Dual-reverse-signal ratiometric fluorescence method for malachite green detection based on multi-mechanism synergistic effect

The proposition of ratiometric detection mode has demonstrated great superiority in improving analysis accuracy by forming self-calibration. Herein, the novel dual-reverse-signal ratiometric fluorescence detection for malachite green (MG) was first achieved based on synergistic effect of fluorescence resonance energy transfer (FRET) and inner filter effect (IFE). The ratiometric fluorescence probe (B-RCDs) was self-assembled via electrostatic attraction between blue-emission carbon dots (BCDs) and red-emission carbon dots (RCDs), followed with FRET effect from BCDs to RCDs and exhibited dual-emission at 450 nm and 627 nm. In the presence of MG, the IFE effect between MG and RCDs quenched the fluorescence at 627 nm and restored the fluorescence at 450 nm, sending out two reverse signals along with an obvious color change from pink to purple (302 nm UV lamp). This ratiometric method not only simplified the preparation process, but also improved the detection sensitivity, showing a low limit of detection (LOD) of 41.8 nM, which exhibited superiority than that of single-signal RCDs (157.3 nM). This method held a rapid response of 10 min and represented satisfactory recoveries (99.14%-109.08%) in real water samples, revealing it was a promising candidate in the fast, sensitive and practical detection of MG. Moreover, the design of synergistic effect supplied a new perspective for the development of ratiometric sensing in the future.