(H-316) Laser-inscribed Graphene-based Potentiometric Sensor for Direct Choline Detection in Infant Formulas

Introduction:: Choline (Ch+) is a water-soluble organic compound used by the human body to regulate brain and nervous system functions such as mood, memory, and muscle control. Choline also plays a structural function since it is involved in producing cellular membrane phospholipids. Ch+ deficiency increases cancer risks, liver damage, and Alzheimer’s and Parkinson’s disease. Diet remains the main supply of choline for the human body. Therefore, getting enough choline in food should be considered, especially for infants, because of their limited dietary sources. Quantifying Ch+ in infant formulas is also necessary to ensure that infants receive the essential amount of choline and grow healthy. Many approaches to quantify choline in infant formulas have been reported, such as mass spectrometry, chromatography, colorimetry, etc. However, these techniques are time-consuming and expensive and require high laboratory experience. Solid-contact ion-selective electrodes SC-ISEs provide an accurate, cost-effective, easy-to-use potentiometric electrochemical platform for choline detection. Graphene material is attractive for SC-ISEs due to its hydrophobicity which prevents the formation of an aqueous interfacial layer between the ion-selective membrane and the underlying electrode. Producing graphene using the laser-engraving method is fast, mask-free, cost-effective, and scalable compared to conventional methods (i.e., wet chemistry and chemical vapor deposition.


Materials and Methods:: We produced the electrochemical electrodes by ablating a polyimide film (127 µm thickness) using a CO2 laser cutter machine with a 1060 nm laser wavelength. The engraving was conducted with an auto-focused laser beam with power and speed of 3 W and 105 mm/s, respectively. A choline-selective membrane was produced by mixing 330 mg of poly(vinyl chloride) (PVC), 660 mg of o-nitrophenyl-octyl-ether (NPOE), 13.8 mg of Sodium tetrakis[3,5 bis(trifluoromethyl)phenyl]borate, and 13.22 mg Calix 4 arene (ionophore) in 3 mL tetrahydrofuran. The membrane was cast on the electrode surface and dried overnight before measurements.


Results, Conclusions, and Discussions:: Results and Discussion: The laser engraving method successfully produced flexible electrochemical electrodes, as shown in Figure 1. a. The scanning electron microscopy images of the laser-engraved areas demonstrated the formation of three-dimensional highly porous graphene on the PI film, as shown in Figure 1 b. Electrochemical cyclic voltammetry measurements were conducted on the produced electrodes at different scan rates against Ag/AgCl reference electrodes to investigate the electrochemical kinetics of the electrode surface. Voltammograms showed the increasing current peak and reduction-oxidation peak separation by increasing the scan rate indicating the quasi-reversible electrochemical behavior of the electrode. The graphene-based choline selective electrode demonstrated high sensitivity toward choline ions with a detection limit of 0.1 mM. Also, the sensor could quantify choline concentration in commercially available infant formulas with a measurement error of less than 5 %.



Conclusion: In summary, the laser-inscribed graphene-based choline potentiometric sensor offers a promising home-used tool for parents to ensure high nutritious and healthy infant diet.




Acknowledgements (Optional): : Abdulrahman Al-Shami would like to acknowledge USC Provost Fellowship.

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