A novel dual-mode colorimetric and ratiometric fluorescence method for detecting isocarbophos based on S, N-CDs inhibiting Fe3O4@Cu-BTC nanozyme activity
Although many colorimetric methods have been developed for on-site pesticide detection, most exhibit low sensitivity and limited resistance to interference. To address these issues, this study developed a novel dual-mode colorimetric-ratiometric fluorescence method for isocarbophos (ICP) detection using sulfur and nitrogen co-doped carbon nanodots (S, N-CDs) to inhibit catalytic Fe 3 O 4 @Cu-BTC nanozyme activity. The synthesized Fe 3 O 4 @Cu-BTC nanozymes with higher peroxidase-like activity were inhibited by S, N-CDs. The inhibitory mechanism was deeply investigated and was ascribed to (1) the restriction of the reaction between Fe 3 O 4 @Cu-BTC and hydrogen peroxide (H 2 O 2 ), which decreased the ·OH production, and (2) the ·OH scavenging ability of the S, N-CDs, forming the basis of the dual-mode method. The Fe 3 O 4 @Cu-BTC/Apt-complementary strand (CS)/S, N-CDs hybridization complexes demonstrated minimal to no peroxidase-like activity, preventing H 2 O 2 from oxidizing o -phenylenediamine (OPD) to produce yellow fluorescent 2,3-diaminophenazine (DAP). Meanwhile, the detection system demonstrated a low fluorescence intensity ratio (I 575 /I 465 ) at an excitation wavelength of 390 nm. However, the presence of ICP caused the CS/S, N-CDs to separate from the Fe 3 O 4 @Cu-BTC/Apt due to the high affinity between Apt and ICP. Then, the Fe 3 O 4 @Cu-BTC/Apt-ICP complexes recovered peroxidase-like activity, which promoted DAP production, accompanied by a pronounced fluorescence intensity ratio (I 575 /I 465 ). In optimum conditions, the detection limits (LODs) were 2.79 ng/mL (colorimetric) and 0.26 ng/mL (ratiometric fluorescence), respectively. The feasibility of the proposed method was verified via three spiked samples, yielding recovery rates of between 86.08 % and 112.64 %, indicating the significant potential for the highly sensitive, accurate on-site detection of ICP in actual samples.
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