A Simple Approach To Detect Caffeine in Tea Beverages

The photophysical properties of commercially available dye Acridine Orange (AO) describe an excellent probe for selective and sensitive detection of caffeine in aqueous solution. AO exists in monomer-dimer equilibrium in water. AO monomer is a fluorophore, but the dimer is not. Addition of caffeine to the AO leads to a shift in the monomer-dimer equilibrium toward the direction of AO monomer (fluorophore) and results in enhancement of AO fluorescence intensity. Enhancement of AO fluorescence intensity in the presence of caffeine has been treated as a signal for caffeine sensor. Furthermore, the caffeine-induced shift in AO monomer-dimer equilibrium is attributed to the binding of caffeine with AO monomer, and the binding constant was higher at a low pH range (pH similar to 2) compared to pH similar to 7 which results in superior caffeine sensitivity at pH similar to 2. Finally, caffeine content in commercial tea beverages has been evaluated and compared with the value obtained with a standard HPLC method.