A microfluidic glucose sensor incorporating a novel thread‐based electrode system

An electrochemical sensor for the detection of glucose using thread‐based electrodes and fabric is described. This device is relatively simple to fabricate and can be used for multiple readings after washing with ethanol. The fabrication of the chip consisted of two steps. First, three thread‐based electrodes (reference, working, and counter) were fabricated by painting pieces of nylon thread with either layered silver ink and carbon ink or silver/silver chloride ink. The threads were then woven into a fabric chip with a beeswax barrier molded around the edges in order to prevent leaks from the tested solutions. A thread‐based working electrode consisting of one layer of silver underneath two layers of carbon was selected to fabricate the final sensor system. Using the chip, a PBS solution containing glucose oxidase (GOx) (10 mg/mL), potassium ferricyanide (K₃[Fe(CN)₆]) (10 mg/mL) as mediator, and different concentrations of glucose (0‐25 mM), was measured by cyclic voltammetry (CV). It was found that the current output from the oxidation of glucose was proportional to the glucose concentrations. This thread‐based electrode system is a viable sensor platform for detecting glucose in the physiological range.     

Simplified current decoupler for microchip capillary electrophoresis with electrochemical and pulsed amperometric detection

There is a need to develop broadly applicable, highly sensitive detection methods for microchip CE that do not require analyte derivatization. LIF is highly sensitive but typically requires analyte derivatization. Electrochemistry provides an alternative method for direct analyte detection; however, in its most common form, direct current (DC) amperometry, it is limited to a small number of easily oxidizable or reducible analytes. Pulsed amperometric detection (PAD) is an alternative waveform that can increase the number of electrochemically detectable analytes. Increasing sensitivity for electrochemical detection (EC) and PAD requires the isolation of detection current (nA) from the separation current (muA) in a process generally referred to as current decoupling. Here, we present the development of a simple integrated decoupler to improve sensitivity and its coupling with PAD. A Pd microwire is used as the cathode for decoupling and a second Au or Pt wire is used as the working electrode for either EC or PAD. The electrode system is easy to make, requiring no clean-room facilities or specialized metallization systems. Sensitive detection of a wide range of analytes is shown to be possible using this system. Using this system we were able to achieve detection limits as low as 5 nM for dopamine, 74 nM for glutathione, and 100 nM for glucose.     

Determination of mannitol and three sugars in Ligustrum lucidum Ait. by capillary electrophoresis with electrochemical detection

A method based on capillary electrophoresis with electrochemical detection has been developed for the separation and determination of mannitol, sucrose, glucose, and fructose in Ligustrum lucidum Ait. for the first time. Effects of several important factors such as the concentration of NaOH, separation voltage, injection time, and detection potential were investigated to acquire the optimum conditions. The detection electrode was a 300 μm diameter copper disc electrode at a working potential of +0.65 V (versus saturated calomel electrode (SCE)). The four analytes can be well separated within 13 min in a 40 cm length fused-silica capillary at a separation voltage of 12 kV in a 75 mM NaOH aqueous solution. The relation between peak current and analyte concentration was linear over about three orders of magnitude with detection limits (S/N = 3) ranging from 1 to 2 μM for all analytes. The proposed method has been successfully applied to monitor the mannitol and sugar contents in the plant samples at different growth stages with satisfactory assay results.     

Sulfide determination in hydrothermal seawater samples using a vibrating gold micro-wire electrode in conjunction with stripping chronopotentiometry

A rapid electrochemical stripping chronopotentiometric procedure to determined sulfide in unaltered hydrothermal seawater samples is presented. Sulfide is deposited at −0.25 V (vs Ag/AgCl, KCl 3 M) at a vibrating gold microwire and then stripped through the application of a reductive constant current (typically −2 μA). The hydrodynamic conditions are modulated by vibration allowing a short deposition step, which is shown here to be necessary to minimize H₂S volatilization. The limit of detection (LOD) is 30 nM after a deposition step of 7 s. This LOD is in the same range as the most sensitive cathodic voltammetric technique using a mercury drop electrode and is well below those reported previously for other electrodes capable of being implemented in situ.     

Using nanoparticle aggregation to give an ultrasensitive amperometric metal ion sensor

Herein we show an electrochemical sensor for the detection of copper ions that has a limit of detection below 1 pM. This extraordinarily low limit of detection is achieved in two ways. The first is to use SAM modified electrodes to give low background current where electron transfer to the underlying polycrystalline electrode is achieved through gold nanoparticles attached to the terminus of the SAM. The gold nanoparticles are modified with cysteine to allow copper accumulation. The second way the low detection limits are achieved is by the addition of cysteine-modified nanoparticles to the sample solution, as well as the SAM modified electrode. The complexation of copper with the nanoparticles in solution causes them to aggregate with these aggregates accumulating on the electrode. Thus a higher percentage of copper in the solution is collected at the electrode giving the enhanced detection limits.     

Electrochemical detection of phenolic compounds using cylindrical carbon-ink electrodes and microchip capillary electrophoresis

A simple method to fabricate cylindrical carbon electrodes for use in capillary electrophoresis (CE) microchips is described. The electrodes were fabricated using a metallic wire coated with carbon ink. Several experimental variables were studied in order to establish the best conditions to fabricate the electrode. Finally, the electrodes were integrated in a poly(dimethylsiloxane) microchip and used for the analysis of phenolic compounds. Using the optimum conditions, the analysis of a mixture of dopamine, epinephrine, catechol, and 4-aminophenol was achieved in less than 240 s, showing good linear responses (R² = 0.999) in the 0.1-190 μM range, and limits of detection (without the use of stacking or a decoupler) of 140 and 105 nM for dopamine and epinephrine, respectively.     

Amperometric Glucose Biosensor Based on Electrochemically Deposited Gold Nanoparticles Covered by Polypyrrole

Graphite rod (GR) modified with electrochemicaly deposited gold nanoparticles (AuNPs) and adsorbed glucose oxidase (GOx) was used in amperometric glucose biosensor design. Enzymatic formation of polypyrrole (Ppy) on the surface of GOx/AuNPs/GR electrode was applied in order to improve analytical characteristics and stability of developed biosensor. The linear glucose detection range for Ppy/GOx/AuNPs/GR electrode was dependent on the duration of Ppy‐layer formation and the linear interval was extended up to 19.9 mmol L⁻¹ after 21 h lasting synthesis of Ppy. The sensitivity of the developed biosensor was determined as 21.7 μA mM⁻¹ cm⁻², the limit of detection – 0.20 mmol L⁻¹. Ppy/GOx/AuNPs/GR electrodes demonstrated advanced good stability (the t _1/2 was 9.8 days), quick detection of glucose (within 5 s) in the wide linear interval. Additionally, formed Ppy layer decreased the influence of electroactive species on the analytical signal. Developed biosensor is suitable for the determination of glucose in human serum samples.     

Metallated porphyrin noncovalent interaction with reduced graphene oxide‐modified electrode for amperometric detection of environmental pollutant hydrazine

A reduced graphene oxide/platinum(II) tetraphenylporphyrin nanocomposite (RGO/Pt‐TPP)‐modified glassy carbon electrode was developed for the selective detection of hydrazine. The RGO/Pt‐TPP nanocomposite was successfully prepared via noncovalent π–π stacking interaction. The prepared nanocomposite was characterized using nuclear magnetic resonance, electrochemical impedance, ultraviolet–visible and Raman spectroscopies, scanning electron microscopy and X‐ray diffraction. The electrochemical detection of hydrazine was performed via cyclic voltammetry and amperometry. The RGO/Pt‐TPP nanocomposite exhibited good electrocatalytic activity towards detection of hydrazine with low overpotential and high oxidation peak current. The fabricated sensor exhibited a wide linear range from 13 nM to 232 μM and a detection limit of 5 nM. In addition, the fabricated sensor selectively detected hydrazine even in the presence of 500‐fold excess of common interfering ions. The fabricated electrode exhibited good sensitivity, stability, repeatability and reproducibility. In addition, the practical applicability of the sensor was evaluated in various water samples with acceptable recoveries.     

Nanostructured cupric oxide electrode: An alternative to amperometric detection of carbohydrates in anion-exchange chromatography

In this paper, a new and low cost copper/cupric oxide nanostructured electrode is presented as an alternative to the amperometric detection of carbohydrates in high-performance anion exchange chromatography. The modified copper electrodes were prepared by a simple and fast method which resulted in the obtainment of homogeneously distributed nanostructures adhered to the surface with controlled chemical nature. The results, when compared to conventional copper electrodes, exhibited considerable improvements in analytical results, including: 1) Better repeatability in consecutive glucose detections, in which the percent relative standard deviation improved from 15.1% to 0.279%. 2) Significant improvements in the stability of the baseline and a decrease of the stabilization time, going from several hours to approximately 15 min. 3) Considerable increase in the sensitivity towards glucose, from 5.02 nA min mg L⁻¹ to 25.5 nA min mg L⁻¹. 4) Improvements in the detectability with limits as low as 1.09 pmol. 5) Wide working range of concentrations (1 × 10⁻² to 1 × 10⁴ mg L⁻¹). 6) Good linearity with correlation coefficients greater than 0.998. 7) Possibility of detecting different molecules of carbohydrates (lactose, maltose, sucrose cellobiose, sorbitol, fructose, glucose, galactose, manose, arabitol, xylose, ribose and arabnose). In comparison to the electrode that is more employed for this type of application (gold electrode), the low cost, the possibility of detection at constant potential and the equivalent detection limits presented by the new electrode material introduced in this work emerge as characteristics that make this material a powerful alternative considering the detection of carbohydrates in anion exchange chromatography.     

Prussian blue modified glassy carbon electrodes-study on operational stability and its application as a sucrose biosensor

Stabilisation of electrochemically deposited Prussian blue (PB) films on glassy carbon (GC) electrodes has been investigated and an enhancement in the stability of the PB films is reported if the electrodes are treated with tetrabutylammonium toluene-4-sulfonate (TTS) in the electrochemical activation step following the electrodeposition. A multi-enzyme PB based biosensor for sucrose detection was made in order to demonstrate that PB films can be coupled with an oxidase system. A tri-enzyme system, comprising glucose oxidase, mutarotase and invertase, was crosslinked with glutaraldehyde and bovine albumin serum on the PB modified glassy carbon electrode. The deposited PB operated as an electrocatalyst for electrochemical reduction of hydrogen peroxide, the final product of the enzyme reaction sequence. The electrochemical response was studied using flow injection analysis for the determination of sucrose, glucose and H₂O₂. The optimal concentrations of the immobilisation mixture was standardised as 8 U of glucose oxidase, 8 U of mutarotase, 16 U of invertase, 0.5% glutaraldehyde (0.025 μl) and 0.5% BSA (0.025 mg) in a final volume of 5 μl applied at the electrode surface (0.066 cm²). The biosensor exhibited a linear response for sucrose (4-800 μM), glucose (2-800 μM) and H₂O₂ (1-800 μM) and the detection limit was 4.5, 1.5 and 0.5 μM for sucrose, glucose and H₂O₂, respectively. The sample throughput was ca. 60 samples h⁻¹. An increase in the operational and storage stability of the sucrose biosensor was also noted when the PB modified electrodes were conditioned in phosphate buffer containing 0.05 M TTS during the preparation of the PB films.     

An intimately bonded titanate nanotube–polyaniline–gold nanoparticle ternary composite as a scaffold for electrochemical enzyme biosensors

In this work, titanate nanotubes (TNTs), polyaniline (PANI) and gold nanoparticles (GNPs) were assembled to form a ternary composite, which was then applied on an electrode as a scaffold of an electrochemical enzyme biosensor. The scaffold was constructed by oxidatively polymerising aniline to produce an emeraldine salt of PANI on TNTs, followed by gold nanoparticle deposition. A novel aspect of this scaffold lies in the use of the emeraldine salt of PANI as a molecular wire between TNTs and GNPs. Using horseradish peroxidase (HRP) as a model enzyme, voltammetric results demonstrated that direct electron transfer of HRP was achieved at both TNT-PANI and TNT-PANI-GNP-modified electrodes. More significantly, the catalytic reduction current of H₂O₂ by HRP was ∼75% enhanced at the TNT-PANI-GNP-modified electrode, compared to that at the TNT-PANI-modified electrode. The heterogeneous electron transfer rate constant of HRP was found to be ∼3 times larger at the TNT-PANI-GNP-modified electrode than that at the TNT-PANI-modified electrode. Based on chronoamperometric detection of H₂O₂, a linear range from 1 to 1200 μM, a sensitivity of 22.7 μA mM⁻¹ and a detection limit of 0.13 μM were obtained at the TNT-PANI-GNP-modified electrode. The performance of the biosensor can be ascribed to the superior synergistic properties of the ternary composite.     

Facile one-step electrochemical fabrication of a non-enzymatic glucose-selective glassy carbon electrode modified with copper nanoparticles and graphene

We have developed a non-enzymatic glucose sensor by using a composite prepared from copper nanoparticles (CuNPs) and graphene which can be prepared by simple 1-step electrochemical reduction using graphene oxide (GO) and copper ion as the starting materials. The GO is electrochemically reduced to graphene at a voltage of ?1.5 V, and this is accompanied by the simultaneous formation of CuNPs on the surface of the graphene. This novel nanocomposite combines the advantages of graphene and of CuNPs and displays good electrocatalytic activity toward glucose in alkaline media. The performance of the respective glucose electrode was evaluated by amperometric experiments and revealed a fast response (<2 s), a low detection limit (200 nM), and high sensitivity (607 μA mM^?1). The sensor also exhibits good reproducibility and very good specificity for glucose over ascorbic acid, dopamine, uric acid, fructose, lactose and sucrose.

Preparation and characterization of Ni(II)/polyacrylonitrile and carbon nanotube composite modified electrode and application for carbohydrates electrocatalytic oxidation

A nickel(II) into porous polyacrylonitrile–carbon nanotubes composite modified glassy carbon electrode (Ni/PAN-CNT/GCE) was fabricated by simple drop-casting and immersing technique. The unique electrochemical activity of Ni/PAN-CNT composite modified glassy carbon electrode was illustrated in 0.10?M NaOH using cyclic voltammetry. The Ni/PAN-CNT/GCE exhibits the characteristic of improved reversibility and enhanced current responses of the Ni(III)/Ni(II) couple compared with Ni/PAN/GCE and Ni/CNT/GCE. The results of electrochemical impedance spectroscopy and scanning electron microscopy indicated the successful immobilization for PAN-CNT composite film. Kinetic parameters such as the electron transfer coefficient, α, and rate constant, k _s, of the electrode reaction were determined. Ni/PAN-CNT/GCE also shows good electrocatalytic activity toward the oxidation of carbohydrates (glucose, sucrose, fructose, and sorbitol). The electrocatalytic response showed a wide linear range (10–1,500, 12–3,200, 7–3,500, and 16–4,200?μM for glucose, sucrose, fructose, and sorbitol, respectively) as well as its experimental limit of detection can be achieved 6, 7, 5, and 11?μM for glucose, sucrose, fructose, and sorbitol, respectively. The modified electrode for carbohydrates determination is of the property of simple preparation, good stability, and high sensitivity.     

Development and evaluation of electrochemical glucose enzyme biosensors based on carbon film electrodes

Electrochemical glucose enzyme biosensors have been prepared on carbon film electrodes made from carbon film electrical resistors. Evaluation and characterisation of these electrodes in phosphate buffer saline solution has been carried out with and without pretreatment by cycling in perchloric acid or at fixed applied potential. Both pretreatments led to a reduction in the carbon surface oxidation peak and enabled better detection of hydrogen peroxide in the pH range of 5-7. Glucose oxidase enzyme was immobilised on the carbon surface by mixing with glutaraldehyde, bovine serum albumin and with and without Nafion. The performance of these two types of electrode was similar, that containing Nafion being more physically robust. Linear ranges were up to around 1.5 mM, with detection limits 60 μM, and pretreatment of the carbon film electrode at a fixed potential of +0.9 V versus SCE for 5 min was found to be the most beneficial. Michaelis-Menten constants between 5 mM and 10 mM were found under the different experimental conditions. Coating the immobilised enzyme layer with a thin layer of Nafion was found to give similar results in the determination of glucose to mixing it but with benefits against interferences for the analysis of complex matrices, such as wine. Potentialities, for a short-term-use or disposable sensors, are indicated.     

Highly selective and sensitive simple sensor based on electrochemically treated nano polypyrrole-sodium dodecyl sulphate film for the detection of para-nitrophenol

An ultrasensitive and highly selective electrochemical sensor for the determination of p-nitrophenol (p-NP) was developed based on electrochemically treated nano polypyrrole/sodium dodecyl sulphate film (ENPPy/SDS film) modified glassy carbon electrode. The nano polypyrrole/sodium dodecyl sulphate film (NPPy/SDS film) was prepared and treated electrochemically in phosphate buffer solution. The surface morphology and elemental analysis of treated and untreated NPPy/SDS film were characterized by FESEM and EDX analysis, respectively. Wettability of polymer films were analysed by contact angle test. The hydrophilic nature of the polymer film decreased after electrochemical treatment. Effect of the pH of electrolyte and thickness of the ENPPy/SDS film on determination of p-NP was optimised by cyclic voltammetry. Under the optimised conditions, the p-NP was determined from the oxidation peak of p-hydroxyaminophenol which was formed from the reduction of p-NP in the reduction segment of cyclic voltammetry. A very good linear detection range (from 0.1 nM to 100 μM) and the best LOD (0.1 nM) were obtained for p-NP with very good selectivity. This detection limit is below to the allowed limit in drinking water, 0.43 μM, proposed by the U.S. Environmental Protection Agency (EPA) and earlier reports. Moreover, ENPPy/SDS film based sensor exhibits high sensitivity (4.4546 μA μM⁻¹) to p-NP. Experimental results show that it is a fast and simple sensor for p-NP.     

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.     

A Nonenzymatic Glucose Sensor Using Nanoporous Platinum Electrodes Prepared by Electrochemical Alloying/Dealloying in a Water‐Insensitive Zinc Chloride‐1‐Ethyl‐3‐Methylimidazolium Chloride Ionic Liquid

We report here a nonenzymatic sensor by using a nanoporous platinum electrode to detect glucose directly. The electrode was fabricated by electrochemical deposition and dissolution of PtZn alloy in zinc chloride‐1‐ethyl‐3‐methylimidazolium chloride (ZnCl₂‐EMIC) ionic liquid. Both SEM and electrochemical studies showed the evidences for the nanoporous characteristics of the as‐prepared Pt electrodes. Amperometric measurements allow observation of the electrochemical oxidation of glucose at 0.4 V (vs. Ag/AgCl) in pH 7.4 phosphate buffer solution. The sensor also demonstrates significant reproducibility in glucose detection; the higher the roughness factor of the Pt electrode, the lower the detection limit of glucose. The interfering species such as ascorbic acid and p‐acetamidophenol can be avoided by using a Pt electrode with a high roughness factor of 151. Overall, the nanoporous Pt electrode is promising for enzymeless detection of glucose at physiological condition.     

Selective and sensitive electrochemical detection of glucose in neutral solution using platinum-lead alloy nanoparticle/carbon nanotube nanocomposites

Electrodeposition of Pt-Pb nanoparticles (PtPbNPs) to multi-walled carbon nanotubes (MWCNTs) resulted in a stable PtPbNP/MWCNT nanocomposite with high electrocatalytic activity to glucose oxidation in either neutral or alkaline medium. More importantly, the nanocomposite electrode with a slight modification exhibited high sensitivity, high selectivity, and low detection limit in amperometric glucose sensing at physiological neutral pH (poised at a negative potential). At +0.30 V in neutral solution, the nanocomposite electrode exhibited linearity up to 11 mM of glucose with a sensitivity of 17.8 μA cm⁻² mM⁻¹ and a detection limit of 1.8 μM (S/N = 3). Electroactive ascorbic acid (0.1 mM), uric acid (0.1 mM) and fructose (0.3 mM) invoked only 23%, 14% and 9%, respectively, of the current response obtained for 3 mM glucose. At −0.15 V in neutral solution, the electrode responded linearly to glucose up to 5 mM with a detection limit of 0.16 mM (S/N = 3) and detection sensitivity of ∼18 μA cm⁻² mM⁻¹. At this negative potential, ascorbic acid, uric acid, and fructose were not electroactive, therefore, not interfering with glucose sensing. Modification of the nanocomposite electrode with Nafion coating followed by electrodeposition of a second layer of PtPbNPs on the Nafion coated PtPbNP/MWCNT nanocomposite produced a glucose sensor (poised at −0.15 V) with a lower detection limit (7.0 μM at S/N = 3) and comparable sensitivity, selectivity and linearity compared to the PtPbNP/MWCNT nanocomposite. The Nafion coating lowered the detection limit by reducing the background noise, while the second layer of PtPbNPs restored the sensitivity to the level before Nafion coating.     

Investigation of plasma-functionalized multiwalled carbon nanotube film and its application of DNA sensor for Legionella pneumophila detection

A novel multiwall carbon nanotube (MWCNT) electrode functionalized with oxygen plasma treatment was prepared and characterized, and its DNA sensing ability for Legionella pneumophila (L. pneumophila) detection was examined using electrochemical measurement. A well-patterned MWCNT working electrode (WE) on a Pt track was fabricated using photolithography, transfer methods and an etching technique. The MWCNT WE was functionalized by oxygen plasma treatment prior to applying for DNA sensor. The surface morphology of the plasma-functionalized MWCNT (pf-MWCNT) WEs were observed by scanning electron microscope (SEM) and the change of chemical composition was characterized by X-ray photoelectron spectroscopy (XPS), and electrochemical measurements were performed using CV with ferricyanide/ferrocyanide redox couple. Effective areas of working electrodes were calculated to be 0.00453 cm² for pristine MWCNT electrode and 0.00747-0.00874 cm² for pf-MWCNT electrodes with different plasma treatment times. Differential pulse voltammetry (DPV) was carried out in methylene blue solution for DNA sensing. The pf-MWCNT based DNA sensor was successfully operated in a target concentration range of 10 pM to 100 nM and had a lower detection limit than a pristine MWCNT based DNA sensor.     

Simple and Inexpensive Electrochemical Platform Based on Novel Homemade Carbon Ink and its Analytical Application for Determination of Nitrite

In this work we present the development of a simple handmade approach for the easy fabrication of three‐electrode electrochemical devices based on newly in‐house developed carbon ink composed of graphite powder and polystyrene. Different proportions of graphite/polystyrene were investigated for the optimization of the ink. The counter and reference electrodes were produced using commercial carbon ink and silver glue. Scanning electron microscopy, electrochemical impedance spectroscopy and cyclic voltammetry were used to investigate the morphology and the electrochemical properties of the sensor. The results showed that the electroactive area of the optimized working electrode was ca . 2.35 times larger than its geometric area. The RSD values obtained for repeatability and reproducibility were 0.20% and 2.78%, respectively, which suggest no significant variation on the electrodes fabricated. The analytical feasibility of the electrode was tested through its application for the determination of nitrite in drinking water. The quantifications were successfully performed at levels below the maximum contaminant level established for nitrite. A limit of detection of 1.42 × 10⁻⁶ mol L⁻¹ and recoveries of ca . 103 % were achieved. The results were validated using ion‐chromatography technique with good agreement. The performance of the unmodified sensor proposed here on nitrite determination was better than some recently reported modified electrodes obtained through complex procedures.