A Next-Generation qPlus-Sensor-Based AFM Setup: Resolving Archaeal S-Layer Protein Structures in Air and Liquid

Abstract

Surface-layer (S-layer) proteins form the outermost envelope in many bacteria and most archaea and arrange in twodimensional quasicrystalline structures via self-assembly. We investigated S-layer proteins extracted from the archaeon Pyrobaculum aerophilium with a qPlus sensor-based atomic force microscope (AFM) in both liquid and ambient conditions and compared it to transmission electron microscopy (TEM) images under vacuum conditions. For AFM scanning, a next-generation liquid cell and a new protocol for creating long and sharp sapphire tips was introduced. Initial AFM images showed only layers of residual detergent molecules (sodium dodecyl sulfate, SDS), which are used to isolate the S-layer proteins from the cells. SDS was not visible in the TEM images, requiring more thorough sample preparation for AFM measurements. These improvements allowed us to resolve the crystallike structure of the S-layer samples with frequency-modulation AFM in both air and liquid.

Interfacial structures and mechanical response of highly viscous polymer melt on solid surfaces investigated by atomic force microscopy

“…[13][14][15][16] In general, FM-AFM analysis in highly viscous liquids is difficult because the viscosity of the liquid depresses the resonant quality factor of sensors and the force sensitivity, 13 and most FM-AFM studies are limited to low-molecular-weight liquids [17][18][19][20] . To overcome this issue, we have developed FM-AFM utilizing a quartz tuning fork sensor (qPlus sensor 21,22 ), which shows a higher quality factor than the conventional cantilevers even in a viscous liquid, 23 and have achieved FM-AFM analysis of the interface between silicone oil (poly(dimethylsiloxane); PDMS) with a viscosity of 970 mPa•s (number-average molecular weight Mn ~ 26000 from calculation 24 ) and mica. We successfully imaged the atomic-scale topography of the solid surface and the layered density distribution on the interface, representing the molecules-layering structures in which the PDMS molecular chains are oriented parallel to the mica surface.…”

Interfacial Structures and Mechanical Response of Highly Viscous Polymer Melt on Solid Surfaces Investigated by Atomic Force Microscopy

“…Dynamic mode AFM, especially frequency modulation (FM-) AFM, would be a more powerful technique to detect conservative and dissipative interactions separately because it detects the interaction force as a change of resonance properties of the force sensor. Frequency-modulation atomic force microscopy (FM-AFM) has widely been applied for high-resolution structural analysis on solid/liquid interfaces. − In general, FM-AFM analysis in highly viscous liquids is difficult because the viscosity of the liquid depresses the resonant quality factor of sensors and the force sensitivity, and most FM-AFM studies are limited to low-molecular-weight liquids. − To overcome this issue, we have employed the quartz tuning fork sensor (qPlus sensor − ), which shows a higher-quality factor than the conventional cantilevers even in a viscous liquid, and have achieved FM-AFM analysis of the interface between silicone oil [poly­(dimethylsiloxane); PDMS] with a viscosity of 970 mPa·s (number-average molecular weight M n ∼ 26,000 from calculation) and mica. We successfully imaged the atomic-scale topography of the solid surface and the layered density distribution on the interface, representing the molecules-layering structures in which the PDMS molecular chains are oriented parallel to the mica surface …”