Using Simple-Structured Split Aptamer for Gold Nanoparticle-based Colorimetric Detection of Estradiol.

Demand for the detection of estradiol, which is a naturally occurring hormone, has been increasing. Gold nanoparticle-based colorimetric aptasensors have been developed for estradiol detection; however, the long sequence of aptamers due to the formation of the secondary structure likely affects the sensitivity of the aptasensors. Herein, a sensitive colorimetric biosensor is developed for label-free detection of estradiol by using an estradiol-specific split aptamer. The results demonstrate that a superior response is observed when a split aptamer with a high free energy of the secondary structure (ΔG > -3 kcal/mol) is used, in comparison to that observed using a split aptamer with a low free energy of the secondary structure (ΔG < -3 kcal/mol) at 27°C. After selecting the appropriate split aptamer, the standard calibration curve obtained for estradiol has a detection limit of 6.7 nM, with a linear range of 6.7 nM - 66.7 μM in the logarithmic scale. Furthermore, this assay is sensitive, easy-to-operate, inexpensive, and non-time-consuming (provides results within 50 min), thereby showing potential for clinical applications (detection of other small molecular targets).