MEMS Seminar: Improving the Time Resolution and Force Precision of bioAFM Reveals a Multitude of Hidden Dynamics in the Unfolding of Membrane Protein

Atomic force microscopy (AFM)-based single-molecule force spectroscopy (SMFS) enables a wide array of studies, from measuring the strength of a ligand-receptor bond to elucidating the complex folding pathway of individual membrane proteins. Such SMFS studies and, more generally, the diverse applications of AFM across biophysics and nanotechnology are improved by enhancing the force stability, force precision and time resolution of bioAFM. For an advanced, small-format commercial AFM, we uncovered how these three metrics were limited by the cantilever itself rather than the larger microscope structure, and then describe three increasingly sophisticated cantilever modifications that yield enhanced data quality. First, sub-pN force precision and stability over a broad bandwidth (¿f = 0.01-20 Hz) is routinely achieved by removing a long (L = 100 ¿m) cantilever's gold coating. Next, this sub-pN bandwidth is extended by a factor of 50 to span five decades of bandwidth (¿f = 0.01-1000 Hz) by using a focused ion
beam (FIB) to modify a shorter (L = 40 ¿m) cantilever. Finally, FIB-modifying an ultrashort (L = 9 ¿m) cantilever improves its force stability and precision while maintaining 1-¿s temporal resolution. We then applied these technological improvements to reexamine the unfolding of a model membrane protein, bacteriorhodopsin, with a 100-fold improvement in time resolution and a 10-fold improvement in force precision. Lunch will be served at 11:30 am