Electrochemical transduction

Small molecular weight organic residues in food (such as pesticides or their metabolites) have few distinguishing optical or electrochemical characteristics, the detection of stoichiometric binding of these compounds to antibodies is typically accomplished using competitive binding assay formats.

The main limitation of these techniques is the electrochemical detection of the immunoreaction because it is necessary to use enzymes that will generate electrochemical active compounds.

Electrochemical immunosensors have been widely used for food analysis in amperometric, potentiometric and conductimetric configurations.

Some examples of new developments are the disposable screen-printed electrodes for the detection of polycyclic aromatic hydrocarbons (PAHs) [90] and the use of recombinant single-chain antibody fragments [91] for atrazine determinations.

Alarcon et al. [92] described a direct, competitive electrochemical ELISA development for the quantitative determination of OTA in wine using polyclonal antibodies. The assay is carried out on carbon-based screen-printed electrodes.

Recently, a novel electrochemical immunosensing strategy for the detection of sulfonamide antibiotics in milk based on magnetic beads has been presented by Zacco et al. [93]. Among the different strategies for immobilizing the class-specific anti-sulfonamide antibody to the magnetic beads — such as those based on the use of Protein A or carboxylate modified magnetic beads, the best strategy was the covalent bonding on tosyl-activated magnetic beads. The immunological reaction for the detection of sulfonamide antibiotics performed on the magnetic bead is based on a direct competitive assay using a tracer with HRP for the enzymatic labeling. After the immunochemical reactions, the modified magnetic beads can be easily captured by a magneto sensor made of graphite-epoxy composite (m-GEC), which is also used as the transducer for the electrochemical immunosensing. The electrochemical detection is thus achieved through a suitable substrate for the enzyme HRP and an electrochemical mediator.

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