Real-time Voltammetric Anion Sensing Under Flow**

The development of real-life applicable ion sensors, in particular those capable of repeat use and long-term monitoring, remains a formidable challenge. Herein, we demonstrate, in a proof-of-concept, the real-time voltammetric sensing of anions under continuous flow in a 3D-printed microfluidic system. Electro-active anion receptive halogen bonding (XB) and hydrogen bonding (HB) ferrocene-isophthalamide-(iodo)triazole films were employed as exemplary sensory interfaces. Upon exposure to anions, the cathodic perturbations of the ferrocene redox-transducer are monitored by repeat square-wave voltammetry (SWV) cycling and peak fitting of the voltammograms by a custom-written MATLAB script. This enables the facile and automated data processing of thousands of SW scans and is associated with an over one order-of-magnitude improvement in limits of detection. In addition, this improved analysis enables tuning of the measurement parameters such that high temporal resolution can be achieved. More generally, this new flow methodology is extendable to a variety of other analytes, including cations, and presents an important step towards translation of voltammetric ion sensors from laboratory to real-world applications.