The Mechanical Behavior Between Self-Assembled Monolayers Of Protein

Proteins play a fundamentally important role in biological functions execution such as movement, transportation, catalysis, protective immunity and mechanical protection in life science. Most of physiological activities of the organisms are achieved by interactions between protein and protein. Studies on micromechanics behavior of protein are important links in learning about its biological functions. Benefit from advantages of high resolution and nano-mechanical detection, the atomic force microscopy(AFM) plays an important role in protein researches. Bovine serum albumin(BSA) and AFM were used as the research target and the main research approach. Combining with self-assembled monolayer(SAM) technique, investigation of micromechanics behavior of BSA was taken in this paper. The main research contents are as follows:(1)BSA monolayer was prepared by chemical modification and characterized on wettability, surface structure and morphology by contact angle test and AFM. Experimental results showed that after the preparation of BSA monolayer, the contact angle of bare gold substrate decreased form 62° to 17°, the surface roughness increased from 1.02 nm to 1.93 nm and the average height of particle increased from 11.0 nm to 15.4 nm. AFM three-dimensional topography showed BSA monolayer prepared is smooth and homogeneous. Moreover, the C/M monolayer with mixed components of 16-Mereaptohexadecanoic acid(MHA) and N-dodecyl mercaptan(NDM) and the P/M monolayer with mixed components of protein and NDM on surface were prepared. The surface free energy and surface roughness of C/M monolayer and P/M monolayer were characterized. Results showed a negative correlation between NDM proportion and surface free energy. Roughness of monolayer with BSA on surfaces was higher than chemical compounds of alkyl acid and alkyl with the identical NDM proportion. The space structure of proteins is a determining factor for the variation of roughness of P/M monolayer;(2)Friction of BSA monolayer was investigated by lateral force microscope(LFM). Experimental results showed the lateral force of protein monolayer in experimental group and exchange group with specific interaction between antigen and antibody was mainly distributed in 100-170 pN. However the blank control group and block grorup with non-specific interaction was mainly distributed in 0-50 pN. This result indicates interaction between protein monolayer and the probe tip has effect on lateral forces. Results from friction test on C/M monolayer and P/M monolayer showed the variation tendency of surface friction was consistent with surface roughness. Results showed that surface roughness and homogeneity are importance cause of the variation of friction forces. With the range of 0-3.0 nN of loading force, there was a positive correlation between the surface friction and the loading force;(3)With investigation of the adhesion force between BSA and anti-BSA by AFM, the interaction force was achieved. Poisson distribution method was used to calculate adhesion force statistically, with results of 125.3±4.8 pN of specific interaction between BSA and anti-BSA in PBS, and 51.3±27.3 pN of non-specific interaction. Experimental results in the drug solution showed that non-salified quinolone solution had no obvious effect on protein-protein interactions. Conversely, because of the pH and ionic strength were changed, salified quinolone solution had a significant effect on protein-protein interactions. Quinolones with similar structures had no significant difference in the influence of protein-protein interactions. Specific interaction between BSA and anti-BSA was changed notably under lower drug concentration(20 mM) and higher drug concentration(100 mM) of quinolone solution. Combining with AFM topography test, this phenomenon occurred on account of the pH was close to the isoelectric point of BSA and the ionic strength was high that the antigen/antibody specificity binding sites were covered respectively.Atomic force microscope as an measurement instrument with nanoscale sensitivity, has a certain advantage on surface analysis and micro-mechanical testing. It has ability to measure topography, friction performance of proteins and specific interaction between antigen and antibody under approximate physiological environment, that has significance in protein regulation, disease diagnosis, drug screening and the discovery of drug targets.