Advances in Atomic Force Microscopy: High Speed Imaging, and Combined AFM/Optical Studies

Applications of Scanning Probe Microscopy have grown dramatically since its invention, particularly for measuring surface properties. With few exceptions, however, imaging speed has remained relatively slow, generally requiring up to 4 minutes per frame for most commercial equipment. To address this limitation, High Speed Scanning Property Mapping is a new SPM variation developed at UConn that allows full frame image acquisition in less than a second. This makes previously impractical studies feasible, including high throughput imaging, high resolution large area scanning, and efficient mapping of surface dynamics as a function of time or some other dimension (voltage, temperature, magnetic field, etc). Focusing on dynamics, the early stages of ferroelectric domain nucleation and growth are uniquely monitored during switching with <20 nm spatial resolution and microsecond scale temporal resolution. The resulting movies provide significantly enhanced statistics over data from standard speed imaging, as literally thousands of domains are imaged in minutes. Significantly, this provides a novel method to locally and quantitatively measure independent activation energies and populations for nucleation and growth.

The presentation will conclude with an introduction to a completely separate area of research, combining AFM and low-light fluorescence to mechanically and optically monitor the response of individual living cells to foreign bodies and drug delivery. Resulting cross-sections of MH-S cells (mouse lung macrophages) transfected with GAP-43 GFP to identify the cell membrane were found to deform by up to 50% when imaged with the AFM, with extensive cell deformation even for relatively small applied forces (7nN or less). The viscoelastic response of the cell membranes to various loading rates and times is also monitored by optics and AFM in situ, with relaxation times on the order of seconds to minutes. Finally, nanoindentations were performed on living HaCaT (human epithelial) cells, both with and without exposure to epidermal growth factor (EGF). This revealed a smooth decrease in the elastic modulus by as much as 60%, from 1 kPa (control) to 400 kPa, upon culturing with 25 ng/mL EGF from 0 to 3 days.