**4. Conclusions**

In this study, a rapid, sensitive TRFM-ICG method based on a portable fluorescence reader was firstly established and confirmed for screening detection of DEX in milk and pork. TRFM was employed as the Ab tracer, and the cut-off values for DEX in milk and pork were 0.25 ng/mL and 0.7 μg/kg, respectively. The LOQs were 0.003 ng/mL and 0.062 μg/kg, respectively. The recovery rates ranged 80.0–106.7%, and 78.6–83.6%, respectively, with the CVs ranging 6.3–12.5% and 7.5–10.3%, respectively. The results could be obtained within 10 min. Parallel testing of blind milk and pork samples with LC-MS/MS demonstrated that the developed quantitative TRFM-ICG method was accurate, reliable, and user-friendly. The establishment of the TRFM-ICG method can provide a new, efficient, and useful technical support for the rapid screening of DEX in food.

**Supplementary Materials:** The following are available online at https://www.mdpi.com/article/10 .3390/foods10061339/s1, Figure S1: The results of particle size of TRFM, Figure S2: The fluorescence intensity, inhibition effect, and inhibition rate results of the activation pH value. (A) Ultraviolet lamp results for milk detection; (B) Fluorescence quantitative results for milk detection; (C) Ultraviolet lamp results for pork detection; (D) Fluorescence quantitative results for pork detection, Figure S3: The fluorescence intensity, inhibition effect, and inhibition rate results of the Ab amount. (A) Ultraviolet lamp results for milk detection; (B) Fluorescence quantitative results for milk detection; (C) Ultraviolet lamp results for pork detection; (D) Fluorescence quantitative results for pork detection, Figure S4: The fluorescence intensity, inhibition effect, and inhibition rate results of the surfactant concentration. (A) Ultraviolet lamp results for milk detection; (B) Ultraviolet lamp results for pork detection; (C) Fluorescence quantitative results for milk detection; (D) Fluorescence quantitative results for pork detection, Table S1: Working parameters of the TRFM-ICG for milk and pork detection, Table S2: The IC50 and CR values of anti-DEX Ab determined by icELISA, and TRFM-ICG.

**Author Contributions:** Conceptualization, writing—original draft preparation, and methodology, X.L. and X.C.; methodology, main data analysis, and writing—review and editing, J.W. (Jinxiao Wu) and Z.L.; validation, data curation, and writing—review and editing, J.W. (Jin Wang), C.S. and S.Z.; and conceptualization, supervision, project administration, and writing—review and editing, H.L. and Y.S. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was funded by National Key Research and Development Program of China (2017YFC1601205), the Natural Science Foundation of China (31701703 and 31871883), Guangzhou Planned Program in Science and Technology (201803020026, 201807010109, and 2017B020207010), and Shanxi Provincial Key Research and Development Program (201803D221028-1).

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Conflicts of Interest:** The authors declare no conflict of interest.
