1. Analytical Chemistry and Laboratory Applications
Acid-base titration indicators, chromatographic analysis reagents
Precisely indicates pH changes in the near-neutral range.

2. Biology and Biochemistry
Monitoring respiration/photosynthesis, microbial culture and identification, enzyme activity detection
Indirectly reflects CO₂ concentration, acid production from microbial metabolism, or pH changes caused by enzymatic reactions through color changes.

3. Medical Diagnostics
Rapid detection of cholinesterase activity (BTB paper method)
Used to assist in the diagnosis of emergencies such as organophosphate poisoning.

4. Industrial and Consumer Products
Fuel cells, optical sensors, textiles, toys, cleaning products
Used as functional additives for sensing, indication, or dyeing.

5. Environmental and Food Testing
Water quality monitoring, food freshness indicators
Reflects water body health or food spoilage processes through pH changes.