Rapid Microfluidic Ion-Exchange Optode System for Point-of-Care Determination of Sodium Concentration in Serum

A microfluidic system for detecting sodium ions (Na⁺) has been developed, incorporating a micro finger-pump chip and a micro-spectrometer platform to measure Na⁺ concentration in human serum. A small volume (10 μL) of serum sample is introduced into the microchip and reacted with a preloaded reagent mixture through a two-step finger-pump actuation process. The resulting purple complex is directed into the detection area of the chip and analyzed using the micro-spectrometer at wavelengths of 555 and 666 nm. The Na⁺ concentration is then inversely derived from the measured A₅₅₅/A₆₆₆ absorbance ratio using self-written software installed on a Raspberry Pi. The entire detection process is completed in just 3 min, offering a significant advantage in meeting clinical needs compared to the traditional reporting turnaround time of several hours in medical institutions. The experimental results indicate a linear relationship between the measured absorbance ratio and Na⁺ concentration within the range of 1-200 mM, with a correlation coefficient of R² = 0.9989. Additionally, the detection results from 60 serum samples collected from chronic kidney disease (CKD) patients showed a strong agreement with those obtained using the conventional indirect ion-selective electrode (ISE) method, achieving a correlation coefficient of R² = 0.9885 and an average recovery rate of 99.4%. In summary, the proposed system provides a practical, affordable, and rapid alternative to conventional Na⁺ detection methods, making it highly promising for point-of-care (POC) testing applications.