Single-Molecule Recognition of Biomolecular Interaction via Kelvin Probe Force Microscopy  

Jinsung Park, Jaemoon Yang, Gyudo Lee, Chang Young Lee, Sungsoo Na, Sang Woo Lee, Seungjoo Haam, Yong-Min Huh, Dae Sung Yoon, Kilho Eom*, Taeyun Kwon*

Hello,

 Recently, I have a problem bothered me alot, anybody please help me out.

 I am using Dimension 3100 AFM. It is a scanned tip SPM. There are two screws to adjust mirrow so that the laser can be reflected to the photodiode. My problem is:

 After the laser was reflected to the center of the photodiode, I do locate tip/focus surface. The red spot will shift to the edge of the photodiode. According to my understanding, the red spot should stay center when I do locate tip/focus surface since it doesn't alter laser optical path. Anybody has same experience before?

Thanks very much for your attention!

I would like to do lateral force microscopy on biological samples.  The more I look into it, it seems it is very difficult to calibrate AFM tips for lateral force microscopy.  Does anyone have any suggestions about how to calibrate tips and which tips are conducive for lateral AFM? 

Cross-posted to Biocurious a blog about biology through the eyes of physicists.

The function and dysfunction of blood clots are often directly related to their mechanical properties: clots stop blood from flowing through wounds but can also break away (embolize) and block blood vessels causing stroke. Strength and plasticity are both important for ensuring the former is more common than the latter and so people have been studying the mechanics of clots for over 50 years. 

Despite this history, or perhaps because of it, new discoveries are being made all the time. Take the recent observations reported by Liu et al. last year in Science (abstract is free). They used a combined fluorescence and atomic force microscope (not unlike the one I've been working with recently!) to stretch single fibrin fibers--the ones that make up the protein mesh of blood clots shown in green in the image above--to see how far they could stretch. They found that some fibers could stretch up to 5 times their relaxed length before breaking! Check out the movies at Martin Guthold's site.