Advances in the voltammetric analysis of small biologically relevant compounds

Black phosphorus nanosheets/poly(allylamine hydrochloride) based electrochemical immunosensor for the selective detection of human epididymis protein 4

In this work, an electrochemical immunosensor based on black phosphorus nanosheets (BPNS)/poly(allylamine hydrochloride) (PAH) nanocomposite modified glassy carbon electrode was developed for the detection of ovarian cancer biomarker HE4. PAH has been applied to retain BPNS in its original honeycomb structure and to anchor biomolecules electrostatically on the transducer surface. The as synthesized nanocomposite was characterized by zeta potential analysis, scanning electron microscopy, x-ray photoelectron spectroscopy, transmission electron microscopy, high-resolution transmission electron microscopy. Subsequently, the performance of the electrochemical immunosensor was evaluated through cyclic voltammetry, differential pulse voltammetry and electrochemical impedance spectroscopy. Under the optimal condition, the developed electrochemical immunosensor permitted to detect HE4 with a linear range of 0.1-300 ng ml^-1and a detection limit of 0.01 ng ml^-1. The developed sensor exhibited good selectivity and specificity to HE4 with negligible interference effect from common biomolecules like bovine serum albumin, lysozyme, protamine, glucose, fructose, hemoglobin and fetal bovine serum. Further, practical application of developed electrochemical immunosensor was demonstrated in spiked human serum which showed satisfactory recovery percentages.

Ultrasensitive Materials for Electrochemical Biosensor Labels

Since the fabrication of the first electrochemical biosensor by Leland C. Clark in 1956, various labeled and label-free sensors have been reported for the detection of biomolecules. Labels such as nanoparticles, enzymes, Quantum dots, redox-active molecules, low dimensional carbon materials, etc. have been employed for the detection of biomolecules. Because of the absence of cross-reaction and highly selective detection, labeled biosensors are advantageous and preferred over label-free biosensors. The biosensors with labels depend mainly on optical, magnetic, electrical, and mechanical principles. Labels combined with electrochemical techniques resulted in the selective and sensitive determination of biomolecules. The present review focuses on categorizing the advancement and advantages of different labeling methods applied simultaneously with the electrochemical techniques in the past few decades.

Direct electrochemical detection of glyphosate at carbon paste electrode and its determination in samples of milk, orange juice, and agricultural formulation

This paper describes a simple, inexpensive, highly sensitive, selective, and efficient electrochemical method to determine glyphosate (GLY) in samples of milk, orange juice, and agricultural formulation. The oxidation reaction on the electrode surface was electrochemically characterised by cyclic voltammetry (CV) and square wave voltammetry (SWV). The investigation of GLY at carbon paste electrode revealed a non-reversible oxidation peak at +0.95 V versus Ag/AgCl, which was used for electrochemical detection of GLY. The operating parameters (pH, frequency, step potential, and amplitude) were optimised in relation to the peak current intensity, and a calibration curve was set up in a concentration range of 4.40 × 10-8-2.80 × 10-6 mol L-1, with a detection limit of 2 × 10-9 mol L-1. After calibration curve was plotted, the developed procedure was applied to determine GLY in previously contaminated samples: milk and orange juice, and in a commercial formulation, obtaining recovery values between 98.31% and 103.75%. These results show that the proposed method can be used for GLY quantification in different samples with high sensitivity, specificity, stability, and reproducibility.

Surface and Electrochemical Properties of Polymer Brush-Based Redox Poly(Ionic Liquid)

Redox-active poly(ionic liquid) poly(3-(2-methacryloyloxy ethyl)-1-(N-(ferrocenylmethyl) imidazolium bis(trifluoromethylsulfonyl)imide deposited onto electrode surfaces has been prepared using surface-initiated atom transfer radical polymerization SI-ATRP. The process starts by electrochemical immobilization of initiator layer, and then methacrylate monomer carrying ferrocene and imidazolium units is polymerized in ionic liquid media via SI-ATRP process. The surfaces analyses of the polymer exhibit a well-defined polymer brushlike structure and confirm the presence of ferrocene and ionic moieties within the film. Furthermore, the electrochemical investigations of poly(redox-active ionic liquid) in different media demonstrate that the electron transfer is not restricted by the rate of counterion migration into/out of the polymer. The attractive electrochemical performance of these materials is further demonstrated by performing electrochemical measurement, of poly(ferrocene ionic liquid), in solvent-free electrolyte. The facile synthesis of such highly ordered electroactive materials based ionic liquid could be useful for the fabrication of nanostructured electrode suitable for performing electrochemistry in solvent free electrolyte. We also demonstrate possible applications of the poly(FcIL) as electrochemically reversible surface wettability system and as electrochemical sensor for the catalytic activity toward the oxidation of tyrosine.

Nanostructured materials in electroanalysis of pharmaceuticals

Basic strategies and recent developments for the enhancement of the sensory performance of nanostructures in the electroanalysis of pharmaceuticals are reviewed. A discussion of the properties of nanostructures and their application as modified electrodes for drug assays is presented. The electrocatalytic effect of nanostructured materials and their application in determining low levels of drugs in pharmaceutical forms and biofluids are discussed.

Selective electrochemical determination of cysteine with a cyclotricatechylene modified carbon electrode

We report the selective electrochemical detection of cysteine in the presence of homocysteine and glutathione with the use of an electrode modified with cyclotricatechylene (CTC).

The selective electrochemical detection of homocysteine in the presence of glutathione, cysteine, and ascorbic acid using carbon electrodes

The detection of homocysteine, HCys, was achieved with the use of catecholvia1,4-Michael addition reaction using carbon electrodes: a glassy carbon electrode and a carbon nanotube modified glassy carbon electrode.

Dual-electrode microfluidic cell for characterizing electrocatalysts

In this paper we introduce a microelectrochemical cell configured for generation-collection experiments and designed primarily for examining the kinetics of electrocatalysts. The heart of the device consists of two, closely spaced, pyrolyzed photoresist microband electrodes enclosed within a microchannel. The cell is suitable for evaluating the efficiency of electrocatalysts under an unprecedented range of conditions. Specifically, compared to the gold-standard rotating ring-disk electrode (RRDE), this device offers four major advantages. First, collection efficiencies of 97% are easily achieved, compared to values of 20-37% that are characteristic of RRDEs. Second, mass transfer coefficients of 0.5 cm s(-1) are accessible for typical redox species, which is significantly higher than RRDEs (up to 0.01 cm s(-1)). Third, we show that the device can operate effectively at temperatures up to 70 °C, which is important for measuring electrochemical kinetics that are relevant to fuel cell catalysts. Finally, much less catalyst and much smaller volumes of electrolyte solution are required to make kinetic measurements using the microelectrochemical device compared to the RRDE. Here, we present the simple procedure used to fabricate the device, fundamental electroanalytical characterization, and electrocatalytic measurements relevant to the oxygen reduction reaction.

Voltammetric determination of the herbicide Linuron using a tricresyl phosphate-based carbon paste electrode

This paper summarises the results of voltammetric studies on the herbicide 3-(3,4-dichlorophenyl)-1-methoxy-1-methylurea (Linuron), using a carbon paste electrode containing tricresyl phosphate (TCP-CPE) as liquid binder. The principal experimental conditions, such as the pH effect, investigated in Britton-Robinson buffer solutions (pH 2.0–7.0), the peak characteristics for the analyte of interest, or instrumental parameters for the differential pulse voltammetric mode were optimized for the method. As found out, the best electroanalytical performance of the TCP-CPE was achieved at pH 2.0, whereby the oxidation peak of Linuron appeared at ca. +1.3 V vs. SCE. The analytical procedure developed offers good linearity in the concentration range of 1.25–44.20 μg mL⁻¹ (1.77 × 10⁻⁴–5.05 × 10⁻⁶ mol L⁻¹), showing—for the first time—the applicability of the TCP-CPE for anodic oxidations in direct voltammetry (without accumulation). The method was then verified by determining Linuron in a spiked river water sample and a commercial formulation and the results obtained agreed well with those obtained by the reference HPLC/UV determination.

Nanofibrous membrane based tyrosinase-biosensor for the detection of phenolic compounds

A tyrosinase-modified electrode is described to be used as amperometric biosensor for the detection of phenolic compounds in food. The enzyme has been immobilized by drop-coating on a glassy carbon electrode covered by a polyamidic nanofibrous membrane prepared by electrospinning. With respect to others, the selectivity of the designed tyrosinase-biosensor resulted modified by the presence of the nanostructured coating which seems to affect the permeability of phenols as a function of the pH of the solution and of their dissociation constants. The biosensor exhibits a response time of 16 s, a detection limit of 0.05 microM, and a linearity up to 100 microM (slope: -304 nA microM(-1); intercept: -191 nA, r(2)=0.996, n=19). Among others, it can be successfully used for monitoring in real time the release kinetics of phenols encapsulated in polymeric microcapsules.

Determination of tryptophan and histidine by adsorptive cathodic stripping voltammetry using H-point standard addition method

A sequential method is proposed for the determination of tryptophane and histidine by adsorptive cathodic stripping voltammetry using standard addition and H-point standard addition method (HPSAM). The complexes of copper(II) with the amino acids were accumulated onto the surface of a hanging mercury drop electrode for 60s. Then the preconcentrated complexes were reduced by square wave voltammetry and the peak currents were measured. The effect of various parameters such as pH, concentration of copper, accumulation potential, accumulation time and scan rate on the sensitivity were studied by one-at-a time and artificial neural network. Under the optimized conditions, the peak currents at about +0.05 to -0.30 V is proportional to the concentration of tryptophan and histidine over the concentration ranges of 5-220 and 100-1200 nM, respectively. Optimization of the parameters by one-at-a time showed that at accumulation potential of 0.10 V (versus Ag/AgCl reference electrode) the peak current is proportional only to the concentration of tryptophan and histidine does not have any contribution to the current. The optimization results by artificial neural network showed that at accumulation potential of -0.06 V (versus Ag/AgCl) the peak current is proportional to the both concentrations of tryptophan and histidine. Therefore, the method of H-point standard addition has been used for resolving overlap voltamograms for determination of histidine in the present of tryptophane. The method was successfully applied to the determination of tryptophan and histidine in synthetic and real samples.

Pulsed amperometric detection with poly(dimethylsiloxane)-fabricated capillary electrophoresis microchips for the determination of EPA priority pollutants

A miniaturized analytical system for separation and detection of three EPA priority phenolic pollutants, based on a poly(dimethylsiloxane)-fabricated capillary electrophoresis microchip and pulsed amperometric detection is described. The approach offers a rapid (less than 2 min), simultaneous measurement of three phenolic pollutants: phenol, 4,6-dinitro-o-cresol and pentachlorophenol. The highly stable response (RSD = 6.1%) observed for repetitive injections (n > 100) reflects the effectiveness of Au working electrode cleaned by pulsed amperometric detection. The effect of solution conditions, separation potential and detection waveform were optimized for both the separation and detection of phenols. Under the optimum conditions (5.0 mM phosphate buffer pH = 12.4, detection potential: 0.7 V, separation potential: 1200 V, injection time: 10 s) the baseline separation of the three selected compounds was achieved. Limits of detection of 2.2 microM (2.8 fmol), 0.9 microM (1.1 fmol), and 1.3 microM (1.6 fmol) were achieved for phenol, 4,6-dinitro-o-cresol and pentachlorophenol, respectively. A local city water sample and two over-the-counter sore-throat medicines were analyzed in order to demonstrate the capabilities of the proposed technique to face real applications.