Hydrophilic/hydrophobic carbon dot pair for ratiometric fluorescence sensing of water in tetrahydrofuran

A novel ratiometric fluorescence sensor based on a hydrophilic/hydrophobic carbon dot (CD) pair is presented for sensitive detection of water in tetrahydrofuran (THF). Hydrophilic blue-emissive CDs (B-CDs) and hydrophobic orange-emissive CDs (O-CDs) are synthesized via a one-pot hydrothermal method, exhibiting distinct structural and optical properties. While B-CDs maintain stable fluorescence in both THF and water, O-CDs undergo aggregation-induced fluorescence quenching upon incorporation of water in THF. Leveraging this contrast, the B-CDs/O-CDs dual-emission system enables ratiometric quantification of water content in a wide range of 0-70% (v/v) with a low detection limit of 0.016%. The intensity ratio (I_orange/I_blue) and emission peak shift (Δλ_orange) provide dual-mode detection, ensuring high accuracy. Additionally, a portable polyvinyl alcohol (PVA) film embedded with the CD pair allows smartphone-assisted on-site determination of water content, achieving recoveries of 91.0-114.0% in commercial THF samples. This work offers a cost-effective and instrument-free approach for water determination, with potential applications in solvent quality control and industrial process optimization.