"One suction and one extrusion" mode-based wash-free platform for determination of breast cancer cell-derived exosomes.

A simple and wash-free POCT platform based on microcapillary was developed, using breast cancer cell-derived exosomes as a model. This method adopted the "one suction and one extrusion" mode. The hybridized complex of epithelial cell adhesion molecule (EpCAM) aptamer and complementary DNA-horseradish peroxidase conjugate (CDNA-HRP) was pre-modified on the microcapillary's inner surface. "One suction" meant inhaling the sample into the functionalized microcapillary. The exosomes could specifically bind with the EpCAM aptamer on the microcapillary's inner wall, and then the CDNA-HRP complex was released. "One extrusion" referred to squeezing the shedding CDNA-HRP into the 3,3',5,5'-tetramethylbenzidine (TMB)/H 2 O 2 solution, and then the enzyme-catalyzed reaction would occur to make the solution yellow using sulfuric acid as the terminator. Therefore, exosome detection could be realized. The limit of detection was 2.69 × 10 4  particles mL -1 and the signal value had excellent linearity in the concentration range from 2.75 × 10 4 to 2.75 × 10 8 particles⋅mL -1 exosomes. In addition, the wash-free POCT platform also displayed a favorable reproducibility (RSD = 2.9%) in exosome detection. This method could effectively differentiate breast cancer patients from healthy donors. This work provided an easy-to-operate method for detecting cancer-derived exosomes without complex cleaning steps, which is expected to be applied to breast cancer screening.