An integrated ion-selective optode sensor cartridge for directly detecting electrolyte ions in blood plasma without pretreatment to adjust pH

We present a new integrated optode sensor cartridge that directly detects potassium, sodium, and chloride ions in blood plasma without pretreatment to adjust pH. Each optode sensor mainly consists of two separate layers, the optode and a dried buffer, which work by introducing plasma without blood cells filtered by a membrane filter. The optode layer uses a neutral ion-selective optode that is composed of an ionophore, a pH indicator dye (chromoionophore), and ionic additives incorporated in a plasticized polyvinyl chloride membrane. The dried buffer layer, which dissolves on contact with plasma, is applied to the optode layer, resulting in the constant pH of the plasma within the optode membrane. We determined the pHs of each dried buffer (potassium, sodium, and chloride) layer to be 7.0, 6.0, and 4.5, respectively, based on the pK(a) of their corresponding chromoionophores and effective buffer ranges. Consequently, the sensor responses varied as a function of the potassium, sodium, and chloride ion concentrations. To validate the accuracy of the ion-selective optode sensors, we investigated the correlations of potassium, sodium, and chloride ion concentrations with a commercial system (cobas (R) 8000) and observed comparable agreement between the two systems with correlation coefficients of 0.976, 0.955, and 0.966, respectively.