An amperometric sensor based on electrochemically triggered reaction: Redox-active Ar–NO/Ar–NHOH from 4-nitrophthalonitrile-modified electrode for the low voltage cysteine detection

Development of a fast-responsive and turn on fluorescent probe with large Stokes shift for specific detection of cysteine in vivo

Cysteine has a great effect on the physiological and pathological processes, which could bring out various diseases such as skin lesions, edema, hair depigmentation, Alzheimer's, Parkinson's, and liver damage due to the abnormal concentrations of cysteine. Therefore, it is of great impoatance to develop a method for imaging Cys. Herein, a novel fluorescent probe was developed for imaging Cys in vivo specially. This turn-on probe exhibited favorable advantages including large Stokes shift (90 nm), fast response (10 min), good selectivity, low cytotoxicity and so on. Furthermore, the probe could be applied to monitoring cysteine in living HeLa cells, which indicates that this turn-on probe could penetrate viable cell membranes and image Cys over other analystes especially HCy and GSH.

A dihydronaphthalene based fluorescence probe for sensitive detection of cysteine and its application in bioimaging

A novel small molecule fluorescent probe NC-Cys for monitoring cysteine based on dihydronaphthalene was developed.

Chemical Sensors Based on Two-Dimensional (2D) Materials for Selective Detection of Ions and Molecules in Liquid

Up until now, two-dimensional (2D) materials have been researched vigorously for application to sensing ions and molecules in liquid due to their unique structural, chemical, and electronic properties. Features of 2D materials such as high surface area-to-volume ratios and various reaction sites are ideal characteristics for fabricating state-of-the-art high-performed chemical sensors. This review particularly focuses on the detection of pH, metal ions, and biomolecules in liquid media. The final goal of the ion/molecule sensors is a development of the electronic tongue or taste sensors that can be used in medical, food, biotechnology, and health applications. Herein, we introduce recent advances in the field of ion/molecule sensors in liquid media based on 2D materials, especially concentrating in graphene and MoS₂, and will emphasize the opportunities and challenges of these unique sensing materials and devices.

Simultaneous recognition of cysteine and cytosine using thiophene-based organic nanoparticles decorated with Au NPs and bio-imaging of cells

Biomolecules like cysteine and cytosine play a significant role in many physiological processes, and their unusual level in biological systems can lead to many diseases including cancer. Indeed, the need for selective detection of these moieties by a fluorescence probe is imperative. Thus, thiophene based Schiff N,N'-bis(thiophene-2-ylmethylene)thiophenemethane (BMTM) was synthesized and then characterized using several analytical techniques before converting it into organic nanoparticles (ONPs). Then, fluorescent organic inorganic nanohybrids (FONs) were obtained after decorating ONPs with AuNPs to yield BMTM-Au-ONPs (FONPs). The morphology of the particles, analyzed using a Transmission Electron Microscope (TEM), shows that AuNPs were embedded with low density organic matter (ONPs). FONPs were employed to recognize cysteine and cytosine simultaneously. No interference was observed from other moieties such as guanine, uracyl, NADH, NAD, ATP, and adenine during the detection. It means that the intensity of the fluorescence signal was significantly changed (enhanced for cytosine and quenched for cysteine). So, FONPs were used to detect cysteine and cytosine in real samples, like Saccharomyces cerevisiae cells. As expected, no considerable fluorescence signal for cysteine was observed, while for cytosine, strong fluorescence signals were detected in the cells. DFT was used to explain the interaction of FONPs with cysteine or cytosine.

Highly specific monitoring and imaging of endogenous and exogenous cysteine in living cells

Cys is one of the important biothiols and its abnormal concentration may pose a threat to human health. Therefore, the monitoring of Cys in organisms is of great significance. GSH and Hcy, as the other two biothiols, have similar chemical structures and active sites to Cys. Consequently, developing fluorescent probes to independently detect Cys has become a challenging problem. Keeping this in mind, α-β unsaturated ketone as a recognition group was integrated into the coumarin group skeleton to synthesize a fluorescent probe SC. After the nucleophilic addition reaction of Cys with SC, the conjugated system of SC was blocked and the fluorescent enhanced obviously. SC was able to detect Cys specifically under the same excitation with a low detection limit (11.1 nM). SC showed a rapid respond to Cys (120 s) and good fluorescent stability over a wide pH range. In addition, it achieved extracorporeal circulation in the presence of H₂O₂ or NEM. In the end, SC could be applied to detecting endogenous and exogenous Cys under biological condition due to its slight cytotoxicity and good biocompatibility. This provided a powerful tool for studying the physiological function of Cys exclusively.

Electroanalytical Determination of Cysteine Using the Electrodes Based on Ternary Silver-Copper Sulfides

The amperometric determination of cysteine, using an electrode based on ternary silver-copper sulfide, is presented. Electrochemical characterizations (using cyclic voltammetry) of three electrode materials revealed that the electrode based on the material that consists of jalpaite (Ag₃CuS₂), doped with a small amount of metallic silver, has the best electrocatalytical performance for cysteine oxidation. For the amperometric determination, 0.142 V at pH 5 and 0.04 V at pH 7 vs. Ag/AgCl, related to the electrocatalytical oxidation of thiol group, were chosen. Electrochemical impedance spectroscopy together with Fourier transform infrared spectroscopy (FTIR) revealed that oxidation takes place on the electrode surface with fouling effect, which does not affect a wide linear working range between 1 μM and 100 μM. Sensitivities, at pH 5 and pH 7, are calculated to be 0.11 μA μM-1 and 0.10 μA μM-1, respectively. The detection limits were determined to be 0.036 μM and 0.024 μM for pH 5 and pH 7, respectively. In the presence of uric acid, folic acid, ascorbic acid, and glucose no interference was noticed. This electrode showed remarkable stability and excellent reproducibility. The electrode was exploited for the determination of cysteine in a dietary supplement with the excellent recoveries.

A Hybrid Coumarin-Semifluorescein-Based Fluorescent Probe for the Detection of Cysteine

A new type of turn-on fluorescent probe CF-AC for the detection of Cys was firstly reported. The probe exhibited an excellent response to Cys with high selectively and sensitivity. In the presence of Cys, two fluorescence emission peaks at 525 nm and 650 nm appeared accompanied by the fluorescence color change from blue to red. Morever, the probe had good biocompatibility and could be successfully used for fluorescence imaging of Cys in MCF-7 cells.

A fast-response two-photon fluorescent probe for the detection of Cys over GSH/Hcy with a large turn-on signal and its application in living tissues

Cysteine (Cys), a small-molecule aminothiol, plays important roles in various physiological processes in connection with various diseases, such as skin lesions, edema, hair depigmentation and liver damage. We developed a novel two-photon fluorescent probe for sensing Cys in presence of GSH and Hcy in vivo. The two-photon fluorescent probe exhibited favorable properties, including fast response (about 20 min), good selectivity, and low cytotoxicity. Furthermore, it was successfully applied for imaging Cys in living cells and tissues.

A novel pyrene based fluorescent probe for selective detection of cysteine in presence of other bio-thiols in living cells

This manuscript reports the synthesis of pyrene-based fluorescent probe (PA-1) containing α,β-unsaturated carbonyl moiety and its application towards the selective and sensitive detection of cysteine (Cys) over other bio-thiols. The probe, 3-(2-hydroxyphenyl)-1-pyrenyl-2-propenone (PA-1) was synthesized through Claisen-Schmidt condensation between acetyl pyrene and salicylaldehyde. The formed product was characterized by (1)H NMR, (13)C NMR and GC-MS techniques. The probe exhibited absorption maximum at 374nm and emission maximum at 467nm (λex=342nm). The emission intensity of PA-1 was greatly enhanced while adding 2.5nM Cys. This can be attributed to the nucleophilic attack of Cys to the α,β-unsaturated ketone resulting in switching off, intramolecular charge transfer (ICT) from pyrene moiety to the phenolic nucleus. This was confirmed by DFT measurements. The PA-1 exhibited an excellent selectivity towards the determination of 40nM cys in the presence of 250,000-fold higher concentration of common interferents. The emission intensity was linearly increased and the limit of detection was found to be 10pM/L (S/N=3). Interestingly, the response of the PA-1 towards Cys is less than 1min. The confocal laser scanning micrographs of HeLa cells confirmed the cell permeability of the PA-1 and its ability to selectively detect Cys in living cells. In addition, the proposed probe was successfully applied for the determination of Cys in blood serum samples.

A sensitive and selective fluorescent thiol probe in water based on the conjugate 1,4-addition of thiols to alpha,beta-unsaturated ketones

Compound 1 was designed and synthesized as a new fluorescent thiol probe. Probe 1 was constructed on the basis of the conjugate 1,4-addition of thiols to alpha,beta-unsaturated ketones. Notably, probe 1 has suitable water solubility, which allows the sensing assay to be performed in water. Probe 1 is highly sensitive for thiols with a 211-fold fluorescence dynamic range and a low detection limit of 9.25x10(-7) M. The major features of probe 1 also include a high selectivity for thiols over other relevant biological species, excitation and emission in the visible region, rapid functioning at pH 7.4, and a good linear relationship between the fluorescence signal and the thiol concentration. Accordingly, these desirable characteristics may render probe 1 as potentially useful for biological applications.

Electrochemical investigations of the reaction mechanism and kinetics between NADH and redox-active (NC)2C6H3-NHOH/(NC)2C6H3-NO from 4-nitrophthalonitrile-(NC)2C6H3-NO2-modified electrode

A simple and sensitive method for the electrocatalytic detection of NADH on a carbon paste electrode modified with a redox-active (NC)(2)C(6)H(3)-NO/(NC)(2)C(6)H(3)-NHOH (NOPH/NHOHPH) electrogenerated in situ from 4-nitrophthalonitrile (4-NPHN) is presented. The electrode modified with 4-NPHN showed an efficient electrocatalytic activity towards the oxidation of NADH with activation overpotential of 0.12V vs. Ag/AgCl. The formation of an intermediate charge transfer complex is proposed for the charge transfer reaction between NADH and the 4-NPHN-resulting system. The second-order rate constant for electrocatalytic oxidation of NADH, kappa(obs), and the apparent Michaelis-Menten constant K(M), at pH 7.0 were evaluated with rotating disk electrode (RDE) experiments, giving 1.0 x 10(4)mol(-1)Ls(-1) and 2.7 x 10(-5)mol L(-1), respectively. Employing the Koutecky-Levich approach indicated that the NADH oxidation reaction involves two electrons. The sensor provided a linear response range for NADH from 0.8 up to 8.5 micromol L(-1) with sensitivity, detection, quantification limits and time response of 0.50 microA L micromol(-1), 0.25micromol L(-1), 0.82 micromol L(-1) and 0.1s, respectively. The repeatability of the measurements with the same sensor and different sensors, evaluated in terms of relative standard deviation, were 4.1 and 5.0%, respectively, for n=10.

Electrocatalytic activity of 4-nitrophthalonitrile-modified electrode for the l-glutathione detection

The present work describes the substantial electrocatalytic activity of (NC)2C6H3-NHOH/(NC)2C6H3-NO redox couple-modified electrode toward the low voltage detection of l-glutathione (GSH), in neutral medium, at an applied potential of 0.4V versus Ag/AgCl. After optimizing the operational conditions, the sensor provided a linear response range for GSH from 8.0 up to 83.0 micromol L(-1) with sensitivity, detection and quantification limits of 54nA L micromol(-1), 2.7 micromol L(-1) and 8.0 micromol L(-1), respectively. The proposed sensor presented higher sensitivity when compared to other modified electrodes described in the literature and showed a stable response for at least 100 successive determinations. The repeatability of the measurements with the same sensor and different sensors, evaluated in terms of relative standard deviation, were 4.1 and 5.0%, respectively, for n=10. The developed sensor was applied for GSH determination in yeast extract and the results were statistically the same with those obtained by the comparative method described in the literature at a confidence level of 95%.