(K-420) SPOON: Sensor for the Periodic Observation of Nutrients, Addressing Sodium Intake in Processed Foods

Introduction::

Point of Care / Mobile Devices

Sodium is an essential nutrient in the human body for its importance in conducting nerve impulses, contracting and relaxing muscles, and maintaining a proper balance of water and minerals. However, most people are unaware of their dietary sodium consumption. For instance, although the Dietary Guidelines for Americans recommend that less than 2,300 milligrams of dietary sodium should be consumed daily, over 90 % of Americans consume 3,400 milligrams of sodium [1]. As a result, Americans are at a higher risk of high blood pressure and heart attacks than those residing in other countries. The Centers for Disease Control and Prevention reports that 500,000 Americans die annually due to high blood pressure-related conditions, with excess dietary sodium being the leading cause [1]. Therefore, monitoring daily dietary sodium intake is essential to prevent devastating medical conditions such as heart attacks and strokes.

However, in global commercial markets, no at-home technology exists to precisely measure sodium intake. This is concerning as older individuals often resort to liquid-based diets due to digestive issues and tooth decay. Additionally, home-cooked meals prepared from scratch lack any nutritional information whatsoever, making it impossible to determine sodium content in food that is cooked, mixed, or pureed. In this work, we developed SPOON, the Sensor for Periodic Observation of Nutrients, a simple, low-cost, robust, and intuitive “smart kitchen” device that can be used as a smart measuring cup to monitor sodium intake from the comfort of your home.

Materials and Methods::

The design of the SPOON uses a bamboo spoon with polyimide film attached to its bowl in a two-electrode setup; a working and reference electrode. Laser-induced graphene is engraved on the polyimide film, and silver/silver chloride ink is screen-printed onto the electrode leads to improve SPOON conductivity. In addition, an ion-selective membrane consisting of polyvinyl chloride, 2-nitrophenyl octyl ether, potassium tetrakis (4-chlorophenyl) borate, and sodium ionophore X is drop-casted onto the surface of the working electrode. The electrode membrane was then allowed to dry for 24 hours, and then the electrode was left in a 100 mM sodium chloride solution to allow ion exchange and membrane conditioning. A Lawson Labs potentiostat was used for data collection.

A 100 mM sodium chloride solution in deionized water was used to test the SPOON. A series of two-fold and ten-fold dilutions with deionized water were performed until the electrode stopped responding appropriately to a concentration change. After mixing, data was collected for two minutes at each concentration, and the average potential of the last 10 seconds was used for the data point. The slope and LOD were determined by this calibration curve, the latter defined as the intersection between the linear and non-linear portions of the curve.

Results, Conclusions, and Discussions::

The electrodes were tested in a linear range of 0-100 mM NaCl solution. The electrodes demonstrated a limit of detection of 0.371 μM with a slope of 51.5 mV/decade. The limit of detection is acceptable for this device since it detects sodium levels in broth. While variable, low-sodium off-the-shelf broth from Swanson nominally contains 25.7 mM sodium, and the regular variant reports 101 mM sodium.

The slope is near the expected Nernstian value of 58.2 mV/decade. We expect that the sensor performance could be improved with further refining of the fabrication process, including acquiring a more precisely-controlled laser and refining the drop-casting method.

Future experiments will include interference testing with different ions and proteins to mimic the condition of real broth and testing in real broth. A simple laser-engraved electronic temperature sensor will also be added to the electrode to account for broth temperature since ion activity and measurements are greatly affected by solution temperature.

This work represents a low-cost entry point to a “smart kitchen” ecosystem. In conjunction with other innovations, this technology could lead to greater nutritional awareness and improve public health by changing our relationship with home-cooked meals.

Acknowledgements (Optional): : The authors would like to thank the USC Summer Provost Fellowship for supporting this work.

References (Optional): : [1] Centers for Disease Control and Prevention. “Sodium.” Centers for Disease Control and Prevention, December 21, 2021. https://www.cdc.gov/heartdisease/sodium.htm#:~:text=Sodium%20intake%20from%20processed%20and,prevent%20thousands%20of%20deaths%20annually.