Capillary electrophoretic enzyme immunoassay with electrochemical detection using a noncompetitive format

A capillary electrophoretic enzyme immunoassay with electrochemical detection (CE-EIA-ED) using a noncompetitive format has been developed. In this method, antigen (Ag) reacts with an excess amount of horseradish peroxidase (HRP)-labeled antibody (Ab*). The free Ab* and the bound Ag–Ab* complex produced in the solution are separated by capillary zone electrophoresis in a separation capillary. Then they catalyze enzyme substrate 3,3′,5,5′-tetramethylbenzide (TMB(Red)) and H2O2 in a reaction capillary following the separation capillary. The reaction product, TMB(Ox), can be determined using amperometric detection on a carbon fiber microdisk bundle electrode at the outlet of the reaction capillary. Due to the amplification of the enzyme, a significant amount of TMB(Ox) can be produced for detection. Therefore, the limit of detection (LOD) of CE-EIA-ED is very low. A tumor marker (CA15-3) was used as a model, in order to test the method. The concentration LOD of CA15-3 is 0.024 U/ml, which corresponds to a mass detection limit of 1.3×10−7 U.