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A new electrochemical magnetoimmunosensor (EMIS) has been developed for the screening of residues of sulfonamide antimicrobials in honey samples. The immunosensor is able to detect up to ten different sulfonamide congeners at levels below the action points established in some European countries (25 μg kg) after a hydrolysis step in which the sulfonamides are released from the corresponding conjugates formed in samples of this type. In spite of the complexity of the sample after the hydrolysis procedure, the EMIS could perform quantitative measurements, directly in these samples, without any additional sample cleanup or extraction step. For example, sulfapyridine, used as a reference, can be detected in hydrolyzed honey with a limit of detection (IC) of 0.1 ± 0.03 μg kg. Considering that the use of antibiotics for bee treatment is prohibited in the European Union, the immunosensor presented here could be an excellent screening tool. Moreover, several samples can be processed in parallel, which facilitates the analysis, reducing the necessity to use more costly confirmatory methods for just screening. As a proof of concept, a set of blind honey samples (spiked and incurred) were analyzed and the results were compared with those obtained by high-performance liquid chromatography-tandem mass spectrometry, demonstrating the potential of the EMIS as a screening tool. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

An electrochemical magneto immunosensor for the detection of low concentrations of paraquat (PQ) in food samples has been developed and its performance evaluated in a complex sample such as potato extracts. The immunosensor presented uses immunoreagents specifically developed for the recognition of paraquat, a magnetic graphite-epoxy composite (m-GEC) electrode and biofunctionalized magnetic micro-particles ( PQ1- BSAMP) that allow reduction of the potential interferences caused by the matrix components. The amperometric signal is provided by an enzymatic probe prepared by covalently linking an enzyme to the specific antibodies (Ab198-cc-HRP). The use of hydroquinone, as mediator, allows recording of the signal at a low potential, which also contributes to reducing the background noise potentially caused by the sample matrix. The immunocomplexes formed on top of the modified MP are easily captured by the m-GEC, which acts simultaneously as transducer. PQ can be detected at concentrations as low as 0.18 ± 0.09 μg L. Combined with an efficient extraction procedure, PQ residues can be directly detected and accurately quantified in potato extracts without additional clean-up or purification steps, with a limit of detection (90 % of the maximum signal) of 2.18 ± 2.08 μg kg, far below the maximum residue level (20 μg kg) established by the EC. The immunosensor presented here is suitable for on- site analysis. Combined with the use of magnetic racks, multiple samples can be run simultaneously in a reasonable time. [ABSTRACT FROM AUTHOR]

Impedance spectroscopy is a rapidly developing technique for the transduction of biosensing events at the surface of an electrode. The immobilization of biomaterial as DNA strands on the electrode surface alters the capacitance and the interfacial electron transfer resistance of the conductive electrodes. The impedimetric technique is an effective method of probing modifications to these interfacial properties, thus allowing the differentiation of hybridization events. In this work, an avidin bulk-modified graphite–epoxy biocomposite (Av-GEB) was employed to immobilize biotinylated oligonucleotides as well as double-stranded DNA onto the electrode surface. Impedance spectra were recorded to detect the change in the interfacial electron transfer resistance ( R et) of the redox marker ferrocyanide/ferricyanide at a polarization potential of +0.17 V. The sensitivity of the technique and the good reproducibility of the results obtained with it confirm the validity of this method based on a universal affinity biocomposite platform coupled with the impedimetric technique. [ABSTRACT FROM AUTHOR]

Impedance spectroscopy is proposed as the transduction principle for detecting the hybridization of DNA complementary strands. In our experiments, different DNA oligonucleotides were used as model gene substances. The gene probe is first immobilized on a graphite-epoxy composite working electrode based genosensor. Detection principle is based on changes of impedance spectra of a redox marker, the ferro/ferricyanide couple, after hybridization with target DNA. Resistance offered to the electrochemical reaction serves as the working signal, allowing for an unlabelled gene assay. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]