Fig. 2

Immuno-TEM observation of the recognition of native or oxidized LDL pre-immobilized on micas by gold-nanoparticle-conjugated receptors (LDLR or CD36). A Gold nanoparticle (5 nm)-conjugated LDLR only. B Native LDL particles only. C–F Binding of gold-nanoparticle-conjugated LDLRs to native LDL particles at pH 7.4, pH 6.4, pH 5.4, and pH 4.4, respectively. A–F Top panels: TEM images; bottom panels: schematic diagrams presenting the binding of gold nanoparticle (red)-conjugated LDLR molecules (purple) onto a LDL particle (brown) layer pre-immobilized on copper grid (gray). LDL–LDLR interaction was conducted in PBS buffer at different pH values, whereas TEM imaging was performed in a vacuum. G Quantitative analysis of the LDL–LDLR binding ratio at different pH values. H Quantitative analysis of the oxLDL–CD36 binding ratio at different pH values (the representative TEM images of oxLDL–CD36 recognition are not shown). The control group (Ctrl) means the group incubating of gold nanoparticles (but no LDLR) with LDL/oxLDL on micas to exclude the possibility of nonspecific interaction. The number of gold nanoparticles (black dots) in each image was counted for calculation of the binding ratio (to the data at pH 7.4). ^***p < 0.001 compared with pH 7.4 (n ≥ 3 images in each group)