Cy5 labeled streptavidin

Membrane proteins were extracted with ProteoExtract Native Membrane Protein Extraction Kit (Merk Millipore, USA) and then biotinylated. An equal amount of biotinylated proteins was applied to the lectin array containing 6 repeated spots of 50 lectins. After 3 h incubation at room temperature, the glass slide was washed 3 times with PBS containing 1% Triton X-100 (PBSTx). 60 μL Cy5-labeled streptavidin (Invitrogen, USA) solution in PBSTx was added to the array and incubated at room temperature for 30 min. The glass slide was rinsed with PBSTx and scanned by an evanescent-field fluorescence scanner (Capitalbio, China). The data was obtained by the Array Pro Analyzer, version 4.5 (Media Cybernetics). The signal intensity of a spot was considered valid when the ratio of spot intensity/background intensity > 1.5. Then, the intensity of each spot was calculated by subtracting the background intensity from the signal intensity. The intensity value for each lectin was the average intensity of 6 repeated spots. The lectin array was repeated in triplicate.

Liposome‐associated cholesterol–oligonucleotide tags were hybridized to complementary oligonucleotides patterned on a glass substrate surface by cycling them through PDMS flow cells 10 times, followed by 3 × 100 µL PBS washing. For experiments with multiple types of liposomes, all liposomes were pooled prior to surface patterning. To verify the presence of spike protein on the liposomes, 9.83 µg mL⁻¹ biotinylated ACE2 (ACROBiosystems) in 2% BSA in PBS was cycled through the PDMS flow cells 10 times, then incubated for 1 h at room temperature. After 3 × 100 µL PBS washing, 0.4 µg mL⁻¹ Cy5‐labeled streptavidin (Invitrogen) in 2% BSA was cycled through 10 times, then incubated for 45 min at room temperature. After washing with PBS, the substrates were imaged using an ImageXpress Micro (IXM) High‐Content Imaging System (Molecular Devices).
For neutralization assays, prior to ACE2 incubation, different concentrations of anti‐SARS‐CoV‐2 receptor binding domain neutralizing antibody (range: 0–100 µg mL⁻¹; Human IgG1, clones AS35, AM122, AM180; ACROBiosystems) in 2% BSA were incubated with the patterned liposomes for 1 h. To visualize binding of the antibody to the liposomes, a fluorescent secondary antibody (mouse anti‐Human IgG1 AlexaFluor 488, Invitrogen) was applied at 1:500 dilution for 45 min at room temperature.