A colorimetric and ratiometric fluorescence dual-mode biosensor based on manganese-doped carbon dots for the detection of chloramphenicol residues.

Abstract

A dual-mode (colorimetric/fluorometric) sensing system for monitoring chloramphenicol (CAP)​ residues has been developed. The detection system was constructed using Fe₃O₄ nanoparticles (Fe₃O₄ NPs) as magnetic separation carriers and Mn-doped carbon dots (Mn-CDs) as signal probes. Fe₃O₄ NPs were conjugated to the CAP aptamer (Apt) via amide linkages, and Mn-CDs were linked to the complementary DNA strand (cDNA).Subsequently, these two components were assembled through base complementarity. In the presence of CAP, the Mn-CDs-cDNA complex undergoes competitive dissociation due to the stronger specific binding between CAP and the aptamer compared with base pairing. Following magnetic separation, the released Mn-CDs-cDNA complex in the supernatant catalyzes the oxidation of o-phenylenediamine (OPD) to 2,3-diaminophenazine (DAP), generating a colorimetric signal with an absorption peak at 450 nm. Simultaneously, a ratiometric fluorescence signal is achieved through the inner filter effect (IFE). DAP formation enhances fluorescence at 550 nm while quenching the blue emission of Mn-CDs at 455 nm. This dual-mode strategy enables the sensitive detection of CAP via monitoring the absorbance intensity and the fluorescence ratio (F550 nm/F455 nm). Under optimized detection conditions, the linear range for the colorimetric mode was 0.002-2 µmol L-1 with a detection limit of 11.6 nmol L-1; the linear range for the fluorometric mode was 0.005-6 µmol L-1 with a detection limit of 4.02 nmol L-1. This method demonstrates reliable performance for the detection of CAP residues in food samples. The dual-mode sensing strategy offers enhanced sensitivity and provides a promising analytical approach for food safety monitoring.

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