Electrocatalysis at a conducting composite electrode doped with a ruthenium(II) metallodendrimer

Development of specific l-methionine sensors by FRET-based protein engineering

Amino acids are essential nutrients that are not only used as protein building blocks but are also involved in various biochemical processes and in the development of human diseases. Quantitative analysis of amino acids in complex biological samples is an important analytical process used for understanding amino acid biochemistry and diagnosis of human diseases. In this study, a protein sensor based on fluorescence resonance energy transfer (FRET) was designed for the quantitative analysis of l-Met, in which a fluorescent unnatural amino acid (CouA) and YFP were used as a FRET pair. A natural Met-binding protein (MetQ) was chosen as a sensor protein, and CouA and YFP were incorporated into the protein by genetic code expansion technology and genetic fusion. Among the four sites screened for CouA incorporation into MetQ, R189 was selected as the best site for l-Met sensing. The sensor protein (YFP-MetQ-R189CouA) showed a large FRET signal change (2.7-fold increase) upon l-Met binding. To improve amino acid specificity of the sensor protein, the ligand-binding site was engineered, and the mutant sensor (YFP-MetQ-R189CouA-H88F) with the H88F mutation was identified, which showed no FRET signal change with d-Met and l-Gln at 50 μM concentration and retained the maximum FRET signal change with l-Met. The optimized sensor protein was evaluated for biochemical applications. l-Met concentration in FBS and optical purity in a mixture of d- and l-Met were successfully determined. Because l-Met is biochemically important owing to its involvement in cancer cell growth and autophagy, the sensor protein would be useful for quantitative analysis of l-Met in a complex biological sample. In addition, the design strategy used in this study can be applied to other small molecule-binding proteins for the development of protein sensors for important biomolecules.

Highly sensitive sensor for picomolar detection of insulin at physiological pH, using GC electrode modified with guanine and electrodeposited nickel oxide nanoparticles

The electrochemical behavior of insulin at glassy carbon (GC) electrode modified with nickel oxide nanoparticles and guanine was investigated. Cyclic voltammetry technique has been used for electrodeposition of nickel oxide nanoparticles (NiOx) and immobilization of guanine on the surface GC electrode. In comparison to glassy carbon electrode modified with nickel oxide nanoparticles and bare GC electrode modified with adsorbed guanine, the guanine/nickel oxide nanoparticles/modified GC electrode exhibited excellent catalytic activity for the oxidation of insulin in physiological pH solutions at reduced overpotential. The modified electrode was applied for insulin detection using cyclic voltammetry or hydrodynamic amperometry techniques. It was found that the calibration curve was linear up to 4muM with a detection limit of 22pM and sensitivity of 100.9pA/pM under the optimized condition for hydrodynamic amperometry using a rotating disk modified electrode. In comparison to other electrochemical insulin sensors, this sensor shows many advantages such as simple preparation method without using any special electron transfer mediator or specific reagent, high sensitivity, excellent catalytic activity at physiological pH values, short response time, long-term stability and remarkable antifouling property toward insulin and its oxidation product. Additionally, it is promising for the monitoring of insulin in chromatographic effluents.

Picomolar Detection of Insulin at Renewable Nickel Powder-Doped Carbon Composite Electrode

A sol-gel technique was used for fabrication of a renewable carbon composite electrode (CCE) modified with nickel powder. This modified electrode shows excellent catalytic activity for the oxidation of insulin in alkaline solutions. The nickel powder was then oxidized to form a nickel oxide film electrode, which was used as an amperometric detector for hydrodynamic amperometry and flow injection analysis of insulin. It was found that the calibration curve was linear up to 30 microM with a detection limit of 40 pM under the optimized conditions for hydrodynamic amperometry using a rotating disk modified CCE. Flow injection amperometric determination of insulin at this modified electrode yielded a calibration curve with the following characteristics; linear dynamic range of 15-1000 pM, sensitivity of 8659.23 pA pM-1 cm-2, and detection limit of 2 pM. This electrode shows many advantages as an insulin sensor such as simple preparation method without using any specific electron-transfer mediator or specific reagent, high sensitivity, excellent catalytic activity, short response time, long-term stability, and remarkable antifouling property toward insulin and its oxidation product. Sensitivity, detection limit, and antifouling properties of this insulin sensor are better than all of the reports in the literature. Additionally, it is promising for monitoring insulin in chromatographic effluents.

Sol-gel based surface modification of electrodes for electro analysis

In chemical analysis and electrochemical catalysis modified electrodes have been used in a wide range. In addition to the several methods of electrode modification reported in literature, the sol-gel route offers a possibility of preparing ceramic like films under rather mild conditions. This enhances the possibility of incorporation of temperature sensitive particles such as enzymes, microorganisms, proteins and several other biomolecules into such composite layers, resulting in very inert and stable matrices useful for analytical applications. The present paper, in addition to providing an overview of the various analytical applications of sol-gel processes, presents the fabrication and evaluation, of a novel sol-gel based potentiometric sensor for pH measurement. The performance characteristics of the sol-gel based pH sensor is evaluated using buffers in the pH range 2-10 prepared using standard buffer compositions reported in literature. The results show a linear correlation between negative logarithm of hydrogen ion concentration and measured millivolt response.

Amperometric detection of insulin at renewable sol–gel derived carbon ceramic electrode modified with nickel powder and potassium octacyanomolybdate(IV)

A renewable three-dimensional chemically modified carbon ceramic electrode (CCE) containing nickel powder and K4[Mo(CN)8] was constructed by sol-gel technique. The electrochemical properties and stability of modified electrode was evaluated by cyclic voltammetry in pH range 4-10. The redox couple of [Mo(CN)8] (4-/3-) was shown both as a solute in electrolyte solution and as a component of a carbon based conducting composite electrode. The apparent electron transfer rate constant (ks) and transfer coefficient (alpha) were determined by cyclic voltammetry and they were about 17.1 and 0.57 s(-1), respectively. The catalytic activity of the modified CCE toward insulin oxidation was investigated at pH range of 3-8 by cyclic votammetry. The modified electrode showed excellent electrocatalytic activity toward insulin electroxidation at physiological pH value. The modified electrode was used for insulin detection chronoamperometrically at pH 7. Under optimized condition in amperometry method, the concentration calibration range, detection limit and sensitivity were 0.5-500 nM, 0.45 nM and 6140 nA/microM, respectively. Flow injection amperometric determination of insulin at pH 7.4, at this modified electrode yielded a calibration curve with the following characteristics, linear dynamic range 100-500 pM; sensitivity 8.1 nA/nM and detection limit 40 pM (based on S/N = 3). The inherent stability at wide pH range, high sensitivity, low detection limit, low cost and ease of preparation are of advantageous of this insulin sensor. This sensor indicates great promise for monitory insulin in chromatographic effluents.

Renewable-surface sol-gel derived carbon ceramic electrode fabricated by [Ru(bpy)(tpy)Cl]PF6 and its application as an amperometric sensor for sulfide and sulfur oxoanions

A highly sensitive and fast responding sensor for the determination of thiosulfate, sulfite, sulfide and dithionite is described. It consists of a chemically modified carbon ceramic composite electrode (CCE) containing [Ru(bpy)(tpy)Cl]PF6 complex that was constructed by the sol-gel technique. A reversible redox couple of Ru(II)/Ru(III) was observed as a solute in acetonitrile solution and as a component of carbon based conducting composite electrode. Electrochemical behavior and stability of modified CCE were investigated by cyclic voltametry, the apparent electron transfer rate constant (kappa(S)) and transfer coefficient (a) were determined by cyclic voltametry which were about 28 s(-1) and 0.43 respectively. Electrocatalytic oxidation of S(2-), SO3(2-), S2O4(2-) and S2O3(2-) were effective at the modified electrode at significantly reduced overpotentials and in the pH range 1-11. Optimum pH values for amperometric detection of thiosulfate, dithionite, sulfide and sulfite are 7, 9, 2 and 2. Under the optimized conditions the calibration curves are linear in the concentration ranges 1-500, 3-80, 2-90 and 1-100 microM for S2O3(2-), SO3(2-), S2- and S2O4(2-) determination. The detection limit (signal to noise is 3) and sensitivity are 0.5 and 12, 2.8 and 6, 1.6 and 8, and 0.65 microM and 80 nA microM(-1) for thiosulfate, sulfite, sulfide and dithionite detection. The modified carbon ceramic electrode doped with Ru-complex shows good reproducibility, a short response time (t < 2 s), remarkable long term stability (> 6 month) and especially good surface renewability by simple mechanical polishing (RSD for eight successive polishing is 2%). The advantages of this sulfur compound amperometric detector based on ruthenium doped CCE are high sensitivity, inherent stability at a broader pH range, excellent catalytic activity, less expense and simplicity of preparation in comparison with recently published papers. This sensor can be used as a chromatographic detector for analysis of sulfur derivatives.

Carbon electrodes modified with ruthenium metallodendrimer multilayers for the mediated oxidation of methionine and insulin at physiological pH

A pentaerythritol-based metallodendrimer with ruthenium(II) terpyridine units, Ru(II)Den, catalyzed the oxidation of L-methionine and insulin at pH 7.0. The Ru(II)Den was immobilized on a carbon surface through layer-by-layer electrostatic deposition; the negatively charged polymer, poly(styrene sulfonate), was its counterpart. These bilayers were assembled on a glassy carbon electrode that was first modified by deposition of a layer of the conjugate base of sulfanilic acid and then with quaternized poly(4-vinylpyridine). Reversible voltammetry for the Ru(II/III) redox couple was observed, the current for which increased linearly with layer number, n, of Ru(II)Den up to n = 12. Cyclic voltammetry was used to demonstrate the mediation of L-methionine oxidation by a Ru(II)Den-containing multilayer assembly. Flow injection amperometric determination of insulin at pH 7.0 at this modified electrode yielded a calibration curve with the following characteristics: linear dynamic range, 6 nM-0.4 microM; sensitivity, 225 nA microM(-1); detection limit (k = 3 criterion), 2 nM. Of particular importance was that the sensitivity was proportional to the number of Ru(II)Den layers.