Voltammetric sensing of sulfamethoxazole using a glassy carbon electrode modified with a graphitic carbon nitride and zinc oxide nanocomposite

A voltammetric sensor is described for the determination the antibiotic sulfamethoxazole (SMZ). It is based on the use of a glassy carbon electrode (GCE) modified with a nanocomposite prepared from graphitic carbon nitride and zinc oxide (g-C₃N₄/ZnO). The nanorod-like ZnO nanostructure were synthesized sonochemically. The g-C₃N₄/ZnO nanocomposite was then prepared by mixing g-C₃N₄ with ZnO, followed by ultrasonication. The morphology and structure of the nanocomposite were characterized by X-ray diffraction, Fourier-transform infrared spectroscopy and transmission electron microscopy. Under the optimal conditions, the response of the electrode, typically measured between 0.8 and 0.9 V (vs. Ag/AgCl), increases linearly in the 20 nM to 1.1 mM SMZ concentration range, and the lower detection limit is 6.6 nM. This is better than that of many previously reported sensors for SMZ. The modified electrode is highly selective, well reproducible and maintains its activity for at least 4 weeks. It was applied to the determination of SMZ in spiked human blood serum samples in with satisfactory results.

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Graphical abstract Schematic presentation of the voltammetric sensor for sulfamethoxazole. It consists of a glassy carbon electrode modified with a nanocomposite prepared from graphitic carbon nitride (g-C₃N₄/ZnO) that was supported with zinc oxide nanorods.

     

Selective voltammetric and flow-injection determination of guanine and adenine on a glassy carbon electrode modified by a ruthenium hexachloroplatinate film

An inorganic film of ruthenium hexachloroplatinate (RuPtCl₆), deposited on the surface of a glassy carbon electrode, exhibits electrocatalytic activity in the oxidation of purine bases, such as adenine and guanine. Appropriate working conditions are found for fabricating a polymer film on the surface of glassy carbon and for recording the maximum electrocatalytic effect for the modified electrode. A method is developed for the selective voltammetric determination of guanine and adenine in their simultaneous presence on an electrode modified by a RuPtCl₆ film. A procedure is proposed for the amperometric detection of purine bases with this modified electrode under the conditions of flow-injection analysis. The dependence of the analytical signal on the concentration of guanine and adenine is linear up to 5 × 10^?6 and 5 × 10^?7 M in the stationary mode and to 5 × 10^?7 and 5 × 10^?8 M under flow conditions, respectively. The proposed method was tested in the analysis of calf thymus DNA for the concentrations of guanine and adenine.     

Voltammetric determination of 2-chlorophenol using a glassy carbon electrode coated with multi-wall carbon nanotube-dicetyl phosphate film

Multi-wall carbon nanotubes (MWNT) were dispersed into water in the presence of dicetyl phosphate (DCP), and MWNT-DCP composite film coated glassy carbon electrodes (GCE) were constructed. The electrochemical properties of 2-chlorophenol at a bare GCE and MWNT-DCP modified GCE were compared. It was found that MWNT-DCP modified GCEs significantly enhance the oxidation peak current of 2-chlorophenol and lowers its oxidation overpotential, suggesting great potential in the sensitive determination of 2-chlorophenol. Finally, a sensitive and simple voltammetric method was developed for the determination of 2-chlorophenol. The oxidation peak current increases linearly with the concentration in the range of 1.0 × 10⁻⁷–2.0 × 10⁻⁵ mol L⁻¹, and the detection limit is 4.0 × 10⁻⁸ mol L⁻¹ for 2 min accumulation. The method was successfully used to determine 2-chlorophenol in waste water samples.     

Voltammetric determination of tinidazole using a glassy carbon electrode modified with single-wall carbon nanotubes.

An electrochemical method based on a single-wall carbon nanotubes (SWNTs) film-coated glassy carbon electrode (GCE) was described for the determination of tinidazole. In a 0.1 M Britton-Robinson buffer with a pH of 10.0, tinidazole yields a very sensitive and well-defined reduction peak at -0.78 V (vs. SCE) on a SWNTs-modified GCE. Compared with that on a bare GCE, the reduction peak of tinidazole increases significantly on the modified GCE. Thus, all of the experimental parameters were optimized and a sensitive voltammetric method is proposed for tinidazole determination. It is found that the reduction peak current is proportional to the concentration of tinidazole over the range from 5 x 10(-8) to 4 x 10(-5) M, and that the detection limit is 1 x 10(-8) M at 3 min open-circuit accumulation. This new analysis method was demonstrated with tinidazole drugs.     

Sensitive voltammetric determination of baicalein at DNA Langmuir-Blodgett film modified glassy carbon electrode

The present paper describes to modify a double stranded DNA-octadecylamine (ODA) Langmuir-Blodgett film on a glassy carbon electrode (GCE) surface to develop a voltammetric sensor for the detection of trace amounts of baicalein. The electrode was characterized by atomic force microscopy (AFM) and cyclic voltammetry (CV). Electrochemical behaviour of baicalein at the modified electrode had been investigated in pH 2.87 Britton-Robinson buffer solutions by CV and square wave voltammetry (SWV). Compared with bare GCE, the electrode presented an electrocatalytic redox for baicalein. Under the optimum conditions, the modified electrode showed a linear voltammetric response for the baicalein within a concentration range of 1.0 × 10⁻⁸-2.0 × 10⁻⁶ mol L⁻¹, and a value of 6.0 × 10⁻⁹ mol L⁻¹ was calculated for the detection limit. And the modified electrode exhibited an excellent immunity from epinephrine, dopamine, glucose and ascorbic acid interference. The method was also applied successfully to detect baicalein in the medicinal tablets and spiked human blood serum samples with satisfactory results.     

Langmuir-Blodgett film of p-tert-butylthiacalix[4]arene modified glassy carbon electrode as voltammetric sensor for the determination of Hg(II)

The π-A isotherms and UV-vis spectra of the transferred films suggested that the monolayer of p-tert-butylthiacalix[4]arene can coordinate with Hg²⁺ at the air-water surface. From these observations, a glassy carbon electrode coated with Langmuir-Blodgett film of p-tert-butylthiacalix[4] arene as a new voltammetric sensor is designed for the determination of trace amounts of Hg²⁺. Compared with bare glassy carbon electrode and modified glassy carbon electrode using direct coating method, the Langmuir-Blodgett film-modified electrode can greatly improve the measuring sensitivity of Hg²⁺. Under the selected conditions, the Langmuir-Blodgett film-modified electrode in 0.1 mol L⁻¹ H₂SO₄ + 0.01 mol L⁻¹ KCl solution shows a linear voltammetric response for Hg²⁺ in the range of 5.0 × 10⁻¹⁰ to 1.5 × 10⁻⁷ mol L⁻¹, with a detection limit of 2.0 × 10⁻¹⁰ mol L⁻¹. The proposed method was also applied to determine Hg²⁺ in water samples (tap, lake and river water). In addition, the fabricated electrode exhibited a distinct advantage of simple preparation, non-toxicity, good reproducibility and good stability.     

石墨烯修饰玻碳电极伏安法测定酪氨酸

制备了石墨烯修饰玻碳电极,研究了酪氨酸在修饰电极上的电化学行为.优化了包括支持电解质、溶液pH、修饰剂用量、富集电位及时间等测定条件.在0.1 mol·L-1pH 7.0的磷酸盐缓冲溶液中,峰电流与酪氨酸的浓度在3×10-6～1.2×10-4mol·L-1的范围内呈良好的线性关系,检出限为2 × 10-7 mol·L-...     

Voltammetric determination of mercury (II) in aqueous media using glassy carbon electrodes modified with novel calix[4]arene

A novel calix[4]arene derivative containing benzothiazole group was coated on glassy carbon electrode (GCE) and then applied to the recognition of mercury ion. Cyclic and square wave voltammetric results showed that the modified electrode selectively recognizes Hg²⁺ ion in aqueous media. A new anodic stripping peak at −0.3 V (vs. Ag/Ag⁺) can be obtained by scanning the potential from −0.6 to 0.6 V, and the peak currents are proportional to the Hg²⁺ concentration. The modified electrode in a 0.1 M H₂SO₄+0.01 M NaCl solution shows linear voltammetric response in the range of 25-300 μg l⁻¹ and detection limit of 5 μg l⁻¹ (ca. 2.5×10⁻⁸ M). This modified GCE does not present any significant interference from alkali, alkaline and transition metal ions except for Pb²⁺, Ag⁺ and Cu²⁺ ions. Only 500, 50 and 100-fold molar excess of Pb²⁺, Ag⁺ and Cu²⁺ ions, respectively, can lead to voltammetric response comparable with that of Hg²⁺. The proposed method was successfully applied to determine mercury in natural water.     

碳量子点/纳米金@碳纳米管修饰电极同时检测鸟嘌呤和腺嘌呤

制备了一种碳量子点(CQDs)/金纳米颗粒(AuNPs)@羟基化多壁碳纳米管(MWCNT-OHs)复合膜修饰电极用于鸟嘌呤(GA)和腺嘌呤(AE)的同时检测.与裸电极和其它修饰电极相比,复合膜修饰电极能显著提高GA和AE的氧化峰电流及峰电位差,能够对GA和AE同时高灵敏检测.研究了GA和AE在复合膜修饰电极上的电化学行为,结果表明,在0.2 mol/L PBS(pH 7.0)中,GA和AE的氧化峰电流与浓度分别在1～200 μmol/L和2～80μmol/L范围内呈良好的线性关系,检测限分别为0.9和1.8 μmol/L.将该修饰电极用于人体血清样品中GA和AE的同时电化学检测,加标回收率在90.4％～107.4％之间,证明了该修饰电极在生物样品分析领域的应用潜力.     

Voltammetric sensor for trichloroacetic acid using a glassy carbon electrode modified with Au@Ag nanorods and hemoglobin

Core-shell Au@Ag nanorods (Ag@GNRs) were synthesized and utilized to construct a voltammetric biosensor for trichloroacetic acid (TCA). The biosensor was prepared by immobilizing hemoglobin (Hb) on a glassy carbon electrode (GCE) that was modified with the Ag@GNRs. Cyclic voltammetry revealed a pair of symmetric redox peaks, indicating that direct electron transfer occurs at the Hb on the Ag@GNR-film. The electron transfer rate constant is as high as 2.32 s^?1. The good electrocatalytic capability and large surface area of the Ag@GNR-film is beneficial in terms of electron transfer between Hb and the underlying electrode. The modified GCE, best operated at ?0.4 V (vs. SCE), exhibits electrocatalytic activity toward TCA in the 0.16 μM to 1.7 μM concentration range, with a 0.12 μM detection limit (at an S/N ratio of 3).

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Graphical abstract Core-shell Au@Ag nanorods (Ag@GNRs) were synthesized and used to immobilize hemoglobin to construct an effective biosensor for trichloroacetic acid.

     

石墨烯修饰玻碳电极伏安法测定美洛昔康

通过在玻碳电极表面电化学还原氧化石墨烯的方法制备了石墨烯修饰电极,研究了美洛昔康在该修饰电极上的电化学行为。优化了包括支持电解质及pH、修饰剂用量、富集电位及时间等测定条件,据此建立了一种直接测定美洛昔康的电化学分析方法。在0.1 mol/L Britton-Robinson缓冲液(pH 3.0)中,氧化峰电流与美洛昔康浓度在1.0×10-6～8.0×10-5mol/L范围内呈现良好的线性关系,检出限为3.0×10-7mol/L(S/N=3)。方法可用于片剂和尿样中美洛昔康的测定。     

Simultaneous determination of guanine and adenine in DNA using an electrochemically pretreated glassy carbon electrode

A simple and reliable method based on adsorptive stripping at an electrochemically pretreated glassy carbon electrode (GCE) was proposed for simultaneous or individual determination of guanine and adenine in DNA. The detection sensitivity of guanine and adenine was improved greatly by activating the GCE electrochemically. After accumulation on pretreated GCE at open circuit for 5 min or at the potential of +0.3 V for 120 s, guanine and adenine produced well-defined oxidation peaks at about +0.8 and +1.1 V, respectively in pH 5 phosphate buffer. The detection limit for individual measurement of guanine and adenine was 4.5 ng ml⁻¹ (3×10⁻⁸ mol l⁻¹) and 4 ng ml⁻¹ (3×10⁻⁸ mol l⁻¹), respectively. Acid-denatured DNA showed two oxidation peaks corresponding to guanine and adenine residues in the same buffer. The proposed method can be used to estimate the guanine and adenine contents in DNA with good selectivity in a linear range of 0.25-5 μg ml⁻¹.     

Voltammetric determination of sinomenine in biological fluid using a glassy carbon electrode modified by a composite film of polycysteic acid and carbon nanotubes

Polycysteic acid based electrochemical oxidation of L-cysteine (CySH) and carbon nanotubes (CNTs) formed a composite thin film material at a glassy carbon electrode (GCE) that was used a novel modifier for electroanalytical determination of sinomenine which is used for rheumatoid arthritis treatment. The determination of sinomenine at the composite modified electrode was studied by differential pulse voltammetry (DPV). The peak current obtained at + 0.632 V (vs SCE) from DPV was linearly dependent on the sinomenine concentration in the range of 1.0 x 10(-7) to 6.0 x 10(-5) M in a B-R buffer solution (0.04 M, pH 1.81) with a correlation coefficient of 0.998. The detection limit (S/N = 3) was 5.0 x 10(-8) M. The electrochemical reaction mechanism of sinomenine was also discussed. This new method was then applied to the high-throughput determination of sinomenine in human serum samples with satisfactory results. This polycysteic acid/CNTs composite film may be considered to be a promising, low-cost, durable, and biocompatible material for the modification of sensors in applications to pharmaceutical and biomedical analysis.     

Simultaneous sensing of L-tyrosine and epinephrine using a glassy carbon electrode modified with nafion and CeO2 nanoparticles

An electrochemical sensor was developed and tested for detection of L-tyrosine in the presence of epinephrine by surface modification of a glassy carbon electrode (GCE) with Nafion and cerium dioxide nanoparticles. Fabrication parameters of a surfactant-assisted precipitation method were optimized to produce 2–3 nm CeO₂ nanoparticles with very high surface-to-volume ratio. The resulting nanocrystals were characterized structurally and morphologically by X-ray diffractometery (XRD), scanning and high resolution transmission electron microscopy (SEM and HR-TEM). The nanopowder is sonochemically dispersed in a Nafion solution which is then used to modify the surface of a GCE electrode. The electrochemical activity of L-tyrosine and epinephrine was investigated using both a Nafion-CeO₂ coated and a bare GCE. The modified electrode exhibits a significant electrochemical oxidation effect of L-tyrosine in a 0.2 M Britton-Robinson (B-R) buffer solution of pH 2. The electro-oxidation peak current increases linearly with the L-tyrosine concentration in the molar concentration range of 2 to 160 μM. By employing differential pulse voltammetry (DPV) for simultaneous measurements, we detected two reproducible peaks for L-tyrosine and epinephrine in the same solution with a peak separation of about 443 mV. The detection limit of the sensor (signal to noise ratio of 3) for L-tyrosine is ~90 nM and the sensitivity is 0.20 μA μM^?1, while for epinephrine these values are ~60 nM and 0.19 μA μM^?1. The sensor exhibited excellent selectivity, sensitivity, reproducibility and stability as well as a very good recovery time in real human blood serum samples.

Simultaneous electrochemical determination of L-tyrosine and epinephrine in blood plasma with Nafion-CeO₂/GCE modified electrode showing a 443 mV peak-to-peak potential difference between species oxidation peak currents.     

Simultaneous sensing of L-tyrosine and epinephrine using a glassy carbon electrode modified with nafion and CeO2 nanoparticles

An electrochemical sensor was developed and tested for detection of L-tyrosine in the presence of epinephrine by surface modification of a glassy carbon electrode (GCE) with Nafion and cerium dioxide nanoparticles. Fabrication parameters of a surfactant-assisted precipitation method were optimized to produce 2–3 nm CeO₂ nanoparticles with very high surface-to-volume ratio. The resulting nanocrystals were characterized structurally and morphologically by X-ray diffractometery (XRD), scanning and high resolution transmission electron microscopy (SEM and HR-TEM). The nanopowder is sonochemically dispersed in a Nafion solution which is then used to modify the surface of a GCE electrode. The electrochemical activity of L-tyrosine and epinephrine was investigated using both a Nafion-CeO₂ coated and a bare GCE. The modified electrode exhibits a significant electrochemical oxidation effect of L-tyrosine in a 0.2 M Britton-Robinson (B-R) buffer solution of pH 2. The electro-oxidation peak current increases linearly with the L-tyrosine concentration in the molar concentration range of 2 to 160 μM. By employing differential pulse voltammetry (DPV) for simultaneous measurements, we detected two reproducible peaks for L-tyrosine and epinephrine in the same solution with a peak separation of about 443 mV. The detection limit of the sensor (signal to noise ratio of 3) for L-tyrosine is ~90 nM and the sensitivity is 0.20 μA μM⁻¹, while for epinephrine these values are ~60 nM and 0.19 μA μM⁻¹. The sensor exhibited excellent selectivity, sensitivity, reproducibility and stability as well as a very good recovery time in real human blood serum samples.

Simultaneous electrochemical determination of L-tyrosine and epinephrine in blood plasma with Nafion-CeO₂/GCE modified electrode showing a 443 mV peak-to-peak potential difference between species oxidation peak currents.

     

A glassy carbon electrode modified with graphene quantum dots and silver nanoparticles for simultaneous determination of guanine and adenine

Microchimica Acta - A glassy carbon electrode (GCE) was modified with graphene quantum dots (GQDs) carrying silver nanoparticles. The modified GCE displays excellent performance in the...     

A glassy carbon electrode modified with poly(eriochrome black T) for sensitive determination of adenine and guanine

A thin film of poly(eriochrome black T) was deposited on the surface of glassy carbon electrode by cyclic voltammetry, and this system is shown to enable the sensitive determination of adenine (A) and guanine (G). Scanning electron microscopy, Fourier transform infrared spectroscopy and electrochemical impedance spectroscopy were carried out to characterize the film which exhibits excellent electrocatalytic activity toward the oxidation of A and G in 0.1 M phosphate buffer solution (pH 4.0). Square wave voltammetry reveals an oxidation peak at 1084 mV whose current is linearly related to the concentration of A in the range from 0.05 to 1.00 μM. The oxidation peak for G occurs at 788 mV, and its current is linearly related to the concentration of G in the range from 0.025 to 1.00 μM. The detection limits are 0.017 μM for A and 0.008 μM for G (at S/N?=?3), respectively. The modified electrode displays good reproducibility and selectivity for the determination of A and G. The sensor was applied to quantify A and G in fish sperm DNA with satisfactory results.