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

Abstract

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.