Surface electrochemical enzyme immunoassay for the highly sensitive measurement of B-type natriureric peptide

B-type natriuretic peptide (BNP), a peptide hormone, was determined by electrochemical enzyme immunoassay through the following procedure. First, a certain concentration of sample BNP was added to the solution containing anti-BNP antibody modified with acetylcholinesterase (AChE) to undergo the immunological reaction. Then BNP-modified gold particles were added into the BNP/AChE-labeled anti-BNP antibody solution so that the unreacted AChE-labeled anti-BNP antibody was removed from the assay solution. Finally the AChE activity in the solution was measured, based on the chemisorption/electrochemical reductive desorption process of a thiol compound on a silver electrode. The chemisorption (accumulation) of thiocholine, which was produced through the enzymatic reaction, resulted in the enhanced sensitivity for the determination of AChE, and accordingly, for that of BNP. BNP could be determined in the concentration range from 20 to 200 ppt (pg mL−1), which indicated that the proposed enzyme immunoassay procedure was high enough for the measurement of the peptide hormone in blood samples.