Clinical studies have already shown that the AGR2 protein is overexpressed in a wide range of human cancers. The sensitive and selective detection of AGR2 is thus of great importance to early cancer diagnostics. Herein, by applying the selected and optimized aptamer C14B1, we designed and developed an allosteric molecular beacon against AGR2, named AGR2-aMB, which converts the molecule recognition property of aptamer to fluorescence flow cytometry signal for AGR2 sensing [55] . Figure 5 illustrates the working principle of AGR2-aMB. An AGR2-aMB is a ssDNA consisting of an streptavidin (SA) aptamer sequence [56] , a C14B1 sequence, a short sequence complimentary to a small part of the SA aptamer sequence, and a fluorophore. A stable hairpin structure is formed by intramolecular hybridization between the SA aptamer sequence and the complementary sequence, temporarily disabling the probe's ability to bind with SA beads. Consequently, when incubated with SA beads, no probe can bind to SA beads, and the beads display very low fluorescence. In the presence of AGR2, however, the C14B1 sequence in the loop of aMB binds to the target sequence, which in turn disrupts the hairpin structure to free the SA binding sequence, thereby activating the probe's binding affinity to SA beads. Thus, the AGR2-bound probe will bind to SA beads, which will fluoresce strongly because the probe is FAM labeled. Target molecules can be detected and quantified by reading the fluorescence intensity of SA beads through flow cytometer.