Artificial enzyme; Molecularly imprinted catalytic polymer; Peroxidase-like catalyst; Core–shell magnetic particles; Electrochemical sensor
5-hydroxyindole-3-acetic BAF312 (5-HIAA) is the main metabolite of serotonin. The levels of this neurotransmitter can be altered in some pathological conditions, such as carcinoid tumors of the enterochromaffin cells of the small intestine, which release large amounts of serotonin, leading to a substantial increase of urinary excretion of 5-HIAA. The normal range for urinary 5-HIAA is 2–8 mg/24 h (roughly ∼2–8 ppm). Excretion levels above 25 mg/24 h (∼25 ppm) are considered positive for carcinoid tumor, although patients with these tumors can produce even 50 times higher amounts of 5-HIAA than normal levels . Unfortunately, concentration levels of 5-HIAA found in urine are diet-dependent and small changes even above abnormal limits may be related to a non-tumor gastric disorder, which implies that consecutive measurements for diagnosis are required in order to prevent false positives.