In this paper, a new approach is demonstrated to measure the compression elasticity of single biomolecule in small force regime (<0.5 nN) using vibrating mode scanning polarization force microscopy (VSPFM). With this method we investigate the compression elasticity of a single DNA molecule in the radial direction (perpendicular to DNA strands). The radial deformation of DNA molecules deposited on mica surface is shown to be able to reach about 50% un der external load, and this remarkable deformation is re- versible. In addition, the compression spring constant of DNA molecules is estimated to be about 0.6 nN/nm according to the height-force curves.
The great implication of nanobubbles at a solid/water interface has drawn wide attention of the scientific community and industries. However, the fundamental properties of nanobubbles remain unknown as yet. In this paper, the temperature effects on the morphology of nanobubbles at the mica/water interface are explored through the combination of AFM direct image with the temperature control. The results demonstrate that the apparent height of nanobubbles in AFM images is kept almost constant with the increase of temperature, whilst the lateral size of nanobubbles changes significantly. As the temperature increases from 28℃ to 42℃, the lateral size of nanobubbles increases, reaching a maximum at about 37℃, and then decreases at a higher temperature. The possible explanation for the size change of nanobubbles with temperature is suggested.
Nanoparticle PCR is a novel method to optimize DNA amplification. It performs well in improving specificity, enhancing sensitivity and speed. Several mechanisms were proposed in previous studies: one was based on the interaction between gold nanoparticles (AuNPs) and DNA while the other was attributed to the heat transfer property of AuNPs. In this paper, we propose that the interaction between AuNPs and DNA polymerase can significantly influence PCR. First, the addition of DNA polymerase can eliminate the inhibitory effects of excess AuNPs. Second, the addition of AuNPs will increase yield of the desired PCR product and make the optimum concentration of DNA polymerase move to higher value. Third, while excess polymerase might inhibit amplification efficiency, AuNPs can reverse this process and the yield of PCR amplification. Based on these results we propose a possible mechanism that AuNPs might modulate the activity of polymerase and improve PCR amplification.
MI LiJuanZHU HongPingZHANG XiaoDongHU JunFAN ChunHai
