S1 nuclease digestion-based rational truncation of PD-L1 aptamer and establishment of a signal dual amplification aptasensor

Truncation optimization of aptamers can improve both specificity and robustness. At present, aptamer truncation is mainly performed based on predictions from molecular docking simulations, but this usually requires tedious trial-and-error and may result in false predictions. Here, we propose a strategy based on digestion by S1 nuclease to rationally truncate the aptamer, using the PD-L1-binding aptamer Apt80 as an example. Due to steric hindrance, recognition and binding regions between Apt80 and PD-L1 are not digested by the enzyme. The truncated form, Apt38, shows higher affinity and larger conformational change after binding, when compared to Apt80. The truncated Apt38 was used as a platform for developing a signal dual amplification fluorescence aptasensor using targeted recycling assisted by exonuclease I and qRT-PCR analysis. This aptasensor exhibited a high sensitivity toward PD-L1 with a limit of detection of 0.076 ng/mL in buffer system and 0.3625 ng/mL in human serum. Owing to its high sensitivity, specificity, ease operation and low cost for detection of PD-L1, this aptasensor should be useful in assisting clinicians to evaluate the status of cancer patient and to decide whether inhibitor drugs are needed.