Dual-Mode Electrochemical Competitive Immunosensor Based on Cd2+/Au/Polydopamine/Ti3C2 Composite and Copper-Based Metal–Organic Framework for 17β-Estradiol Detection

Herein, a dual-mode electrochemical competitive immunosensor was constructed for the detection of 17β-estradiol (E2) based on differential pulse voltammetry (DPV) and chronoamperometry (i–t). During the immune recognition process, the E2 antibody (E2-Ab) was immobilized on the Cd2+/Au/polydopamine/Ti3C2 (Cd2+/Au/pDA/Ti3C2) composite-modified electrode; then, the E2-conjugated bovine serum albumin (E2-BSA) was labeled with a copper-based metal–organic framework (Cu-MOF) and competed with E2 in combining the E2-Ab. The Cu-MOF was not only an electroactive species but also possessed good electrocatalytic activity toward H2O2. Thus, E2 could be quantified according to the peak current change of the Cu-MOF in DPV curve or the variation of H2O2 reduction current. For DPV quantification, Cd2+ was introduced as an internal reference in this case, and a highly reproducible ratio readout was obtained. The as-prepared dual-mode E2 electrochemical immunosensor showed good linear relationship in the ranges of 1 pg mL–1–10 ng mL–1 (DPV) and 10 pg mL–1–10 ng mL–1 (i–t), and the detection limits were 0.47 and 5.4 pg mL–1 (S/N = 3), respectively. Furthermore, the dual-mode electrochemical immunosensor exhibited good practicability in real sample analysis.