The procedure for preparing cresol red ion pair solution was described in detail in a previous work [25]. Two solutions, named solution A and solution B were prepared separately. Solution A was prepared by dissolving 24 mg of cresol red powder in 22.5 mL of 0.1 mol NaOH. Solution B was made by adding 3 mL of toluene into 37.39 mg tetraoctylammonium bromide (ToABr). The cresol red ion pair solution was obtained by extracting the organic phase of the mixture of solution A and solution B. Similar to the Zn-TPP encapsulation process, cresol red ion pair solution was poured into 560 mg anion exchange resin microbeads (Sigma-Aldrich). The mixture of these two was stirred on the stirrer for 5 hours at room temperature to ensure full encapsulation of dyes in microbeads [24].