A multi-loop aptamer-based fluorescent aptasensor for enhanced detection of 17β-estradiol†

The modulation of 17β-estradiol (E2) level, even in trace amounts outside the normal range, plays a critical role in diagnosing and treating various diseases in females. This work presents a novel, simple, and highly sensitive method for E2 detection based on the designed repetitive-loop aptamer. The method is based on the different fluorescence intensities of SYBR Green I (SGI) to intercalate the DNA aptamer structures, which are changed upon interacting with E2. Among the designed aptamers containing 1–5 loop structures (designated as O1–O5), the O5-aptamer exhibited the highest E2 interaction and was employed to construct the O5-aptasensor. Under optimal conditions, the aptasensor displayed excellent sensitivity, with a linear detection range of 1–200 pM, a limit of detection (LOD) of 1.34 pM, and a limit of quantification (LOQ) of 4.48 pM. Its LOD is 13.5 folds lower than that of the L1-aptasensor. The O5-aptasensor specifically detected E2, distinguishing it from structurally similar compounds such as progesterone, genistein, diethylstilbestrol, bisphenol A, and chloramphenicol. Furthermore, the O5-aptasensor accurately detects E2 spiked in artificial urine and human serum samples, with recovery rates ranging from 98.73% to 109.00%, and relative standard deviations below 8%. The O5-aptasensor was tested on blood serum samples from seven hospital patients, and its performance was comparable to that of the hospital analysis for E2 measurement. These findings highlight the potential of the O5-aptasensor as a highly sensitive platform for clinical E2 detection, offering a viable alternative to existing methods.