Ultrasensitive sensing of Androctonus australis hector scorpion venom toxins in biological fluids using an electrochemical graphene quantum dots/nanobody-based platform.

Rapid and sensitive detection of low levels of scorpion venom toxins in biological fluids is of tremendous importance for decision-taking in cases of envenomation by scorpions stings. In Tunisia, at least 1200 severe envenomation cases by Androctonus australis hector (Aah) scorpion stings were reported annually. In this work, we report on a novel electrochemical immuno-sandwich to detect the Aah50 toxic fraction within the Aah scorpion venom using the bispecific nanobody format specially designed to highly recognize and neutralize the two most toxic molecules in the AahG50 venom fraction (i.e. AahI and AahII toxins), graphene quantum dots (GQDs) constructed on the surface carbon screen-printed electrodes. Hydroquinone/HO/peroxidase system was used to amplify the current in order to achieve the detection of low levels of AahG50. Electrochemical studies revealed a high sensitivity toward the AahG50 with a sensitivity of 18.2 nA mL pg and a picomolar limit of detection as low as 0.55 pg mL. The platform exhibits very good metrological performances such as repeatability, reproducibility, selectivity and long storage stability. Matrix effect was found to be insignificant as demonstrated by assays performed in human blood serum and urine.