Mechanical properties play an important role in regulating cellular activities and are critical for unlocking the mysteries of life. Atomic force microscopy (AFM) enables researchers to measure mechanical properties of single living cells under physiological conditions. Here, AFM was used to investigate the topography and mechanical properties of red blood cells (RBCs) and three types of aggressive cancer cells (Burkitt's lymphoma Raji, cutaneous lymphoma Hut, and chronic myeloid leukemia K562). The surface topography of the RBCs and the three cancer cells was mapped with a conventional AFM probe, while mechanical properties were investigated with a micro-sphere glued onto a tip-less cantilever. The diameters of RBCs are significantly smaller than those of the cancer cells, and mechanical measurements indicated that Young's modulus of RBCs is smaller than those of the cancer cells. Aggressive cancer cells have a lower Young's modulus than that of indolent cancer cells, which may improve our understanding of metastasis. atomic force microscopy, red blood cell, cancer cell, mechanical properties, Young's modulus Citation:Li M, Liu L Q, Xi N, et al. Atomic force microscopy imaging and mechanical properties measurement of red blood cells and aggressive cancer cells. Sci China Life Sci, 2012, 55: 968 -973,

Atomic force microscopy (AFM) was used to examine the morphology of live mammalian adherent and suspended cells. Time-lapse AFM was used to record the locomotion dynamics of MCF-7 and Neuro-2a cells. When a MCF-7 cell retracted, many small sawtooth-like filopodia formed and reorganized, and the thickness of cellular lamellipodium increased as the retraction progressed. In elongated Neuro-2a cells, the cytoskeleton reorganized from an irregular to a parallel, linear morphology. Suspended mammalian cells were immobilized by method combining polydimethylsiloxane-fabricated wells with poly-L-lysine electrostatic adsorption. In this way, the morphology of a single live lymphoma cell was imaged by AFM. The experimental results can improve our understanding of cell locomotion and may lead to improved immobilization strategies.atomic force microscopy, cell locomotion, lamellipodia, cytoskeleton, polydimethylsiloxane Citation:Li M, Liu L Q, Xi N, et al. Atomic force microscopy imaging of live mammalian cells.

Atomic force microscopy (AFM) can probe single living cells and single native membrane proteins in natural fluid environments with label-free high spatial resolution. It has thus become an important tool for cellular and molecular biology that significantly complements traditional biochemical and biophysical techniques such as optical and electron microscopy and X-ray crystallography. Imaging surface topography is the primary application of AFM in the life sciences. Since the early 1990s, researchers have used AFM to investigate morphological features of living cells and native membrane proteins with impressive results. Steady improvements in AFM techniques for imaging soft biological samples have greatly expanded its applications. Based on the authors' own research in AFM imaging of living cell morphologies, a review of sample preparation procedures for single-cell and single-molecule imaging experiments is presented, along with a summary of recent progress in AFM imaging of living cells and native membrane proteins. Finally, the challenges of AFM high-resolution imaging at the single-cell and single-molecule levels are discussed.

Atomic force microscopy (AFM) was used to locate CD20 molecules on the surface of lymphoma Raji cells. Rituximab (a monoclonal antibody against CD20) molecules were linked onto the AFM tip via a polyethylene glycol (PEG) linker. Raji cells were adsorbed onto glass slides coated with poly-L-lysine. First, the CD20 distribution in a local area of the cell surface was visualized using the AFM lift scan mode. Second, 16 × 16 force curves were obtained from the same cell area to construct the CD20-rituximab binding force map. Finally, free rituximab was added to block the CD20 molecules on the cell surface and the lift phase image and CD20-rituximab force map were obtained again. The experimental results indicated that when the lift height was greater than the length of the PEG linker, no recognition sites were observed in the lift phase image. However, as the lift height decreased to the length of the PEG linker, some recognition sites were observed in the lift phase image and these sites were generally consistent with the pixels in the force map. After blocking, both the recognition sites in the lift phase image and the gray pixels in the binding force map decreased markedly. These results can improve our understanding of the distribution of protein molecules on the cell surface and facilitate further investigations into cellular functions. atomic force microscopy, CD20, rituximab, lift scan, force curve Citation:Li M, Liu L Q, Xi N, et al. Mapping CD20 molecules on the lymphoma cell surface using atomic force microscopy.