Non-Equilibrium Diffusion Controlled Ion-Selective Optical Sensor for Blood Potassium Determination.

Blood electrolyte measurements play important roles in clinical diagnostics. Optical ion sensors as simple and elegant as a mercury thermometer are in high demand. We present here an analytical method to quantify potassium ions in undiluted human blood and plasma by measuring the distance or the rate of the color propagation. The sensor was composed of K+-selective nanospheres embedded in an agarose hydrogel where mass transport was diffusion controlled. The sensor's color-changing rate and the distance of color propagation depended linearly on the logarithm of K+ activity. A theoretical model was established and fully supported the experimental findings. This work lays the foundation of a new family of optical ion sensors for direct determination of common blood electrolytes.