Hexadecylpyridinium chloride micelles for the simultaneous kinetic determination of cysteine and cystine by their induction of the iodine-azide reaction

Tellurium-based chemical sensors

The various tellurium-based chemical sensors are described. This article focuses on four types of Tellurium sensors such as CdTe quantum dots-based sensor, Te thin films-based sensor, Te nanostructures or nanoparticles-based sensor, and TeO2-based sensor.

Luminescence Enhancement based Sensing of L-Cysteine by Doped Quantum Dots

The interaction of a presynthesized orange emitting Mn²⁺ -doped ZnS quantum dots (QDs) with L-Cysteine (L-Cys) led to enhance emission intensity (at 596 nm) and quantum yield (QY). Importantly, the Mn²⁺ -doped ZnS QDs exhibited high sensitivity towards L-Cys, with a limit of detection of 0.4±0.02 μM (in the linear range of 3.3-13.3 μM) and high selectivity in presence of interfering amino acids and metal ions. The association constant of L-Cys was determined to be 0.36×10⁵  M^-1 . The amplified passivation of the surface of Mn²⁺ -doped ZnS QDs following the incorporation and binding of L-Cys is accounted for the enhancement in their luminescence features. Moreover, the luminescence enhancement-based detection will bring newer dimension towards sensing application.

Colorimetric detection of cysteine based on dispersion–aggregation mechanism of chitosan stabilized gold nanoparticles

A simple and selective colorimetric method for detection of cysteine using chitosan stabilized gold nanoparticles has been developed. L-cysteine is a sulfur containing amino acid. Cysteine binds with the gold nanoparticles through a sulfur group and induces aggregation of the nanoparticles, which leads to a visible colour change from pale red to blue. A good linearity was observed from 0.1 to 30 μmol/L (R = 0.9958) cysteine, and the limit of detection was found to be 0.1 μmol/L. The gold nanoparticles showed a high selectivity towards the detection of cysteine even in the presence of 10 000 fold higher concentration of common interferences such as glutathione, methionine, and homocysteine. A plausible mechanism for the selective detection of cysteine in presence of interferences based on a dispersion–aggregation mechanism has been proposed.

A highly sensitive and selective competition assay for the detection of cysteine using mercury-specific DNA, Hg and Sybr Green I

We here report a rapid, sensitive, selective and label-free fluorescence detection method for cysteine (Cys). The conformation of mercury-specific DNA (MSD) changes from a random coil form to a hairpin structure in the presence of Hg2+ due to the formation of a thymine-Hg2+ -thymine (T-Hg2+ -T) complex. Cys can selectively coordinate with Hg2+ and extract it from the thymine-Hg2+ -thymine complex. The hairpin structure dehybridizes and the fluorescence intensity of Sybr Green I (SG) decreases upon addition of Cys because SG efficiently discriminates mercury-specific DNA and mercury-specific DNA/Hg2+ complex. The detection can be finished within 5 min with high sensitivity and selectivity. In addition, we can obtain variable dynamic ranges for Cys by changing the concentration of MSD/Hg2+.

Determination of trace amounts of mercury(II) in water samples using a novel kinetic catalytic ligand substitution reaction of hexacyanoruthenate(II)

A simple, sensitive, selective and rapid kinetic catalytic method has been developed for the determination of Hg(II) ions at micro-level. This method is based on the catalytic effect of Hg(II) ion on the rate of substitution of cyanide in hexacyanoruthenate(II) with nitroso-R-salt (NRS) in aqueous medium and provides good accuracy and precision. The concentration of Hg(II) catalyst varied from 4.0 to 10.0x10(-6)M and the progress of reaction was followed spectrophotometrically at 525nm (lambda(max) of purple-red complex [Ru(CN)(5)NRS](3-), epsilon=3.1x10(3)M(-1)s(-1)) under the optimized reaction conditions; 8.75x10(-5)M [Ru(CN)(6)(4-)], 3.50x10(-4)M [nitroso-R-salt], pH 7.00+/-0.02, ionic strength, I=0.1M (KCl), temp 45.0+/-0.1 degrees C. The linear calibration curves, i.e. calibration equations between the absorbance at fixed times (t=15, 20 and 25min) versus concentration of Hg(II) ions were established under the optimized experimental conditions. The detection limit was found to be 1.0x10(-7)M of Hg(II). The effect of various foreign ions on the proposed method has also been studied and discussed. The method has been applied to the determination of mercury(II) in aqueous solutions.

Flow-injection determination of cysteine in pharmaceuticals based on luminol-persulphate chemiluminescence detection

A flow injection (FI) method is reported for the determination of l-cysteine, based on its enhancement on chemiluminescence (CL) emission of luminol oxidized by sodium persulphate in alkaline solution. The calibration graph was linear over the range 1.0 x 10(-9)-5.0 x 10(-7) mol/L (r(2) = 0.9992), with relative standard deviations (RSDs) in the range 1.1-2.3% (n = 4). The limit of detection (3 sigma blank) was 5.0 x 10(-10) mol/L with a sample throughput of 120/h. The method was applied to pharmaceuticals and the results obtained were in reasonable agreement with the amount labelled. The proposed method was also applied to cysteine in synthetic amino acid mixtures. Calibration graphs of N-acetylcysteine and glutathione over the range 1.0-50 x 10(-8) and 0.5-7.5 x 10(-7) mol/L were also established (r(2) = 0.998 and 0.9986) with RSDs in the range 1.0-2.0% (n = 4), and the limits of detection (3 sigma blank) were 5.0 x 10(-9) and 1.0 x 10(-8) mol/L, respectively.

Highly sensitive fluorimetic determination of gluthione based inhibitory effect on multienzyme redox system

A highly sensitive spectrofluorimetric method for the determination of reduced glutathione (GSH,gamma-L-glutamyl-L-cysteinylglycine) based on its inhibitory effect on hemoglobin activity was developed. Multienzyme redox system is the most important biological oxidation process in cellular respiration chain. Under the action of hemoglobin, NADH can be oxidized by hydrogen peroxide (H2O2) to form a dimmer that is optimally fluorescent. Under the optimum conditions, the degree of inhibitory effect was linear to the GSH concentration in the range of 5.00 x 10(-8) to 9.60 x 10(-6) mol l(-1). The relative standard deviation was 3.70% for 11 determinations of 5.00 x 10(-6) mol l(-1) GSH and the detection limit was 8.00 x 10(-9) mol l(-1). Further experimental results revealed that the inhibition of GSH on this system was of the competitive type.

Electrochemiluminescent determination of L-cysteine with a flow-injection analysis system

A flow-injection electrochemiluminescent method for L-cysteine determination has been developed based on its enhancement of the electrochemiluminecence of luminol at a glassy carbon electrode. This method is simple and sensitive for cysteine determination. Under the selected experimental parameters, the linear range for cysteine concentration was 1.0 x 10(-6) - 5.0 x 10(-5) mol/l, and the detection limit was 0.67 micromol/l (S/N = 3). The relative standard deviation for 11 measurements of 1.0 x 10(-5) mol/l cysteine was 4.5%. The proposed method has been applied to the detection of cysteine in pharmaceutical injections with satisfactory results.