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.