The organic electrochemical transistor (OECT) is one of the most versatile building blocks within the bioelectronics device toolbox. While p-type organic semiconductors have progressed as OECT channel materials, only a few n-type semiconductors have been reported, precluding the development of advanced sensor-integrated OECT-based complementary circuits. Herein, green aldol polymerization is uses to synthesize lactone-based n-type conjugated polymers. Fluorination of the lactone-based acceptor endows a fully locked backbone with a low-lying lowest unoccupied molecular orbital, facilitating efficient ionic-to-electronic charge coupling. The resulting polymer has a record-high n-type OECT performance with a high product of mobility and capacitance (µC* = 108 F cm⁻¹ V⁻¹ s⁻¹), excellent mobility (0.912 cm² V⁻¹ s⁻¹), low threshold voltage (0.02 V), and fast switching speed (τ_ON, τ_OFF = 336 µs,108 µs). This work demonstrates two types of device architectures and applications enabled by the high performance of this n-type OECT, i.e., an artificial synapse and a complementary amplifier for detecting α-synuclein, a potential biomarker of Parkinson's disease. This study shows that materials that enable high gain and fast speed n-type OECTs can be developed via a green polymerization route, and the diverse form factors that these devices take promise for exploration of other application areas.