A Crosstalk- and Interferent-Free Dual Electrode Amperometric Biosensor for the Simultaneous Determination of Choline and Phosphocholine

Choline (Ch) and phosphocholine (PCh) levels in tissues are associated to tissue growth and so to carcinogenesis. Till now, only highly sophisticated and expensive techniques like those based on NMR spectroscopy or GC/LC- high resolution mass spectrometry permitted Ch and PCh analysis but very few of them were capable of a simultaneous determination of these analytes. Thus, a never reported before amperometric biosensor for PCh analysis based on choline oxidase and alkaline phosphatase co-immobilized onto a Pt electrode by co-crosslinking has been developed. Coupling the developed biosensor with a parallel sensor but specific to Ch, a crosstalk-free dual electrode biosensor was also developed, permitting the simultaneous determination of Ch and PCh in flow injection analysis. This novel sensing device performed remarkably in terms of sensitivity, linear range, and limit of detection so to exceed in most cases the more complex analytical instrumentations. Further, electrode modification by overoxidized polypyrrole permitted the development of a fouling- and interferent-free dual electrode biosensor which appeared promising for the simultaneous determination of Ch and PCh in a real sample.

Theoretical Description for the Electrochemical Determination and Retention of Heavy Metals over the Overoxidized Polypyrrole by Complex Formation

An interesting electrochemical potentiodynamic amperometric heavy metal concentration monitoring system based on overoxidized polypyrrole has been proposed. A model describing the electrochemical behavior in potentiostatic mode of the system with metal complex oxidation during the formation has been developed and analyzed using linear stability theory and bifurcation analysis. It has been shown that the oscillatory behavior may occur more probably in this system than in similar ones due to the cyclical electrode surface impedance change during the chemical and two electrochemical stages. Nevertheless, this system may be efficient for heavy-metal concentration monitoring in vitro and in vivo.

Overoxidized Polypyrrole/Sodium Dodecyl Sulfate/Single Wall Carbon Nanotubes Matrix for the Simultaneous Electrochemical Determination of Heavy Metal Ions by Adsorptive Stripping Voltammetry

In this work, we report an overoxidized polypyrrole (oPPy)/single-wall carbon nanotubes (SWCNTs) matrix, electrochemically coated onto a glassy carbon electrode (GCE). This matrix was characterized by AFM, FTIR, and cyclic voltammetry. It is shown that the developed permslective matrix allows the simultaneous quantification of multiple metal ions, including zinc, cadmium, and lead, using square wave anodic stripping voltammetry. The sensitivities of the oPPy/SWCNTs/GCE for Zn2+, Cd2+, and Pb2+ are respectively, 8.89, 41.3, and 45.4 μA mol L~1. The detection limits of Cd2+ and Pb2+ were found to be respectively equal to 37 μg/L and 69 μg/L In addition, the developed oPPy/SWCNTs based sensor has been successfully used for the detection of lead and cadmium in wastewater samples.

Assay of Phospholipase D Activity by an Amperometric Choline Oxidase Biosensor

A novel electrochemical method to assay phospholipase D (PLD) activity is proposed based on the employment of a choline biosensor realized by immobilizing choline oxidase through co-crosslinking on an overoxidized polypyrrole film previously deposited on a platinum electrode. To perform the assay, an aliquot of a PLD standard solution is typically added to borate buffer containing phosphatidylcholine at a certain concentration and the oxidation current of hydrogen peroxide is then measured at the rotating modified electrode by applying a detection potential of +0.7 V vs. SCE. Various experimental parameters influencing the assay were studied and optimized. The employment of 0.75% (v/v) Triton X-100, 0.2 mM calcium chloride, 5 mM phosphatidylcholine, and borate buffer at pH 8.0, ionic strength (I) 0.05 M allowed to achieve considerable current responses. In order to assure a controlled mass transport and, at the same time, high sensitivity, an electrode rotation rate of 200 rpm was selected. The proposed method showed a sensitivity of 24 (nA/s)⋅(IU/mL)−1, a wide linear range up to 0.33 IU/mL, fast response time and appreciable long-term stability. The limit of detection, evaluated from the linear calibration curve, was 0.005 IU/mL (S/N = 3). Finally, due to the presence of overoxidized polypyrrole film characterized by notable rejection properties towards electroactive compounds, a practical application to real sample analysis can be envisaged.