fabricated in-house by chemical plating on polystyrene substrate. PGEs were found having extremely high capacity of DNA immobilization compared with gold electrodes fabricated by standard sputtering based photolithography. Unique nano-structured surface was observed on PGEs through morphology techniques, which would to some extend give an explanation to higher capacity of DNA immobilization on PGEs. A probable mechanism of carboxylic acid produced on polystyrene substrate after exposure to UV irradiation was proposed and discussed for the first time. This biosensor was applied to detection and manipulate of DNA hybridization. Detection limit of 7.2×10−11 M and 1–500 nM of linearity range was obtained.

Analyte oriented selection of the preparation procedure is essential for improving the sensing performance. Herein, we report a one-step approach to synthesize highly fluorescent polymeric nanoparticles through a solvothermal method and their application for sensitive detection of TNT in soil samples by a fluorescence spectrometric method. The polymeric nanoparticles with bright cyan fluorescence were obtained through polycondensation between melamine and terephthalaldehyde at 180 °C for 3 h. The nanoparticles were fully characterized and the effect of synthesis methods was compared based on the fluorescence intensity and quantum yield (QY). The results indicated that trace amounts of TNT could effectively quench the fluorescence of the polymeric nanoparticles. The effect of the possible co-existing substances was systematically investigated and it was proved that nanoparticles could be used for selective and robust detection of TNT. A limit of detection of 1.8 nmol L−1 was achieved. The standard addition recoveries for different soil samples were in the range of 95.3% and 106.4% with relative standard deviations below 5.2%.

Self-assemblies of polyelectrolytes have been widely used to tailor surface charges, but their stability varies significantly due to the diverse properties of both polyelectrolytes and surfaces. Fast and reliable evaluation of the stability of the assembled layers is essential to optimize the assembling processes and select the proper working conditions. In this work, the applicability of the pulsed streaming potential measurement for real-time evaluation of stability of assembled layers was demonstrated. Polyethyleneimine (PEI) with a molecular weight of 1800 was selected as the model polyelectrolyte and the results confirmed the dependence of the stability of the assembled layers on the assembling conditions. A parameter SR, which is defined as the relative zeta potential change rate, was adopted to reflect the difference of the positively charged layer. Effect of assembling conditions, including pH, polyelectrolyte concentration and contact time, on the change of the streaming potential were evaluated based on SR values. The feasibility of the technique for the evaluation of the stability of adsorbed proteins, oligonucleotides and cells onto the formed PEI layer was also investigated and its reliability was confirmed by capillary electrophoresis.

•Double helix microchannels on microchips were fabricated for online derivatization.•Efficient mixing and reaction could be realized within double helix microchannels.•Aldehyde flavors were used as model analytes to evaluate the performance.•Rapid on-line derivatization and electrophoretic separation were achieved.•Determination of aldehydes in chocolate and infant cereal samples was performed.Micro-channels that contain a special inner structure are critical for efficient mixing and chemical reactions. In this paper, we described the facile fabrication of an integrated microchip with double-helix type micro-channels to improve mixing efficiency and to facilitate multi-step derivatization reactions prior to electrophoretic separation. With a prepared microchip, reagents, samples and reaction products could be driven through micro-channels by siphon, and no other pumping device was necessary. To test its performance, reductive amination of aldehydes with 8-aminonaphthalene-1,3,6-trisulfonate acid disodium (ANTS) was attempted via microchip electrophoresis with laser induced fluorescence (LIF). The effect of the geometry of the reaction micro-channel on the reaction's efficiency was evaluated. Under the selected conditions, successful derivatization of five aldehydes was realized for highly reproducible analysis. The relative standard deviations of the peak areas for 30 consecutive injections were in the range of 0.28–1.61%. The method was applied for the determination of aldehydes in real samples with standard addition recoveries of 87.8–102.8%. Good tolerance of organic solvents was achieved, and the proposed method can potentially be employed for rapid screening of excessively added aldehyde food flavoring.

Here, we construct an open-channel on-chip electroosmotic pump capable of generating pressures up to ∼170 bar and flow rates up to ∼500 nL/min, adequate for high performance liquid chromatographic (HPLC) separations. A great feature of this pump is that a number of its basic pump units can be connected in series to enhance its pumping power; the output pressure is directly proportional to the number of pump units connected. This additive nature is excellent and useful, and no other pumps can work in this fashion. We demonstrate the feasibility of using this pump to perform nanoflow HPLC separations; tryptic digests of bovine serum albumin (BSA), transferrin factor (TF), and human immunoglobulins (IgG) are utilized as exemplary samples. We also compare the performance of our electroosmotic (EO)-driven HPLC with Agilent 1200 HPLC; comparable efficiencies, resolutions, and peak capacities are obtained. Since the pump is based on electroosmosis, it has no moving parts. The common material and process also allow this pump to be integrated with other microfabricated functional components. Development of this high-pressure on-chip pump will have a profound impact on the advancement of lab-on-a-chip devices.

For rapid and low-cost determination of saccharides with microchip electrophoresis, a domestic microwave oven was used to perform the derivatization of saccharides with 8-aminonaphthalene-1,3,6-trisulfonate (ANTS) for laser-induced fluorescence detection with a 405 nm laser diode. The influence of the reaction conditions was systematically examined. Derivatization of xylose, glucose and lactose was fulfilled within 3 min under the optimized condition. With appropriate selection of the separation medium, these model analytes could be resolved within 30 s in borate solutions containing hydroxypropyl cellulose using disposable cyclic olefin copolymer microchips. Theoretical plate numbers of 1.0 × 106 m−1 and limits of detection of 0.15–0.23 μM were achieved. Peak areas were linear up to 1000 μM for all analytes. The applicability of the proposed method was verified by the determination of glucose in human urine and serum. Separation of oligosaccharides from konjac powder was also demonstrated. The domestic microwave oven, the cheap laser diode and disposable microchips used here make the method an economical way for rapid analysis of saccharides.

•Highly fluorescent oligo(ethylene glycol) capped carbon dots were prepared.•The prepared carbon dots exhibit high bio-compatibility and low cytotoxicity.•Bright fluorescence emission can be obtained in a wide pH range.•The product can easily penetrate the intact plant cell walls and membranes.•The carbon dots can dye nucleus specifically and are suitable for cell imaging.Fluorescent carbon dots are potential candidates for replacing traditional dyes for cell imaging, but their bulky sizes may hinder their passage through cell membranes, which may result in extra work to inject them into the cells. Here, a simple one-step method is proposed to synthesize brightly fluorescent carbon dots that can be endocytosed by intact plant cells and can thus directly dye the nucleus. The morphology, composition and effects of acidity and excitation wavelength on the photoluminescence of the obtained glutamic acid-based carbon dots were systematically investigated. The particles have a size of 4–8 nm and possess large amounts of oligo(ethylene glycol) groups with a quantum yield of 30.7%. The material exhibited high biocompatibility and low cytotoxicity. Confocal microscopy confirmed that the carbon dots prepared with the proposed method could dye HeLa cells within 1 min and intact onion epidermal cells in 10 min through endocytosis.

Zwitterionic layers immobilized on various surfaces exhibit ideal biocompatibility and antifouling capability, but direct immobilization of zwitterionic molecules provides limited choice of surface charges. In this paper, the formation of charge tunable zwitterionic polyampholyte layers onto the surface of microfluidic channels of cyclic olefin copolymer by photochemical graft polymerization of mixed acrylic monomers, [2-(acryloyloxy) ethyl] trimethyl ammonium chloride and 2-acrylamido-2-methyl-1-propanesulfonic, under UV illumination was reported. With this method, surface charge of the resulting modification layers could be tailored through the initial monomer ratio and reaction conditions. The incorporation of both monomers into the grafted layers was confirmed by X-ray photoelectron spectroscopy (XPS) and attenuated total reflection Fourier transform infrared (ATR-FTIR). The results indicate that the modified layers are hydrophilic with contact angles of 33.0–44.3°, and the isoelectric points of the modified layers can be tuned from <3 to >9 simply by adjusting the monomer ratios. Elimination of the nonspecific adsorption of proteins on the zwitterionic layers thus formed was proved by fluorescent microscopy and streaming potential measurement. The uniformity of the modified layers was verified through a comparison of electrophoresis inside the modified and native microchannels. A whole blood coagulation time measurement was performed to show its applicability.Keywords: nonspecific adsorption; protein; streaming potential; surface charge; tunable; zwitterionic;

Hollow, spherical nitrogen-rich porous carbon shells were prepared as supercapacitor electrode materials through the carbonization of structure-controlled porous organic frameworks at high temperature. The structure and electrochemical properties of the resulting carbonized materials were systematically characterized. Experimental results revealed that the nitrogen-rich hollow carbon spheres obtained at 800 °C were a kind of amorphous carbon with micropores on the shell frame and with specific surface areas as high as 525 m2 g–1. The prepared porous carbon possessed a specific capacitance of 230 F g–1 at a current density of 0.5 A g–1 and could retain ∼98% of the initial capacitance after 1500 successive charge–discharge cycles. Electrochemical impedance spectroscopy indicated that the material has a small equivalent series resistance (0.62 Ω). All of these values demonstrated that the prepared porous carbon is a promising supercapacitor material. The proposed method represents a simple approach towards the preparation of unique structures of nitrogen-containing porous carbon that exhibit the advantages of having a simple preparation process, a wide availability of precursors, flexible control of the structure, and an easier adjustment of the amount of heteroatoms.Keywords: carbonization; hollow sphere; nitrogen-rich porous carbon; porous organic framework; supercapacitor;

With an increasing concern on food safety, fast screening of residues of widespread herbicides becomes necessary. Herein we report a microchip electrophoresis system with laser induced fluorescence (LIF) detection for rapid and sensitive analysis of glyphosate (GLYP) and glufosinate (GLUF) residues. Disposable cyclic olefin copolymer microchips and a low-cost LIF detector were employed to minimize the cost of the analysis. Systematic optimization of experimental conditions was performed to achieve highly efficient analysis. Under the selected condition, GLYP and GLUF were efficiently resolved from sample matrices with a buffer containing 10 mmol/L borax and 2.0% (m/v) hydroxypropyl cellulose at pH 9.0. The number of theoretical plates of 1.0 × 106 m–1 was attained for both analytes. Derivatization at lower concentrations (<10 μg/L) was also examined, successful detection of 0.34 μg/L GLYP and 0.18 μg/L GLUF was confirmed. The system was applied for the determination of both analytes in real samples without any preconcentration involved. Recoveries of GLYP and GLUF spiked in these samples were 84.0–101.0% and 90.0–103.0%, respectively.Highlights► Microchip electrophoresis was adopted for analysis of glyphosate and glufosinate. ► Easy-to-make low-cost plastic microchips and hardwares were utilized. ► Anodic separation was used to get rid of potential interferences. ► The method was fast, sensitive and excellent in interference tolerance. ► The method was applied in the analysis of real samples with complicated matrices.

This paper describes a successful synthesis of water soluble CdTe(S) nanocrystals (NCs) with high quantum yields (QYs) via a mild photochemical route in one step with thioglycolic acid as the stabilizer and sulfur source. The precursor solution of mixed cadmium chloride, freshly prepared sodium hydrogen telluride and thioglycolic acid was subjected directly to UV irradiation using a 500 W high-pressure mercury lamp under the protection of N2. NCs with a small particle size (2.2 nm) and a high photoluminescence quantum yield (up to 80% at room temperature) were formed within 25 min. The NCs were characterized by UV-vis absorption and fluorescence spectroscopy, transmission electron microscopy, powder X-ray diffraction and energy-dispersive X-ray spectroscopy to evaluate their structure, size and composition. The photochemically prepared NCs were compared with CdTe NCs prepared by conventional hydrothermal synthesis and CdTe/CdS core/shell NCs obtained by post-preparative photochemical passivation. The effects of UV irradiation intensity, illumination time, temperature and concentration of Te2− on the optical properties of NCs were studied in detail.

In this article, we introduce a chip-capillary hybrid device to integrate capillary isoelectric focusing (CIEF) with parallel capillary sodium dodecyl sulfate- polyacrylamide gel electrophoresis (SDS-PAGE) or capillary gel electrophoresis (CGE) toward automating two-dimensional (2D) protein separations. The hybrid device consists of three chips that are butted together. The middle chip can be moved between two positions to reroute the fluidic paths, which enables the performance of CIEF and injection of proteins partially resolved by CIEF to CGE capillaries for parallel CGE separations in a continuous and automated fashion. Capillaries are attached to the other two chips to facilitate CIEF and CGE separations and to extend the effective lengths of CGE columns. Specifically, we illustrate the working principle of the hybrid device, develop protocols for producing and preparing the hybrid device, and demonstrate the feasibility of using this hybrid device for automated injection of CIEF-separated sample to parallel CGE for 2D protein separations. Potentials and problems associated with the hybrid device are also discussed.

An economical fluorescence detector was developed with an LED as the exciting source and a low-cost avalanche photodiode (APD) module as a photon sensor. The detector was arranged in an epifluorescence configuration using a microscope objective (20× or 40×) and a dichroic mirror. The low-cost APD was biased by a direct current (DC) high voltage power supply at 121 V, which is much lower than that normally used for a PMT. Both DC and square wave (SW) supplies were used to power the LED and different data treatment protocols, such as simple average for DC mode, software based lock-in amplification and time specific average for SW mode, were tested to maximize the signal-to-noise ratio. Using an LED at a DC mode with simple data averaging, a limit of detection of 0.2 nmol L−1 for sodium fluorescein was attained, which is among the lowest ever achieved with an LED as an excitation source. The detector was successfully used in both capillary and chip electrophoresis. The most significant advantages of the detector are the compact size and low cost of its parts. The aim of the work is to prove that widely available, low-cost components for civilian use can be successfully used for miniaturized analytical devices.

A mesoporous silica SBA-15-supported palladium with spindle-like nitrogen donor groups, 1,4-diaza-bicyclo[2.2.2]octane, has been successfully prepared and applied for homocoupling of terminal alkynes. The catalyst exhibited very high activity for terminal alkynes carrying various substitution groups, yields ranging from 70% to 94%, with a significant advantage that air acted as the oxidant. It also showed good reusability, could be easily recovered through filtration and washing, and reused at least five times with virtually no evident loss of catalytic performance. Furthermore, it was also proved to be an effective and air-stable heterogeneous catalyst for Suzuki coupling of aryl halides (X = I, Br) with arylboronic acids. The catalyst was systematically characterized by elemental analysis, X-ray photoelectron spectroscopy, high-resolution transmission electron microscope, nitrogen physical adsorption, Brunauer–Emmett–Teller method and X-ray powder diffraction. The analyses indicated that the mesoporous structure of the materials was retained during the immobilization process.Graphical abstractA mesoporous SBA-15 supported palladium catalyst with a spindle-like nitrogen containing ligand was proved to be effective for homocoupling of terminal alkynes and Suzuki cross-coupling reactions.Highlights► Mesoporous SBA-15-supported palladium with spindle-like DABCO was synthesized. ► High activity for homocoupling of terminal alkynes and Suzuki coupling was proved. ► The catalyst was reusable and air was used as the oxidant for the homocoupling.

A new, rapid, and sensitive method was proposed for the determination of sulfonamide residues in milk and chicken muscle samples by microchip electrophoresis with laser-induced fluorescence detection. Separation of fluorescamine-labeled sulfonamides was accomplished by using a buffer containing 5 mmol/L boric acid and 1% (w/v) polyvinyl alcohol (PVA). The pH, amount of PVA, and concentration of boric acid in the running buffer were found to have great influence on the separation. By optimizing these conditions, the separation of four sulfonamides, sulfamethazine, sulfamethoxazole, sulfaquinoxaline, and sulfanilamide, was achieved within 1 min with limits of detection (S/N = 3) of 0.2–2.3 μg/L, which are well below the maximum residue limit. The proposed method also exhibited very good repeatability; the relative standard deviations for both within-day and between-day measurements were ≤3.0%. With a simplified sample pretreatment protocol, fast determination of sulfonamides in real samples was successfully performed with standard addition recoveries of 93.3–100.8 and 82.9–92.3%, respectively.

A practical open channel microfluidic reactor with immobilized palladium complex was built on a cyclic olefin copolymer (COC) chip that was fabricated with a very simple hot-embossing technique. Palladium complex was immobilized on a photochemically grafted layer of polymerized N-[3-(dimethylamino)propyl]methacrylamide. Surface modification and catalyst immobilization onto COC were systematically characterized with streaming potential, surface contact angle, attenuated total reflection Fourier transform infrared spectrometry, scanning electron microscopy, atomic force microscopy and X-ray photoelectron spectroscopy. The reactor was comprised of a single 15 cm long serpentine channel of 120 μm (i.d.) and exhibited high efficiency for the Suzuki cross-coupling reaction of aryl iodides and bromides with arylboronic acids, affording good to excellent yields of the corresponding products. The reactions could be carried out smoothly with reduced reaction time and lower reactant consumption in the microreactor thermostated at 50°C. The proposed system may have great potential for high-throughput screening of catalysts and reaction conditions.

An ethylene glycol solution was used as the electrophoretic running buffer in unmodified cyclic olefin copolymer (COC) microchips to minimize the interactions between the analytes and the hydrophobic walls of the plastic microchannels, enhance the resolution of the analytes and eliminate the uncontrollable dispersion caused by uneven liquid levels and non-uniform surfaces of the separation channels. Five amino acids that were labeled with fluorescein isothiocyanate (FITC) were used as model analytes to examine the separation efficiency. The effects of ethylene glycol concentration, pH and sodium tetraborate concentration were systematically investigated. The five FITC-labeled amino acids were effectively resolved using a COC microchip with an effective length of 2.5 cm under optimum conditions, which included using a running buffer of 20 mmol/L sodium tetraborate in ethylene glycol:water (80:20, v/v), pH 6.7. A theoretical plate number of 4.8 × 105/m was obtained for aspartic acid. The system exhibited good repeatability, and the relative standard deviations (n = 5) of the peak areas and migration times were no more than 3.4% and 0.7%, respectively. Furthermore, the system was successfully applied to elucidate these five amino acids in human saliva.Highlights► Ethylene glycol solution was used as the running buffer in COC microchips. ► Five amino acids labeled with FITC were used to examine the separation efficiency. ► The system was applied in the determination of these amino acids in human saliva.

The feasibility of microwave-accelerated derivatization for capillary electrophoresis (CE) with laser-induced fluorescence (LIF) detection was evaluated. The derivatization reaction was performed in a domestic microwave oven. Histidine (His), 1-methylhistidine (1-MH) and 3-methylhistidine (3-MH) were selected as test analytes and fluorescein isothiocyanate (FITC) was chosen as a fluorescent derivatizing reagent. Parameters that may affect the derivatization reaction and/or subsequent CE separation were systematically investigated. Under optimized conditions, the microwave-accelerated derivatization reaction was successfully completed within 150 s, compared to 4–24 h in a conventional water-bath derivatization process. This will remarkably reduce the overall analysis time and increase sample throughput of CE-LIF. The detection limits of this method were found to be 0.023 ng/mL for His, 0.023 ng/mL for 1-MH, and 0.034 ng/mL for 3-MH, respectively, comparable to those obtained using traditional derivatization protocols. The proposed method was characterized in terms of precision, linearity, accuracy and successfully applied for rapid and sensitive determination of these analytes in human urine.

A simple and highly selective flow injection on-line preconcentration and separation–flame atomic absorption spectrometric method was developed for the routine analysis of trace amounts of silver, gold, palladium and platinum in geological and metallurgical samples. The selective preconcentration of the noble metals was achieved in a wide range of sample acidities (0.5–3.0 M HNO3 or HCl for Ag, Au and Pd) on a microcolumn packed with an isodiphenylthiourea immobilized silica gel (DPTSG). The noble metals retained on the microcolumn were effectively eluted with thiourea solution. With the use of a 0.85 mL microcolumn (about 0.14 g of DPTSG) the present system tolerated up to 25.0 mg mL−1 of common base metal ions and 100.0 mg mL−1 of anion when 0.040 µg mL−1 of AgI, 0.200 µg mL−1 of AuIII, 0.200 µg mL−1 of PdII and 1.00 µg mL−1 of PtIV were preconcentrated for 60 s with a sample flow rate of 5.0 mL min−1. The limits of detection were 0.33 ng mL−1 for AgI, 3.2 ng mL−1 for AuIII, 4.7 ng mL−1 for PdII and 69 ng mL−1 for PtIV, respectively, with the relative standard deviation being not more than 3.0%. The analytical results obtained by the proposed method for geological and metallurgical samples were in good agreement with the certified values.

Analyte oriented selection of the preparation procedure is essential for improving the sensing performance. Herein, we report a one-step approach to synthesize highly fluorescent polymeric nanoparticles through a solvothermal method and their application for sensitive detection of TNT in soil samples by a fluorescence spectrometric method. The polymeric nanoparticles with bright cyan fluorescence were obtained through polycondensation between melamine and terephthalaldehyde at 180 °C for 3 h. The nanoparticles were fully characterized and the effect of synthesis methods was compared based on the fluorescence intensity and quantum yield (QY). The results indicated that trace amounts of TNT could effectively quench the fluorescence of the polymeric nanoparticles. The effect of the possible co-existing substances was systematically investigated and it was proved that nanoparticles could be used for selective and robust detection of TNT. A limit of detection of 1.8 nmol L−1 was achieved. The standard addition recoveries for different soil samples were in the range of 95.3% and 106.4% with relative standard deviations below 5.2%.

This paper describes a successful synthesis of water soluble CdTe(S) nanocrystals (NCs) with high quantum yields (QYs) via a mild photochemical route in one step with thioglycolic acid as the stabilizer and sulfur source. The precursor solution of mixed cadmium chloride, freshly prepared sodium hydrogen telluride and thioglycolic acid was subjected directly to UV irradiation using a 500 W high-pressure mercury lamp under the protection of N2. NCs with a small particle size (2.2 nm) and a high photoluminescence quantum yield (up to 80% at room temperature) were formed within 25 min. The NCs were characterized by UV-vis absorption and fluorescence spectroscopy, transmission electron microscopy, powder X-ray diffraction and energy-dispersive X-ray spectroscopy to evaluate their structure, size and composition. The photochemically prepared NCs were compared with CdTe NCs prepared by conventional hydrothermal synthesis and CdTe/CdS core/shell NCs obtained by post-preparative photochemical passivation. The effects of UV irradiation intensity, illumination time, temperature and concentration of Te2− on the optical properties of NCs were studied in detail.