Abstract: Platinum electrodes modified with non-conducting films were assembled and used for the rapid amperometric detection of nitrites and nitrates in water by batch and flow injection analysis (FIA). Parameters such as the permeability of electropolymerised films to nitrites and nitrates, interference effects and recovery studies of these kinds of sensors have been optimized to demonstrate the analytical suitability of the proposed method. Contrary to the standard colorimetric method, which is based on carcinogenic reagents, the amperometric detection of nitrites and nitrates is very simple and rapid and does not require any reagent for nitrite detection. In addition, this method could be easily extended to the analysis of nitrites and nitrates in various types of samples such as food, soils, vegetables and fertilizers.

Abstract: Glucose oxidase, lactate oxidase, -aminoacid oxidase and alcohol oxidase were immobilized on new films based on 2,6-dihydroxynaphthalene (2,6-DHN) copolymerised with 2-(4-aminophenyl)-ethylamine (AP-EA) onto the Pt electrodes. The electropolymerisation was performed by cyclic voltammetry. Different scan rates and scan potential ranges were investigated and selected according to the monomers used. These sensors were tested for hydrogen peroxide, ascorbic acid and acetaminophen by cyclic voltammetry and amperometry. The amperometric studies were carried out in batch as well as in a flow injection analysis (FIA) system. Analytical parameters such as reproducibility, interference rejection, response time, buffer, storage and operational time of the sensors have been studied. These films were also characterized by X-ray photoelectron spectroscopy (XPS). Different strategies for enzyme immobilization were performed and discussed: enzyme entrapment in the film during the electropolymerisation and covalent attachment of the enzyme to the film via a carbodiimide (1-ethtl-3-(3-dimethylaminopropyl)carbodiimide, EDC) or glutaraldehyde. Different parameters were considered in order to optimise the immobilization procedures. Results provide a guide to design high sensitive, stable and interference-free biosensors. In addition, studies were performed using these probes in an original FIA based on solenoidal valves. Sensor stability, life time and dynamic range were also optimized in these conditions.

Abstract: A flow-injection immunoassay (FI-IA) method with amperometric detection for aflatoxin M1 (AFM1) determination in milk has been developed. The first step consists in an incubation of the sample containing AFM1 (Ag) with fixed amounts of anti-AFM1 antibody (Ab) and of the tracer (Ag*, AFM1 covalently coupled to HRP) until equilibrium is reached. In this mixture a competition occurs between Ag and Ag* for the Ab. The mixture is then injected into a flow system where the separation of the free tracer (Ag*) and the antibody-bound tracer (AbAg*) is performed in a column with immobilized Protein G. The antigen-antibody complexes are retained in the column due to the high affinity of the Protein G for the antibody. The activity of the eluted enzyme label is then amperometrically detected. The immunoassay was optimized relative to conditions for antibody-antigen incubation (pH, incubation time, ionic strength, temperature) and enzymatic label detection. This method showed a dynamic concentration range between 20 and 500 ppt AFM1, a low detection limit (11 ppt), good reproducibility (RSD < 8%) and a high throughput (six samples per hour in triplicate). Different milk samples were analyzed and the results were in good agreement with those obtained by HPLC using the AOAC 2000.08 method.