In-line preconcentration of oxidized and reduced glutathione in capillary zone electrophoresis using transient isotachophoresis under strong counter-electroosmotic flow

A simple and convenient dry-state SEIRS method for glutathione detection based on citrate functionalized silver nanoparticles in human biological fluids

Graphical representation for determination of glutathione using citrate functionalized AgNPs enriched dry-state SEIRS method.

A water-stable zinc(ii)–organic framework as an “on–off–on” fluorescent sensor for detection of Fe3+ and reduced glutathione

A zinc(ii) metal–organic framework exhibits fluorescence on–off–on behaviour for Fe³⁺ and reduced glutathione in PBS solution and in real samples.

Visual Assay of Glutathione in Vegetables and Fruits Using Quantum Dot Ratiometric Hybrid Probes

Future food safety monitoring with simple, fast, and visual methods has become increasingly important. Accordingly, this work was designed to construct a new-style dual-emission ratiometric fluorescent probe (CdSe@SiO₂@CdTe) for visual assay of glutathione (GSH) with a "turn on" strategy. After adding Hg²⁺, the red fluorescence of the outer CdTe quantum dots (QDs) was quenched through both electron transfer and ion-binding processes. Upon the addition of GSH, the red fluorescence occurred again owing to the strong affinity between GSH and Hg²⁺, whereas the inner green fluorescence of CdSe QDs was unchanged, leading to a clearly recognizable fluorescence color change (from green to orange-red). In the concentration range from 0.1 to 10 μM, the relative fluorescence intensity ratios ( I₆₁₉/ I₅₃₅) showed an excellent linear correlation with the concentration of GSH, and the detection limit was as low as 42 nM under optimal conditions. Meanwhile, the ratiometric hybrid probes were successfully applied for direct visual sensing GSH in real vegetable and fruit samples.

New Application of pH-Mediated Acid Stacking Technique for Amphoteric Compounds in Capillary Electrophoresis: Example Assay of Blood Glutathiones

Both reduced and oxidized forms of glutathiones were firstly stacked and detected using pH-mediated acid stacking method, in which glutathiones were stacked as cations and separated as anions. Factors, such as injection time, sweeping time, buffer pH, concentration of sodium chloride in sample matrix, that influenced stacking and separation were systematically studied and optimized. Under the optimum condition, the enhancement factors of ~20 times for both reduced and oxidized forms of glutathiones could be easily obtained within 20 min with satisfied sensitivities (limit of detections were 0.12 and 0.06 μmol/L for reduced and oxidized glutathione, respectively, at signal-to-noise ratio, S/N = 3), linearity range (0.3-300.0 and 0.6-300.0 μmol/L for reduced and oxidized glutathione, respectively), recoveries (>98%) and reproducibilities (relative standard deviation <5.1% for peak height). The proposed method provides an alternation way for assaying of glutathiones, as well as amphoteric compounds, in blood sample.

A novel and sensitive fluorescence sensor for glutathione detection by controlling the surface passivation degree of carbon quantum dots

A novel fluorescence sensor based on controlling the surface passivation degree of carbon quantum dots (CQDs) was developed for glutathione (GSH) detection. First, we found that the fluorescence intensity of the CQDs which was obtained by directly pyrolyzing citric acid would increased largely after the surface passivation treatment by 1-ethyl-3-(3-dimethylaminopropyl)-carbodiimide (EDC). In the light of this phenomenon, we designed a simple, rapid and selective fluorescence sensor based on the surface passivated CQDs. A certain and excess amount of EDC were mixed with GSH, part of EDC would form a stable complex with GSH owing to the exposed sulfhydryl group of GSH. As the synthesized CQDs were added into the above mixture solution, the fluorescence intensity of the (EDC/GSH)/CQDs mixture solution could be directly related to the amount of GSH. Compared to other fluorescence analytical methods, the fluorescence sensor we design is neither the traditional fluorescent "turn on" probes nor "turn off" probes. It is a new fluorescence analytical method that target object indirectly control the surface passivation degree of CQDs so that it can realize the detection of the target object. Moreover, the proposed method manifested great advantages including short analysis time, low cost and ease of operation.

On–off–on fluorescence sensing of glutathione in food samples based on a graphitic carbon nitride (g-C3N4)–Cu2+ strategy

A novel fluorescence sensor based on a g-C₃N₄ nanosheet–Cu²⁺ system has been developed for rapid, sensitive and selective sensing of glutathione (GSH) in food samples.

A one-pot hydrothermal synthesis of graphene/CdS:Mn photocatalyst for photoelectrochemical sensing of glutathione

The GR/CdS:Mn composite was fabricated by a simple hydrothermal synthesis which illustrates excellent performance for the photoelectrochemical detection of glutathione.

Switch-on fluorescence sensing of glutathione in food samples based on a graphitic carbon nitride quantum dot (g-CNQD)-Hg²⁺ chemosensor

Fluorescence sensing of specific biological molecules by artificial chemosensors is a versatile technique. In the present work, a switch-on fluorescence sensor for rapid, sensitive, and selective sensing of glutathione (GSH) in food samples was developed. This method was based on the g-CNQDs-Hg(2+) system, in which the initial fluorescence from g-CNQDs was quenched by Hg(2+) with an electron transfer process. In the presence of GSH, the fluorescence sensor was switched to the "on" state, which was attributed to a competitive affinity of Hg(2+) to GSH and the functional groups on the surface of g-CNQDs. Under the optimal conditions, the limit of detection (LOD) of 37 nM for GSH was achieved with a wide range of 0.16-16 μM. The repeatability was better than 5.3% for GSH in both standard and food samples (n = 3). Finally, this fluorescence sensor was successfully employed for the determination of GSH in various kinds of food samples with excellent recoveries. Furthermore, this application may pave a new way for fluorescence sensing of other substances in food samples.

High-sensitivity analysis of anionic sulfonamides by capillary electrophoresis using a synergistic stacking approach

A synergistic stacking approach whereby field-enhanced sample injection and micelle-to-solvent stacking in capillary zone electrophoresis are combined has been developed and has been applied to the separation and quantification of anionic sulfonamides. Electrokinetic injection of the sample in a low conductivity alkaline diluent was performed for 90s at -15kV. Micelle-to-solvent stacking was then undertaken by hydrodynamic injection of micellar cetyltrimethylammonium bromide solution prior to the electrokinetic injection of sample that also contained 50% methanol. This combined stacking approach, when compared to a typical hydrostatic injection, provided improvements in peak height and corrected peak area in the range of 397-1024 and 758-1246, respectively. Limits of quantification in the range of 0.01-0.03μg/mL were obtained for sulfamerazine, sulfamethazine and sulfamethizole and were sufficient for the determination of these analytes in river water. The percentage recovery and accuracy values obtained for a fortified river water sample that had been subjected to sample preparation by evaporation and reconstitution with diluent were 74-135%. Intra-day and inter-day repeatabilities for migration time, peak height, and corrected peak area were in the range 0.5-5.0% (percentage relative standard deviation, n=8) and these relatively low values were attributed to the use of a stable capillary coating established by the successive multiple ionic-polymer layer technique.

Theoretical and experimental studies on isotachophoresis in multi-moving chelation boundary system formed with metal ions and EDTA

In this paper, a general mode and theory of moving chelation boundary based isotachophoresis (MCB-based ITP), together with the concept of decisive metal ion (DMI) having the maximum complexation constant (lg Kmax) with the chelator, were developed from a multi-MCB (mMCB) system. The theoretical deductions were: (i) the reaction boundary velocities in the mMCB system at steady state were equal to each other, resulting in a novel MCB-based ITP separation of metal ions; (ii) the boundary directions and velocities in the system were controlled by the fluxes of chelator and DMI, rather than other metal ions; and (iii) a controllable stacking of metal ions could be simultaneously achieved in the developed system. To demonstrate the deductions, a series of experiments were conducted by using model chelator of EDTA and metal ions of Cu(II) and Co(II) due to characteristic colors of blue [Cu-EDTA](2-) and pink [Co-EDTA](2-) complexes. The experiments demonstrated the correctness of theoretical deductions, indicating the validity of the developed model and theory of ITP. These findings provide guidance for the development of MRB-based ITP separation and stacking of metal ions in biological sample matrix and heavy metal ions in environmental samples.

Review of recent developments of on-line sample stacking techniques and their application in capillary electrophoresis

Capillary electrophoresis (CE) has become one of the most useful tools in separation science because of its high separation efficiency, low cost, versatility, ease of sample preparation and automation. However, some limitations of CE, such as poor concentration sensitivity due to its lower sample loading and shorter optical path length, limits its further applications in separation science. In order to solve this problem, various on-line sample preconcentration techniques such as transient isotachophoresis preconcentration, field-enhanced sample stacking, micelle to solvent stacking, micelle collapse, dynamic pH junction, sweeping, solid phase extraction, single drop microextraction and liquid phase microextraction have been combined with CE. Recent developments, applications and some variants together with different combinations of these techniques integrating in CE are reviewed here and our discussions will be confined to the past three years (2008–2011).

Recent advances in enhancing the sensitivity of electrophoresis and electrochromatography in capillaries and microchips (2008-2010)

Capillary electrophoresis has been alive for over two decades now; yet, its sensitivity is still regarded as being inferior to that of more traditional methods of separation such as HPLC. As such, it is unsurprising that overcoming this issue still generates much scientific interest. This review continues to update this series of reviews, first published in Electrophoresis in 2007, with an update published in 2009 and covers material published through to June 2010. It includes developments in the fields of stacking, covering all methods from field-amplified sample stacking and large volume sample stacking, through to ITP, dynamic pH junction and sweeping. Attention is also given to on-line or in-line extraction methods that have been used for electrophoresis.