Phenol Red (sodium salt)

Phenol red (Phenolsulfonephthalein) sodium salt is a pH indicator dye. Phenol Red sodium salt is also an antagonist of rat P2X1R. Phenol Red sodium salt enhances the halogenating activity of myeloperoxidase. Phenol Red sodium salt shows a distinct color change from pink to yellow in a positive pH reaction^[1][2][3][4]. In Vitro:Phenol Red sodium salt acts as an indicator of AChE activity^[4]
1.Solutions Preparation
Concentration of Phenol Red sodium salt in water is set to 500 µM.
2. Reaction
1) Thirty-five microliters of PBS, 25 µL of PBS 7.4 or tacrine solution, 20 µL of Phenol Red sodium salt, and 20 µL of 5 mM AChCl are consequently added to the surface of paper with immobilized AChE.
2) After 5 min of incubation, the surface of the paper is photographed using a smart phone camera placed on a 3D-printed, tube-shaped holder.
Note: in neutral pH of PBS 7.4, Phenol red gives a red color. After addition of AChCl, immediately forming acetic acid acidifying medium and the Phenol Red sodium salt turns yellow.