Optimization of dielectrophoretic DNA stretching in microfabricated devices.

We have found that the surface and bulk solution properties in a microfabricated device affect the degree and probability of electrostretching of DNA molecules. Using lambda phage DNA, we found that significantly hydrophilic surfaces between the electrodes decrease the efficiency of stretching. Surfaces treated with higher silane (trimethylchlorosilane) concentrations performed better presumably due to the decreased nonspecific adsorption of DNA on these surfaces compared to their more hydrophilic counterparts. The shape and dimensions of the electrodes also affected the efficiency of stretching. Both liftoff and metal etching methods produced electrodes with random microscopic peaks along the electrode's edge and were poorly suited for stretching. Annealing the electrodes (450 degrees C for 10 min) removed most of these peaks and allowed for more controlled stretching to be obtained. We also found that thin electrodes (65 nm) gave close to a 90% success rate of DNA stretching but stretching with thick electrodes (350 nm) produced only a 20% success rate.