Figure 4.

Schematic of edge tracking approach. (A) Schematic illustration of the experimental setup based on an inverted phase-contrast microscope with a 40× phase objective. (B) Differential optical detection for accurate tracking of cell edge changes induced by analyte–receptor interaction. (C) Schematic of a typical binding curve as determined from the cell edge movement. (D) The root mean square of the fixed cell edge change is 0.46 nm. (E) Illustration of cell edge changes over time during the binding process where i, ii, and iii correspond to the stages marked in (C). Blue and red rectangles in (B,E) are the ROIs for differential detection, reprinted with permission from Ref. [34].