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Background: Estriol (E3) is a common estrogen responsible for regulating the female reproductive system, but excessive amount can pose health risks to humans and wild life. Therefore, sensitive and accurate detection of estriol level is crucial. A novel competitive ECL immunosensor based on a dual signal amplification strategy of AuNPs@GO@SmMoSe 2 and Gd 2 (MoO 4 ) 3 was fabricated for ultrasensitive detection of estriol. Graphene oxide (GO) increased the electric conductivity and surface area of SmMoSe 2 and gold nanoparticles (AuNPs) improved the electrochemical active sites of GO@SmMoSe 2 . In order to further amplify the ECL signals, Gd 2 (MoO 4 ) 3 with excellent electron transfer capability were used for binding E3-antigen (Ag). Then, Gd 2 (MoO 4 ) 3 -Ag/BSA competed with Standard E3 for limited number of antibodies to construct a competitive ECL immunosensor., Results: Under optimized condition, the proposed competitive ECL immunosensor was used to detect various concentrations of Standard E3 samples. In addition, the proposed ECL immunosensor showed the high sensitivity for E3 detection in range between 0.001 and 500 ng/mL with the detection limit of 0.0073 ng/mL (S/N = 3). The wider linear range and lower detection limits of the proposed ECL immunosensor might be attributed to outstanding ECL properties of AuNPs@GO@SmMoSe 2 and Gd 2 (MoO 4 ) 3 nanosheets. Furthermore, the proposed competitive ECL immunosensor was also compared with various detection methods. Based on above, the fabricated ECL immunosensor was employed for real sample analysis with acceptable RSD values and recoveries., Significance: A dual signal amplification strategy enhanced the potential of the well-prepared ECL immunosensor for detecting E3 samples in the real environment. Thereby, the successfully fabricated competitive ECL immunosensor with excellent electrochemical properties, long term storage stability, and high sensitivity and selectivity validated its potential application for environmental monitoring and analysis., Competing Interests: Declaration of competing interest Here, we confirm that there are no potential conflicts of interest. We confirm that there are no known conflicts of interest associated with this publication and all authors declare there is no competing financial interest., (Copyright © 2025 Elsevier B.V. All rights reserved.)

Estrogens in aquatic environments pose significant ecological and health risks due to their cumulative effects rather than individual impacts. This study investigates the voltammetric behavior of estrone (E1), 17β-estradiol (E2), estriol (E3), and 17α-ethinylestradiol (EE2), presenting a cost-effective and straightforward method for their simultaneous determination. Using differential pulse voltammetry (DPV) with a boron-doped diamond electrode, the method demonstrates high precision (deviations under 4%) and a linear dynamic range of 15.35-134.55 µmol·L -1 . Integration of a vacuum evaporation step reduced detection limits to 10 -8 mol·L -1 , enabling effective analysis of real water samples. This optimized approach ensures practical applicability for monitoring total estrogen content in aquatic systems, providing an accessible and reliable alternative to conventional methods.