Electrochemical Detection of Epinephrine Based on a Screen-printed Electrode Modified with NiO−ERGO Nanocomposite Film

This study presents a new electrochemical sensor (NiO−ERGO/SPE) for sensitive and selective detection of epinephrine (EPI) on the screen-printed electrode (SPE) which is modified with a nanocomposite film consisting of electrochemically reduced graphene oxide and NiO nanoparticles. After surface functionalization, structural and electrochemical characterization of NiO−ERGO film, DPV signals of NiO−ERGO/SPE towards the oxidation of EPI exhibited a linear correlation in the concentration range of 0.025 μM to 175 μM with a detection limit of 0.015 μM, which reveals NiO−ERGO film is manifested a good electrocatalytic activity for EPI detection compared with the previous reports. The selectivity of NiO−ERGO film was also tested on a very wide scale of possible interferents (ascorbic acid, uric acid, dopamine, lactic acid, phenylalanine, tyrosine, tryptophan, Li⁺, Na⁺, K⁺, Ca²⁺, and Zn²⁺). Moreover, to evaluate the applicability of the proposed sensor for real sample analysis, NiO−ERGO/SPE was successfully utilized for the determination of EPI in pharmaceutical samples.     

An Efficient Novel Electrochemical Sensor for Simultaneous Determination of Vitamin C and Aspirin Based on a PMR/Zn-Al LDH/GCE

A sensitive, low-cost, and simple electrochemical sensor based on Zn−Al layered double hydroxide (Zn−Al LDH) combined with a polymer film of methyl red (PMR) to modify a GCE has been created for the first time. Using cyclic voltammetry (CV), the electrochemical characteristics of the newly fabricated sensor were investigated. The characterised PMR/Zn−Al LDH/GCE shows high electro-catalytic activity towards the vitamin C (AA) and aspirin (ASA) oxidation. Schematic fabrication of PMR/Zn−Al LDH/GCE for the determination of AA or ASA was presented. The new sensor demonstrated superior analytical efficiency for the simultaneous identification of AA and ASA traces in well-spaced anodic peaks, even in the presence of certain intervening species. According to experimental results, the fabricated sensor represented two well-separated oxidation peaks for AA and ASA oxidation with potential difference of 799 mV (vs. Ag/AgCl). The linear dependences of the anodic peak currents of AA and ASA on their concentrations in the ranges of 0.10–53.17 μM are good. The detection limits of AA and ASA at the PMR/Zn−Al LDH/GCE were found to be 1.26 and 1.27 μM, respectively. Meanwhile, the quantification limits of AA and ASA were calculated as 4.21 and 4.25 μM, respectively. On other hand, the limit of detection (LODs) of AA and ASA oxidation were determined to be 0.47 and 0.21 μM, respectively, according to DPV method. The effect of scan rate (100 to 800 mV/s) on the anodic peak currents of AA and ASA was examined. A sensing model mechanism has been suggested and discussed in detail. Finally, the proposed sensor displayed a good reproducibility, stability and selectivity. The developed sensor was eventually used to successfully detect AA and ASA in urine samples.     

Self‐Assembled Redox System for Bioelectrocatalytic Assay of L‐Ascorbylphosphate and Alkaline Phosphatase Activity

Ferrocene‐terminated self‐assembled monolayer (Fc‐SAM) on gold was used as an electron‐transfer mediator in the electrochemical assay of L ‐ascorbic acid 2‐phosphate (AAP). The assay is based on the enzymatic action of alkaline phosphatase (ALP), which triggers the release of vitamin C (L ‐ascorbic acid, AA) from AAP. The latter is easily oxidized on the Fc‐SAM under the diffusion limiting conditions that favors quantitative measurement of the AA concentration on a rotating disk electrode. We demonstrate the utility of the electrochemically active Fc‐SAM to probe the mechanism and to determine the kinetic parameters of an enzymatic reaction. The electrochemical technique was compared to a conventional spectrophotometric method of ALP activity detection using p‐nitrophenylphosphate (p‐NPP) as a substrate. We demonstrate that our new technique is also suitable for the analytical determination of ALP activity. The detection limits for both AAP and ALP were found to be 13 μM and 2 pM, respectively.     

Ultrasonic‐electrodeposition of Flower‐like Graphene Nanosheets in Ionic Liquid and Its Sensing for Ascorbic Acid

Choline chloride–based ionic liquid Ethaline were employed as the supporting electrolyte, graphene (GE) nanosheet was prepared with ultrasonic wave assisted electrodeposition for the first time. Scanning electron microscope results indicated that flower‐like GE nanosheets were obtained at the electrode surface. Energy dispersive X–ray spectroscopy, Fourier transform infrared spectra and Raman spectra were used to characterize the composition of the flower‐like GE nanosheets. Electrochemical methods showed that the flower‐like GE nanosheets based sensor exhibited high electrocatalytic activity for ascorbic acid (AA) oxidation and can be potentially used for the sensitive amperometric sensing of AA. Amperometric experiments showed that the sensor displayed broad linearity from 0.25 μM to 2.0 mM with a relative low detection limit of 0.1 μM (S/N = 3).     

Synthesis of Carbon Nanofibers for Mediatorless Sensitive Detection of NADH

Highly sensitive amperometric detection of dihydronicotinamide adenine dinucleotide (NADH) by using novel synthesized carbon nanofibers (CNFs) without addition of any mediator has been proposed. The CNFs were prepared by combination of electrospinning technique with thermal treatment method and were applied without any oxidation pretreatment to construct the electrochemical sensor. In amperometric detection of NADH, a linear range up to 11.45 μM with a low detection limit of 20 nM was obtained with the CNF‐modified carbon paste electrode (CNF‐CPE). Good selectivity was exhibited for the simultaneous detection of NADH and its common interferent of ascorbic acid (AA) by differential pulse voltammogram. The attractive electrochemical performance and the versatile preparation process of the CNF‐CPE made it a promising candidate for designing effective NADH sensor.     

Electrochemical reduced graphene oxide-poly(eriochrome black T)/gold nanoparticles modified glassy carbon electrode for simultaneous determination of ascorbic acid,dopamine and uric acid

This work reports on the preparation of electrochemically reduced graphene oxide (ERGO)-poly(eriochrome black T) (pEBT) assembled gold nanoparticles for the simultaneous determination of ascorbic acid (AA), dopamine (DA) and uric acid (UA) in PBS pH 6.0. Characterisations of the composite were carried out by scanning electron microscopy (SEM), Fourier transform infrared (FTIR), electrochemical impedance spectroscopy (EIS) and cyclic voltammetry. As a result of the synergistic effect, the modified glassy carbon electrode (GCE) possessed an efficient electrochemical catalytic activity with a high selectivity and sensitivity in oxidising AA-DA and DA-UA as compared to the bare GCE. The peak separations of AA and DA, DA and UA were 183 mV and 150 mV, respectively. The linear response ranges for AA, DA and UA were 10–900 μM, 0.5–20 μM and 2–70 μM with detection limits of 0.53 μM, 0.009 μM and 0.046 μM (S/N = 3), respectively. The sensitivity of ERGO-pEBT/AuNPs was measured as 0.003 µA/μM, 0.164 µA/μM and 0.034 µA/μM for AA, DA, and UA, respectively. The modified electrochemical sensor was used in the determination of AA, DA, and UA in vitamin C tablets and urine sample with good recovery.     

分子印迹聚合物修饰电化学晶体管检测抗坏血酸分子

以抗坏血酸(AA)为模板分子、邻苯二胺(o-PD)为功能单体,在金电极表面电聚合制备分子印迹聚合物膜(MIP),并以该MIP修饰的电极为栅极制备了具有高选择性、高灵敏度的AA电化学晶体管(OECT)传感器件。应用循环伏安法(CV)、交流阻抗法(EIS)对分子印迹聚合物电极进行一系列的表征与检测。实验结果表明:以pH=5.2,浓度为0.2mol/L HAc-NaAc(体积比2.1∶7.9)的缓冲液为背景溶液,o-PD与AA的物质的量之比为1∶2,以0.5V/s的扫描速率在0~0.8V内扫描20圈,所得分子印迹膜电极性能最佳。应用以该分子印迹修饰电极作为栅极的电化学晶体管检测AA,得到AA浓度的检测限为0.3μmol/L,沟道电流与AA浓度在0.3~3μmol/L(低浓度)与3~100μmol/L(高浓度)这2个范围内成线性关系。     

Cathodized Gold Nanoparticle‐Modified Graphite Pencil Electrode for Non‐Enzymatic Sensitive Voltammetric Detection of Glucose

A highly sensitive enzymeless electrochemical glucose sensor has been developed based on the simply prepared cathodized gold nanoparticle‐modified graphite pencil electrode (AuNP‐GPE). Cyclic voltammetry (CV) experiments show that AuNP‐GPE is able to oxidize glucose partially at low potential (around −0.27) whereas the bare GPE cannot oxidize glucose in the entire tested potential windows. Besides, fructose and sucrose cannot be oxidized at potential lower than +0.1 V at AuNP‐GPE. As a result, the glucose oxidation peak at around −0.27 V is suitable enough for selective detection of glucose in the presence of fructose and sucrose. Cathodization of AuNP‐GPE under optimum condition (‐1.0 V for 30 s) in the same glucose solution before voltammetric measurement enhanced glucose oxidation peak current around −0.27 V to achieve an efficient electrochemical sensor for glucose with a detection limit of 12 μM and dynamic range between 0.05 to 5.0 mM with a good linearity (R²= 0.999). Almost no interference effect was observed for sensing of glucose in the presence of ascorbic acid, alanine, phenylalanine, fructose, sucrose, and NaCl.     

Polyaniline Sheathed Black Phosphorous: A Novel,Advanced Platform for Electrochemical Sensing Applications

Despite its excellent properties, the inherent unstable nature of black phosphorus (BP) in ambient atmosphere has severely restricted its use in electrochemical sensing applications. In this work, polyaniline (PANI) sheathed BP was prepared via the electrochemical polymerisation of aniline on BP coated screen printed carbon electrode (i. e., SPCE/BP) which resulted in an efficient, stable electrochemical platform (i. e., SPCE/BP@PANI) with improved properties which was evaluated for electrochemical detection of two model bioanalytes namely, ascorbic acid (AA) and Hydrazine (Hy). The formation of PANI on the SPCE/BP exhibited a pair of stable and well‐defined redox peaks indicating the better adsorption energy and fast electron transfer nature of BP as compared to other 2D materials like graphene and transitional metal dichalcogenides. FESEM and XPS studies revealed the formation and uniform growth of PANI on BP surface without any aggregation. Electrochemical impedance spectroscopy analyses revealed that SPCE/BP@PANI can act as a suitable electrocatalyst material for the sensing of AA and Hy. Thus, SPCE/BP@PANI electrode exhibited low limit of detection (D_L; 1.69 μM), excellent reproducibility and better selectivity towards AA oxidation over glucose, sucrose, urea, citric acid, sodium, nitrate, nitrite and magnesium with a sensitivity of 3.38 A M^?1 cm^?2 (R²=0.98) in the dynamic range of 10–1100 μM. The excellent analytical performance of the BP@PANI is plausible due to better adsorption energy and fast electron transfer of BP. Further, SPCE/BP@PANI was also used for successful detection of AA in processed fruit juice with good recovery. Under the optimal DPV conditions, the modified electrode was extended for detection of Hy in a linear range of 100–1500 μM with sensitivity of 0.09 A M^?1 cm^?2 (R²=0.99) and D_L=89 μM validating the potential of BP based composites in wide range of electrochemical applications.     

CuO Nanostructures Based Electrochemical Sensor for Simultaneous Determination of Hydroquinone and Ascorbic Acid

A simple, sensitive and reliable electrochemical sensor has been developed based on CuO nanostructures modified glassy carbon electrode for simultaneous determination of hydroquinone (HQ) and ascorbic acid (AA). The CuO nano material was synthesized by aqueous chemical growth method using different sources of OH. The characterization of nano material was performed by Fourier transform infrared spectroscopy, X‐ray diffraction, field emission scanning electron microscopy and energy dispersive X‐ray spectroscopy. The glassy carbon electrode was modified by CuO nano material using drop cast method and studied by cyclic voltammetry. The CuO/GCE exhibited excellent electrocatalytic activity towards the oxidations of HQ and AA in borate buffer solution (pH 8.0) and the corresponding electrochemical signals have appeared as two well resolved oxidation peaks with significant peak potential differences of (0.21V vs. Ag/AgCl). Differential pulse voltammetry was used for simultaneous determination of HQ and AA using the CuO/GCE. At the optimum conditions, for simultaneous determination by synchronous change of the analyte concentrations, the linear response ranges were between 0.0003–0.355 mM for HQ and 0.0001–0.30 mM for AA respectively. Furthermore, CuO/GCE was successfully applied for the independent determination of AA in fruit juices as well as for the simultaneous determination of HQ and AA in cosmetic samples.     

RNA Modified Electrodes for Simultaneous Determination of Dopamine and Uric Acid in the Presence of High Amounts of Ascorbic Acid

A promising electrochemical biosensor was fabricated by electrochemical grafting of ribonucleic acid (RNA) at 1.8 V (vs. SCE) on glassy carbon electrode (GCE) (denoted as RNA/GCE), for simultaneous detection of dopamine (DA) and uric acid (UA) with coexistence of excess amount of ascorbic acid (AA). The electrode was characterized by X‐ray photoelectron spectroscopy (XPS), cyclic voltammetry (CV) and differential pulse voltammetry (DPV) techniques. The RNA modified layer on GCE exhibited superior catalytic ability and anionic exclusive ability in comparison with the DNA modified electrode. Three separated anodic DPV peaks were obtained at 0.312, 0.168 and ?0.016 V for UA, DA and AA, respectively, at the RNA/GCE in pH 7.0 PBS. In the presence of 2.0 mM AA, a linear range of 0.37 to 36 μM with a detection limit of 0.2 μM for DA, and in the range of 0.74 to 73 μM with a detection limit of 0.36 μM for UA were obtained. The co‐existence of 5000 fold AA did not interfere with the detection of DA or UA. The modified electrode shows excellent selectivity, good sensitivity and good stability.     

Nanohybrid Comprising Gold Nanoparticles – MoS2 Nanosheets for Electrochemical Sensing of Folic Acid in Serum Samples

Folic acid (FA) deficiency is associated with several clinical conditions such as megaloblastic anemia, neuropsychiatric, and pregnancy-related syndromes, this makes FA an important metabolite to be monitored. We have fabricated an electrochemical biosensor based on gold nanoparticles decorated molybdenum disulfide nanosheets (AuNPs−MoS₂NSs) nanocomposite as a transducer matrix for specific and rapid electrochemical detection of FA. Differential pulse voltammetry (DPV) studies displayed a rapid analytical response of the fabricated AuNPs−MoS₂NSs/GCE sensor probe towards FA in a wide concentration range of 0.001–100 μM with a very low detection limit of 0.72±0.03 nM. The selectivity of the fabricated sensor probe has been examined in the presence of interferents such as dopamine, uric acid, ascorbic acid, glucose, and urea. The clinical potential of the fabricated biosensor was established by monitoring FA in human serum samples. The developed AuNPs−MoS₂NSs/GCE sensor probe showed high reproducibility and stability, indicating its promise for FA detection in clinical settings.     

Covalently Anchored p‐Aminobenzene Sulfonate Multilayer on a Graphite Pencil Lead Electrode: A Highly Selective Electrochemical Sensor for Dopamine

An electrochemical sensor for dopamine (DA) has been developed based on the electrografting of 4‐aminobenzene sulfonic acid (4‐ABSA) onto the graphite pencil lead electrode (GPLE). The process of covalent anchoring and presence of 4‐ABSA on the GPLE was studied using cyclic voltammetry and electrochemical impedance spectroscopy. Electrochemical behaviour of the sensor towards DA, ascorbic acid (AA), and uric acid (UA) was studied in detail in phosphate buffer of pH 7. After optimizing the various parameters that influence the differential pulse voltammetric (DPV) signal for DA, the sensor exhibited a linear response over the 0.5 – 10 μmol⋅L^‐1concentration range with a limit of detection, 0.095 μmol⋅L^‐1 (at an S/N of 3). The sensor can selectively quantify DA even in the presence of 1 mmol⋅L^‐1 AA. Distinct DPV signals were obtained for DA (at 0.191 mV vs. Ag/AgCl) and for UA (at 0.343 mV vs. Ag/AgCl). The sensor is highly selective, sensitive and stable. It was applied to the quantification of DA in injections and urine. Recovery studies were done by spiking both the real samples with a known quantity of DA.     

An enhanced Nonenzymatic Electrochemical Glucose Sensor Based on Copper‐Palladium Nanoparticles Modified Glassy Carbon Electrodes

Novel copper‐palladium nanoparticles modified glassy carbon electrodes (Cu−Pd/GC) with enhanced nonenzymatic sensing for glucose were facilely prepared by one‐step electrodeposition. The structure and composition of the prepared nanoparticles were characterized by XRD, SEM, TEM and EDS, respectively. The electrode modified process was characterized by electrochemical impedance spectroscopy. Cyclic voltammetry and chronoamperometric experiments were used to evaluate the electrocatalytic activities of the electrodes toward glucose. The surface morphology and the electrocatalytic activities of Cu−Pd/GC was compared to Pd and Cu nanoparticles modified glassy carbon electrodes (Pd/GC and Cu/GC), respectively. Thanks to homogeneous distribution of Cu−Pd nanoparticles and the synergistic effect of Cu and Pd atoms, Cu−Pd/GC exhibited the highest sensitivity (298 μA mM⁻¹ cm⁻²) and the widest linear amperometric response (0.01 mM to 9.6 mM, R²=0.996) toward glucose compared to Pd/GC and Cu/GC. The detection limit of Cu−Pd/GC was 0.32 μM (S/N=3). In addition, the as‐prepared Cu−Pd/GC glucose sensor also exhibited exceptional capabilities of anti‐interference, reproducibility and long‐term stability. The as‐prepared sensor was also evaluated for determination of glucose concentration in human blood serum samples, which exhibited high reliability and accuracy, having great potential in clinical application.     

Gold-dendrimer Nanocomposite Based Electrochemical Sensor for Dopamine

An electrochemical sensor for dopamine was developed by electrodepositing poly(propylene imine) (PPI) dendrimer and gold nanoparticles (AuNPs) onto a glassy carbon electrode (GCE). Electrochemical characterisation of the sensor was carried out by cyclic voltammetry and electrochemical impedance spectroscopy in ferri/ferrocyanide electrolyte. The nanocomposite electrode (GCE-PPI-AuNPs) showed improved electroactive surface area and electrochemical response over bare GCE. The sensor recorded a detection limit of 0.16 μM over a concentration range of 0.1 μM to 125 μM. The sensor was applied for dopamine detection in human serum samples and in the presence of interfering substances such as ascorbic acid and epinephrine.     

Graphene-Multiwall Carbon Nanotube-Gold Nanocluster Composites Modified Electrode for the Simultaneous Determination of Ascorbic Acid,Dopamine, and Uric Acid

In this paper, graphene-multiwall carbon nanotube-gold nanocluster (GP-MWCNT-AuNC) composites were synthesized and used as modifier to fabricate a sensor for simultaneous detection of ascorbic acid (AA), dopamine (DA), and uric acid (UA). The electrochemical behavior of the sensor was investigated by electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV) and differential pulse voltammetry (DPV) techniques. The combination of GP, MWCNTs, and AuNCs endowed the electrode with a large surface area, good catalytic activity, and high selectivity and sensitivity. The linear response range for simultaneous detection of AA, DA, and UA at the sensor were 120–1,701, 2–213, and 0.7–88.3 μM, correspondingly, and the detection limits were 40, 0.67, and 0.23 μM (S/N?=?3), respectively. The proposed method offers a promise for simple, rapid, selective, and cost-effective analysis of small biomolecules.     

Imidazolium Based Surface Active Ionic Liquids as Novel Micellar Media for Simultaneous and Sensitive Electrochemical Detection of Dopamine and Ascorbic Acid

Surface active ionic liquid (SAIL) micelle assisted, simultaneous and highly sensitive electrochemical sensing of dopamine (DA) and ascorbic acid (AA) is presented. Results presented herein establish that SAILs viz.1‐dodecyl‐3‐methyl imidazolium chloride ([DDMIM][Cl]), 1‐octyl‐3‐methyl imidazolium chloride ([OMIM][Cl]) and 1‐butyl‐3‐methyl imidazolium chloride ([BMIM][Cl]) exhibit a probe and SAIL nature/concentration specific impact on the redox behaviour of hydroquinone (H₂Q), dopamine (DA) and ascorbic acid (AA). To our observations, the electrochemical behaviour of DA and AA is affected oppositely by SAILs with the apparent effects being more appreciable in presence of [DDMIM][Cl]. In the presence of [DDMIM][Cl] micelles, the electro‐oxidation of AA was observed to occur at potentials about 350 mV less positive than required for electrooxidation of DA, an important advantage that minimises the interference of former in sensing of the later. The peak to peak potential separation of 350 mV observed in presence of [DDMIM][Cl] micelles is the largest to be reported so far. The DPV signal for DA and AA displayed a linear response in the concentration range of 6.6 to 99.9 μM and 6.6 to 131.5 μM respectively. Very low detection limits of 0.0161 μM for DA in presence of 39.8 μM AA and 0.0227 μM for AA in presence of 39.8 μM DA were estimated in micellar phase of [DDMIM][Cl].     

An electrochemical ascorbic acid sensor based on palladium nanoparticles supported on graphene oxide

In this study, an electrochemical ascorbic acid (AA) sensor was constructed based on a glassy carbon electrode modified with palladium nanoparticles supported on graphene oxide (PdNPs-GO). PdNPs with a mean diameter of 2.6 nm were homogeneously deposited on GO sheets by the redox reaction between PdCl₄²⁻ and GO. Cyclic voltammetry and amperometric methods were used to evaluate the electrocatalytic activity towards the oxidation of AA in neutral media. Compared to a bare GC or a Pd electrode, the anodic peak potential of AA (0.006 V) at PdNPs-GO modified electrode was shifted negatively, and the large anodic peak potential separation (0.172 V) of AA and dopamine (DA), which could contribute to the synergistic effect of GO and PdNPs, was investigated. A further amperometric experiment proved that the proposed sensor was capable of sensitive and selective sensing of AA even in the presence of DA and uric acid. The modified electrode exhibited a rapid response to AA within 5 s and the amperometric signal showed a good linear correlation to AA concentration in a broad range from 20 μM to 2.28 mM with a correlation coefficient of R = 0.9991. Moreover, the proposed sensor was applied to the determination of AA in vitamin C tablet samples. The satisfactory results obtained indicated that the proposed sensor was promising for the development of novel electrochemical sensing for AA determination.     

A novel voltammetric sensor for ascorbic acid based on molecularly imprinted poly(o-phenylenediamine-co-o-aminophenol)

A molecularly imprinted copolymer, poly(o-phenylenediamine-co-o-aminophenol) (PoPDoAP), was prepared as a new ascorbic acid (AA) sensor. The copolymer was synthesized by incorporation of AA as template molecules during the electrochemical copolymerization of o-phenylenediamine and o-aminophenol, and complementary sites were formed after the copolymer was electrochemically reduced in ammonium aqueous solution. The molecularly imprinted copolymer sensor exhibited a high sensitivity and selectivity toward AA. Differential pulse voltammograms (DPVs) showed a linear concentration range of AA from 0.1 to 10 mM, and the detection limit was calculated to be 36.4 μM. Compared to conventional polyaniline-based AA sensors, the analytical performance of the imprinted copolymer sensor was improved due to the broadened usable pH range of PoPDoAP (from pH 1.0 to pH 8.0). The sensor also exhibited a good reproducibility and stability. And it has been successfully applied in the determination of AA in real samples, including vitamin C tablet and orange juices, with satisfactory results.     

Sensitive and selective electrochemical detection of carbon monoxide in saline at a Pt-Ru/Nafion/MnO2-modified electrode

We fabricated a sensitive and selective electrochemical carbon monoxide (CO) sensor for physiological conditions based on the Pt-Ru system. At a bare Pt-Ru electrode, a linear amperometric response to CO concentration was obtained in the range of 0.9-9 μM. However, significant current response to model electroactive interferents for physiological conditions, uric acid (UA), ascorbic acid (AA) and hydrogen peroxide (HP), was also recorded at the Pt-Ru electrode. The response to UA and AA was highly suppressed by coating the Pt-Ru electrode surface with a Nafion layer, and the response to HP was almost completely eliminated by the additional coating with a MnO(2)/chitosan layer. Finally, at the Pt-Ru/Nafion/MnO(2) electrode, amperometric CO detection with a sensitivity of 173 nA cm(-2) μM(-1) was obtained in the concentration range of 0.9-9 μM with the UA, AA and HP signal being below 1.7% at the same concentration of CO.