Fig. 4

Comparison of the effects of two AFM probe functionalization methods, a traditional immersion method and our micro-droplet method, on force spectroscopic measurements. A Representative force spectroscopy of nonspecific interactions (force–distance curves) between bare micas and low-density lipoprotein receptors (LDLRs) functionalized on AFM probes via the immersion method (left panels) and our micro-droplet method (right panels), respectively. From top to bottom: the probes were functionalized with nothing, PEG, and PEG + LDLR, respectively. B Quantitative analysis of the average nonspecific interaction force. C Representative force spectroscopy of specific interactions between LDL particles deposited on mica and LDLRs functionalized on AFM probes via immersion method (left panels) and micro-droplet method (right panels), respectively. The red arrows on the force–distance curves show the number of interactions. D Quantitative analyses of the average peak number (left panel) and average force (right panel) of specific LDL–LDLR interaction. In the schematic diagrams alongside representative force–distance curves, PEG, LDLR, and LDL are displayed as a blue curly line, red dot, and blue dot, respectively (more PEG and LDLR are shown in the left panels than in the right panels). AFM force spectroscopy were performed in PBS buffer at pH 7.4. In B and D, n = 200 interactions in each group from three independent experiments. ^*p < 0.05 and ^**p < 0.01 compared our micro-droplet method with the immersion method