*4.3. Preparation of the ZEN-McAb-GNP Probes*

The ZEN-McAb-GNP probes were the essential biosensor materials for reflecting the detection results, which were prepared as per the previously reported method [30,31]. Firstly, appropriate dosages of 0.2 mol/L K2CO<sup>3</sup> of an aqueous solution were used to adjust the GNPs solution (1 mL) to pH 8.5. Next, the 3.0 µL diluted ZEN-McAb was coupled with the GNPs at room temperature for 0.5 h after mixing well. Then, the BSA in purified water was used to block the nonspecific surface for 0.5 h. After removing the weak particles at low speed centrifugation, the reaction solution was separated through centrifugation in 8000 r/min at 4 ◦C for 15 min. Finally, the sediment resulted in the ZEN-McAb-GNP probes, which were redissolved in a 10 mmol/L Tris buffer containing a stabilizer and were stored at 4 ◦C.
