Colorimetric optical pH sensor production using a dual-color system

Utilizing a dual color design, a rapid, convenient and in situ applicable pH sensor was constructed based on a dual light-emitting diode (LED) system. One LED lamp with a maximum emission wavelength of 465 nm was used to excite the pH fluorescent indicator, 5(6)-carboxyfluorescein (CF), and the other LED lamp with red color emission (λmax 660 nm) was selected to supply a stable color background (the reference light). The dual light from the fluorescent emission of CF and the background light were captured using a commercial charge coupled device camera. Under constant and stable background light, the change of the CF fluorescence intensity in solutions at different pH values appeared as different colors. The sensor characteristics, including the effects of temperature, co-existing ions, and the sample analysis performance, were investigated.