Electrochemical Sensor for Sensitive Determination of Capsaicin Using Pd Decorated Reduced Graphene Oxide

In this work, the reduced graphene oxide functionalized with poly dimethyl diallyl ammonium chloride (PDDA) modified palladium nanoparticles (PDDA‐rGO/Pd) had been facile synthesized and used as the sensing layer for sensitive determination of capsaicin. The prepared composite was characterized by transmission electron microscopy, UV‐visible absorption spectroscopy. The image demonstrated that Pd nanoparticles were uniformly distributed on the graphene surface. The electrochemical properties of the prepared sensor were investigated by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The results showed that the nanocomposite exhibits attractive electrocatalytic activity towards the oxidation of capsaicin. This attributed to the synergistic action of the excellent properties of Pd nanoparticles and graphene nanosheets. Under optimized conditions, the electrochemical sensor possessed a dynamic linear range from 0.32 μM to 64 μM with a detection limit of 0.10 μM (S/N=3) for capsaicin detection. Moreover, the cost‐effective and simple fabrication procedure, good reproducibility and stability as well as acceptable accuracy for capsaicin determination in actual samples are also the main advantages of this method, which might have broad application in other amide alkaloid detection.     

Graphene Doped Molecularly Imprinted Electrochemical Sensor for Uric Acid

A highly sensitive uric acid molecularly imprinted electrochemical sensor was prepared by using graphene doped chitosan as the functional matrix and uric acid as the template molecule; a electrodeposition technique was used to form a controllable graphene–chitosan–uric acid composited film on glassy carbon electrode whose uric acid was removed via electrochemical induce elution. Under the optimized preparation and detection conditions, the detection sensitivity of uric acid at graphene doped molecularly imprinted sensor was improved significantly compared with the undoped molecularly imprinted sensor. The mechanisms of sensitivity enhancement were studied by a.c. electrochemical impedance, adsorption model, and chronocoulometry. The observations suggest the effect of sensitivity enhancement resulted from magnified surface area and good electronic conduction of graphene. Additionally, the developed sensor exhibited specific recognition to uric acid against the competitors which consisted of structure liked substances and coexisting interference in blood serum.     

Electrochemical Sensing Performances for Uric Acid Detection on Various Amine Adlayers Used in Immobilizing Reduced Graphene Oxide

We investigated an influence of amine adlayer on electrochemical sensing performances for uric acid detection on reduced graphene oxide (RGO)‐decorated indium‐tin oxide electrode surfaces. Various amine‐terminated molecules including aminoethyl aryldiazonium cation, 2,2′‐(ethylenedioxy)bis(ethylamine), 3‐aminopropyltriethoxysilane, polyethyleneimine were introduced as adlayers to electrostatically immobilize RGO on the electrode surfaces. The anodic oxidation current of uric acid was observed on the various surfaces with differential pulse voltammetry. The current was highly enhanced by electrocatalytic activity of RGO. The sensing performances including linearity, sensitivity, limit of detection, and correlation coefficient were measured and compared. The adlayer with 3‐aminopropyltriethoxysilane showed the best performances on the RGO‐modified surface.     

Treated Screen Printed Electrodes Based on Electrochemically Reduced Graphene Nanoribbons for the Sensitive Voltammetric Determination of Dopamine in the Presence of Uric Acid

In this research, the graphene oxide nanoribbons (GONRs) were substantially synthesized by the oxidative longitudinal unzipping of the multi‐walled carbon nanotubes (MWCNTs). Then, a direct electrochemical technique was employed for reducing GONRs adsorbed on the screen printed carbon electrode (SPCE). Electrochemical reduction effectively eliminated the oxygen‐containing groups in the GONRs and produced the electrochemically reduced graphene nanoribbons (ERGNRs). Field emission scanning electron microscopy (FE‐SEM), transmission electron microscopy (TEM), and X‐ray diffraction (XRD) were employed to characterize the materials. The modified SPCE with ERGNRs (ERGNRs/SPCE) displayed acceptable electrocatalytic characteristics towards the oxidation of dopamine (DA) and uric acid (UA) and applied to the simultaneous determination of these two analytes. ERGNRs/SPCE has a peak potential difference of 245 mV between DA and UA. The anodic peak currents of DA and UA were linear within the concentration ranges between 0.5 and 300.0 μM and 1.0 to 400.0 μM in phosphate buffer (pH=7.0) respectively. The detection limit of the technique for DA is 0.15 μM (S/N=3) and for UA is 0.3 μM (S/N=3). The proposed approach has been applied to the determination of DA and UA in real samples and generated acceptable outputs.     

二氧化锆/石墨烯复合材料对亚硝酸盐的电化学传感研究

制备了一种二氧化锆/还原氧化石墨烯(ZrO2NPs/rGO)复合材料修饰电极的亚硝酸盐电化学传感器,并成功用于亚硝酸盐的检测.采用循环伏安法和电流-时间曲线考察了修饰电极的电化学行为.实验结果表明,ZrO2NPs/rGO复合材料修饰电极对亚硝酸盐具有良好的电流响应.在最优实验条件下,电流-时间曲线中的电流响应信号与亚硝酸盐浓度在3.0×10Symbolm@@_7～1.0×10Symbolm@@_6 mol/L和1.0×10Symbolm@@_6～6.0×10Symbolm@@_6 mol/L的范围内呈良好的线性关系,检测限为1.0×10Symbolm@@_7 mol/L(S/N 3).该传感器灵敏性高、稳定性和重现性好.使用此传感器检测实际样品香肠中的亚硝酸盐的回收率为93.7％～110.4％,相对标准偏差为1.6％～2.1％.     

Graphene Nanocomposites Based Electrochemical Sensing Platform for Simultaneous Detection of Multi-drugs

Three reduced graphene oxide nanocomposites were employed to achieve the simultaneous electrochemical determination of multi-drugs including acetaminophen (ACTM), carbendazim (CB) and ciprofloxacin (CFX). All nanocomposite modified electrodes showed improved current responses for three drugs. Notably cauliflower-like platinum nanoparticles decorated reduced graphene oxide modified electrode (or Pt−RGO/GCE) exhibited the best performance in terms of electrochemical stability. Using Pt−RGO/GCE, the linear detect ranges of 30–120 μM, 25–115 μM and 10–25 μM, and detection limit values of 3.49, 2.96, and 1.53 μM were achieved for ACTM, CB and CFX respectively. The electrode was further used for the successful determination of above drugs in tap and river water using differential pulse voltammetry. From the obtained results, we believe that Pt-RGO/GCE is highly promising for the fabrication of robust electrochemical sensors for simultaneously determining ACTM, CB and CFX or similar types of drugs in the future.     

Cauliflower‐like Platinum Particles Decorated Reduced Graphene Oxide for Sensitive Determination of Acetaminophen

Over the past years, the development of electrochemical sensing platforms for the sensitive detection of drug molecules have received great interests. In this research study, we introduced cauliflower‐like platinum particles decorated reduced graphene oxide modified glassy carbon electrode (Pt?RGO/GCE) as an electrochemical sensing platform for highly sensitive determination of acetaminophen (ACTM). The sensor was prepared via a simple and environmentally friendly two‐step electrodeposition method at room temperature. The combination of conductive RGO nanosheets and unique structured Pt particles (average 232 nm in diameter) provided an efficient interface with large effective surface area which greatly facilitated the electron transfer of ACTM. The experimental conditions that might affect the drug detection were studied in detail and optimized for best performance. The Pt?RGO/GCE was able to detect ACTM up to the limit of 2.2 nM with a linear concentration range from 0.01 to 350 μM. With its high reproducibility, excellent stability and selectivity, the as‐fabricated sensor was successfully applied to the ACTM content measurement in commercial tablets.     

PSS功能化海绵状石墨烯电化学传感灵敏检测瑞香素的研究

通过绿色环保、简单易行的方法合成聚苯乙烯磺酸钠(PSS)功能化的海绵状石墨烯(3D-PSS-rGO),利用紫外-可见吸收光谱及扫描电镜对复合材料进行表征和分析,构筑了基于3D-PSS-rGO复合材料修饰玻碳电极检测瑞香素的电化学传感器。结果表明,3D-PSS-rGO/GCE对瑞香素有较强富集作用,对瑞香素表现出优异的电催化活性。在优化实验条件下,瑞香素浓度在0.08～10.0μmol/L和10.0～60.0μmol/L范围内与其氧化峰电流呈良好的线性关系,检出限(S/N=3)为0.04μmol/L。将该传感用于祖师麻粉中瑞香素含量的检测,回收率为90.0%～96.0%。该研究为中药材中瑞香素含量的测定提供了方法参考。     

Simultaneous Determination of Ascorbic Acid,Dopamine and Uric Acid,at a Graphene Paste Electrode Modified with Functionalized Graphene Sheets

The present study reports the simultaneous determination of ascorbic acid (AA), dopamine (DA) and uric acid (UA) in phosphate buffer solution (pH 7.0) using graphene paste electrode modified with functionalized graphene sheets (GPE‐MFGSs). The presence of FGS inhibited the adsorption of AA owing to the electrostatic repulsion, but was favorable for the affinity adsorption of DA and UA via the ion exchange and hydrogen bonding mechanisms, respectively. This led to the decrease in the oxidation potential of AA and the significantly enhanced oxidation peak currents of DA and UA at the GPE‐MFGSs. By cyclic voltammetry and differential pulse voltammetry, the oxidation potentials of AA, DA, and UA, at the GPE‐MFGSs in a ternary mixture were found to be well resolved so that their simultaneous determination could be achieved. Furthermore, the influence of some experimental variables such as graphene paste composition, working solution pH, scan rate and pulse amplitude was studied. In addition, by differential pulse voltammetry, the linear dependence of peak current on the concentration was obtained in the ranges of 0.05–9.0, 0.03–13, and 0.03–5.5 µM with the lowest detection limits of 0.02, 0.01, and 0.01 µM for AA, DAand UA, , respectively.     

Electrochemical Detection of Epinephrine Using an L-Glutamic Acid Functionalized Graphene Modified Electrode

The development and application of an L-glutamic acid functionalized graphene nanocomposite, modified glassy carbon electrode are reported for the determination of epinephrine. The properties of the nanocomposite were characterized by scanning electron microscopy, ultraviolet-visible absorption spectroscopy, infrared spectroscopy, cyclic voltammetry, and electrochemical impedance spectroscopy. The modified electrode had high sensitivity and strongly catalytic activity for the detection of epinephrine. A linear relationship between the epinephrine concentration and the current response was obtained in the range of 1 × 10^?7 M to 1 × 10^?3 M by differential pulse voltammetry with a limit of detection of 3 × 10^?8 M. The modified electrode was employed to determine epinephrine in urine with satisfactory results.     

Electrochemical Enhanced Detection of Uric Acid Based on Peroxidase-like Activity of Fe3O4@Au

Fe₃O₄@Au nanomaterials were prepared by the self-assembly method. An enzyme-free, ultrasensitive electrochemical detection of uric acid was achieved based on the peroxidase-like activity of Fe₃O₄@Au. The proposed procedure has exhibited excellent catalytic activities and achieved significant enhancements of the current responses to uric acid. The detection range was from 0.1 to 10 mmol/L, and the limit of detection was 0.087 μmol/L. Under the action of external magnetic field, the magnetic particles can be easily separated from the bottom liquid, which has the advantages of simple operation and high separation efficiency. Moreover, this detection method combining a simulated enzyme and electrochemical can enhance the effective output of the overall electrochemical signal without modifying the electrode, and excellent reproducibility can be achieved. Compared to colorimetric assay, the electrochemical one has higher sensitivity and selectivity, and was further applied in ultrasensitive detection of uric acid in food samples. In short, the proposed electrochemical assay has great potential in the fields of food quality control and biomedical analysis.     

Electrochemical Determination of Uric Acid,Dopamine and Tryptophan at Zinc Hexacyanoferrate Clay Modified Electrode

A Cameroonian smectite clay has been transformed into Zn²⁺ homoionic form and then used to prepare film modified glassy carbon electrodes and carbon paste electrodes. These electrodes containing Zn²⁺ were exploited to prepare a mixed valence zinc hexacyanoferrate (ZnHCF). Cyclic voltammetry has been employed to monitor the in situ growth of ZnHCF on clay modified electrodes. Although interesting electrocatalytic properties toward UA were observed with these modified electrodes, the modified carbon paste electrodes were the most suitable for dopamine, uric acid and tryptophan detection and exhibited for these analytes extended linear range, high sensitivities, selectivity and low limit.     

Fabrication of a Nanostructure Based Electrochemical Sensor for Voltammetric Determination of Epinephrine,Uric Acid and Folic Acid

A carbon paste electrode (CPE) was modified by incorporation of graphene nano sheets and a ferrocene derivative. The modified electrode showed an excellent electrocatalytic effect on the oxidation of epinephrine. In phosphate buffer solution (PBS) of pH 7.0, the oxidation current increased linearly with concentration of epinephrine in the range of 0.05–550.0 µM and a detection limit (3σ) 27.0 nM was obtained for epinephrine. Then the modified electrode was used to determine epinephrine in an excess of uric acid and folic acid by SWV.     

Manganese Oxide Nanoparticles/Reduced Graphene Oxide as Novel Electrochemical Platform for Immobilization of FAD and its Application as Highly Sensitive Persulfate Sensor

In this study, manganese oxide nanoparticles/reduced graphene oxide(MnOxNPs/rGO) was used as support for strong immobilization of flavin adenine dinucleotide(FAD). A thin film of rGO cast on the electrode surface, followed by performing electrodeposition of MnOxNPs at applied constant potential of +1.4 V vs. Ag/AgCl for 200 s. Finally, FAD was electrodeposited onto the rGO/MnOxNPs film by potential cycling between 1.0 to ?1.0 V in solution containing 1 mg ml^?1 FAD. Electrochemical properties and catalytic activity of GCE/rGO‐MnOxNPs/FAD toward persulfate (S₂O₈^2?) reduction was investigated. Under optimized condition, the concentration calibration range, detection limit, and sensitivity were 0.1 μM–2 mM, 90 nM and 125.8 nA/μM, respectively, using hydrodynamic amperometry technique.     

Electrochemical Sensing of Uric Acid Using Glassy Carbon Modified with Multiwall Carbon Nanotubes Dispersed in Polyethylenimine

This work reports the advantages of using glassy carbon electrodes modified with multiwall carbon nanotubes (MWCNT) dispersed in polyethylenimine (PEI). The presence of MWCNTs wrapped by PEI largely facilitated the strong adsorption of uric acid (UA) and allowed its highly sensitive and selective quantification even in the presence of high excess of ascorbic acid. The selected conditions for the electrochemical sensing were 5 s accumulation at ?0.300 V under stirring and quantification in a 0.050 M phosphate buffer solution pH 7.40 by differential pulse voltammetry adsorptive‐stripping after medium exchange. The platform allowed the successful application in the quantification of UA in urine.     

A Self‐assembled L‐Cysteine and Electrodeposited Gold Nanoparticles‐reduced Graphene Oxide Modified Electrode for Adsorptive Stripping Determination of Copper

Glassy carbon electrode (GCE) modified with L‐cysteine and gold nanoparticles‐reduced graphene oxide (AuNPs‐RGO) composite was fabricated as a novel electrochemical sensor for the determination of Cu²⁺. The AuNPs‐RGO composite was formed on GCE surface by electrodeposition. The L‐cysteine was decorated on AuNPs by self‐assembly. Physicochemical and electrochemical properties of L‐cysteine/AuNPs‐RGO/GCE were characterized by scanning electron microscopy, atomic force microscopy, energy dispersive spectroscopy, Raman spectroscopy, X‐ray diffraction, cyclic voltammetry and adsorptive stripping voltammetry. The results validated that the prepared electrode had many attractive features, such as large electroactive area, good electrical conductivity and high sensitivity. Experimental conditions, including electrodeposition cycle, self‐assembly time, electrolyte pH and preconcentration time were studied and optimized. Stripping signals obtained from L‐cysteine/AuNPs‐RGO/GCE exhibited good linear relationship with Cu²⁺ concentrations in the range from 2 to 60 μg L⁻¹, with a detection limit of 0.037 μg L⁻¹. Finally, the prepared electrode was applied for the determination of Cu²⁺ in soil samples, and the results were in agreement with those obtained by inductively coupled plasma mass spectrometry.     

Electrochemical Synthesis of β‐Cyclodextrin Functionalized Silver Nanoparticles and Reduced Graphene Oxide Composite for the Determination of Hydrazine

β‐cyclodextrin (β‐CD) functionalized silver nanoparticles (AgNPs) and reduced graphene oxide (RGO) via one step electrochemical potentiodyanamic method has been prepared. Scanning electron microscopy, Energy‐Dispersive X‐ray spectroscopy, electrochemical impedance spectroscopy and cyclic voltammetry were used to study the role of β‐CD on preparation of AgNPs and RGO. RGO/β‐CD/AgNPs modified GCE showed good electrochemical activity towards electro‐oxidation of hydrazine in terms of decreasing the over potential and increasing the peak current. The kinetic parameters such as electron transfer coefficient (α) and diffusion coefficient (Do) of the modified electrode towards hydrazine were determined to be 0.66 and 0.97×10^?6 cm² s^?1, respectively. The LOD of our sensor was many folds lower than that of recommended concentration of hydrazine in drinking water by United States Environmental Protection Agency and World Health Organization. The sensor exhibited a wide linear range from 0.08 to 1110 µM and a very low detection limit (LOD) of 1.4 nM. In addition, the sensor selectively determined hydrazine even in the presence of common interferents.     

Fabrication of Electrochemical Sensor Modified with Porous Graphene for Determination of Trace Calycosin

In this study, the porous graphene (PG) with excellent structure was successfully prepared by a simple pyrolysis process, and applied to construct electrochemical sensor (PG@GCE) for detection of calycosin (CYS). PG was characterized by Raman spectroscopy, Fourier transform infrared spectroscopy and scanning electron microscopy. Also, the electrochemical properties of the proposed sensors were characterized by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS), and the results indicated that sensors had relatively large specific surface area and higher electron transport rate. Based on all those characteristics, CYS, a traditional Chinese medicine (TCM) active ingredient, displayed a great response on the surface of PC@GCE. Under the optimized conditions, the sensors displayed a good linear relationship between the peak current and the CYS concentration in the range of 1.8 × 10^–7–4.4 × 10^–5 M with the detection limit of 5.8 × 10^–8 M (S/N = 3). This study provided a novel analytical method for detection of CYS, rapid identification of Radix Hedysari and Radix Astragali, and gave another way for the trace analysis of CYS in biological samples. Furthermore, it would also deepen the application of PG in the field of pharmaceutical analysis.     

An Electrochemical Biosensor with Uricase Immobilized on Functionalized Gold Coated Copper Wire Electrode for Urinary Uric Acid Assay

A new second generation uricase electrode for urinary uric acid determination has been developed by chemically binding both uricase and redox mediator to inexpensive copper wire through simple electrodeposition of gold on copper surface and subsequent functionalization of the gold with L‐methionine. During a 209‐day testing period, the overall electrode performance exhibits in average a low oxidation potential of 0.33 V, a response time of 5 s, a widest linear calibration concentration range (0–2.38 mM, r²>0.9952), a sensitivity of 50 μA mM^?1, and a detection limit of 2.4 μM. The measurement accuracy and precision for the determination of uric acid in human urine specimens were 85.6–95.5 % and 0.3–2.4 %, respectively. The developed uricase electrode is potential for clinical applications.     

Disposable Multiwalled Carbon Nanotube Printed Film Electrochemical Determination of Acetaminophen,Dopamine, and Uric Acid

A novel printed film consisting of multiwalled carbon nanotubes was fabricated on a polyethylene terephthalate substrate by means of a mass flexographic printing process. Potential applications of this film for electrochemical biosensing were examined through the oxidation of acetaminophen, dopamine, and uric acid in phosphate buffer (pH 7.0). The results demonstrate that the printed carbon nanotube film exhibits an enhanced electrochemical response toward these molecules. Dopamine and uric acid did not interfere with each other and, thus, their simultaneous determination may be performed. The results suggest the mass flexographic printing technique has potential application for the construction of low-cost, precise, and disposable multiwalled carbon nanotube films.