A matrix-assisted single-round selection strategy to evolve a circular DNA aptamer low-density lipoprotein (LDL-CAPT2) targeting LDL is developed with high affinity (K _d = 18 nM), strong specificity, and exceptional stability in biological matrices. Leveraging these properties, it is constructed a label-free fluorescence biosensing platform that achieves ultrasensitive LDL detection, with a detection limit of 0.4 μM and a broad linear dynamic range spanning three orders of magnitude. This work establishes an efficient paradigm for rapid selection of functional circular aptamers for clinical diagnostics.

The accurate and rapid detection of human serum biomakers is crucial for the early diagnosis of related diseases. Circular aptamers emerge as promising candidates for the precise recognition of these biomakers due to their remarkable biological and structural stability. In this study, a high-affinity circular DNA aptamer for low-density lipoprotein (LDL), a key biomarker for cardiovascular diseases, is successfully identified through a matrix-assisted efficient selection strategy conducted directly in human serum. This circular aptamer demonstrated a dissociation constant (K _d) as low as 18 nM and exhibited exceptional specificity for LDL, showing negligible responses to closely related analogs such as high-density lipoprotein and other abundant human serum substances. A sensitive aptasensor is subsequently developed that utilizes the superior recognition capability of the circular DNA aptamer, which performed well even in human serum (with a limit of detection down to 0.4 μM and a wide linear concentration range of three orders of magnitude). This work underscores the feasibility of rapidly isolating highly functional circular DNA aptamers in one selection round, thereby accelerating the discovery of various circular DNA aptamers that are well-suited for molecular recognition of a wide array of emerging human serum biomarkers.