Ultrasensitive electrochemical strategy for trace detection of APE-1 via triple signal amplification strategy.

A novel ultrasensitive electrochemical immunoassay for the determination of apurinic/apyrimidinic endonuclease (APE-1) using a three-step signal amplification process was reported in this work. The first-step signal amplification process was based on the labeled biotinylated alkaline phosphatase (bio-AP) on the nickel hexacyanoferrates nanoparticle-decorated Au nanochains (Ni-AuNCs) toward the biocatalysis of ascorbic acid 2-phosphate (AA-P) to in-situ produce ascorbic acid (AA). Then the signal was further amplified by electrochemical oxidation of the in-situ-produced AA because of the catalysis of Ni-AuNCs. Finally, with the nanochain-modified streptavidin (SA), the stoichiometry of bio-AP could be increased through the specific and high affinity interaction of streptavidin-biotin. On the other hand, a kind of organic material (PTC-NH(2)), owing the amino-functionalized interface and unique electrochemical properties, as matrix for primary antibodies (Ab(1)) immobilization could lower the background current signal and enhance the amount of immobilized Ab(1). With a sandwich-type immunoreaction, the triple signal amplification greatly enhanced the sensitivity for the detection of APE-1. Under optimal conditions, the electrochemical immunosensor exhibited a linear range of 0.01-100 pg/mL with an extremely low detection limit of 3.9 fg/mL (signal/noise=3).