Fig. 7: Sensor manufacturing using an extrusion-based 3D-printer.

a Schematic illustration of the 3D-printed sensor that interfaced with a potentiostat to detect SCH in different mediums of biofluids. b 3D printing process for sensor manufacturing. An extrusion 3D printer was used to build sensor structures using a high-temperature polymeric resin. A lateral layer-by-layer printing results in a periodic structure (~78 ± 2.5 µm) of polymer. The printed structure of high-temperature resin was cured by exposing a UV light resulting in wrinkled surfaces along with a constant temperature of 80°C. These lateral layers are interconnected with each other. c The wrinkled surfaces were coated with a thin layer of Au using an e-beam evaporation technique. d The printed sensor contains three electrodes out of which two served WEs for Ca²⁺ and P detectors and one electrode is shared RE. The middle electrode is RE and was made of Ag/AgCl and Nafion layers. Both WEs were first coated with POT layers and then coated with Ca-ISM and P-ISM solutions. A real photograph of the sensing set-up for on-site testing of SCH in dairy cows. Figs. a–d were created in part using images from BioRender.com released under a CC-BY 4.0 license.