Analytical detection of biological thiols in a microchip capillary channel

Investigation of interactions between biological thiols and gold nanoparticles by capillary electrophoresis with laser-induced fluorescence

Biological thiols spontaneously form a stable Au-S dative bond with gold nanoparticles (AuNP) that might be used for their selective extraction and enrichment in biological samples. In this work, interactions of selected biological thiols (glutathione, cysteine, homocysteine [Hcys], cysteamine [CA], and N-acetylcysteine) with AuNP stabilized by different capping agents (citrate, Tween 20, Brij 35, CTAB, SDS) were investigated by UV-Vis spectroscopy and capillary electrophoresis with laser-induced fluorescence. Spectrophotometric measurements showed aggregation of Hcys and CA with AuNP. In contrast, it was confirmed by CE-LIF that biological thiols were adsorbed to all types of AuNP. Citrate-capped AuNP were selected for AuNP-based extraction of biological thiols from exhaled breath condensate (EBC). Dithiothreitol was utilized for desorption of biological thiols from the AuNP surface, which was followed by derivatization with eosin-5-maleimide and CE-LIF analysis. AuNP-based extraction increased the sensitivity of CE-LIF analysis; however, further optimization of methodology is necessary for accurate quantification of biological thiols in EBC.

Long-Term Imaging of Cys in Cells and Tumor Mice by a Solid-State Fluorescence Probe

Cysteine is an important biological thiol and is closely related to cancer. It remains a challenge to develop a probe that can provide long-term fluorescence detection and imaging of Cys in cells as well as in living organisms. Here, a solid-state fluorophore HTPQ is combined with an acrylate group to construct a solid-state fluorescent probe HTPQC for Cys recognition. The fluorescence of the probe is quenched when the photoinduced electron transfer (PET) process is turned on and the excited-state intramolecular proton transfer (ESIPT) process is turned off. In the presence of Cys, an obvious solid-state fluorescence signal can be observed. The double quenching mechanism makes the probe HTPQC have the advantages of high sensitivity, good selectivity, and high contrast of biological imaging. Due to low cytotoxicity, the probe HTPQC can be used to detect exogenous and endogenous Cys in living cells and is capable of imaging over long periods of time. By making full use of long wavelengths, the probe can be applied for the detection of Cys levels in tumor mice and equipped with the ability to conduct long-term imaging in vivo.

Gold alloy-based nanozyme sensor arrays for biothiol detection

Biothiols play an important role in living cells and are associated with many diseases. Thus, it is necessary to develop a facile, cost-effective, and convenient analytical method for the detection of biothiols. Nanozymes are functional nanomaterials with enzymatic activities. Due to their unique advantages (e.g., low cost, high stability, and multifunctionality), nanozymes have been extensively used to construct sensing systems. Previous studies demonstrated colorimetric assays for biothiol detection because they could competitively inhibit the peroxidase-like activities of nanozymes. However, few studies were able to differentiate biothiols from each other. To address these challenges, herein, we first synthesized Au alloy nanozymes with better peroxidase-like activities than gold nanoparticles (AuNPs). Then, cross-reactive sensor arrays were constructed with three alloy nanozymes. Six typical biothiols (i.e., glutathione, cysteine, dithiothreitol, mercaptoacetic acid, mercaptoethanol, and mercaptosuccinic acid) were successfully detected and discriminated by the as-prepared nanozyme sensor arrays. Moreover, the practical application of the nanozyme sensor arrays was demonstrated by discriminating biothiols in serum successfully.

Photoluminescence and Electrochemiluminescence Dual-Signaling Sensors for Selective Detection of Cysteine Based on Iridium(III) Complexes

Cysteine (Cys) is important in biosynthesis, detoxification, and metabolism. The selective detection of Cys over structurally similar homocysteine (Hcy) or glutathione (GSH) remains an immense challenge. Although there are many methods for detecting Cys, photoluminescence (PL) and electrochemiluminescence (ECL) techniques are well-suited for clinical diagnostics and analytical technology because of their high sensitivities. Herein, we report PL and ECL dual-channel sensors using cyclometalated iridium(III) complexes for the discrimination of Cys from Hcy and GSH. The sensors react with cysteine preferentially because of kinetic differences in intramolecular conjugate addition/cyclization, enabling phosphorescence enhancement and ECL decrease in the blue-shifted region. Sensor 1 shows ratiometric PL turn-on and ECL turn-off for Cys. In addition, unique ECL-enhancing behavior of sensor 1 toward GSH enables discrimination between Cys and GSH. Sensor 1 was successfully applied to the detection of Cys in human serum by the ECL method. We demonstrate the first case of a Cys-selective PL and ECL dual-channel chemodosimetric sensor based on cyclometalated iridium(III) complexes and expect that the rational design of efficient PL and ECL dual-channel sensors will be useful in diagnostic technology.

Multiplex detection of quality indicator molecule targets in urine using programmable hairpin probes based on a simple double-T type microchip electrophoresis platform and isothermal polymerase-catalyzed target recycling

Recently, it has been crucial to be able to detect and quantify small molecular targets simultaneously in biological samples. Herein, a simple and conventional double-T type microchip electrophoresis (MCE) based platform for the multiplex detection of quality indicator molecule targets in urine, using ampicillin (AMPI), adenosine triphosphate (ATP) and estradiol (E2) as models, was developed. Several programmable hairpin probes (PHPs) were designed for detecting different targets and triggering isothermal polymerase-catalyzed target recycling (IPCTR) for signal amplification. Based on the target-responsive aptamer structure of PHP (Domain I), target recognition can induce PHP conformational transition and produce extension duplex DNA (dsDNA), assisted by primers & Bst polymerase. Afterwards, the target can be displaced to react with another PHP and initiate the next cycle. After several rounds of reaction, the dsDNA can be produced in large amounts by IPCTR. Three targets can be simultaneously converted to dsDNA fragments with different lengths, which can be separated and detected using MCE. Thus, a simple double-T type MCE based platform was successfully built for the homogeneous detection of multiplex targets in one channel. Under optimal conditions, the assay exhibited high throughput (48 samples per hour at most, not including reaction time) and sensitivity to three targets in urine with a detection limit of 1 nM (ATP), 0.05 nM (AMPI) and 0.1 nM (E2) respectively. The multiplex assay was successfully employed for the above three targets in several urine samples and combined the advantages of the high specificity of programmable hairpin probes, the excellent signal amplification of IPCTR, and the high through-put of MCE which can be employed for screening in biochemical analysis.

Silver-ion-mediated Mg2+-dependent DNAzyme activity for amplified fluorescence detection of cysteine

Schematic illustration of a DNAzyme-based fluorescent biosensor for amplified Cys detection.

Simple and facile preparation of silver–polydopamine (Ag–PDA) core–shell nanoparticles for selective electrochemical detection of cysteine

A simple one-step method for the preparation of silver–polydopamine (Ag–PDA) core–shell nanoparticles is proposed and its application for non-enzymatic electrochemical detection of cysteine is demonstrated.

Present state of microchip electrophoresis: state of the art and routine applications

Microchip electrophoresis (MCE) was one of the earliest applications of the micro-total analysis system (μ-TAS) concept, whose aim is to reduce analysis time and reagent and sample consumption while increasing throughput and portability by miniaturizing analytical laboratory procedures onto a microfluidic chip. More than two decades on, electrophoresis remains the most common separation technique used in microfluidic applications. MCE-based instruments have had some commercial success and have found application in many disciplines. This review will consider the present state of MCE including recent advances in technology and both novel and routine applications in the laboratory. We will also attempt to assess the impact of MCE in the scientific community and its prospects for the future.

A simple and effective coumarin-based fluorescent probe for cysteine

Acrylic acid 3-acetyl-2-oxo-2 H-chromen-7-yl ester (ACA) was rationally designed and synthesized as a simple and effective fluorescent probe for sensing cysteine with high selectivity and naked-eye detection. The probe can detect cysteine by fluorescence spectrometry with a detection limit of 0.657 μM and can be used with calf serum and in live cell imaging. The conjugate addition/cyclization sequence mechanism of the reaction between ACA and cysteine was confirmed by ESI-MS and fluorescence spectra.

Stable label-free fluorescent sensing of biothiols based on ThT direct inducing conformation-specific G-quadruplex

In this work, a new, label-free, turn-on fluorescent sensor for biothiols detection based on ThT direct inducing conformation-specific G-quadruplex is developed. The sensing approach is based on a conformational switch of oligonucleotide controlled by Hg(2+) and a commercially available water-soluble fluorescent dye, Thioflavin T (ThT). A noticeable fluorescence light-up in ThT on binding to the G-quadruplex grants the sensor excellent sensitivity. The specific quadruplex conformation induced directly by ThT and pronounced structural selectivity of ThT for G-quadruplexes could generate more stable luminescence and make sure high specificity in complex biological samples. The present assay allows for the selective determination of cysteine and glutathione in the range of 2.0 × 10(-8)-2.5 × 10(-6)M and 3.0 × 10(-8)-2.0 × 10(-6)M with a detection limit of 8.4 nM and 13.9 nM respectively. The diagnostic capability and potential in practical applications of this method have been demonstrated by detecting biothiols in human blood serum.