Development of a hypoxanthine biosensor based on immobilized xanthine oxidase chemically modified electrode

Brushite nanoparticles based electrochemical sensor for detection of uric acid, xanthine, hypoxanthine and caffeine

The research in the field of biosensors has recently been focused on the design and development of functional electrode materials that can respond to changes in their biochemical environment. Here, we report the synthesis of dicalcium phosphate dihydrate (DCPD), also known as brushite (CaHPO₄·2H₂O) by soft chemical method and its application for electrochemical sensing of four different analytes. Phase purity, structure, chemical composition and surface morphology of the synthesized nanoparticles have been investigated using powder XRD, FTIR, SEM, XPS and HRTEM methods. Electrochemical sensor was prepared by modifying GCE with brushite and the modified electrodes were successfully used for either independent or simultaneous determination of uric acid, xanthine, hypoxanthine and caffeine in their mixture. The brushite/GCE exhibited four strong well-defined separate peaks corresponding to the oxidation of UA, XN, HXN and CF in phosphate buffer saline (PBS) at pH 7.4. The fabricated electrode showed low detection limits (S/N = 3) of 0.576, 1.0, 0.076 and 1.26 μM for UA, XN, HXN and CF respectively. Practical application of the fabricated electrode has been demonstrated by determining UA, XN, HXN and CF in human urine and coffee samples by direct method. The brushite offers scope for fabrication of sensor systems for implantable medical applications.

An amperometric hypoxanthine biosensor based on Au@FeNPs for determination of hypoxanthine in meat samples

A xanthine oxidase (XOD) from buttermilk was immobilized covalently onto boronic acid functionalized gold coated iron nanoparticles (Au@FeNPs) electrodeposited on pencil graphite (PG) electrode, via the boroester linkages, between free hydroxyl groups of boronic acid, α-COOH and -NH2 groups of enzyme. The surface functionalization of Fe/Au nanoparticles with boronic acid (Au@FeNPs) on pencil graphite (PG) electrode was characterized by Fourier transform infrared (FTIR), cyclic voltammetry (CV), scanning electron microscopy (SEM), atomic force microscopy (AFM) and Electrochemical impedance spectroscopy (EIS) before and after immobilization of XOD. The biosensor exhibited optimum response within 3s at pH 7.2 and 30 °C and linearity in the range, 0.05 μM to 150 μM for hypoxanthine with a detection limit of 0.05 μM (S/N=3). Apparent Michaelis Menten constant (Km(app)) for hypoxanthine was 40 μM and Imax 0.125 mA. The biosensor was employed to determine hypoxanthine in fish, chicken, pork, beef meat and lost 50% of its initial activity after its 200 uses over 100 days, when stored at 4 °C.

Progress and recent advances in fabrication and utilization of hypoxanthine biosensors for meat and fish quality assessment: a review

This review provides an update on the research conducted on the fabrication and utilization of hypoxanthine (Hx) biosensors published over the past four decades. In particular, the review focuses on progress made in the development and use of Hx biosensors for the assessment of fish and meat quality which has dominated research in this area. The various fish and meat freshness indexes that have been proposed over this period are highlighted. Furthermore, recent developments and future advances in the use of screen-printed electrodes and nanomaterials for achieving improved performances for the reliable determination of Hx in fish and meat are discussed.

An Amperometric Biosensor for Uric Acid Determination Prepared from Uricase Immobilized in Polypyrrole Film

In order to prepare a biosensor for the determination of uric acid, electropolymerization of pyrrole on Pt surface was carried out with an electrochemical cell containing pyrrole, ferrocene (as a electron mediator) and tetrabutylammonium tetrafluoroborat in acetonitrile by cyclic voltammetry between 0.0 and 1.0 V (vs. Ag/AgCl) at a scan rate of 50 mV/s upon Pt electrode. Uricase was immobilized by a glutaraldehyde/gelatine croslinking procedure on to polypyrrole film after the electropolymerization processes. The response of the biosensor against uric acid was measured after 330 seconds following the application of a constant potential of +0.7 V (vs. Ag/AgCl). The resulting biosensor exhibits excellent electrocatalysis for the uric acid. The amperometric determination is based on the electrochemical detection of H2O2, which is generated in enzymatic reaction of uric acid. The sensor responds to uric acid with a detection limit of 5.0 x 10(-7) M. The sensor remains relatively stable for 5 weeks. Interference effect were investigated on the amperometric response of the biosensor. Determination of uric acid was carried out in the biological fluids by biosensor.

An Amperometric Biosensor for Uric Acid Determination Prepared From Uricase Immobilized in Polyaniline-Polypyrrole Film

A new amperometric uric acid biosensor was developed by immobilizing uricase by a glutaraldehyde crosslinking procedure on polyaniline-polypyrrole (pani-ppy) composite film on the surface of a platinum electrode. Determination of uric acid was performed by the oxidation of enzymatically generated H₂O₂ at 0.4 V vs. Ag/AgCl. The linear working range of the biosensor was 2.5×10-6 - 8.5×10-5 M and the response time was about 70 s. The effects of pH, temperature were investigated and optimum parameters were found to be 9.0, 55 oC, respectively. The stability and reproducibility of the enzyme electrode have been also studied.

An amperometric biosensor for xanthine determination prepared from xanthine oxidase immobilized in polypyrrole film

In order to prepare a biosensor for the determination of xanthine, electropolymerization of pyrrole on Pt surface was carried out with an electrochemical cell containing pyrrole, ferrocene (as a electron mediator) and tetrabutylamonium tetrafluoroborat in acetonitrile by cyclic voltammetry between 0.0 and 0.9V (vs SCE) at a scan rate of 50mV/s upon Pt electrode. Xanthine oxidase was immobilized by a glutaraldehyde/bovine serum albumin (BSA) crosslinking procedure on to polypyrrole film after the electropolymerization processes. The response of the biosensor against xanthine was measured after 3-4 min following the application of a constant potential of + 0.7 V (vs SCE). The resulting biosensor exhibits excellent electrocatalysis for the xanthine. The amperometric determination is based on the electrochemical detection of H202, which is generated in enzymatic reaction of xanthine. The effect of various experimental conditions was examined for the determination of the analytical performance. The sensor responds to xanthine with a detection limit of 1.0 x 10(-6)M. The response current increases linearly with xanthine concentration up to 4.0 x 10(-4) M. The sensor remains relatively stable for 45 days.

Voltammetric and impedance studies of inosine-5'-monophosphate and hypoxanthine

The oxidation mechanism and adsorption of inosine 5'-monophosphate and hypoxanthine were investigated in solutions of different pH using voltammetric and impedance methods at glassy carbon electrodes. For both compounds, the pH dependence from differential pulse voltammetry showed that the same number of electrons and protons are involved in the rate-determining step of the electrochemical reaction. In the case of hypoxanthine, it was also possible to study the effect of different concentrations. At high concentrations of hypoxanthine, two oxidation peaks were observed, the first due to hypoxanthine oxidation with formation of oligomers and the second due to hypoxanthine oligomer oxidation, both compounds adsorbing strongly. Impedance measurements corroborated the voltammetric results and enabled the study of the adsorption of hypoxanthine on glassy carbon.

Selective and sensitive biosensor for theophylline based on xanthine oxidase electrode

Milk and microbial xanthine oxidases (XOs) were used for the construction of amperometric enzyme electrodes. Substrate specificity differences of these enzymes were studied. Of the two enzymes, only the microbial XO was found to oxidize theophylline, but not theobromine and caffeine. The substrate specificity of microbial XO was affected by pH, where the optimum for xanthine was 5.5, while for theophylline it was in the range from 6.5 to 8.5. The theophylline biosensor showed a low detection limit of 2 x 10(-7) M and signal linearity up to 5 x 10(-5) M. The sensitivity of the microbial XO electrode to theophylline could be selectively eliminated by immersion in alkaline phosphate solution, thus allowing for the construction of a blank electrode for differential measurements. The feasibility of this approach has been demonstrated by the determination of free (unbound) and total theophylline in blood samples. The biosensor exhibited good operational (>6 h) and shelf (>3 months) stability when trehalose was used as a stabilizer of the biocatalytic layer.