Fig. 4. Quantification of DNA conformation changes.
a Two types of protein interaction modes on antibody-modified surface: hit and stay (binding), and bind and unbind rapidly (dancing). b Time trace of z-displacement of one IgM molecule on the anti-IgM modified surface under two protein interaction modes. c Probability density determined from the statistical distribution of z-displacement amplitude. d Free energy profile achieved from the probability density and fitted results with a polynomial function. The effective spring constant obtained from fitting was also presented. For Fig. 4a–d, incident wavelength is 450 nm, and incident light intensity and camera exposure time are 60 kW cm-2 and 5 ms. e Schematic showing the structure of ssDNA anchored gold nanoparticle (AuNP) on the glass surface before and after hybridization with miRNA. Time trace of z-displacement of one nanoparticle linked by the soft ssDNA and rigid hybridized duplex structures was also presented. f Probability density determined from the statistical distribution of z-displacement amplitude for the gold nanoparticle shown in Fig. 4e. g Free energy profile achieved from the probability density and fitted results with a polynomial function. The effective spring constant obtained from the fitting was also presented. h Effective spring constant colormap for 64 gold nanoparticles linked by ssDNA molecules on the surface before and after hybridization with miRNA. i Effective spring constant statistical distribution for 64 gold nanoparticles linked by ssDNA molecules on the surface before and after hybridization with miRNA, where the solid curves are Gaussian fitting. For Fig. 4e–i, incident wavelength is 532 nm, and incident light intensity and camera exposure time are 2 kW cm−2 and 0.2 ms.