Rapid quantification of ions is important for preventive care and diagnostics. This is particularly significant for emergency room and clinical settings, where a quick quantification of an electrolyte imbalance can guide required treatments. We are currently developing an alternative ion sensing platform. This platform will involve measurement of the shift in potential of the redox peak of an electroactive layer as a function of the presence of a targeted ion (Figure A - Scheme of cyclic voltammograms shifting due to the increasing concentration of potassium ions in tested solution). This is caused by the intercalation of the ion into the electrodeposited layer (Figure B - Concept of electroactive sensing layer immobilized on electrode). One ion of interest is potassium. The potassium ion is present in the human body at 3.5 – 5.0 mmol/L [1]. A patient that is below the healthy range can be diagnosed with hypokalemia. This could cause an abnormal heart rhythm, and even result in cardiovascular issues. Currently, the levels of electrolyte ions are measured using ion-selective electrodes. There is a need for alternative ion quantification systems for in-field applications because the current ion-selective electrodes can be difficult to use outside of a clinical setting as they are fragile, subject to biofouling, and can be expensive.

We electrodeposited Prussian blue on a screen-printed electrode for our first platform. Prussian blue has been previously reported as a sensing layer for potassium and sodium ions on platinum, alumina, and nanotubes [2], as well as on pencil graphite electrodes [3]. The measured shift of potential of the redox peak indicates the presence of the analyte, which is a result of the intercalation of the targeted ion in the electrodeposited layer. Using a screen-printed electrode, we tested a solution containing potassium ions and compared it to a similar solution containing magnesium ions. We also measured the potential shifts in the presence of sodium ions. The solution of potassium ions displayed a significant shift of the potential of the oxidative peak of Prussian blue when compared to the other two electrolytes.

We are quantifying potassium as a proof-of-concept of a novel electrochemical micronutrient sensing system. Paper-based sensing platforms are very useful for resource-limited settings and field testing due to advantages such as simplicity, low cost, portability and disposability [4]. By developing an accurate, portable ion-sensing paper-based platform, we will provide a more rapid and versatile alternative to current ion-selective electrode devices. Future work includes the development of a panel of multiplexed systems with various sensing layers allowing for the detection and quantification of different clinically useful ions. 

References

1)      Alexander Kratz, M. F., Patrick M. Sluss, Kent B. Lewandrowski (2004). "Normal Reference Laboratory Values." The New England Journal of Medicine 351: 1548-1563.

2)      Kuo-Chuan Ho, C.-L. L. (2001). "A Novel Potassium Ion Sensing Based on Prussian Blue Thin Films." Sensors and Actuators B: Chemical 76: 512-518.

3)      Jin Qiang Ang1, B. T. T. N., Chee-Seng Toh (2011). "A dual K+–Na+ selective Prussian blue nanotubes sensor." Sensors and Actuators B: Chemical 157(2): 417-423.

4)      Wen-Jie Lan, X. U. Z., Mahiar M. Hamedi, Jinbo Hu, Claudio Parolo, E. Jane Maxwell, Philippe Buhlmann, George M. Whitesides (2014). "Paper-Based Potentiometric Ion Sensing." Analytical Chemistry 86: 9548-9553.