Organic mixed ionic‐electronic conductors (OMIEC) have emerged as pivotal materials in organic bioelectronics, particularly when integrated into organic electrochemical transistors (OECTs). Conducting polymer‐based devices have indeed demonstrated their capability to transduce biological signals into amplified output signals, harnessing the high transconductance of OECTs. The OECT operating principle and sensing capability strongly depend on ion‐conjugated backbone coupling: the dual nature of OMIECs, i.e. ion‐conductor and electron/hole‐conductor, presents an intrinsic interface in the bulk of the thin film across which transduction of ionic signals into electronic signals and vice versa occurs. Recent works have shown how selective sodium and potassium detection can be achieved by direct chemical modification of the polymer. Such modifications introduce ligands with affinity for the cations of interest as substituents on the polymer chain. The present work explores the integration of specifically modified conducting polymers into OECT channels, offering selectivity for zinc cations. Zinc fluxes are crucial in various biological processes, and their reliable detection, especially at low concentrations, is an important challenge. By electropolymerizing a thiophene‐based trimer, modified with a dipicolylamine (DPA) substituent, a conducting polymer‐based OECT is obtained that can selectively detect Zn 2+ in the 10 −6 to 10 −3 mol L −1 concentration range in physiological buffers.