Tip Pressure on Semicircular Specimens in Tapping Mode Atomic Force Microscopy in Viscous Fluid Environments

Area of Science:

• Biophysics
• Fluid Dynamics
• Materials Science

Background:

• Tapping mode atomic force microscopy (AFM) is crucial for imaging biological specimens in liquid.
• Hydrodynamic pressure from the AFM probe can affect measurement accuracy and specimen integrity.
• The impact of specimen size on hydrodynamic pressure and resulting deformation remains understudied.

Purpose of the Study:

• To analyze hydrodynamic pressure and vorticity distributions around biological specimens of varying sizes during AFM scanning.
• To investigate the influence of tip-specimen size ratio and tip location on specimen deformation.
• To understand the relationship between fluid dynamics and contour distortion in AFM measurements.

Main Methods:

• A semi-analytical method was utilized to model a semicircular biological specimen.
• Analysis focused on vorticity and pressure distributions for different specimen sizes and tip positions.
• Simulations captured changes in pressure, fluid spin, and specimen deformation as the AFM tip approached.

Main Results:

• Maximum pressure on the specimen surface occurred when the specimen diameter equaled the tip width.
• Complex vorticity patterns were observed between the tip and specimen near the specimen's center line.
• Specimen inflation was identified when the AFM tip was aligned with the specimen's center line.

Conclusions:

• Specimen size and AFM tip geometry significantly influence hydrodynamic pressure and deformation.
• Understanding these fluid-structure interactions is vital for accurate AFM measurements of biological samples.
• The study provides insights into optimizing AFM parameters to minimize specimen distortion.