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Cheng et al. Soft Sci. 2026, 6, 36 Page 7 of 15

Figure 2. (A and B) Morphologies of NiHCF and NiHCF-MIP NCs; (C) TEM image of NiHCF-MIP NCs; (D and E) HRTEM image of the
core-shell microstructure of one NiHCF-MIP nanocube and its EDXS mapping; (F) HRTEM image of the interface between the NiHCF core
and the MIP shell; (G) FTIR and (H) XRD curves of NiHCF, NiHCF-MIP (BE), and NiHCF-MIP (AE) samples. NiHCF: Nickel
hexacyanoferrate; MIP: molecularly imprinted polymer; NCs: nanocubes; TEM: transmission electron microscopy; HRTEM: high-resolution
transmission electron microscopy; EDXS: energy-dispersive X-ray spectroscopy; FTIR: Fourier-transform infrared spectroscopy; XRD:
X-ray diffraction; BE: before elution; AE: after elution; PDF: Powder Diffraction File.

Chemical compositions and crystal structures of NiHCF, NiHCF-MIP (BE), and NiHCF-MIP (AE) samples
are characterized by FTIR and XRD technologies. Their characteristic peaks in FTIR are generally similar,
except for the emergence of a new peak at 1,065 cm in the NiHCF-MIP (BE) and NiHCF-MIP (AE)
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samples, which corresponds to the in-plane deformations of C-H and N-H from polypyrrole , confirming
[28]
the fabrication of a polypyrrole shell [Figure 2G]. Both NiHCF-MIP(BE) and NiHCF-MIP(AE) display
characteristic absorption bands at 1,707 and 1,204 cm , respectively, assigned to steroid C-O and C-O-C
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stretching vibrations, along with a 1,437 cm feature arising from methylene C-H bending vibrations .
[29]
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These spectral features collectively originate from cortisol and the EGDMA cross-linker incorporated during