# High-Efficiency Adsorption of SARS-CoV-2 Spike 1 Protein by Plasma-Modified Porous Polymers
## 2 Materials and Methods  
**Chemicals and materials.** MaPR with a particle size between 30-60 mesh and a surface area of approximately 300 m\({}^{2}\) g\({}^{-1}\) was purchased from Sigma-Aldrich (cat. no.9003-70-7). SARS-CoV-2 Spike Glycoprotein S1 (cat. no. ab273068) was purchased from Abcam.  
The MaPR was pretreated with anhydrous ethanol (Tianjin Fuyu Fine Chemical Co., Ltd., Tianjin, China).  
**Preparation of modified porous polymers.** The MPPs in this study were obtained by nanosecond pulsed discharge plasma treatment. Firstly, 40 g of MaPR was soaked in anhydrous ethanol overnight for pretreatment. Subsequently, MaPR was washed continuously with distilled water until the pH of the soaking solution became neutral. MaPR was dried at 37 \({}^{\circ}\)C for 24 h. Then, 2 g of MaPR was placed into the plasma reactor and modified with nanosecond pulse discharge plasma under the condition of artificial air for 20 min. The pulse peak voltage was 30 kV, and the pulse repetition frequency was 120 Hz. The plasma modification device and detailed process are shown in the Supplementary Materials.  
**Adsorption experiments of SARS-CoV-2 S1 protein.** S1 protein with a concentration of 1 mg/mL was diluted into 0.5 ug/mL or 0.1 ug/mL protein solution with sterile Phosphate Buffered Saline. A total of 0.1 g of MaPR or MPP was weighed and placed in sterile six-well plates, respectively. A total of 500 uL of protein solution was added to each well and then incubated for 1 min. The solution in each well was collected after incubation. The protein-adsorbed sample and the collected solution were further analyzed. The adsorption capacity of the S1 protein by resin was determined by measuring the consumption of protein in solution. The adsorption efficiency of the S1 protein was calculated as follows:  
\[\text{w (\%)}=\text{(C}_{0}-\text{C}_{1})/\text{C}_{0}\times 100\% \tag{1}\]  
where w (%) represents the adsorption efficiency, C\({}_{0}\) (mg/mL) represents the S1 protein concentration without adding resin, and C\({}_{1}\) (mg/mL) represents the S1 protein concentration when adding 100 mg resin for 1 min.  
**Characterization.** The surface morphology of the materials was scanned by scanning electron microscopy (SU8020, Hitachi) with a secondary electron beam and an accelerating voltage of 10 kV. The elemental composition and valence of the surface of the materials were analyzed by XPS (ESCALAB 250 Xi, Thermo Fisher, Waltham, MA, USA). The spectrum data of C1s (284.6 eV) was obtained and then fitted with XPSPEAK4.1 software to analyze the oxygen functional groups. An FTIR spectroscopy spectrometer (EQUINOX55, Bruker) was used to measure the surface functional groups.  
**ELISA.** Concentrations of the SARS-CoV-2 S1 protein after adsorption in each group were measured by a FastScanTM SARS-CoV-2 Spike protein ELISA Kit (Cell Signaling Technology, Inc., cat. no. 76349, Danvers, MA, USA) according to the manufacturer's instructions. The detailed steps are shown in the Supplementary Materials.  
**Western blot.** After adsorption, the protein solution of each group was collected for western blotting analysis. The proteins were separated using Sodium Dodecyl Sulfate-Polyacrylamide Gel Electrophoresis (SDS-PAGE, 8% gel) and transferred to polyvinylidene fluoride membranes (Invitrogen; Thermo Fisher Scientific, Inc., Waltham, MA, USA). After that, the membranes were blocked in 5% skim milk for 2 h to avoid nonspecific binding. Then, the membranes were incubated at 4 \({}^{\circ}\)C with anti-SARS-CoV-2 Spike Glycoprotein S1 antibody (1:1000 dilution, Abcam, cat. no. ab283942). On the next day, the membranes were incubated with HRP-labeled anti-rabbit IgG (1:10,000 dilution, Beijing Zhongshan Jinqiao Biotechnology Co., cat. no. ZB-5301, Beijing, China) at room temperature for 2 h. After exposure, the gray values of immunoreactive bands were analyzed by ImageJ software (v.1.8.0, National Institutes of Health, Bethesda, MD, USA).