Advancing Multi‐Ion Sensing with Poly‐Octylthiophene: 3D‐Printed Milker‐Implantable Microfluidic Device

Abstract On‐site rapid multi‐ion sensing accelerates early identification of environmental pollution, water quality, and disease biomarkers in both livestock and humans. This study introduces a pocket‐sized 3D‐printed sensor, manufactured using additive manufacturing, specifically designed for detecting iron (Fe ²⁺ ), nitrate (NO ₃ ^– ), calcium (Ca ²⁺ ), and phosphate (HPO ₄ ²⁻ ). A unique feature of this device is its utilization of a universal ion‐to‐electron transducing layer made from highly redox‐active poly‐octylthiophene (POT), enabling an all‐solid‐state electrode tailored to each ion of interest. Manufactured with an extrusion‐based 3D printer, the device features a periodic pattern of lateral layers (width = 80 µm), including surface wrinkles. The superhydrophobic nature of the POT prevents the accumulation of nonspecific ions at the interface between the gold and POT layers, ensuring exceptional sensor selectivity. Lithography‐free, 3D‐printed sensors achieve sensitivity down to 1 ppm of target ions in under a minute due to their 3D‐wrinkled surface geometry. Integrated seamlessly with a microfluidic system for sample temperature stabilization, the printed sensor resides within a robust, pocket‐sized 3D‐printed device. This innovation integrates with milking parlors for real‐time calcium detection, addressing diagnostic challenges in on‐site livestock health monitoring, and has the capability to monitor water quality, soil nutrients, and human diseases.