Effects of intermediate bound states in dynamic force spectroscopy

We revisit here some aspects of the interpretation of dynamic force spectroscopy experiments. The standard theory predicts a typical unbinding force $f^*$ linearly proportional to the logarithm of the loading rate $r$ when a single energetical barrier controls the unbinding process; for a more complex situation of $N$ barriers, it predicts at most $N$ linear segments for the $f^*$ vs. $\log(r)$ curve, each segment characterizing a different barrier. We here extend this existing picture using a refined approximation, we provide a more general analytical formula, and show that in principle up to $N(N+1)/2$ segments can show up experimentally. As a consequence the interpretation of data can be ambiguous, for the characteristics and even the number of barriers. A further possible outcome of a multiple-barrier landscape is a bimodal or multimodal distribution of the unbinding force at a given loading rate, a feature recently observed experimentally.Comment: 7 pages, 5 figure

Transverse electrokinetic and microfluidic effects in micro-patterned channels: lubrication analysis for slab geometries

Off-diagonal (transverse) effects in micro-patterned geometries are predicted and analyzed within the general frame of linear response theory, relating applied presure gradient and electric field to flow and electric current. These effects could contribute to the design of pumps, mixers or flow detectors. Shape and charge density modulations are proposed as a means to obtain sizeable transverse effects, as demonstrated by focusing on simple geometries and using the lubrication approximation.Comment: 9 pages, 7 figure