There is considerable interest in measuring, with
nanoscale spatial resolution, the physical properties of lipid
membranes because of their role in the physiology of living
systems. Due to its ability to nondestructively image surfaces in
solution, tapping mode atomic force microscopy (TMAFM) has
proven to be a useful technique for imaging lipid membranes.
However, further information concerning the mechanical
properties of surfaces is contained within the time-resolved
tip/sample force interactions. The tapping forces can be
recovered by taking the second derivative of the cantilever
deflection signal and scaling by the effective mass of the
cantilever; this technique is referred to as scanning probe
acceleration microscopy. Herein, we describe how the
maximum and minimum tapping forces change with surface
mechanical properties. Furthermore, we demonstrate how these
changes can be used to measure mechanical changes in lipid
membranes containing cholesterol.
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Photo-induced force microscopy (PiFM) – principles and implementations
Photo-induced force microscopy (PiFM) is a scan probe technique that offers images with spectroscopic contrast at a spatial resolution in the nanometer range. PiFM utilizes the non-propagating, enhanced near field at the apex of a sharp tip to locally induce a polarization in the sample, which in turn produces an additional force acting on the cantilevered tip. This photo-induced force, though in the pN range or less, can be extracted from the oscillation properties of the cantilever, thus enabling the generation of photo-induced force maps. Since its inception in 2010, the PiFM technique has grown into a useful nano-spectrocopic tool that has expanded its reach in terms of imaging capabilities and applications. In this review, we present various technical implementations of the PiFM approach. In addition, we discuss the physical origin of the PiFM signal, highlighting the contributions from dipole–dipole forces as well as forces that derive from photo-thermal processes.
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- Award ID(s):
- 1905582
- PAR ID:
- 10347637
- Date Published:
- Journal Name:
- Chemical Society Reviews
- Volume:
- 51
- Issue:
- 11
- ISSN:
- 0306-0012
- Page Range / eLocation ID:
- 4208 to 4222
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract Soft tissue biopsy is a necessary diagnostic and therapeutic procedure, but traditional biopsy needles can cause harm to the patient, including tissue damage, bleeding, and pain. These can compromise the accuracy of the sample and negatively impact the patient’s well-being. Hence, there has been a growing interest in developing bio-inspired surgical needles that are safer, more effective, and more comfortable for the patient. The scorpion-inspired curved tip needle study focuses on analyzing the mechanics of needle-tissue interaction and creating needles that travel through soft tissue with minimum resistance at the tip. An essential aspect of the study is the mechanics and geometry of the needle tip, which plays a crucial role in its performance. The study incorporates structures of curved scorpion’s stinger to balance between penetration and minimal needle-tissue interaction forces. In this study, various parameters of curved tip geometry are explored to decrease the insertion and extraction forces. Tests are initially performed on brain tissue mimicking medical gelatin with Young’s modulus of 2kPa. It is observed that the insertion force with curved tip needles is decreased by up to 21.7%, and the extraction force is decreased by up to 28.2%. This study shows that a scorpion-inspired tip design can minimize insertion and extraction forces, leading to less tissue damage and deformation. Furthermore, the proposed tip design has great potential to improve surgical needles for more effective minimally invasive percutaneous procedures with various applications such as biopsy, brachytherapy, tumor ablation, and drug delivery to the brain.
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Although graphene is well known for super-lubricity on its basal plane, friction at its step edge is not well understood and contradictory friction behaviors have been reported. In this study, friction of mono-layer thick graphene step edges was studied using atomic force microscopy (AFM) with a Si tip in dry nitrogen atmosphere. It is found that, when the tip slides over a ‘buried’ graphene step edge, there is a resistive force during the step-up motion and an assistive force during the step-down motion due to the topographic height change. The magnitude of these two forces is small and the same in both step-up and step-down motions. As for the ‘exposed’ graphene step edge, friction increases in magnitude and exhibits more complicated behaviors. During the step-down motion of the tip over the exposed step edge, both resistive and assistive components can be detected in the lateral force signal of AFM if the scan resolution is sufficiently high. The resistive component is attributed to chemical interactions between the functional groups at the tip and step-edge surfaces, and the assistive component is due to the topographic effect, same as the case of buried step edge. If a blunt tip is used, the distinct effects of these two components become more prominent. In the step-up scan direction, the blunt tip appears to have two separate topographic effects elastic deformation of the contact region at the bottom of the tip due to the substrate height change at the step edge and tilting of the tip while the vertical position of the cantilever (the end of the tip) ascends from the lower terrace to the upper terrace. The high-resolution measurement of friction behaviors at graphene step edges will further enrich understanding of interfacial friction behaviors on graphene-covered surfaces.more » « less
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- Free Publicly Accessible Full Text
-
Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1039/D2CS00052K
