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Title: Simple, clickable protocol for atomic force microscopy tip modification and its application for trace ricin detection by recognition imaging

item CHEN, GUOJUN - University Of Georgia
item NING, XINGHAI - University Of Georgia
item BOONS, JEERT-JAN - University Of Georgia
item Park, Bosoon
item XU, BINGQIAN - University Of Georgia

Submitted to: Langmuir
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/7/2009
Publication Date: 1/7/2009
Citation: Chen, G., Ning, X., Boons, J., Park, B., Xu, B. 2009. Simple, clickable protocol for atomic force microscopy tip modification and its application for trace ricin detection by recognition imaging. Langmuir. 25(5):2860-2864.

Interpretive Summary: Food toxins pose a serious danger to human lives and even low dosage of threat agents can be harmful. Therefore, agent detection systems must have high sensitivity and specificity. This paper reports nanotechnology for food toxin detection using an atomic force microscope (AFM). To develop AFM-based sensing method, the tip modification plays an important role, since it directly determines the quality of the image and probability of the force measurement. We developed the protocol which includes AFM tip modification to carry a specific chemical function group, the cross-linker attachment to the tip, and modification of biological molecule to connect target molecule with a tip. Since the specific interaction between antibody and antigen, we were able to detect ricin quantitatively. This innovative nanotechnology detection method can be used for a sub femto-gram level sensitivity. This detection method will have great potential for food safety and security.

Technical Abstract: There are three standard steps for AFM tip functionalization in a single molecule recognition force microscope (SMRFM). First, AFM tip is modified to carry a specific chemical function group; second, the cross-linker PEG is attached to the tip; finally, the modified biological molecule is connected to the end of PEG. Due to the complexity of AFM tip functionalization, a full functionalization protocol for the tip and substrate was built. A cross-linker, PEG2000 with one thiol and one azide end group, and several active succinimidyl esters were synthesized. The PEG form self-assembly monolayer (SAM) on the gold-coated tip; and then modified anti-ricin molecules with alkyne group were attached to the tip using ‘click reaction’. In addition, the ricin molecules were immobilized on the gold surface, which was modified by active ester. The results of ricin detection were obtained from the image easily and quickly with a sub femto-gram level sensitivity. Furthermore, the unbinding force between anti-ricin and ricin was observed and the force-distance curves (F-D) were complied with worm-like model. The most probable unbinding force, which is about 64.89292±1.67119 pN was also observed from the histogram.