Comparison of Atomic Force Microscopy and Scanning Ion Conductance Microscopy for Live Cell Imaging

Abstract

Atomic force microscopy (AFM) and scanning ion conductance microscopy (SICM) are excellent and commonly used techniques for imaging the topography of living cells with high resolution. We present a direct comparison of AFM and SICM for imaging microvilli, which are small features on the surface of living cells, and for imaging the shape of whole cells. The imaging quality on microvilli increased significantly after cell fixation for AFM, whereas for SICM it remained constant. The apparent shape of whole cells in the case of AFM depended on the imaging force, which deformed the cell. In the case of SICM, cell deformations were avoided, owing to the contact-free imaging mechanism. We estimated that the lateral resolution on living cells is limited by the cell's elastic modulus for AFM, while it is not for SICM. By long-term, time-lapse imaging of microvilli dynamics, we showed that the imaging quality decreased with time for AFM, while it remained constant for SICM.

Mapping surface charge density of lipid bilayers by quantitative surface conductivity microscopy

“…As the pipette is approached to a non-conductive sample, the resulting occlusion of ion flow can be used for distance feedback. The unique feedback mechanism enables non-contact imaging, and several studies have underlined the advantages compared with the traditional tapping mode AFM181920. The lateral and vertical resolution of SICM is influenced by the size of the nanopipette21, and subnanometre vertical resolution has previously been attained with small pipettes2223, while the lateral resolution is limited to around two times the tip inner radius24 corresponding to 30 nm in this study.…”

“…1). The height of biological matter measured by AFM and SICM is influenced by surface charges38, and while SICM is a non-contact method the force applied in AFM can lead to physical deformation of the sample1820. A very low loading force (around 100 pN) was used to minimize deformation, and a height of 5 nm matches the expected height from the molecular structure.…”

Image detection of yeast Saccharomyces cerevisiae by light-addressable potentiometric sensors (LAPS)

“…Electrochemical imaging methods are alternative techniques for live-cell imaging, including scanning electrochemical microscopy (SECM) [4,5], scanning ion conductance microscopy (SICM) [6,7], plasmonic-based electrochemical impedance microscopy (EIM) [8], and lightaddressable potentiometric sensors (LAPS) [9]. They can map parameters such as Faradaic current, ion conductivity, local impedance, extracellular potentials and charges, which cannot be measured with optical microscopy.…”

Advances and Perspectives in Chemical Imaging in Cellular Environments Using Electrochemical Methods

“…For example, SECM-AFM probes are now commercially available, and SECM-SICM probes can be fabricated in minutes at low cost (excluding the large initial cost of a laser-based pipette puller). Using SECM-AFM to image soft cellular samples can be problematic due to the nature of feedback of AFM in which tip-sample contact is made throughout the image, whereas SECM-SICM probes do not make contact with the substrate making them a non-destructive probe [40].…”

“…Scanning ion conductance microscopy, as a contact-free SPM, is particularly attractive for its use in imaging living cells by avoiding cell deformation, which could occur using AFM, where tip-sample contact is unavoidable (in standard imaging modes) [40]. Live cells have been imaged by SICM, and exceptionally high resolution imaging (comparable to scanning electron microscopy) of the 3D surfaces of tissues have been imaged using hopping mode scans (vide infra) [59], although obtaining chemical information is not trivial.…”