Effects of Topology and Ionic Strength on Double-Stranded DNA Confined in Nanoslits

We investigate experimentally the effects of electrostatic interactions and topological constraints on DNA dynamics in nanoslit confinement by studying the equilibrium shape and dynamics of single linear and circular λ-DNA confined in a silicon/glass nanoslit. Having examined the dependence of chain radius of gyration <i>R</i>_∥, shape asphericity <i>A</i>, and relaxation time τ on chain topology, slit height <i>h</i> (20–782 nm), and solvent ionic strength <i>I</i> (8.2–268.8 mM), it is found that the chain shape becomes more aspherical as <i>h</i> and <i>I</i> decrease. Moreover, in strong sub-Kuhn length confinement, the DNA relaxation time increases with decreasing <i>h</i> in a smooth and broad transition. Our results provide experimental evidence to confirm that the scaling exponents of radius of gyration and of relaxation time are the same for linear and circular DNA and help resolve conflicting observations of the qualitative dependencies of chain radius of gyration and relaxation time in sub-Kuhn length slits

Electrofluidic Circuit-Based Microfluidic Viscometer for Analysis of Newtonian and Non-Newtonian Liquids under Different Temperatures

This paper reports a microfluidic viscometer with an integrated pressure sensor based on electrofluidic circuits, which are electrical circuits constructed by ionic liquid-filled microfluidic channels. The electrofluidic circuit provides a pressure-sensing scheme with great long-term and thermal stability. The viscosity of the tested fluidic sample is estimated by its flow resistance, which is a function of pressure drop, flow rate, and the geometry of the microfluidic channel. The viscometer can be exploited to measure viscosity of either Newtonian or non-Newtonian power-law fluid under various shear rates (3–500 1/s) and temperatures (4–70 °C) with small sample volume (less than 400 μL). The developed sensor-integrated microfluidic viscometer is made of poly­(dimethylsiloxane) (PDMS) with transparent electrofluidic circuit, which makes it feasible to simultaneously image samples under tests. In addition, the entire device is disposable to prevent cross-contamination between samples, which is desired for various chemical and biomedical applications. In the experiments, viscosities of Newtonian fluids, glycerol water solutions with different concentrations and a mixture of pyrogallol and sodium hydroxide (NaOH), and non-Newtonian fluids, xanthan gum solutions and human blood samples, have been characterized. The results demonstrate that the developed microfluidic viscometer provides a convenient and useful platform for practical viscosity characterization of fluidic samples for a wide variety of applications

Electrofluidic Circuit-Based Microfluidic Viscometer for Analysis of Newtonian and Non-Newtonian Liquids under Different Temperatures

This paper reports a microfluidic viscometer with an integrated pressure sensor based on electrofluidic circuits, which are electrical circuits constructed by ionic liquid-filled microfluidic channels. The electrofluidic circuit provides a pressure-sensing scheme with great long-term and thermal stability. The viscosity of the tested fluidic sample is estimated by its flow resistance, which is a function of pressure drop, flow rate, and the geometry of the microfluidic channel. The viscometer can be exploited to measure viscosity of either Newtonian or non-Newtonian power-law fluid under various shear rates (3–500 1/s) and temperatures (4–70 °C) with small sample volume (less than 400 μL). The developed sensor-integrated microfluidic viscometer is made of poly­(dimethylsiloxane) (PDMS) with transparent electrofluidic circuit, which makes it feasible to simultaneously image samples under tests. In addition, the entire device is disposable to prevent cross-contamination between samples, which is desired for various chemical and biomedical applications. In the experiments, viscosities of Newtonian fluids, glycerol water solutions with different concentrations and a mixture of pyrogallol and sodium hydroxide (NaOH), and non-Newtonian fluids, xanthan gum solutions and human blood samples, have been characterized. The results demonstrate that the developed microfluidic viscometer provides a convenient and useful platform for practical viscosity characterization of fluidic samples for a wide variety of applications

Nanoslit Confined DNA at Low Ionic Strengths

We present nanoslit confined DNA conformations at very low ionic strengths and a theory to explain most measurements for single DNA molecule size under strong nanoslit confinement. Very low ionic strength conditions not only increase the DNA persistence length dramatically, but also cause DNA molecules to swell to the extent that the effective diameter of DNA becomes larger than the nanoslit height. By accounting for these effects, our results and theory provide a reasonable clue for a current controversy regarding the dependence of the DNA conformation on slit height (<i>h</i>), persistence length (<i>p</i>), and effective diameter (<i>w</i>)