Attomolar Sensitive Milk Fever Sensor using Wrinkled 3D Printed Multiplex Sensing Structures

The diagnosis of milk fever or hypocalcemia in lactating cows has a significant economic impact on the dairy industry. It is challenging to identify asymptomatic subclinical hypocalcemia in transition dairy cows. Monitoring hypocalcemia in milk samples can expedite treatment and improve the health, productivity, and well-being of dairy cows. In this study, an attomole-sensitive sensor was developed using extrusion-based 3D printed sensing structures to detect the ratio of ionized calcium to phosphate levels in milk samples. The unique geometries of the lateral structure of 3D printed sensors, along with the wrinkled surfaces, provide a limit of detection down to the attomole (138 aM) concentration of the target analyte. Unlike traditional sensors, the periodic wrinkled surfaces (~78 µm) of poly (3-octyl-thiophene), along with their high surface areas, acted as the ion-to-electron transducers for calcium and phosphate detection. The calcium-to-phosphate ratio in milk samples not only provides early disease indications but also enables on-site testing. This highly selective test was validated using cow’s milk, whole milk, and fetal bovine serum samples, and the results were compared with those of commercial meters. This fast response (~10 s) low-cost sensor opens a promising and new tool for the farm-side diagnostic of dairy cows that can promote best practice management of dairy cows.