Ultrasensitive electrochemical immunoassay based on counting single magnetic nanobead by a combination of nanobead amplification and enzyme amplification

An ultrasensitive electrochemical immunoassay method based on Counting single magnetic nanobead (MNB) with combined amplification of nanobead and enzyme. Carcinoembryonic antigen (CEA) and MNB were initially immobilized on substrate at 1:1 molar ratio through sandwich immunoreactions. The MNBs were then labeled with alkaline phosphatase (AP) and continuously introduced to capillary with disodium phenyl phosphate (DPP). APs convert DPPs into a phenol zone around each moving MNB, i.e., one CEA. The phenol zones can be electrochemically detected as peaks and Counted for CEA quantification. The detection limit for CEA is 5.0 x 10(-17) mol/L. (c) 2009 Elsevier B.V. All rights reserved.