Phi 5000 versaprobe 3

The organic element content was determined using elemental analysis (EA) (EA 2400 II, PerkinElmer, USA). Because the nitrogen content of various proteins was 16%, the amount of protein in the samples was obtained by multiplying the percentage of nitrogen element by 6.25 [36 (link)]. The morphology, structure, and elemental maps of the samples were determined by scanning electron microscopy (SEM) (Sigma 300, Zeiss, German) with energy dispersive X-ray spectroscopy (EDS). A fluorescence microscope (IX73P2F, Olympus, Japan) was used to collect optical and fluorescence microscopy images. Other characteristics were determined using Fourier transform infrared spectroscopy (FT-IR) (Vertex 70, Bruker, USA), X-ray photoelectron spectroscopy (XPS) (PHI-5000 Versaprobe III, ULVAC-PHI, Japan), X-ray diffraction (XRD) (SmartLab, Rigaku, Japan), and flow cytometry (FCM) (MoFlo Astrios EQ, Beckman Coulter, USA).

The elemental analyses (C, H and N) were measured on an EA-3000 elemental analyser (Euro Vector, Italy). FT-IR spectra were recorded on Thermo IS 5 FT-IR spectrometers (Walthamm, MA, USA) in the range of 4000–400 cm⁻¹. The PXRD data of the samples were measured on a Bruker D8 ADVANCE (Karlsruhe, Germany). Thermogravimetric analyses (TGA) were measured using a Japan Shimadzu DTG-60 H thermal analyser (Shimadzu, Tokyo, Japan). The UV-vis absorption spectra were collected on a UT-1950 spectrophotometer (Persee, Beijing, China) in the range of 200–800 nm. The liquid CD spectra were measured on a JASCO J-1500 spectropolarimeter (JASCO, Tokyo, Japan) in the range of 200–800 nm and the solid CD spectra were measured by KBr pellet (sample: KBr = 1: 200). ESI-MS spectra were measured using a Thermo Scientific (Walthamm, MA, USA) Q Exactive HF-X mass spectrometer equipped with an ESI source and in the positive ion mode from m/z 100 to 1600. HPLC were measured with Waters upc2 (Waters, Milford, MA, USA) Chiralpak IG using MeOH/CO₂ = 20:80 with flow rate of 2.0 mL/min and detection at 214 nm. X-ray photoelectron spectra (XPS) were measured with a PHI 5000 Versaprobe III (ULVAC-PHI, Kanagawa, Japan) with monochromatized Al Kα-X-rays (Hv,1486.6 eV) operating at 150 W, and were calibrated by the BE of the C component (BE = 284.6 eV) coming from contamination carbon.

An X-ray photoelectron spectroscopy (XPS) spectrometer (PHI 5000 VersaProbe III, ULVAC Inc., Chigasaki, Japan) was used to assess the surface elemental composition with a monochromatic Al Kα X-ray source (45°, 50 W, 1486.6 eV, sampling area; 200 μm diameter spot) of the peptide-immobilized surfaces and controls. Survey spectra were collected with a step size of 1.0 eV and a pass energy of 280.0 eV with charge compensation. Spectra were calibrated to the C 1s signal at 284.8 eV using the associated software (MultiPak, 9.6.0).

The synthesis of CNPs has been described in detail in our previous study (Yu et al., 2022 (link)). The particle size and morphology of CNPs were evaluated using transmission electron microscopy (TEM, JEM-2100, JEOL, Japan). In order to reduce the agglomeration phenomenon during CNPs detection, the obtained CeO₂ solution was dispersed in water and sonicated for 1 h. The solution was then added dropwise onto a copper mesh (with a 20-nm thickness of carbon support attached to the mesh) using a dropper and left to dry for observation. Moreover, a small amount of CeO₂ solution dispersed in water was diluted. About 1/3–2/3 of the liquid was put in the cuvette, and the hydrated particle size and distribution of CNPs were measured using dynamic light scattering (DLS, Nanosizer ZS90, Malvern, UK). X-ray photoelectron spectrometer (PHI-5000 Versaprobe III, ULVAC-PHI, Japan) was used to detect the valence distribution of Ce in CNPs. After freeze-drying the sample, a certain amount of powder was taken under the XPS for detection. The binding energy of C1s (285eV) was used as the internal reference for all measurements.