Atomic force microscopy contact, tapping, and jumping modes for imaging biological samples in liquids

Researchers have long sought reliable methods to image biomolecules in liquid environments. Traditional imaging techniques often fail to preserve sample integrity under physiological conditions. Atomic force microscopy (AFM) has emerged as a promising tool for such studies. Prior work has demonstrated AFM's ability to capture high-resolution images of biological samples. However, the optimal imaging mode remains unclear for liquid environments. Different AFM modes—contact, dynamic, and jumping—offer distinct advantages and limitations. The choice of mode depends heavily on sample characteristics and preparation methods. This uncertainty motivates a comparative analysis of AFM modes for biological imaging. The study addresses a critical gap in understanding how each mode performs across diverse biological systems.

This study aims to evaluate the performance of AFM imaging modes for biological samples in liquids. The focus is on determining which mode is most suitable for different types of biological systems. The researchers selected four diverse samples: DNA, purple membrane, Alzheimer paired helical filaments, and bacteriophage phi29. These samples differ in size and substrate interaction properties. The goal is to identify the most effective imaging mode for each sample type. The study also seeks to clarify how sample characteristics influence mode selection. By comparing contact, dynamic, and jumping modes, the researchers aim to provide practical guidance for AFM users. The findings may help improve imaging quality and sample preservation in liquid environments.

The study employed atomic force microscopy to image four biological samples in liquid environments. The selected samples included DNA, purple membrane, Alzheimer paired helical filaments, and bacteriophage phi29. These samples were chosen to represent a range of biological systems with varying sizes and substrate interactions. Contact mode imaging was used for samples requiring high-speed acquisition. Dynamic mode was tested for its ability to reduce lateral forces. Jumping mode was applied to minimize both lateral and normal forces. The researchers evaluated each mode's performance based on image quality and sample preservation. The study compared these modes across all four samples to determine their relative strengths and weaknesses.

The study found that dynamic mode AFM is most effective for soft samples in air but not in liquids. In liquid environments, no single mode outperformed the others across all samples. Contact or dynamic modes were best for imaging crystalline structures like purple membrane. These modes allowed faster image acquisition despite higher lateral forces. Jumping mode was preferable for macromolecules weakly bonded to the substrate. This mode minimized lateral and normal forces, preserving sample integrity. The results suggest that mode selection should be based on sample characteristics. The study demonstrated that no one mode is universally optimal in liquid environments. Instead, the best mode depends on factors like sample structure and bonding strength.

The authors conclude that mode selection in AFM imaging of biological samples in liquids depends on sample characteristics. Contact and dynamic modes are suitable for crystalline structures like purple membrane. Jumping mode is better for weakly bonded macromolecules. The study highlights the importance of matching imaging mode to sample properties. The findings suggest that no single mode is universally optimal in liquid environments. The researchers emphasize the need for careful mode selection based on sample-specific factors. The study provides practical guidance for AFM users working with biological samples in liquids. The results may help improve imaging quality and sample preservation in future studies.