A smartphone-assisted hybrid sensor for simultaneous potentiometric and distance-based detection of electrolytes

At home electrolyte analysis is of growing interest due to the importance for early diagnosis for various diseases. This work presents the first device that integrates a potentiometric ion-selective electrode (ISE) with distance-based colorimetric detection for the simultaneous analysis of K⁺ and Cl^- ions at the point of care (POC). This hybrid sensing device was designed in a two-dimensional configuration using a plastic transparency sheet containing a stencil printed K⁺-ISE and a paper substrate for distance-based colorimetric detection of Cl^-. K⁺ quantification was performed using a low-cost (<$25) lab-made Wi-Fi supported potentiometer with a custom smartphone application while Cl^- ions were quantified with an instrument-free distance-based paper analytical device (dPAD). The total analysis time is 5 min once the sample is added. The K⁺-ISE showed a sensitivity of 55.89 ± 2.52 mV/decade from 0.1 to 100 mM with a limit of detection (LOD) of 0.01 mM. The linear working range for Cl^- detection was 0.5-50 mM whereas the LOD was 0.16 ± 0.05 mM. The proof-of-concept application of the sensing hybrid device was demonstrated in human urine and artificial sweat samples containing K⁺ and Cl^- ions at physiologically relevant ranges. The recoveries were found to be 88-108% for K⁺ and 90-104% for Cl^-, showing the potential use of the proposed device for low-cost routine analysis of biological samples at POC.