Figure 5
Lateral force microscopy analysis of binding affinity between AuNPs and chemically functionalized surfaces. (a, b) AFM topographic images and lateral force images of AuNPs immobilized on Si substrates, respectively, functionalized with (a) amino groups (AuNP-SA) and (b) catecholamine molecules (AuNP-SD) by different normal spring constants (kN) of microcantilevers. The inset shows left embankment (indicated by a red arrowhead) due to swept AuNPs formed by scanning the surface in AFM contact mode with kN = 0.7 N/m of microcantilever. All scale bars including that of the inset are 250 nm. (c) Line profiles corresponding to the white arrow in each image of (a) and (b) show the curves of scanner retracting distance versus the AuNP lateral displacement and the lateral force versus the lateral displacement, respectively. (d) Graph of the average lateral force of >100 AuNPs in (a) and (b) (the asterisk indicates p < 0.001) was extracted and calculated from the line profiles of lateral forces (c). (e) The model illustrates the physical interaction between the AFM tip and AuNPs attached on the chemically functionalized substrate (i.e., AuNP-SA and AuNP-SD).