Reagentless system for sulphite determination based on polyaniline

A new reagentless system for sulphite (or sulphur dioxide) determination is reported based on the use of an organic conducting polymer, polyaniline, and its absorbance variation at 550 nm, depending on the sulphite concentration. After chemical polymerisation of aniline a very thin film of polyaniline is obtained. Although the response is not fully reversible, each film can be used for at least 10 measurements for low analyte concentrations (up to 0.5 mg l⁻¹) and five measurements for higher sulphite concentrations. Moreover, the reproducibility, ease of preparation and low cost of the films, permit the use of a new disposable system for each measurement. When the change in absorbance at 550 nm was measured for 210 s (stabilisation time), the system showed a linear response, which ranged from 0.025 to 1.50 mg l⁻¹ of sulphite. A theory with regard to the reaction mechanism between the polyaniline films and sulphite is also proposed. The system was applied to sulphite determination in wine samples and the results were in agreement with those obtained by the Official Method of Analysis (iodometric titration).     

Reagentless Glucose Biosensor Based on the Direct Electrochemistry of Glucose Oxidase on Carbon Nanotube‐Modified Electrodes

The direct electrochemistry of glucose oxidase (GOD) was revealed at a carbon nanotube (CNT)‐modified glassy carbon electrode, where the enzyme was immobilized with a chitosan film containing gold nanoparticles. The immobilized GOD displays a pair of redox peaks in pH 7.4 phosphate buffer solutions (PBS) with the formal potential of about ?455 mV (vs. Ag/AgCl) and shows a surface‐controlled electrode process. Bioactivity remains good, along with effective catalysis of the reduction of oxygen. In the presence of dissolved oxygen, the reduction peak current decreased gradually with the addition of glucose, which could be used for reagentless detection of glucose with a linear range from 0.04 to 1.0 mM. The proposed glucose biosensor exhibited high sensitivity, good stability and reproducibility, and was also insensitive to common interferences such as ascorbic and uric acid. The excellent performance of the reagentless biosensor is attributed to the effective enhancement of electron transfer between enzyme and electrode surface by CNTs, and the biocompatible environment that the chitosan film containing gold nanoparticles provides for immobilized GOD.     

Combining ferrocene,thiophene and a boronic acid: a hybrid ligand for reagentless electrochemical sensing of cis-diols

A redox-active affinity ligand suitable for reagentless sensing of cis-diols was synthesised and characterised. 4-[(Ferrocenylamino)methyl]thiophene-3-boronic acid (FcTBA) was allowed to interact with the model cis-diol, sorbitol. A discrete, cathodic shift of the redox potential was observed upon interaction of FcTBA with sorbitol thus providing simultaneous differentiation between the free and bound forms of this sensor molecule. Similar behaviour was observed also for FcTBA co-immobilised with thiophene in a mixed self-assembled monolayer on a gold electrode.     

Direct and rapid electrochemical immunosensing system based on a conducting polymer

A system device using multifunctional conjugated copolymer poly(5-hydroxy-1,4-naphthoquinone-co-hydroxy-2-thioacetic acid-1,4-naphthoquinone) acting both as immobilizing and transducing element for reagentless immunosensor has been constructed. Its functionality was evaluated in an antigen-antibody interaction model using ovalbumin-anti-ovalbumin. It was shown that the system specifically detects via electrochemical signal the antigen-antibody immune interaction in a reagentless context. Comparison to the conventional ELISA technique relevant to performance and sensitivity was presented.     

Construction of L‐Lysine Sensor by Layer‐by‐Layer Adsorption of L‐Lysine 6‐Dehydrogenase and Ferrocene‐Labeled High Molecular Weight Coenzyme Derivative on Gold Electrode

A ferrocene‐labeled high molecular weight coenzyme derivative (PEI‐Fc‐NAD) and a thermostable NAD‐dependent L ‐lysine 6‐dehydrogenase (LysDH) from thermophile Geobacillus stearothermophilus were used to fabricate a reagentless L ‐lysine sensor. Both LysDH and PEI‐Fc‐NAD were immobilized on the surface of a gold electrode by consecutive layer‐by‐layer adsorption (LBL) technique. By the simple LBL method, the reagentless L ‐lysine sensor, with co‐immobilization of the mediator, coenzyme, and enzyme was obtained, which exhibited current response to L ‐lysine without the addition of native coenzyme to the analysis system. The amperometric response of the sensor was dependent on the applied potential, bilayer number of PEI‐Fc‐NAD/LysDH, and substrate concentration. A linear current response, proportional to L ‐lysine concentration in the range of 1–120 mM was observed. The response of the sensor to L ‐lysine was decreased by 30% from the original activity after one month storage.     

ZnS quantum dots derived a reagentless uric acid biosensor

A reagentless amperometric uric acid biosensor based on zinc sulfide (ZnS) quantum dots (QDs) was firstly developed. It could detect uric acid without the presence of an electron mediator. The carboxyl group functionalized ZnS QDs were synthesized, and they were soluble biocompatible and conductive. ZnS QDs conjugates could provide increased enzyme binding sites, which may result in higher enzyme loading. Thus, the proposed uricase/ZnS QDs/l-cys biosensor exhibited higher amperometric response compared to the one without QDs (uricase/l-cys biosensor). In addition, there was little AA interference. It showed a linear dependence on the uric acid concentration ranging from 5.0 × 10⁻⁶ to 2.0 × 10⁻³ mol L⁻¹ with a detection limit of 2.0 × 10⁻⁶ mol L⁻¹ at 3σ.     

Silicate electrochemical measurements in seawater: Chemical and analytical aspects towards a reagentless sensor

From the study of molybdenum oxidation in aqueous solutions we developed a semi-autonomous method to detect silicate in aqueous samples. Molybdenum oxidation was used to form molybdate in acidic media. The silicomolybdic complex formed with silicate is detectable by amperometry or cyclic voltammetry. The new electrochemical method is in good agreement with the method conventionally used for environmental water silicate analysis. In the second stage, a completely reagentless method was developed using molybdate and proton produced during molybdenum oxidation. Reproducibility tests show a precision of 2.6% for a concentration of 100 μmol L⁻¹. This new method will be very suitable for the development of new autonomous silicate sensors easy to handle and without reagents. In this paper we present the analytical and chemical aspects necessary for a complete documentation of the method before the development of a new reagentless sensor.     

A reagentless electrochemiluminescent immunosensor for apurinic/apyrimidinic endonuclease 1 detection based on the new Ru(bpy)3/bi-arginine system

Apurinic/apyrimidinic endonuclease 1 (APE-1), a kind of multifunctional protein widely-distributed in the body, plays an essential role in the DNA base excision repair and serves as multiple possible roles in the response of human cancer to radiotherapy and chemotherapy. In this work, an ultrasensitive solid-state electrochemiluminescence (ECL) immunosensor is designed to determine APE-1 based on the new Ru(bpy)₃²⁺/bi-arginine system. The bi-arginine (bi-Arg) is decorated on the Au nanoparticles functionalized magnetic Fe₃O₄/reduced graphene oxide (bi-Arg/Au@Fe₃O₄–rGO) according to the self-assembling and covalent cross-linking interaction to obtain the functionalized nanocomposite of bi-Arg/Au@Fe₃O₄–rGO. Herein, the bi-Arg/Au@Fe₃O₄–rGO plays not only an amplification label to enhance the ECL signal of Ru(bpy)₃²⁺ due to the coreactant of bi-Arg but also an ideal nanocarrier to load numerous secondary antibody. Based on sandwich-type immunoassay format, this proposed method offers a linear range of 1.0 fg mL⁻¹–5.0 pg mL⁻¹ and an estimated detection limit of 0.3 fg mL⁻¹ for the APE-1. Moreover, the reagentless ECL immunosensor also exhibits high sensitivity, excellent selectivity and good stability, which has greatly potential development and application in clinical diagnostics, immunology and biomedical research.     

The Sensitized Solid‐Phase Electrochemiluminescence of Electrodeposited Poly‐Luminol/Aniline on AuAg/TiO2 Nanohybrid Functionalized Electrode for Flow Injection Analysis

In this study, a copolymer of luminol with aniline is electrochemically deposited onto the AuAg/TiO₂ nanohybrid functionalized indium tin oxide coated glass. It is used as a reagentless electrochemiluminescent (ECL) electrode for flow‐injection‐analysis (FIA). The properties of this solid phase ECL electrode are characterized by cyclic voltammetry, electrochemical impedance spectroscopy and scanning electron microscopy etc. It has stronger ECL emission, sensitive response for target analytes and excellent stability. The so‐prepared ECL electrode shows sensitive response to reactive oxygen species thereafter to be applied for determination of hydrogen peroxide with FIA mode. Under optimized conditions, a mass detection limit of 0.822 pg of hydrogen peroxide was obtained. Thus the hydrogen peroxide residues in samples were detected with satisfactory result.     

A Reagentless Electrochemical DNA Sensor Based on a Self-powered DNA Machine

Herein, a reagentless electrochemical DNA sensor based on a self-powered DNA machine for detecting survivin mRNA in cells is developed. The metal-organic framework (MOFs) loaded with DNAzyme cofactors (Mn²⁺) is coated on PTFE rods on the Au surface and assembled with the DNA walker, overcoming the complexity of adding metal ions from the external environment. In addition, the orbital chain is modified by a synthetic bisferrocene signal marker, which further enables signal amplification. Under optimal conditions, the sensor exhibits a range from 1×10⁻¹⁴ mol/L to 1×10⁻⁸ mol/L with a detection limit (S/N=3) of 1.28 fM.