Ultra-sensitive electrochemiluminescence biosensor for abrin detection based on dual-labeled phage display affibodies and polystyrene nanospheres

Abrin is a plant cytotoxin that poses a high threat to public safety and therefore requires highly sensitive and efficient detection methods. Affibody molecules are artificial affinity proteins that have been widely studied in bioimaging and medical treatment but rarely used in bioassays. In this work, an electrochemiluminescence (ECL) biosensor for abrin was established with biotin and Ru(bpy)32+ dual-labeled phage display affibodies as molecular recognition and signal element. On this basis, dual-labeled polystyrene nanospheres (nano-PSs) were chosen to link with phages and further achieve ultra-sensitive detection. This assay has a triple signal amplification. First, capsid proteins of M13 phages have connected numerous signal molecules. Second, the nano-PSs bound to the surface of the phages also contained quite a few signal molecules. Third, with the theoretically infinitely repeatable “biotin - streptavidin (SA) - biotin” composite unit as the “mortise and tenon structure”, the dual-labeled nano-PSs further formed highly stacked nano-aggregates, ultimately achieving significant signal amplification. Besides, the detection platform of this assay is a portable electrochemiluminescence sensor based on the screen-printed electrode, which is small and easy to operate. Limit of detection (LOD) for abrin of the ECL biosensor was 9.3 fg/mL and the linear detection range was observed from 10 fg/mL to 100 pg/mL. This new biosensing system has also demonstrated good reproducibility, specificity, practicability and has great potential for highly sensitive detection of contaminants, toxins and biomarkers in environmental monitoring and clinical application.