Construction of an electrochemical–fluorescent dual-mode sensor with a dual-mode signal AgNC probe synthesized from cytosine-rich DNA for OTA detection

Herein, we have used DNA-silver nanocluster (DNA-AgNC) signal probes with both electrochemical and fluorescent signals for the first time to construct an electrochemical-fluorescent dual-mode sensor. The sensor has an easy-to-prepare dual-signal property combined with the magnetic separation technique for dual-mode detection of ochratoxin A (OTA). In the absence of OTA, the DNA strand used to synthesize AgNCs was not available in the system after magnetic separation. DNA-AgNCs probes could not be synthesized in the system, resulting in low fluorescence and electrochemical signals. In the presence of OTA, it led to the shedding of sulfhydryl-modified and cytosine-rich DNA (C-DNA). DNA-AgNCs probes with high fluorescence and electrochemical signals were formed by adding AgNO₃ and NaBH₄ to the supernatant after magnetic separation. Dual-mode detection of OTA was achieved by the signal response of fluorescence and electrochemistry. The detection ranges were 2.5 × 10^-4-50 ng mL^-1 and 2.5 × 10^-4-25 ng mL^-1 in the fluorescence mode and electrochemical mode with detection limits of 0.11 pg mL^-1 and 0.025 pg mL^-1, respectively. Meanwhile, the dual-mode sensor displayed better specificity, repeatability and reproducibility than conventional electrochemical and fluorescent single-mode sensors. The results of the spiked peanut and wheat flour detection showed that the fluorescence and electrochemical modes of the sensor exhibited satisfactory average recoveries.