Various ligands have been developed for specific molecular recognition, such as small molecules, antibodies, and peptides [11] [12] [13] . More recently, another type of molecular ligand, named aptamer, has drawn significant attention. Aptamers, singlestranded modified or unmodified oligonucleotides (RNA or DNA), are generated through in vitro selection process or SELEX (Systematic Evolution of Ligands by EXponential enrichment) with high binding affinity and specificity towards defined targets [14, 15] . The selected aptamers can recognize a wide variety of targets, including small molecules, proteins, cells and tissues relying on their diverse tertiary structures. Compared to antibodies, aptamers have low molecular weight, fast tissue penetration rate, high stability and low immunogenesis [16] . They can be chemically synthesized with low cost and modified easily with various reporters [17] . Furthermore, they can be ligated and/or amplified by enzymes in vitro [18] . These advantages make aptamers promising ligands for medical and pharmaceutical research, such as drug development, disease diagnosis, and targeted therapy [19] .