Development Of A Low-noise Non-contact Cryogenic Atomic Force Microscope For Biological Applications

Atomic force microscopy has been a powerful tool for the study of the surface topography of the samples,especially in the field of material science and biological science.Although atomic force microscopy has been widely applied to the detection of a variety of different types of biological macromolecules,and made many commendable success,getting the resolution to 1 nm,especially less than 1 nm of the fine structures stably and reliably is still very difficult and challenging.To resolve the problem described above,we developed the cryogenic non-contact atomic force microscope which is capable of high resolution imaging.Firstly,we utilize the change of the resonant frequency of the cantilever probe as the feedback signal,through the precise control of the probe and sample surface distance,to achieve the non-contact mode AFM successfully.Then,we put the instrument into the cryogenic environment and ensured it to work well.To accomplish this goal,we redesigned a different AFM head compared with the commercial AFM head.We designed the magnetic damping suspension system in order to reduce the mechanical noise and coupling vibration.Moreover,controlling pressure properly so as to effectively suppress the boiling point of liquid nitrogen and reduce liquid nitrogen gasification which can bring more noise in the imaging process was designed.And the gear group can help us ensure that the probe and the sample is parallel when the probe is approaching the sample surface because of the linkage of three supporting points.Through increasing the optical path of optical lever and the highly efficient focusing method,we got the necessary detection sensitivity.In addition,we also redesigned the circuit to reduce the noise,improving the ratio of signal to noise of the whole system.The deflection noise density of our system can achieve 12fm/?Hz which are smaller than the values of commercial atomic force microscope.With this cryogenic non-contact frequency modulation atomic force microscope,we successfully detected the topography of the biological sample surfaces in high resolution and demonstrated that cryogenic noncontact AFM is much easier to obtain high resolution images compared with contact AFM.