Fabrication of micrometer and submicrometer-sized ion-selective optodes via a solvent displacement process

Microsphere-based ion optodes represent a promising and versatile tool to measure ionic activities in confined samples. The reported methods of micro- and nanosphere optode fabrication, however, suffer from various degrees of complexity. We propose a large-scale fabrication of polymeric ion-selective optodes using a solvent displacement method. Plasticized poly(vinyl chloride) along with the optode components was dissolved in a solvent miscible with water. Injection of a polymer solution into a stirred aqueous phase containing a surfactant causes spontaneous emulsification. This technique does not require additional preparation steps and allows one to control the composition of the sensor matrix precisely. Several factors affecting the particle size distribution are examined such as composition of continuous and disperse phases. The concentration of the polymer in the organic solvent and the choice of the solvent nature allowed us to control the particle size distribution within 200 nm-30 microm. The concentration and the nature of the surfactant had a little influence on the particle size distribution. We fabricated three different batches of ion-selective optodes using chromoionophore I, lipophilic ion-exchanger and sodium ionophore X, BME-44, and ETH 5234 for sodium, potassium, and calcium optodes, respectively. The sensors were fully functional with excellent selectivity to interfering ions.