Visualization of tannic acid in wine and beverages with BO-CDs as ratiometric fluorescence sensing reporter

This work reported the first development of a BO-CDs-based ratiometric fluorescence nanoprobe (RFP) for visual detection of tannic acid (TA). Constructed via electrostatic self-assembly of blue-emitting B-CDs and orange-emitting O-CDs, the BO-CDs showed dual emission at 449 nm and 595 nm under 400 nm excitation. Adding TA quenched 595 nm emission while 449 nm signal remained stable. The RFP demonstrated two linear detection ranges of 0.01-5.0 μM and 5.0-25.0 μM, with ultralow LODs of 7.65 nM and 1.12 nM, respectively. Notably, TA triggered distinct fluorescence color transitions from tangerine to rose pink and finally to blue-purple, facilitating the development of smartphone-assisted and paper-based visual sensing platforms with LODs of 1.11 and 1.07 μM, respectively. The sensing platforms were successfully applied to on-site TA detection in wine and beverages with satisfactory results, highlighting the great potential of smartphone-integrated CDs-based RFP as a portable tool for on-site TA analysis.