Laser-Induced Graphene Potentiometric Platform for At-Home Quantification of Choline in Infant Formula and Milk Powders

<b>Introduction: </b><br/>Choline (Ch+) is a water-soluble vitamin-like micronutrient used by the human body to regulate brain and nervous system functions such as mood, memory, and muscle control. Ch+ also has a structural function since it is involved in synthesizing phospholipids within cell membranes. Deficiency of Ch+ in infants’ diet has been correlated with long-term visual and neurocognitive deficits and impaired learning capabilities and memory function. The U.S. Food and Drug Administration (FDA) and similar agencies have set guidelines and requirements for choline levels in commercialized infant formula. Not all families have access to well-standardized infant formula, and some families practice formula stretching due to economic limitations or difficulties obtaining infant formula, similar to the COVID-19 pandemic. In the U.S., 31% of families relying on infant formula for infant feeding encountered difficulties accessing these products during the COVID-19 pandemic. Moreover, 33% of infant formula users adopted adverse formula-feeding practices, encompassing the dilution of formula, the preparation of smaller feeding bottles, and the retention of partially used formula mixtures for subsequent utilization. These practices affect infants’ choline intake and, therefore, their health. Precise quantifying of choline in infant formula is essential to ensure that infants receive the required nutritional intake, and yet there are no accessible tools for this purpose. Here, we report an innovative integrated sensor for the periodic observation of choline designed for at-home quantification of choline in infants’ formulas and milk powders. This system comprises a choline potentiometric sensor and ionic-liquid reference electrode developed on laser-induced graphitic structure (LIG). The platform also includes a micro-potentiometer that conducts the potentiometric measurements and transmits results wirelessly to the parent’s mobile devices.<br/> <br/><b>Materials: </b><br/>We fabricated the electrochemical electrodes through CO2 laser ablation of a polyimide film using a laser cutter machine emitting at a 1060 nm wavelength. The choline-selective electrode was created by depositing a 40 µL choline-selective membrane composed of a mixture containing 330 mg of poly(vinyl chloride) (PVC), 660 mg of o-nitrophenyl-octyl-ether (NPOE), 13.8 mg of sodium tetraki [3,5 bis(trifluoromethyl)phenyl] borate, and 13.22 mg of calix 4 arene (ionophore) dissolved in 3 mL of THF, onto the electrode surface. The reference membrane solution was formulated by blending 50 mg of MeOctIm TFSI with 316 mg of PVC and 634 mg of o-NPOE in 3.0 mL of THF.<br/> <br/><b>Results and Discussion:</b><br/>The LIG structure electrochemical electrodes were characterized using Raman, EDX, XPS, and SEM. Characterization results confirmed the successful carbonization of P.I. film and the formation of a 3D multilayered porous graphitic structure with a thickness of 20 µm. The obtained LIG-based choline-detecting platform showed a sensitivity of 55.3 ± 0.17 mV/decade, close to the Nernstian theoretical value of 59.2 mV/decade. The achieved limit of detection by our platform is about 95.4 μM. The choline platform also showed an outstanding selective performance toward choline compared to other milk components such as vitamins, minerals, proteins, and sugars. Moreover, the reference electrode demonstrated a highly stable and sample-independent response, which is desired to obtain accurate and precise analysis results. The developed device was used to quantify choline in different commercially available infant formulas and milk powders, showing an accuracy between 100.4 and 108.6 %.<br/><b> </b><br/><b>Conclusion:</b><br/>The LIG-based choline sensing platform showed outstanding sensitivity, selectivity, stability, and accuracy in choline analysis. Leveraging the unique properties of LIG, the platform is flexible, portable, cost-effective, and efficient, making it a promising tool for choline periodic quantification in at-home settings.