Split aptamers and their applications in sandwich aptasensors

Most aptasensors are designed based on aptamers' conformational change or structural transformation upon interaction with their targets. A limitation of these strategies is the unpredictability of such structural alterations that may yield false-positive or nonspecific signals. In bioanalysis, a dominant strategy for protein determination is the sandwich assay because of its high specificity and sensitivity resulting from the dual recognition mechanism. However, the approach is poorly suited to detection of low molecular weight targets, which unlikely bind to two aptamers simultaneously due to steric hindrance. To circumvent this drawback, a split aptamer strategy was recently developed, in which nucleic acid aptamers were split into two fragments that could specifically form a ternary assembly in the presence of ligand. This elegant approach has been extensively adopted for detection of various targets, especially small molecular weight targets, with different transduction methods including colorimetric, fluorescence, and electrochemical techniques. This review first introduced split aptamers and how to obtain split aptamers, and then summarized recent advances in the development of sandwich-format biosensing assays based on split aptamer fragments, aiming at providing a general guide for the design of split-aptamer-based sandwich assays. Furthermore, we discussed possible challenges in the development of split-aptamer-based sandwich assay regarding stability, sensitivity and multiplicity, so as to offer future opportunities of this assay.