Fig. 3

Traditional immersion methods and our novel micro-droplet method for AFM probe functionalization. A The schematic diagram comparing AFM probe functionalization between traditional immersion methods (a, b) and our micro-droplet method (c). From top to bottom: the main steps of each method. The process of probe functionalization is controlled by operator’s hands and a stepping motor, respectively, in traditional immersion methods and our micro-droplet method. B Observation of micro-droplets on a mica under an AFM cantilever/probe (even the smallest micro-droplets of up to several microns in diameter can be selected for probe functionalization)