As shown in Fig. , with the concentration of S-protein RBD increased, more FAMaptamer molecules bound the RBD and dissociated from MBs-cDNA, making the fluorescence intensity of the liquid phase increased. Fig. shows the result of electrophoresis of mixtures composed of different oligonucleotides and RBD. From the DNA bands we can see clearly that the sample containing cDNA and aptamer shows a single, slower-moving complex due to the hybridization of the aptamer and cDNA.