Reduced nonspecific protein adsorption by application of diethyldithiocarbamate in receptor layer of diphtheria toxoid electrochemical immunosensor

Robert Ziółkowski , Adrianna Kaczmarek , Ilona Kośnik , Elżbieta Malinowska

Abstract

The immunoassay technology is of particular importance for both the environmental industry and clinical analysis. Biosensors, with the sensing layer based on antibodies or their fragments, offer high selectivity and short detection times. However, analytical devices where the electrochemical signal corresponds to changes in the interfacial region (sensing layer/electrode surface) are very susceptible to any nonspecific adsorption. Unfortunately, proteins (including antibodies) belong to the molecules showing high non-specific interactions with solid substrates. Herein, we propose diethyldithiocarbamate as a new antifouling and highly conductive agent. The investigations were conducted to evaluate its interaction with chosen proteins and the mechanism of its co-adsorption with biotinylated thiol (an anchor point for immune-sensing elements). The developed receptor layer is characterised by reduced nonspecific protein adsorption and high conductivity with the same preserved specificity of the antibodies (immobilised by the streptavidin/biotin bioaffinity technique). This allowed for selective detection of the diphtheria toxoid, an inactive toxin secreted by virulent strains of Corynebacterium diphtheria, at the level of 5 ⋅ 10⁻⁶ μg⋅ml⁻¹ (1 ⋅ 10⁻⁶ Lf⋅ml⁻¹) and in the real-life sample.