3.2.1. Sensitivity

Based on the above optimization conditions, negative milk and pork samples were spiked with DEX at different concentrations and tested by the optimized TRFM-ICG. As shown in Figure 4, the cut-off values of TRFM-ICG for DEX in milk and pork were 0.25 ng/mL and 0.7 μg/kg, respectively. The LOQ were 0.003 ng/mL and 0.062 μg/kg, respectively. The dynamics ranged 0.05–0.3 ng/mL and 0.12–1.35 μg/kg, respectively.

**Figure 4.** The results of TRFM-ICG for milk and pork detection: (**A**) the cut-off value for milk was 0.25 ng/mL; (**B**) calibration curve for quantitative detection of DEX in milk; (**C**) the cut-off value for pork was 0.7 μg/kg; and (**D**) calibration curve for quantitative detection of DEX in pork.
