A digital method for the detection of MCF-7 cells using magnetic microparticles-DNA-enzyme

Interaction between enzymes and beads due to the nonspecific binding is a strong limitation to digital enzyme-linked immunosorbent assay (ELISA). To overcome the limitation and broaden the application in digital ELISA, we herein introduce the aptamer, which is capable of binding various molecules with high affinity and specificity, to replace the role of antibody for recognizing target molecules. We construct a digital sensor that regulated by magnetic microparticles-DNA-enzyme (MMPs-DNA-enzyme) system for MCF-7 cells detection. This system is consisting of enzyme-labeled aptamer, and nucleic acids modified-magnetic microparticles that can lock aptamer-labeled enzyme, preventing the negative reaction in the absence of target MCF-7 cells. The presence of target MCF-7 cells can trigger the release of enzyme-labeled aptamer from magnetic microparticles because aptamer and target protein react specifically, resulting in strong fluorescence signal. We successfully applied this digital detection method in the detection of MCF-7 cells by using the aptamer of mucin 1 protein (MUC 1) and epithelial cell adhesion molecule (EpCAM). This designed method can realize MCF-7 cells sensitive detection with a limit of detection of 2 cells/mu L. Since this method can eliminate the nonspecific binding compared to traditional digital ELISA, it provides a new development for digital technology.