Amphiphilic Diketopyrrolopyrrole Polymers Enable Intrinsic Selective Perchlorate Transduction in Organic...

Controlling ion-specific interactions in organic mixed ionic-electronic conductors (OMIECs) remains a major challenge for high-gain electrochemical sensors, particularly in aqueous environments where detection of emerging contaminants such as perchlorate (ClO₄ ^-) is limited by ion hydration dynamics and sluggish volumetric electrochemical doping. Herein, we report a membrane-free organic electrochemical transistor (OECT) platform based on a fully methoxylated diketopyrrolopyrrole (DPP)-based amphiphilic copolymer. Backbone methoxylation promotes preferential volumetric electrochemical doping by perchlorate ions, enabling efficient bulk polaron stabilization. Consequently, the fully methoxylated polymer exhibits a five-fold increase in volumetric charge (Q_V = 32 C cm^{- 3}) and a four-fold enhancement in doping level (y = 0.38) relative to its non-methoxylated analogue. Integrated into OECTs, the material delivers a 300-fold improvement in detectivity, achieving detection limits of 22 ± 1 ppb in pristine electrolyte and 37 ± 2 ppb in a mixed-ion background containing 5 mM each of F^-, Cl^-, NO₃ ^-, SO₄ ^2-, and ClO₃ ^-. Mixed-interference studies demonstrate ∼12-fold selectivity for perchlorate with 83% signal recovery, while control experiments and impedance spectroscopy reveal an auxiliary glycol effect, in which backbone methoxylation and glycol side chains cooperatively facilitate efficient bulk doping. These findings establish backbone functionalization as an effective strategy for realizing selective, membrane-free OMIEC-based chemical sensors.