Firstly, the morphology of the synthesized materials was examined using scanning electron microscopy (SEM). As depicted in
Figure 1A, the synthesized Zr MOFs exhibited a uniform cubic shape, averaging 800 nm in diameter. Due to the linkage of PEI, the previously smooth surface of Zr MOFs showed an obvious rough texture (
Figure 1B). Meanwhile, the cubic morphology of Zr MOFs-PEI could also be observed by the transmission electron microscopy (TEM) image (
Figure 1C). The elemental mapping image of Zr MOFs-PEI (
Figure 1D) depicted a uniform distribution of Zr, C, O, and N elements, verifying that Zr MOFs-PEI composite was successfully prepared. The X-ray diffraction (XRD) pattern in
Figure 1E revealed that the characteristic peaks of Zr MOFs were significantly consistent with those of the simulated pattern [
33]. It proved that the synthesized Zr MOFs achieved the expected results.
Figure 1F presented the UV-vis absorption spectrum of Zr MOFs, revealing a distinct absorption peak at 420 nm. The XPS spectra revealed the elemental composition and chemical states of the Zr-based MOFs. The full spectrum shown in
Figure 1G indicated the presence of O, C and Zr elements. In
Figure 1H, the O 1s peak split into two peaks at 529.7 eV and 531.0 eV, attributed to the oxo compounds of H
4TCBPE and the Zr-O bonds in the Zr MOFs. In
Figure 1I, the C 1s spectrum displayed two distinct peaks at 284.1 eV and 288.4 eV, corresponding to the benzoic acid rings of the organic ligand H
4TCBPE and the C=O bonds, respectively. In the Zr 3d spectrum (
Figure 1J), the peaks fitted at binding energies of 181.8 eV and 184.2 eV attribute to Zr 3d
5/2 and Zr 3d
3/2, respectively, confirming the presence of Zr (IV). These XPS results supported the formation of the MOFs.
Figure S1 depicted the Fourier transform infrared (FT-IR) spectral image of Zr MOFs and Zr MOFs-PEI. Compared with Zr MOFs, Zr MOFs-PEI exhibited a peak at 3300 cm
-1, indicating the N-H stretching vibration, which confirmed the successful loading of PEI onto the Zr MOFs. In addition,
Figure S2 showed the Zeta potentials of Zr MOFs, PEI and Zr MOFs-PEI, the changes in potential further proved the successful loading of PEI, which established the foundation for the subsequent construction of the ECL aptamer sensor. The results conclusively verified the successful preparation of Zr MOFs and Zr MOFs-PEI composite.