Development of a fluorescent optical potassium-selective ion sensor with ratiometric response for intracellular applications

A small, fluorescent fiber-optic potassium sensor is described with a working range which covers both intracellular cytosolic and blood levels of potassium at the respective physiological pH values. The highly potassium-selective ionophore, BME-44, is retained in a plasticized poly(vinyl chloride) (PVC) Nm which is placed on the end of an optical fiber. Three optode configurations are given, employing different lipophilic, fluorescent pH chromoionophores (Nile Blue derivatives), demonstrating the ability to improve the detection limit and tune the dynamic range to the desired region of interest. These optodes also have excellent selectivity over sodium, calcium and magnesium Use of fluorescence (in contrast to absorbance) provides a means to reduce the sensor size dramatically while retaining the same signal-to-noise ratio. These optodes measure the sample's potassium activity (rather than concentration) provided that the sample's pH is measured simultaneously by another sensor, such as a glass pH electrode.