ToF-secondary ion mass-spectrometric study of copper deposition and stripping on directly heated screen-printed gold electrodes

We report about a new kind of directly heated gold electrode. All electrodes including a directly heated gold loop electrode, a Ag pseudo reference, and a carbon counter electrode have been screen-printed on a ceramic alumina substrate. Thermal behaviour was studied by potentiometry using either an external or the integrated reference electrode. Stripping voltammetric copper signals were greatly improved at elevated deposition temperature. Secondary ion mass spectrometric studies (ToF-SIMS) revealed that different negative ionic species of copper complexes can be found on the gold electrode surface as a result of ion bombardment during SIMS analysis like Cu^?, CuCl^? and CuCl₂ ^?. SIMS surface imaging using a fine focussed ion beam over the surface allowed us to obtain ion images (chemical maps) of the analyzed sample. SIMS depth profile analysis of the gold loop electrode was performed after copper deposition at room temperature (23 °C) and at 60 °C. CuCl₂ ^? ion was used for the depth profile studies as it has shown the highest intensity among other observed species. Surface spectroscopic analysis, surface imaging and depth profile analysis have shown that the amount of deposited copper species on the gold loop electrode was increased upon increasing electrode temperature during the deposition step. Therefore, the presence of chloride in the solution will hinder underpotential deposition of Cu(0) and lead to badly defined and resolved stripping peaks.     

Biosensor for atrazin based on aligned carbon nanotubes modified with glucose oxidase

A sensitive method was developed for the determination of the hebicide atrazine. It based on the use of glucose oxidase that is self-assembled on aligned carbon nanotubes on the surface of a copper electrode. The surface morphology and electrochemical properties of the electrode were characterized by field emission scanning electron microscopy and cyclic voltammetry. The effects of buffer solution and incubation time on the response of the electrode were investigated. Response to atrazine is linear in the range from 0.58 µM to 42 µM, and the detection limit is 39 nM. The performance of the biosensor was verified by determination of atrazine in environmental water samples.     

Multiwall Carbon Nanotube (MWCNT) Based Electrochemical Biosensors for Mediatorless Detection of Putrescine

γ‐Aminopropyltriethoxysilane (APTES)‐induced solubilization of multi‐wall carbon nanotube CNTs allowed for the modification of electrode surfaces. APTES also served as an immobilization matrix for putrescine oxidase (POx) to construct an amperometric biosensor. Although CNTs modified by APTES acted as semiconductors to reduce the exposed sensing surface, we reasoned that nanoscale “dendrites” of CNTS modified by APTES formed a network and projected outwards from the electrode surface and acted like bundled ultra‐microelectrodes that allowed access to the active site and facilitated direct electron transfer to the immobilized enzyme. Our biosensor was able to efficiently monitor direct electroactivity of POx at the electrode surface. The putrescine biosensor prepared using the modified glassy carbon electrode exhibited current response within 10 s with a detection limit of 500 nM.     

Study on the immobilization of anti-IgG on Au-colloid modified gold electrode via potentiometric immunosensor, cyclic voltammetry, and electrochemical impedance techniques

The immobilization of anti-IgG on Au-colloid modified gold electrodes has been investigated. A cleaned gold electrode was first immersed in a mercaptoethylamine (AET) solution, and then gold nanoparticles were chemisorbed onto the thiol groups of the mercaptoethylamine. Finally, anti-IgG was adsorbed onto the surface of the gold nanoparticles. Potentiometric immunosensor, cyclic voltammetry, and electrochemical impedance techniques were used to investigate the immobilization of anti-IgG on Au colloids. In the impedance spectroscopic study, an obvious difference of the electron transfer resistance between the Au-colloid modified electrode and the bare gold electrode was observed. The cyclic voltammogram tends to be more irreversible with increased anti-IgG concentration. Using the potentiometric immunosensor, the proposed technique is based on that the specific agglutination of antibody-coated gold nanoparticles, averaging 16 nm in diameter, in the presence of the corresponding antigen causes a potential change that is monitored by a potentiometry. It is found that the developed immunoagglutination assay system is sensitive to the concentration of IgG antigen as low as 12 ng mL(-1). Experimental results showed that the developed technique is in satisfactory agreement with the ELISA method, and that gold nanoparticles can be used as a biocompatible matrix for antibody or antigen immobilization.     

Highly porous magnetite/graphene nanocomposites for a solid-state electrochemiluminescence sensor on paper-based chips

Graphene-nanosheet-based highly porous magnetite nanocomposites (GN-HPMNs) have been prepared using a simple solvothermal method and used as an immobilization matrix for the fabrication of a solid-state electrochemiluminescence (ECL) sensor on paper-based chips. Highly porous Fe₃O₄ nanocrystal clusters were coated with acrylate and wrapped tightly on the skeleton of graphene nanosheets. The structures and sizes of the GN-HPMNs could be tuned by varying the proportions of the solvents ethylene glycol and diethylene glycol. Then, the relatively highly porous ones with an average diameter of about 65 nm were combined with Nafion to form composite films on an electrode surface for immobilization of Ru(bpy)₃ ²⁺ (bpy is 2,2′-bipyridine). Because of their porosity, negatively charged surface, and cooperative characteristics of magnetic nanomaterials and graphene, under an external magnetic field, the GN-HPMNs ensured effective immobilization, excellent electron transfer, and long-term stability of Ru(bpy)₃ ²⁺ in the composite film. The sensor developed exhibited excellent reproducibility with a relative standard deviation of 0.65 % for 30 continuous cycles. It was found to be much more favorable for detecting compounds containing tertiary amino groups and DNAs with guanine and adenine. A detection limit (signal-to-noise ratio of 3) of 5.0 nM was obtained for tripropylamine. As an application example, 0.5 nM single-nucleotide mismatch could be detected. This was the first attempt to introduce magnetic nanomaterials and an external magnetic field into paper-based chips. The sensor developed has the advantages of high sensitivity, good stability, and wide potential applicability as well as simplicity, low cost, and good disposability.

Novel Hydrogen Peroxide Biosensor Based on Hemoglobin Combined with Electrospinning Composite Nanofibers

A facile strategy to construct an amperometric biosensor was described for the determination of hydrogen peroxide (H₂O₂). This biosensor relied on an electrospinning gold nanoparticle-chitosan-poly(vinyl alcohol) composite nanofibers modified ITO electrode, followed by immobilization of hemoglobin (Hb) on the surface. The introduction of nanofibers and gold nanoparticles in the modification of electrode surface not only enhanced the surface area of the modified electrode for enzyme immobilization but also facilitated the electron transfer rate. Under optimum conditions, the sensor was characterized in terms of its morphology by scanning electron microscopy and its electroactivity by cyclic voltammetry and chronoamperometry. Scanning electron microscopy revealed that the obtained nanofibers were uniform. The chronoamperometric behavior of the modified electrode indicated that the immobilized Hb retained electrochemical activity inside the electrospinning fibrous membranes. The electrode responded linearly to H₂O₂ in a wider concentration range of 5.6 × 10^?7 M to 5.2 × 10^?2 M with a low detection limit (S/N = 3) of 1.98 × 10^?7 M and a short response time of ～4 s, suggesting a much better performance than that of other sensors. Moreover, the biosensor achieved bulk production and exhibited superior properties for the sensitive determination of H₂O₂, studied namely, long-term stability, good reproducibility, and high selectivity.     

Titanium dioxide nanorod-based amperometric sensor for highly sensitive enzymatic detection of hydrogen peroxide

Titanium dioxide nanorods (TNR) were grown on a titanium electrode by a hydrothermal route and further employed as a supporting matrix for the immobilization of nafion-coated horseradish peroxidase (HRP). The strong electrostatic interaction between HRP and TNR favors the adsorption of HRP and facilitates direct electron transfer on the electrode. The electrocatalytic activity towards hydrogen peroxide (H₂O₂) was investigated via cyclic voltammetry and amperometry. The biosensor exhibits fast response, a high sensitivity (416.9 μA·mM^?1), a wide linear response range (2.5 nM to 0.46 mM), a detection limit as low as 12 nM, and a small apparent Michaelis-Menten constant (33.6 μM). The results indicate that this method is a promising technique for enzyme immobilization and for the fabrication of electrochemical biosensors.

Electrochemiluminescence (ECL) Detection of Ammonium Ion Based on a Novel Iridium Complex Modified Electrode

We report that ammonium ion, as its organic amine counterparts, can be sensitively detected as a coreactant in the electrochemiluminescence (ECL) reaction of a novel iridium complex (pq)₂Ir(N-phMA), where pq is 2-phenylquinoline anion and N-phMA is N-phenylmethacrylamide. The modified ECL electrode was fabricated by casting deposition of a homogeneous MWNTs/PVA/(pq)₂Ir(N-phMA) dispersion solution onto the surface of a glassy carbon electrode. The electrode responds sensitively to ammonium ion in a wide concentration range. Two regression equations were established: Y = 0.7016X + 46.8 (R² = 0.9985) and Y = 0.2565X + 174.2 (R² = 0.9991) for the concentration from 1–180 nM and 180–1800 nM, respectively. The limit of detection was as low as 0.13 nM (S/N = 3).     

Electrochemical behavior of bisphenol A at glassy carbon electrode modified with gold nanoparticles, silk fibroin, and PAMAM dendrimers

A glassy carbon electrode was modified with a composite made from gold nanoparticles and silk fibroin whose surface was further modified with amino-terminated G4 poly(amidoamine) dendrimer. This electrode shows distinct electrochemical response to bisphenol A (BPA). Electrochemical impedance spectroscopy was used to characterize the surface. The electrode displayed improved adsorption capacity and an increased response to BPA, compared to a surface without modification. Under the optimal detection conditions, the respeonse is linear in the concentration range from 1 nM to 1.3 μM, the correlation coefficient is 0.9991, and the detection limit is 0.5 nM (at an S/N of 3). The method was applied to the determination of BPA in water samples, and the recovery was in the range from 97% to 105%.     

Electrochemical biosensor for sensitively simultaneous determination of dopamine, uric acid, guanine, and adenine based on poly-melamine and nano Ag hybridized film-modified electrode

An electrochemical sensor for simultaneous determination of dopamine (DA), uric acid (UA), guanine (G), and adenine (A) has been constructed by copolymerizing melamine monomer and Ag ions on a glassy carbon electrode (GCE) with cyclic voltammetry. The poly-melamine and nano Ag formed a hybridized film on the surface of the GCE. The morphology of the film was characterized by scanning electron microscope. The electrochemical and electrocatalytic properties of this film were characterized by cyclic voltammetry, linear sweep voltammetry, and square wave voltammetry (SWV). In 0.1 M phosphate buffer solution (pH 4.5), the modified electrode resolved the electrochemical response of DA, UA, G, and A into four well-defined voltammetric oxidation peaks by SWV; the oxidation peak current of DA, UA, G, and A increased 13-, 6-, 7-, and 9-fold, respectively, compared with those at the bare GCE and the SWV peak currents of DA, UA, G, and A with linear concentrations in the ranges of 0.1–50, 0.1–50, 0.1–50, and 0.1–60 μM, respectively. Based on this, a method for simultaneous determination of these species in mixture was setup. The detection limits were 10 nM for DA, 100 nM for UA, 8 nM for G, and 8 nM for A.     

Developmental aspects of amperometric ATP biosensors based on entrapped enzymes

A novel concept for a dual-enzyme-based microbiosensor for the detection of adenosine-5′-triphosphate (ATP) was developed. The employed enzymes pyrroloquinoline quinone-dependent glucose dehydrogenase (PQQ-GDH) and hexokinase were entrapped, using pH-shift-induced precipitation of electrodeposition paint (EDP) at platinum microelectrodes (diameter of 25 µm). PQQ-GDH is known showing a superior activity for glucose conversion at the relevant conditions (low oxygen concentration) for ATP detection in targeted biomedical studies. For immobilizing the two enzymes PQQ-GDH and hexokinase, the deposition conditions of EDP Resydrol AY498w/35WA were adapted to ensure high immobilization rates. Prior to ATP sensing, the conversion of glucose, which is the co-substrate for both enzymatic reactions, was optimized. Optimization was targeted towards ATP measurements in biomedical environments by optimizing the PQQ-GDH sensor for glucose. Therefore, different mediators were tested regarding their electron transfer rate and their compatibility with the enzyme: free-diffusing N-methylphenazonium methyl sulfate (PMS) and ferrocenemethanol, and an immobilized chromium hexacyanoferrate layer at platinum electrode. Free-diffusing ferrocenemethanol reveals high sensitivity towards glucose of 1.5?±?0.4 nA/mM. In a next step, hexokinase was co-entrapped in the polymer film resulting in a sensitivity of up to 290 pA/µM.     

Titanium dioxide nanorod-based amperometric sensor for highly sensitive enzymatic detection of hydrogen peroxide

Titanium dioxide nanorods (TNR) were grown on a titanium electrode by a hydrothermal route and further employed as a supporting matrix for the immobilization of nafion-coated horseradish peroxidase (HRP). The strong electrostatic interaction between HRP and TNR favors the adsorption of HRP and facilitates direct electron transfer on the electrode. The electrocatalytic activity towards hydrogen peroxide (H₂O₂) was investigated via cyclic voltammetry and amperometry. The biosensor exhibits fast response, a high sensitivity (416.9 μA·mM⁻¹), a wide linear response range (2.5 nM to 0.46 mM), a detection limit as low as 12 nM, and a small apparent Michaelis-Menten constant (33.6 μM). The results indicate that this method is a promising technique for enzyme immobilization and for the fabrication of electrochemical biosensors.

A TiO₂ nanorod film was directly grown on Ti substrate by a hydrothermal route, and was further employed for a supporting matrix to immobilize horseradish peroxidase as a biosensor electrode. The as-prepared hydrogen peroxide biosensor based on Nafion/HRP/TNR/Ti electrode exhibited fast response and excellent electrocatalytic activity toward H₂O₂, i.e., a high sensitivity (416.9 μA mM⁻¹), a wide linear range (2.5 × 10⁻⁸ to 4.6 × 10⁻⁴ M) with a low detection limit (0.012 μM) and a small apparent Michaelis-Menten constant (33.6 μM).

     

Label-Free Detection of DNA Hybridization Based on MnO2 Nanoparticles

Abstract

Nano-MnO₂/chitosan composite film modified glassy carbon electrode (MnO₂/CHIT/GCE) was fabricated and a DNA probe was immobilized on the electrode surface. The immobilization and hybridization events of DNA were characterized by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The EIS was applied to the label-free detection of the target DNA. The human immunodeficiency virus (HIV) gene fragment was successfully detected by this DNA electrochemical sensor. The dynamic detection range was from 2.0 × 10^?11 to 2.0 × 10^?6 mol/L, with a detection limit of 1.0 × 10^?12 mol/L.     

Electrochemical determination of piroxicam on the surface of pyrolytic graphite electrode modified with a film of carbon nanoparticle-chitosan

The electrochemical behavior of the anti-inflammatory drug piroxicam is studied at the surface of a plain pyrolytic graphite electrode modified with chitosan-doped carbon nanoparticles. An electroactive surface was produced by drop-casting a suspension of the modifier and characterized by atomic force microscopy. A remarkable enhancement is found in studies on the cyclic voltammetric response towards piroxicam. This is described on the basis of the thin-layer mass transport regimes within the porous films, which leads to a considerable increase in the active surface area of the electrode. The electrode shows a linear response to piroxicam in the range of 0.05–50 μM, with a detection limit of 25 nM (at S/N of 3). The electrode was successfully applied to the determination of piroxicam in pharmaceutical and clinical preparations with satisfactory accuracy and precision.     

Voltammetric behavior of acebutolol on pencil graphite electrode: highly sensitive determination in real samples by square-wave anodic stripping voltammetry

In this work, an electrochemical investigation of acebutolol (ACE), a beta-blocker drug, was carried out in alkaline medium using pencil graphite (PG) electrode. In cyclic voltammetry, the compound displayed a reversible and adsorption-controlled oxidation peak. By using square-wave anodic stripping voltammetry, the oxidation peak current observed at +0.78 V showed a linear relationship with concentration at 0.4–7 nM interval in Britton–Robinson buffer (pH 10.0) and a detection limit of 0.09 nM. The relative standard deviation of 4.72% for the concentration level of 2.0 nM (n = 11) was also calculated. The PG electrode that is used for the first time in this method was successfully applied to determine the ACE in pharmaceutical formulations and urine.     

Fabrication of an amperometric tyramine biosensor based on immobilization of tyramine oxidase on AgNPs/l-Cys-modified Au electrode

An amperometric tyramine biosensor was constructed based on covalent immobilization of black gram tyramine oxidase onto citric acid-capped silver nanoparticles bound to surface of Au electrode through cysteine self-assembled monolayer. The enzyme electrode was characterized by scanning electron microscopy, Fourier transform infrared spectroscopy, and cyclic voltametry. The biosensor showed optimum response within 8 s, when polarized at 0.25 V, pH 8.5, and 35 °C, with linearity from 0.017 to 0.25 mM and a detection limit of 0.01 mM. The biosensor was employed for measurement of tyramine in beer and sauce. The mean analytical recovery of added tyramine in beer at 0.36 and 0.72 mM were 97.2?±?2.7 and 95.8?±?4.1 %, respectively, and within and between batches coefficients of variation were 0.33–0.38 and 0.34–0.62 %, respectively. The enzyme electrode lost 35 % of its initial activity after its 100 uses, over a period of 2 months, when stored at 4 °C.     

Application of spinel-structured MgFe<Subscript>2</Subscript>O<Subscript>4</Subscript> nanoparticles for simultaneous electrochemical determination diclofenac and morphine

The paper describes a sensitive method for simultaneous sensing of morphine (MOR) and diclofenac (DCF). The surface of a MgFe₂O₄/graphite paste electrode was modified with multi-walled carbon nanotubes, and the resulting sensor was characterized by cyclic voltammetry, differential pulse voltammetry, chronoamperometry, and electrochemical impedance spectroscopy. The electrode showed an efficient synergistic effect in term of oxidation of DCF and MOR, with sharp oxidation peaks occurring at +0.370 and 0.540 V (vs Ag/AgCl) at pH 7.0. The calibration plot for MOR is linear in the 50 nM to 920 μM concentration range, and the detection limit is 10 nM (at a signal-to-noise ratio of 3). The respective data for DCF are 100 nM to 580 μM, with a 60 nM LOD. The sensor was applied to the determination of MOR and DCF in spiked serum and urine samples, with recoveries ranging between 91.4 and 100.7 %.

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Graphical abstract A sensitive method for simultaneous sensing of morphine (MOR) and diclofenac (DCF) is described. The surface of MgFe₂O₄/graphite paste electrode was modified with multi-walled carbon nanotubes, and the resulting sensor showed an efficient synergistic effect in terms of oxidation of DCF and MOR. The calibration plot for MOR is linear in the 50 nM to 920 μM concentration range, and the detection limit is 10 nM. The respective data for DCF are 100 nM to 580 μM, with a 60 nM LOD.

     

Anodic stripping voltammetric determination of copper (II) ions at a graphene quantum dot-modified pencil graphite electrode

A simple and sensitive electrochemical sensor based on graphene quantum dot-modified pencil graphite electrode (GQD/PGE) was fabricated and used for highly selective and sensitive determination of copper (II) ions in nanomolar concentration by square wave adsorptive stripping voltammetric method. The sensing mechanism could be attributed to the formation of a complex between Cu²⁺ ions and oxygen-containing groups in GQDs which result in an increased SWV signal in comparison with the bare electrode. Optimization of various experimental parameters such as pre-concentration time, pre-concentration potential, pH, and buffer type which influence the performance of the sensor, was investigated. Under optimized condition, GQD-modified electrode has been used for the analysis of Cu²⁺ in the concentration range from 50 pM to 4 nM and a lower detection limit of 12 pM with good stability, repeatability, and selectivity. Finally, the practical applicability of GQD-PGE was confirmed via measuring trace amount of Cu (II) in water samples. The GQD/PGE surface could be regenerated by exerting more positive potentials than the stripping potential of the Cu (II) ion and then used for another deposition.     

Amperometric Determination of Cholesterol-Reducing Drug,Ezetimibe, Using Glassy Carbon Electrode Modified with Multiwalled Carbon Nanotubes and Sodium Dodecylsulfate

A simple and sensitive electrochemical method is described for the determination of the cholesterol-reducing drug ezetimibe in aqueous solution. A glassy carbon electrode, modified with multiwalled carbon nanotubes and sodium dodecylsulphate was used as the working electrode. Ezetimibe yields a well-defined anodic peak at the surface of the electrode in an aqueous solution of pH 13. A linear amperometric calibration curve was obtained in the range of 1.2–78 μM (0.5–32.0 μg/mL) of ezetimibe, with a sensitivity of 88.6 nA/μM and a detection limit of 300 nM (0.12 μg/mL). The sensor was applied successfully to the determination of ezetimibe in pharmaceutical preparations.     

Application of multivariate optimization method in nanomolar simultaneous determination of morphine and codeine in the presence of uric acid using a glassy carbon electrode modified with a hydroxyapatite-Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> nanoparticle/multiwalled carbon nanotubes composite

The electrochemical oxidation of morphine (MO) and codeine (COD) has been investigated by the application of a novel glassy carbon electrode modified with a hydroxyapatite-Fe₃O₄ nanoparticles/multiwalled carbon nanotubes composite (HA-FeNPs-MWCNTs/GCE). The modified electrode worked as an efficient sensor for simultaneous determination of MO and COD in the presence of uric acid. Response surface methodology was utilized to optimize the voltammetric response of the modified electrode for the determination of MO and COD. The amount of HA-FeNPs in the modifier matrix (%HA-FeNPs), the solution pH and the accumulation time were chosen as the three important operating factors through the experimental design methodology. The central composite design as a response surface approach was applied for obtaining the optimum conditions leading to maximum oxidation peak currents for MO and COD. The differential pulse voltammetry results showed that the obtained anodic peak currents were linearly proportional to concentration in the range of 0.08–32 µM with a detection limit (S/N = 3.0) of 14 nM for MO and in the range of 0.1–28 µM and with a detection limit of 22 nM for COD. The proposed method was successfully applied to determine these compounds in human urine and blood serum samples.