Label-free detection of exosomes based on ssDNA-modulated oxidase-mimicking activity of CuCo2O4 nanorods.

A label-free method for exosome detection was proposed. It is based on the target-responsive controllability of oxidase-like activity of Cu/Co bimetallic metal-organic frameworks (CuCo2O4 nanorods). In the absence of exosomes, the oxidase-like activity was inhibited due to the adsorption of CD63 aptamer onto nanorods' surface. In the presence of exosomes, CD63 aptamer was disassembled from CuCo2O4 nanorods by virtue of CD63 aptamer-exosome recognition, which resulted in the recovery of oxidase-like activity. The activity inhibition is attributed to the fact that the ssDNA adsorption hindered the electron transfer between CuCo2O4 nanorods and colorimetric substrates. Under optimal conditions, a sensitive colorimetric method for detecting exosomes was established over a range of 5.6 × 104 to 8.9 × 105 particles μL-1 with a detection limit of 4.5 × 103 particles μL-1. The method was further applied in distinguishing healthy people and breast cancer patients by testing exosomes in the serum samples and showed satisfying differentiation ability.