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Device Technologies and Biomedical Robotics

Point of Care Devices and Biosensors - Session 1

Laser-Induced Graphene-based Calcium Sensor for Diagnosis of Milk Fever

Saturday, October 14, 2023
2:45 PM – 3:00 PM PDT
Location: 335 (Center, Level 3)
Introduction:: Milk fever is a metabolic disorder that occurs when lactation begins in dairy cattle and can lead to a range of clinical symptoms, including loss of appetite, muscle spasms, lateral recumbency, and eventually coma or death if left untreated. The primary cause of these symptoms is a significant decrease in blood calcium levels, hypocalcemia, which is the defining characteristic of milk fever. Previous studies have categorized cows into three groups based on their serum calcium levels: normocalcemia (≥ 2.0 mmol/L), subclinical hypocalcemia (< 2.0 mmol/L but without any observable clinical signs), and clinical hypocalcemia (with clinical signs). Based on previous studies, the prevalence of subclinical and clinical hypocalcemia in the pasture-based system was 33% and 5%, respectively. Moreover, the productive life of dairy cows with hypocalcemia decreases by 3.4 years, which can have economic impacts on animal husbandry businesses. Since subclinical milk fever does not have symptoms and frequent testing of calcium levels is expensive, subclinical milk fever is rarely diagnosed. Thus, having a Point-of-Use inexpensive sensor for frequent and on-demand calcium measurement is beneficial. For this purpose, we fabricated an inexpensive carbon-based potentiometric electrode to detect calcium levels in the clinically relevant range.

Materials and Methods:: We prepared the calcium selective membrane by mixing poly(vinyl chloride) (PVC) (33%), 2-nitrophenyl octyl ether (66%), calcium Ionophore (IV) and potassium tetrakis(4-chlorophenyl)borate (KTPClB) (1%), with tetrahydrofuran. We fabricated the LIG sensors by directly operating a CO2 laser on a Kapton film. Then, we drop-casted the membranes on the electrodes. We performed all the measurements at room temperature with freshly prepared solutions using the standard addition of deionized water (18.2 MΩ/cm) using a 16-channel potentiometer relative to a commercial reference electrode.


Results, Conclusions, and Discussions:: We used laser engraving to pattern graphene on a low-cost polyimide film (laser-induced graphene or LIG). The results indicate that the sensitivity of our LIG-based sensors is 28.75 mV/dec, which is close to the theoretically expected value (29.6 mV/dec). Moreover, the limit of detection (LOD) of the sensor is 6.1 µM, which is ~ 3 orders of magnitude lower than the clinically relevant range of calcium in the body. Another important characteristic of the sensor that ensures its reliability is the selectivity toward the ion of interest. The separate solution method (SSM) was utilized to calculate the selectivity coefficient of the sensor. The SSM result illustrates that the selectivity coefficient of the sensor is -4.9, -4.7, and -3.8 over potassium, sodium, and magnesium, respectively.

We fabricated a LIG-based potentiometric sensor that can be used for point-of-use detection of calcium in the clinically relevant range. Moreover, using a laser as an inexpensive, fast, and mass-producible method for fabricating the sensors makes them a suitable choice for in-field frequent use.




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