Title: Mini review: Feeling the forces: atomic force microscopy in cell biology
Journal: Life Sciences
Authors: Jose´ Luis Alonso1, Wolfgang H. Goldmann*

Institute: 

Department of Medicine, Renal Unit, Massachusetts General Hospital, Harvard Medical School, Building 149, 13th Street, Room 8200, Charlestown, MA 02129, USA
 
The original and creativity of paper: The paper introduces the principle of atomic force microscopy (AFM) and also explains its ability of application.
  
Summary: 
AFM was report as the promising instrument due to it provides three-dimensional imaging. Furthermore, this microscope also provides resolution on the nanometer scale as well as the investigation of changing of surface properties. Surface properties can be expressed as several parameters such as surface stiffness or elasticity.  

1.    Principle of operation
Cantilever is the key element of AFM which consist of sharp tip at the end of cantilever. This tip is used to scan image and sense the force between the tip and surface of the sample. Then, an optical system is used to measure changes of the laser beam reflected from the gold-coated back of the cantilever onto a position-sensitive photodiode (PSPD). There are several operating modes which can be chosen according to sample characteristic, environment, and measurements required: 
-    Contact mode: In this mode, tip contact with the sample surface, scan the surface, and then generate the image the surface of the sample.
-    Tapping mode: In this mode, tip is vertically oscillated at or near the resonant frequency of the integrated cantilever. The image is generated by mapping the vertical distance the scanner moves as it maintain a constant oscillation amplitude at each lateral data point.
-    Phase imaging: Phase imaging can detect the different components in polymer based on their stiffness on area. The image can be obtained during tapping mode.
-    Force mode: this mode provides elastic properties or adhesion on the surface. Those values can be obtained by performing controlled vertical tip-sample interaction.
-    Other force microscope techniques (lateral force microscopy, LFM): It is meaningful for mapping frictional properties on surface, which is monitored during contact mode by applying torsional forces to the cantilever. These forces are related to the friction of the sample surface.

2.    Previous application
-    Characterize the surface morphology
-    Quantify adhesion force
-    Quantify the molecular binding interaction
-    Investigate changing of surface properties (e.g., elasticity)
-    Quantify the adhesion force between live cell and selected surface

3.    Future direction
-    AFM shows variety of abilities for scanning several samples at high resolution. However, this instrument can be applied to the broad aspects such as molecular science due to its convenience (without pretreatment) and flexibility.

Contribution: AFM can be applied to observe the changing of interested sample at nano-scale and it provides high resolution image.   

By Monruedee Moonkhum
Email: moon@gist.ac.kr