A ratiometric fluorescence and colorimetric dual-mode sensing platform based on sulfur quantum dots and carbon...

A new dual-mode ratiometric fluorescence and colorimetric probe for selective determination of Cu²⁺ was developed based on blue-emission sulfur quantum dots (SQDs) and yellow-emission carbon quantum dots (CQDs). The fluorescence and absorbance of CQDs increased in the presence of Cu²⁺ due to the Cu²⁺ -oxidized o-phenylenediamine group on the surface of the CQDs. Because of the inner filter effect between SQDs and CQDs-Cu²⁺, the fluorescence response of SQDs decreased following the introduction of Cu²⁺. Furthermore, in the presence of Cu²⁺, the dual-mode SQD-CQD probe showed visible color changes under both ultraviolet light and sunlight. Under optimal conditions, the dual-mode probe was used to quantitatively detect Cu²⁺ with a linear range of 0.1-5.0 μM for ratiometric fluorescence and colorimetry, with a limit of detection of about 31 nM and 47 nM, respectively. Finally, the dual-mode probe was used for the determination of Cu²⁺ in practical samples to expand the practical application, and the difference between ratiometric fluorescence and colorimetric methods was compared. The recovery results confirmed the high accuracy of the dual-mode probe, showing that it has immense potential for sensitive and selective detection of Cu²⁺ in practical samples.