Transport of polymers and particles microfabricated array devices
Long, Brian R.
Brownian ratchets generate transport at the micron scale with the help of thermal motion. The Brownian ratchet studied here is the flashing ratchet which transports particles by switching on and off a spatially asymmetric, periodic potential. Experimental work in the literature indicates that interdigitated electrode arrays can been used to create such potentials in solution, but no detailed study of particle trajectories has accompanied such experiments. Here, interdigitated electrode array devices were fabricated. Analysis of the trajectories of individual particles moving in response to a switching voltage revealed that the transport is likely due to electroosmotically driven fluid flow, not the Brownian ratchet effect. Simulation work in the literature predicts that polymers in a ratchet potential will exhibit qualitatively different transport from the particle case. Here, polymer transport was tested experimentally using interdigitated electrode array devices, collecting images of individual Ã Ã Ã Ã Ã Ã Â» DNA molecules and applying a flashing voltage. The DNA was observed to move in response to the applied potential and the resulting images contain DNA trajectories and also information about its conformations and dynamics. Conformations were analyzed using principal components analysis, extracting the normal modes of the variations amongst large sets of polymer images. These results iv show no conformational changes indicative of the polymer ratchet mechanism, despite the polymer motion. This result and detailed analysis of the DNA trajectories, suggest that the observed motion was driven by bulk flow generated through electroosmosis, in agreement with results from experiments using particles in similar devices. Deterministic Lateral Displacement (DLD) uses an array of obstacles in a microfluidic channel to sort micron-scale objects with Ã Ã Ã Ã Ã Â¢ Ã Ã Ã Ã Ã Â¼10nm precision. However, very little work has been done to quantitatively address the role of diffusion in DLD sorting. Here, modeling of transport in DLD arrays has shown that using arrays of obstacles that are small compared to their separation can create sorting that is robust against changes in flow velocity. Also, novel sorting modes were revealed when the model was applied to unconventional array geometries that have not been discussed in the literature.