A new ratiometric electrochemical immunoassay for reliable detection of nuclear matrix protein 22

Ratiometric signal transducing strategies can improve the precision of immunoassay, which possess the unique merits of spatial-resolved signal readout and self-correcting towards possible false positive results. In this work, a new ratiometric electrochemical immunosensor has been developed for reliable detection of Nuclear matrix protein 22 (NMP22). Bioinspired synthetic melanin nanospheres (SMNPs) were elaborately chosen for the following considerations: 1) SMNPs can supply good biocompatible biorecognition interface for antibody anchoring; 2) SMNPs can chelate a large amount of lead ions (Pb²⁺) and copper ions (Cu²⁺) to fabricate two spatial-resolved electrochemical signals with different response manners towards NMP22. SMNPs chelated with Pb²⁺ were used for the immobilization of captured primary anti-NMP22. And SMNPs chelated Cu²⁺ were employed to prepare signal labels after anchored with anti-NMP22 antibody. After sandwich-type immunoreaction, with the increasing concentration of NMP22, the stripping peak current of Pb²⁺ decreases while the stripping peak current of Cu²⁺ increases. Thus, ratiometric electrochemical signals could be provided for NMP22 detection. The immunosensor presented a linear concentration range from 0.013 U mL^-1 to 6.7 U mL^-1 with a limit of detection of 0.005 U mL^-1 towards NMP22. Meanwhile, satisfactory reproducibility, stability and selectivity of the immunosensor were demonstrated.