Atomic Force Microscope With Quartz Tuning Fork Sensor (TF-AFM) For Cell Imaging

Looking into cell and its dynamics has always been a challenge for biologist to betterunderstand complex biological systems. The use of a simple microscope by Robert Hookemade the cell discovery possible. With the passage of time new microcopy techniques havebeen evolved. Optical microscopes and electron microscopes have been two major kindsof instruments for cell imaging for a long time. Soon after invention AFM was added onboard as third major kind of instrument for cell imaging and characterization.Conventional AFM with optical lever system (for force detection) has severallimitations e.g. low Q factor of cantilever, higher thermal drifts and cumbersome laseralignment routine. In addition like in other fluorescence microscopes, the laser can causephototoxicity to biological samples. Fortunately the tuning fork probe (tuning fork sensor)has not only resolved above mentioned constrains but also has additional features like lowpower dissipation, high spatial resolution, high temperature stability and force sensitivity.Although tuning fork sensors (in different configuration) have been employed widely forimaging but a little research have been carried out about their use in bioimaging.Realizing the fact that Quartz tuning fork (QTF) sensors based AFM (TF-AFM) can bea better solution than their conventional counterpart for bioimaging, in this work tuningfork force sensor have been studied thoroughly. Quartz tuning fork sensor (QTFs) withhigh Quality factor has been prepared. Commercial tips as well as fabricated tips byelectrochemical etching were mounted on one prong of QTF with other set free. The sensorperformance in air and liquid has been characterized before using for imaging. High Qfactors2000to8000(average) are recorded for sensor in air. A drastic drop in Q factor dueto hydrodynamic damping was observed when the tip was immersed in liquid,500-2000(average) Q factor have been measured in liquid.Tuning fork force sensor based AFM (TF-AFM) have been realized using a home-builtAFM. Mouse fibroblast NIH3T3cell line culture cultivation and sample preparation wasdone in our lab facility. The incubated cells were adhered to inner bottom of petri dish.AFM Images of fibroblast cells were acquired in physiological solution. All images wereacquired in tapping mode to avoid any damage to soft cellular membrane. Although QTFshas several advantages but there are still challenges in using TF-AFM for cell imaging, I-If both or one tine touch liquid surface drastic Q factor drop and loss in output can lead totip-sample distance control instabilities, and sometime the control instability can damagecell as well as the tip. II-The evaporation of liquid and condensation on prongs can causea slide damping due incremental mass. III-For imaging in liquid comparatively longer tipshould be mounted on one prong which results in Q factor drop; however careful masscompensation can restore the Q factor successfully.