pH-based immunoassay: explosive generation of hydrogen ions through an immuno-triggered nucleic acid exponential amplification reaction
In this work, we propose a novel concept and a proof-of-concept strategy for the fabrication of an pH-based immunoassay platform with certain universality and scalability to make it adaptable for different application scenarios. The immunoreactions for the target detection are converted to the pH changes through an engineered and optimized isothermal nucleic acid amplification, named exponential amplification reaction (EXPAR). Thus, a variety of well-developed methods for pH analysis, e.g. pH indicator, pH-strip and pH meter, can be applied for immunoassay directly. Here, we show that this proof-of-concept strategy is applicative for both macromolecular and micromolecular antigens by adopting human platelet-derived growth factor-BB (PDGF-BB) and chloramphenicol (CAP) as the model targets respectively. The detection can be achieved using a colorimetric pH indicator after a 15 min reaction of the immuno-triggered isothermal nucleic acid amplification. In addition, compared with the traditional enzyme-linked immunosorbent assay (ELISA), the performance of our strategy, especially the detection limits, is improved to varying degrees for different targets, making the strategy a promising alternative for diverse application scenarios of immunoassay.