Determination of Phosphate in Human Serum with Zirconium/Reduced Graphene Oxide Modified Electrode.

An electrochemical phosphate sensor based on zirconium and reduced graphene oxide modified pencil graphite electrode (Zr/rGO-PGE) is proposed. The XRD, CV and EIS confirmed that GO was partially reduced on the PGE. Scanning electron microscopy (SEM) exhibited the layered and wrinkled structures for the rGO-PGE and Zr/rGO-PGE, respectively. Cyclic voltammetry showed the immobilized rGO was highly stable and had high activity toward zirconium adsorption. The prepared electrode was used for the electrochemical determination of phosphate. Based on the optimum condition using differential pulse voltammetry, the limit of detection and sensitivity for phosphate was obtained as [0.011(± 0.004) µM] (S/N = 3) and [622.4(± 9.6) µA µM-1 cm-2], respectively. The sensor was successfully evaluated for phosphate determination in human serum samples. In practical terms, the construction of this sensor was exceptionally simple, fast, cost effective and reproducible.

Green synthesis of copper oxide nanoparticles decorated reduced graphene oxide for high sensitive detection of glucose.

A non-enzymatic glucose sensor based on pencil graphite electrode (PGE) modified by copper oxide nanoparticles decorated reduced graphene oxide (CuO(NP)/rGO-PGE) was prepared. XRD patterns showed partially electrochemically reduction of GO and monoclinic structure of CuO on the PGE. The prepared CuO(NP)/rGO exhibited a nanoporous structure by scanning electron microscopy (SEM). Transmittance electron microscopy (TEM) revealed copper oxide nanoparticles were well distributed on rGO and had semispherical shapes with diameter 3-5 nm. Cyclic voltammetry at CuO(NP)/rGO-PGE showed the immobilized CuO(NP)s were highly stable in alkaline solutions and had high electrocatalytic activity toward glucose oxidation. Using amperometry, the detection limit of [0.091 (±0.003) µM] and concentration sensitivity of [4760 (±3.2) µA mM-1 cm-2] for glucose was obtained at optimum conditions. The applicability of the sensor was evaluated to determine the glucose concentration in human blood serum samples and the experimental results were comparable with those measured by traditional spectrophotometric methods. The preparation of CuO(NP)/rGO-PGE was reproducible, very simple, fast and inexpensive for practical application.

Biomolecule-assisted synthesis of Ag/reduced graphene oxide nanocomposite with excellent electrocatalytic and antibacterial performance.

In this work, an environmentally friendly method was applied for the synthesis of aqueous suspension of l-cysteine modified Ag nanoparticles (NPs)-decorated reduced graphene oxide (rGO) nanocomposite. l-cysteine played a triple role as reducing agent, stabilizer and linker of Ag NPs onto the surface of rGO. The resultant nanocomposite was characterized by Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction studies (XRD), zeta potential, Raman spectroscopy, scanning electron microscopy (SEM) and energy dispersive analysis of X-ray (EDX). Meanwhile, minimum inhibitory concentration (MIC), minimum bacterial concentration (MBC), agar well diffusion and cyclic voltammetry (CV) techniques were used for the investigation of antibacterial and electrocatalytic behaviors of the nanocomposite, respectively. The obtained nanocomposite showed not only enhanced electrocatalytic activity for glucose but also excellent antibacterial activity against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus).

Nonenzymatic glucose sensor based on disposable pencil graphite electrode modified by copper nanoparticles.

A nonenzymatic glucose sensor based on a disposable pencil graphite electrode (PGE) modified by copper nanoparticles [Cu(NP)] was prepared for the first time. The prepared Cu(NP) exhibited an absorption peak centered at ∼562 nm using UV-visible spectrophotometry and an almost homogenous spherical shape by scanning electron microscopy. Cyclic voltammetry of Cu(NP)-PGE showed an adsorption controlled charge transfer process up to 90.0 mVs-1. The sensor was applied for the determination of glucose using an amperometry technique with a detection limit of [0.44 (±0.01) µM] and concentration sensitivity of [1467.5 (±1.3) µA/mMcm-2]. The preparation of the Cu(NP)-PGE sensor was reproducible (relative standard deviation = 2.10%, n = 10), very simple, fast, and inexpensive, and the Cu(NP)-PGE is suitable to be used as a disposable glucose sensor.

Electrochemical monitoring of the interaction of UO2(2+) with immobilized DNA.

Interaction of uranyl ion (UO2(2+)) with immobilized double strand calf thymus DNA (ds-ct-DNA) on zirconium attached gold-mercaptopropionic acid self-assembled monolayer (Au-MPA-Zr(IV) SAM) is monitored by electrochemical techniques. The results show that after 15 min proximity of the immobilized DNA with UO2(2+), the peak currents of the square wave voltammograms are decreased (about 80%), and the equivalent circuit model of electrochemical impedance spectroscopy (EIS) data, requires two constant phase elements (CPE) instead of only one. By using the surface concentration of DNA (≈2.3×10(-13) mol/cm(2)) and the number of the anthraquinonedisulfonic acid (AQDS) adsorbed on DNA (1.34×10(-10) mol/cm(2)) the ration of AQDS per DNA base pairs is obtained ≈1/30 before proximity to UO2(2+). Based on EIS technique, we find that the double strand structure of immobilized DNA on the electrode surface has been changed (damaged) by UO2(2+). This modified electrode has potential of becoming a screening tool for the rapid assessment of the interaction and genotoxicity of existing and new chemicals.

Electrochemical determination of calf thymus DNA on Zr(IV) immobilized on gold-mercaptopropionic-acid self-assembled monolayer.

An electrochemical biosensor, constructed by immobilization of Zr(IV) on the topside of gold-mercaptopropionic acid self-assembled monolayer (Au-MPA-Zr SAM), is developed for the sensitive quantification of calf thymus DNA (ct-DNA). The sensor is based on ionic adsorption of ct-DNA from its phosphate backbone onto the Au-MPA-Zr(IV) SAM electrode. Preparation, characterization, and application of the sensor for determination of ct-DNA are described by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and Osteryoung square wave voltammetry (OSWV) in the presence of an appropriate redox reaction probe. Parameters influencing the method have been tested. A linear range calibration curve from 1.0x10(-4) to 5.0x10(-7) g mL(-1) ct-DNA with a detection limit of 9.5x10(-8) g mL(-1) and mean of relative standard deviations (R.S.D) of 2.5% for n=4 at each point was observed in the best conditions by EIS. Regeneration of the surface was carried out successfully by 5 min sonication in 0.1 M KOH solution and then 1 min incubation in 1.0x10(-3) M Zr(IV) with a good reproducibility, R.S.D=1.5% for n=4 as detected by EIS. The long-term storage stability of the electrode was also studied.

Zirconium immobilized on gold-mercaptopropionic acid self-assembled monolayer for trace determination of phosphate in blood serum by using CV, EIS, and OSWV.

Preparation, characterization, and application of a new sensor for the determination of phosphate in blood serum is described by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and osteryoung square wave voltammetry (OSWV) in the presence of an appropriate redox reaction probe. The sensor was based on ionic adsorption of phosphate on Zr(IV) immobilized on gold-mercaptopropionic acid self-assembled monolayer (Au-MPA-Zr(IV) SAM) electrode. Parameters influencing the method were optimized. A linear range calibration curve from 1.0 x 10(-7) to 1.0 x 10(-6)M PO(4)(3-) with a detection limit of 5.30 x 10(-8)M and mean of relative standard deviations (R.S.D.) of 2.75% for n=4 was observed in the best conditions by OSWV. Possible interferences from the coexisting ions were also investigated. The results demonstrated that sensor could be used for the determination of phosphate in the presence of various ions. Regeneration of the surface was carried out successfully by 5-min sonication in 0.1M KOH solution and then 1-min incubation in 1.0x10(-3)M Zr(IV) with a good reproducibility, R.S.D.=1.47% for n=4 by OSWV. The validity of the method and applicability of the sensor were successfully tested by detection of phosphate in blood serum after deproteinization of sample without interference from sample matrix. The long-term storage stability of the electrode was studied. The experimental data is presented and discussed from which the new sensor is characterized.

Renewable sol-gel carbon ceramic electrodes modified with a Ru-complex for the amperometric detection of l-cysteine and glutathione.

A renewable three-dimensional chemically modified carbon ceramic electrode containing Ru [(tpy)(bpy)Cl] PF(6) was constructed by sol-gel technique. It exhibits an excellent electro-catalytic activity for oxidation of l-cysteine and glutathione at pH range 2-8. Cyclic voltammetry was employed to characterize the electrochemical behavior of the chemically modified electrode. The electrocatalytic behavior is further exploited as a sensitive detection scheme for l-cysteine and glutathione by hydrodynamic amperometry. Optimum pH value for detection is 2 for both l-cysteine and glutathione. The catalytic rate constants for l-cysteine and glutathione were determined, which were about 2.1x10(3) and 2.5x10(3) M(-1)s(-1), respectively. Under the optimized condition the calibration curves are linear in the concentration range 5-685 and 5-700 muM for l-cysteine and glutathione determination, respectively. The detection limit (S/N=3) and sensitivity is 1 muM, 5 nA/muM for l-cysteine and 1 muM, 7.8 nA/muM for glutathione. The relative standard deviation (RSD) for the amperogram's currents with five injections of l-cysteine or glutathione at concentration range of linear calibration is <1.5%. The advantages of this amperometric detector are: high sensitivity, good catalytic effect, short response time (t<3 s), remarkable long-term stability, simplicity of preparation and reproducibility of surface fouling (RSD for six successive polishing is 3.31%). This sensor can be used as a chromatographic detector for analysis of l-cysteine and glutathione.

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.