Electrophoresis titration model of moving redox boundary chip for point-of-care test of ELISA.

ELISA has been widely used in clinical examination, food safety and environmental analyses. However, it still faces great challenge in designing a device of point-of-care test (POCT) due to its bulk optical detector and complexity. Herein an electrophoresis titration (ET) model of moving redox boundary (MRB) was proposed for constructing ET-ELISA chip of POCT just with a sextuplet electrode pairs and laminated cells. The chip had an anodic well, middle well, and cathode well which were connected by micro-channels. ELISA process was conducted in the bottom of middle well, where HRP catalyzed 3,3',5,5'-tetra-methyl benzidine (TMB) as blue TMB dimer with two positive charges. Under an electrical field of 29 V, the TMB dimer migrated into the titration channel and reacted with the ascorbic acid, creating an MRB. The MRB motion was a function of antigen content, indicating a visual distance-based assay. As a proof of concept, C-reactive protein was chosen as a model antigen. The experiments systemically validated the ET-ELISA model and method. Particularly, the chip was smartphone-detected, traditional power supply-free, and did not use sulfuric acid used in typical ELISA, making the ET-ELISA method extremely simple, portable and safe. The ET-ELISA has great potential to visual and portable ELISA in clinic medicine, environment and food safety immunoassay.