Highly Sensitive Detection of Estradiol Using Glass Micropipette Constructed via Polydopamine Nanotubes Filling and Small Molecule-Induced DNA Strand Dissociation.

Endocrine-disrupting chemicals, particularly estradiol (E2), pose significant risks to environmental and human health due to their persistence and bioactivity. In this study, we developed a highly sensitive and label-free electrochemical sensor for E2 detection, based on a glass micropipette (GMP) filled with polydopamine nanotubes (PDA-NTs) and coupled with a small molecule-induced DNA strand dissociation strategy. PDA-NTs self-assemble into a densely packed structure at the tip of the GMP, providing abundant binding sites for E2 aptamer (Apt) immobilization and achieving the first signal amplification, which yields a detection limit of 1.29 pM. To further enhance sensitivity, a partially complementary DNA (cDNA) strand was hybridized with the aptamer to form an Apt-cDNA duplex. Upon E2 binding, the Apt in the Apt-cDNA duplex undergoes a conformational change that releases the sterically large cDNA, resulting in a significant increase in ionic current and enabling the second signal amplification. This second amplification improves the detection limit by 112-fold, reaching as low as 11.5 fM. The sensor can detect E2 in the detection range of 10 fM-10 nM and demonstrates high selectivity in complex mixed solutions such as fetal bovine serum (FBS) and environmental water. Beyond highly sensitive detection of E2, this dual-signal amplification also allows the detection of other small molecules through aptamer sequence replacement.