Ultrasensitive detection of domoic acid in mouse blood by competitive ELISA using blood collection cards

Domoic acid (DA), an analog of the excitatory amino acid glutamate, is produced by the diatom genus Pseudo-nitzschia and acts as a neurotoxin in humans. During diatom blooms, DA can contaminate shellfish, as well as other filter feeding organisms, and can be transferred by ingestion to higher trophic levels, including marine mammals and humans. The prevalence of this algal toxin and its effects on protected species makes measurement of domoic acid in living animals a necessary biomonitoring tool for the near future. Blood collection cards have already been used for the sampling, extraction and detection of brevetoxin in blood from exposed laboratory animals and, more recently, marine mammals. However, a difficulty unique to measuring DA in blood is the rapid rate (>95% in 2 h) at which it is cleared from blood. To meet this challenge, a direct competitive ELISA (cELISA), a method of detection with extremely high sensitivity and specificity, was used to analyze the blood of DA-exposed mice after extraction from the blood collection cards. More than 99% of DA was cleared from blood within 4 h post dosage; however, domoic acid was still quantifiable (>0.7  ng ml−1) at 4 h from blood spot extracts and still detectable at 24 h when compared to control blood spots. By using this highly sensitive assay in conjunction with the use of blood spot cards for easy blood sample extraction, this method could be a very effective means of biomonitoring domoic acid in marine mammals in the field, as well as human populations.