Self-Validated Homogeneous Immunoassay by Single Nanoparticle in-Depth Scrutinization.

The most convenient method for the clinical routine analysis of disease biomarkers is homogeneous immunoassay, which minimizes the requirements for automation and time-/lab-consumption. Despite great success, because sample constituents are not removed by a separation or washing step, a major challenge in conducting homogeneous immunoassays for the practical application is the matrix effect-related inaccuracy. Herein, to guarantee an accurate quantification, a self-validated homogeneous immunoassay was proposed, by simultaneously scrutinizing both frequency and intensity of single gold nanoparticles. The two analytical modes of single particle inductively coupled plasma mass spectrometry (ICPMS) correlated well with each other, resulting in a self-validation mechanism for the accurate immunoassay. Both two modes of the proposed method provided linear ranges of 2 orders of magnitude and LODs of pM level. Thanks to the self-validated strategy and the high tolerance of the matrix effect of ICPMS, the proposed homogeneous immunoassay was successfully demonstrated in a series of human serum samples, with results in good accordance with clinical routine methods.