**4. Conclusions**

In this paper, a novel NaYF4:Yb,Tm surface-functionalized fluorescent probe was proposed based on upconverted nanomaterials. Quantitative analysis of the effects of Yb3+ and Tm3+ ion concentrations on the morphology, size, and luminescence properties of NaYF4:Yb,Tm and NaGdF4:Yb,Tm indicated that the optimal doping concentration ratio of Yb3+:Tm3+ is 40:1. In the study, by comparing the fluorescence emission of NaYF4: 20% Yb, 0.5% Tm and NaGdF4: 20% Yb, 0.5% Tm, upconverted nanomaterials with better luminescence properties were obtained. A novel fluorescent probe was designed for the surface carboxylation of NaYF4:Yb,Tm and the connection with amino group and DNA. The probe can be used for the detection of different specific biological miRNAs. When the fluorescent probes are used to detect different miRNAs, they can distinguish different miRNAs, especially miRNAs with base mismatches, from non-specific RNA molecular analytes. The preliminary studies indicate that the upconverted probes have a good potential for protein detection in early cancer diagnosis.

**Author Contributions:** Conceptualization, Instruction, Funding and Writing: Y.L., L.Z. and W.C.; Experimental design and processing: Z.D.; Material Characterization, data analysis and simulation: Y.H., H.R., J.W., W.N. and Y.W.; Data analysis and editing: C.H., C.X. and C.Y.; Z.D. and edited and formatted the figures: Z.D. and J.W.; Supervision and approval for submission: Y.L. and W.C. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was funded by National Natural Science Foundation of China gran<sup>t</sup> number 61971207, Postgraduate Research & Practice Innovation Program of Jiangsu Province gran<sup>t</sup> number (KYCX20\_2213) and Natural Science Foundation of the Jiangsu Higher Education Institutes of China gran<sup>t</sup> number 19KJA510003 and 20KJA430003.

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

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** Not applicable.

**Acknowledgments:** W.C. would like to thank Solgro. Inc. and the University of Texas at Arlington for support.

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