We present an experimental study of double-stranded DNA diffusion in slitlike channels. The channel heights span the regime from moderate confinement (height ∼ bulk radius of gyration of the DNA) to strong confinement (height ∼ persistence length). Scalings of diffusivity with channel height differ from blob model predictions. The diffusivity scales inversely with molecular weight when the channel height is smaller than the bulk radius of gyration. This scaling is indicative of hydrodynamic screening. A scaling analysis shows that the screening of hydrodynamic interactions arises from a combination of two mechanisms. After using a Zimm preaverage approximation, the unique symmetry of the thin-slit disturbance velocity and the isotropic nature of the polymer conformation together cause a cancellation of hydrodynamic interactions due to symmetry. We also find that the algebraic decay of the far-field velocity magnitude is sufficient to eliminate large-length scale hydrodynamic cooperativity in diffusion of quasi-two-dimensional polymers in good solvents.
In blood vessels with luminal diameter less than 300 µm, red blood cells (RBCs) which are smaller in size and more deformable than leukocytes, migrate to the axial centre of the vessel due to flow velocity gradient within the vessels. This phenomenon displaces the leukocytes to the vessel wall and is aptly termed as margination. Here, we demonstrate using microfluidics that stiffer malaria-infected RBCs (iRBCs) behave similar to leukocytes and undergo margination towards the sidewalls. This provides better understanding of the hemodynamic effects of iRBCs in microcirculation and its contribution to pathophysiological outcome relating to cytoadherence to endothelium. In this work, cell margination is mimicked for the separation of iRBCs from whole blood based on their reduced deformability. The malaria infected sample was tested in a simple long straight channel microfluidic device fabricated in polydimethylsiloxane. In this microchannel, cell margination was directed along the channel width with the iRBCs aligning near each sidewall and then subsequently removed using a 3-outlet system, thus achieving separation. Tests were conducted using ring stage and late trophozoite/schizont stage iRBCs. Device performance was quantified by analyzing the distribution of these iRBCs across the microchannel width at the outlet and also conducting flow cytometry analysis. Results indicate recovery of approximately 75% for early stage iRBCs and >90% for late stage iRBCs at the side outlets. The simple and passive system operation makes this technique ideal for on-site iRBCs enrichment in resource-limited settings, and can be applied to other blood cell diseases, e.g. sickle cell anemia and leukemia, characterized by changes in cell stiffness.
We have characterized glass-glass and glass-Si bonding processes for the fabrication of wide, shallow nanofluidic channels with depths down to the nanometer scale. Nanochannels on glass or Si substrate are formed by reactive ion etching or a wet etching process, and are sealed with another flat substrate either by glass-glass fusion bonding (550 degrees C) or an anodic bonding process. We demonstrate that glass-glass nanofluidic channels as shallow as 25 nm with low aspect ratio of 0.0005 (depth to width) can be achieved with the developed glass-glass bonding technique. We also find that silicon-glass nanofluidic channels, as shallow as 20 nm with aspect ratio of 0.004, can be reliably obtained with the anodic bonding technique. The thickness uniformity of sealed nanofluidic channels is confirmed by cross-sectional SEM analysis after bonding. It is shown that there is no significant change in the depth of the nanofluidic channels due to anodic bonding and glass-glass fusion bonding processes.
We report here a microfabricated nanofilter array chip that can size-fractionate SDS-protein complexes and small DNA molecules based on the Ogston sieving mechanism. Nanofilter arrays with a gap size of 40-180nm were fabricated and characterized. Complete separation of SDS-protein complexes and small DNA molecules were achieved in several minutes with a separation length of 5mm. The fabrication strategy for the nanofilter array chip allows further increasing of the nanofilter density and decreasing of the nanofilter gap size, leading, in principle, to even faster separation.Gel electrophoresis is a widely-used method for separating proteins and nucleic acids in laboratories. However, theoretical studies of the sieving mechanism in gel electrophoresis have been limited because little information on the structure and pore size of gels exist. In addition, most microchip-based separation systems rely on liquid or solid polymeric sieving media contained in microchannels. While providing fast separation, such foreign sieving matrices pose intrinsic difficulties for the integration of multiple analytic steps into an automatic bioanalysis microsystem. As an alternative to random nanoporous gels, micro/nanofluidic molecular sieving structures fabricated with semiconductor fabrication technology have been used to separate biomolecules with much greater speed than their conventional counterparts 1-5 . Such micro/nanofluidic devices have also been adopted as model systems to study molecular dynamics and stochastic motion in constrained spaces because of their regular sieving structures 6-9 . To date, microfabricated sieving systems have only been used for large biomolecules such as viral DNA, mainly because it is generally challenging to fabricate sieves with comparable molecular dimensions. In this Letter, we demonstrate the separation of small biomolecules such as proteins and small double-stranded DNA molecules (dsDNA) in a regular nanofilter array chip, based on the Ogston sieving mechanism 10-12 .It is important to recognize that Ogston sieving is the sieving process in which the size of the molecule is smaller than the size of the nanopore. In this regime, the configurational freedom of the molecules inside the nanopore is limited due to steric repulsion from the wall, and this creates a size-dependent configurational entropic energy barrier for the molecule passage from open space to the confined space of the nanopore 13 . This entropic energy barrier is presumably also responsible for the sieving process of small and relative globular molecules in gel 14 . In this Letter, we will examine the interesting possibility of separating biomolecules with nanofilters larger than the molecular dimensions. NIH-PA Author ManuscriptNIH-PA Author Manuscript NIH-PA Author ManuscriptThe nanofilter array chip was fabricated by conventional photolithography and reactive ion etching (RIE) techniques on a silicon wafer, as described previously 15 . The layout of the chip is presented in Fig. 1. Nanofilters with a thin region t...
Many fabrication technologies have been used to build nano/mesoporous materials/filters with a good size control, but the integration of these systems into a microsystem format has been a challenge. Microfabricated nanofilters suffer from small open volume and low throughput. In this paper, we developed a novel fabrication strategy for massively-parallel, regular vertical nanochannel membranes with a uniform, well-controlled gap size of ~50 nm and a depth up to ~40 μm, by using only standard semiconductor fabrication techniques. The vertical nanofilter membranes were fabricated into an anisotropic nanofilter array, which demonstrates the ability to integrate nanofilters and micron-sized channels/pores seamlessly. We demonstrated efficient continuous-flow separation of large DNAs and small molecules in a two-dimensional vertical nanochannel array device. These ultrahigh-aspect-ratio nanochannels have the advantage of large open volume, enabling for high-throughput applications.
Improved emission inventories combining detailed source information are crucial for better understanding of the atmospheric chemistry and effectively making emission control policies using air quality simulation, particularly at regional or local scales. With the downscaled inventories directly applied, chemical transport models might not be able to reproduce the authentic evolution of atmospheric pollution processes at small spatial scales. Using the bottom-up approach, a high-resolution emission inventory was developed for Jiangsu China, including SO 2 , NO x , CO, NH 3 , volatile organic compounds (VOCs), total suspended particulates (TSP), PM 10 , PM 2.5 , black carbon (BC), organic carbon (OC), and CO 2 . The key parameters relevant to emission estimation for over 6000 industrial sources were investigated, compiled, and revised at plant level based on various data sources and on-site surveys. As a result, the emission fractions of point sources were significantly elevated for most species. The improvement of this provincial inventory was evaluated through comparisons with other inventories at larger spatial scales, using satellite observation and air quality modeling. Compared to the downscaled Multi-resolution Emission Inventory for China (MEIC), the spatial distribution of NO x emissions in our provincial inventory was more consistent with summer tropospheric NO 2 VCDs observed from OMI, particularly for the grids with moderate emission levels, implying the improved emission estimation for small and medium industrial plants by this work. Three inventories (national, regional, and provincial by this work) were applied in the Models-3 Community Multi-scale Air Quality (CMAQ) system for southern Jiangsu October 2012, to evaluate the model performances with different emission inputs. The best agreement between available ground observation and simulation was found when the provincial inventory was applied, indicated by the smallest normalized mean bias (NMB) and normalized mean errors (NME) for all the concerned species SO 2 , NO 2 , O 3 , and PM 2.5 . The result thus implied the advantage of improved emission inventory at local scale for high-resolution air quality modeling. Under the unfavorable meteorology in which horizontal and vertical movement of atmosphere was limited, the simulated SO 2 concentrations at downtown Nanjing (the capital city of Jiangsu) using the regional or national inventories were much higher than those observed, implying that the urban emissions were overestimated when economy or population densities were applied to downscale or allocate the emissions. With more accurate spatial distribution of emissions at city level, the simulated concentrations using the provincial inventory were much closer to observation. Sensitivity analysis of PM 2.5 and O 3 formation was conducted using the improved provincial inventory through the "brute force"Published by Copernicus Publications on behalf of the European Geosciences Union. 212Yaduan Zhou et al.: Development and evaluation of a regional emiss...
A hybrid micro-/nanofluidic device which contains an array of parallel nanochannels has been employed to study polyelectrolyte multilayer (PEM) deposition in confined geometries. Layer-by-layer (LbL) assembly of poly(allylamine hydrochloride) (PAH) and poly(styrenesulfonate) (PSS) at pH 4 and salt concentrations ranging from 0.1 to 1 M was used to conformally coat the nanochannel walls, systematically narrowing the channel width from 222 to 11 nm in the wet state. The thicknesses of confined multilayers were measured using SEM and these results were compared with those obtained on planar, unconfined surfaces. A procedure for direct measurement of the gap thickness using dc conductance was also developed. LbL assembly in the nanochannels resulted in lower bilayer thicknesses than those obtained on planar surfaces. This observation is attributed to the surface charge-induced depletion of unadsorbed polyelectrolytes within the channel. The ability to conformally coat the walls of the nanochannels with functional PEMs opens up new possibilities in the design of active nanochannel devices.
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