Direct ELISA analysis of 5-HT was performed by coating wells of a 96-well plate with 50 µL per well of 5-HT-BSA diluted in carbonate/bicarbonate buffer, at a concentration of 1 µg/mL overnight at 4℃. Wells of the plate were washed, blocked with 1%BSA blocking buffer, and incubated with 50 µL per well of 5-HT-HRP monoclonal antibody serial diluted starting from a concentration of 4µg/mL for 45 min at 37℃. Detection was performed using an Ultra TMB Substrate for 10 minutes at 37℃ in the dark. The reaction was stopped with sulfuric acid and absorbances were read on a spectrophotometer at 450 nm.