Bimetallic-doped carbon quantum dots with enhanced photoluminescence and peroxidase-mimicking activity for dual-mode colorimetric and ratiometric fluorescence assay of alendronate.

Carbon quantum dots (CQDs) are powerful signal transducers in dual-mode assays while still being challenged by their poor peroxidase-mimicking activity and photoluminescence property. Herein, bimetallic copper-iron-doped CQDs (CuFe-CQDs) as a multifunctional nanozyme were proposed for dual-mode colorimetric and ratiometric fluorescence assays of alendronate sodium (ALDS). Notably, CuFe-CQDs were identified to show enhanced and tunable photoluminescence and peroxidase-mimicking activities with bimetallic doping, ascribed to the boosting activation ability of H₂O₂ into HO• and ¹O₂, and the improving carrier mobility in the π-conjugated structure of CuFe-CQDs. Based on the inhibition of ALDS on the peroxidase-mimicking activity of CuFe-CQDs, which further disturbed the inner filter effect (IFE) between CuFe-CQDs and the chromatic product, a dual-mode colorimetric and ratiometric fluorescence assay for the differentiation and determination of ALDS and its analogues was developed with better quantification and high identification, reaching a limit of detection of 0.019 μM in colorimetric mode and 0.146 μM in ratiometric fluorescence mode. The developed dual-mode assay also demonstrated accurate analysis of ALDS in diluted tablets and human urine with recoveries of 92-110%. Our work provides a new approach for the development of functional nanozymes and holds great prospects in multi-mode/signal sensing in complex matrix.