Fig. 1. FTIR spectra of PAA, OA-UCNPs and PAA-UCNPs
a: PAA; b: OA-UCNPs; c: PAA-UCNPs

Fig. 2. SEM images of OA-UCNPs (a) and PAA-UCNPs (b)

Fig. 3. UV-Vis absorption spectra of Aptamer, PAA-UCNPs and Apt-UCNPs

Fig. 4. Schematic diagram of Apt-UCNPs used to detect SDM

Fig. 5. Fluorescence spectra of Apt-UCNPs and absorption spectra of cDNA-BHQ1

Fig. 6. (a) Fluorescence spectra and (b) quenching efficiency of Apt-UCNPs at different concentrations of cDNA-BHQ1

Fig. 7. (a) Fluorescence spectra and (b) standard curve of Apt-UCNPs under different concentrations of SDM system

Fig. 8. Fluorescence spectra of Apt-UCNPs in the presence of different substances