Mapping nanomechanical properties of live cells using multi-harmonic atomic force microscopy.

The nanomechanical properties of living cells, such as their surface elastic response and adhesion, have important roles in cellular processes such as morphogenesis, mechano-transduction, focal adhesion, motility, metastasis and drug delivery. Techniques based on quasi-static atomic force microscopy techniques can map these properties, but they lack the spatial and temporal resolution that is needed to observe many of the relevant details. Here, we present a dynamic atomic force microscopy method to map quantitatively the nanomechanical properties of live cells with a throughput (measured in pixels/minute) that is ∼10-1,000 times higher than that achieved with quasi-static atomic force microscopy techniques. The local properties of a cell are derived from the 0th, 1st and 2nd harmonic components of the Fourier spectrum of the AFM cantilevers interacting with the cell surface. Local stiffness, stiffness gradient and the viscoelastic dissipation of live Escherichia coli bacteria, rat fibroblasts and human red blood cells were all mapped in buffer solutions. Our method is compatible with commercial atomic force microscopes and could be used to analyse mechanical changes in tumours, cells and biofilm formation with sub-10 nm detail.

Cell volume increase in murine MC3T3-E1 pre-osteoblasts attaching onto biocompatible tantalum observed by magnetic AC mode atomic force microscopy.

Magnetic AC mode (MACmode) atomic force microscopy (AFM) was used to study murine (mouse) MC3T3-E1 preosteoblastic cells attached to biocompatible tantalum substrates. Cell volumes of attached cells derived from AFM images were compared to volumes of detached cells in suspension measured by the Coulter sizing technique. An increase of approximately 50% in cell volume was observed when the cells attached to planar tantalum substrates and developed a flattened structure including lamellipodia. We address thoroughly the issues general to the AFM determination of absolute cell volumes, and compare our magnetic AC mode AFM measurements to hitherto reported cell volume determinations by contact mode AFM.

Ambient STM and in situ AFM study of nitrite reductase proteins adsorbed on gold and graphite: influence of the substrate on protein interactions.

Trimeric Achromobacter cycloclastes Cu-containing nitrite reductase (CuNIR) proteins adsorbed on gold and graphite have been studied by ambient STM and in situ AFM. STM resolves them individually and in layers, distinguishing the sub-molecular individual units of the trimer. The Cu atoms are not visible to STM. STM shows that individual CuNIR denatures as it adsorbs on Au, although a deformed trimeric shape can be identified in some cases. CuNIR forms disordered layers on gold. On graphite, ordered self-assembled layers of CuNIR have been resolved by in situ AFM and ambient STM forming parallel rows whose separation distance corresponds to the size of one of the units of the trimer, 5nm. Ambient STM can achieve better resolution than in situ AFM in the images of the layers. We observe differences between domains showing the parallel row structure and unstructured parts of the CuNIR layer by in situ phase imaging AFM.