To make surface features of TMV visible in the AFM image, the intensity processing involved reduction of stripe noises, histogram equalization, and calculations of mixed partial derivative of pixel intensity, i.e. Dxy2I(x,y) = d2I(x,y)/dxdy, where I(x,y) is the intensity at pixel (x,y).
Using this dedicated image processing, we found that at low resolution (i.e., 1.95 nm per pixel), the extracted surface features of TMV can be interpreted as a partial or full helical repeat (three complete turns with 7.0 nm in length), while individual protein subunits ( 2.5 nm) were perceivable only at high resolution.
The analytical processing of the AFM images was developed by Wendy Chen. AFM measurements were performed by Michael Odorico and Jean-Marie Teulon. SAM surfaces were performed by Matthieu Meillan under the supervision of Luc Vellutini.
Chen S-wW, et al. (2013) Nanoscale structural features determined by AFM for single virus particles. Nanoscale 22 : 10877-10886.