Nanofluidic Channels

Guo, L.J. Cheng, X. Chou, C.F. Fabrication of size-controllable nanofluidic channels by nanoimprinting and its application for DNA stretching. Nano Lett. 2004, 4 (1), 69-73. 

A nanofluidic channel device, consisting of many entropic traps, was designed and fabricated for the separation of long DNA molecules. The channel comprises narrow constrictions and wider regions that cause size-dependent trapping of DNA at the onset of a constriction. This process creates electrophoretic mobility differences, thus enabling efficient separation without the use of a gel matrix or PEF. Samples of long DNA molecules (5000-... 

In a qualitative sense, the measured position of the meniscus as a function of time was found to qualitatively follow the Washburn model (refer to the entry on Surface-Tension-Driven Flow, for details of this model). Quantitatively, however, a lowering of capillary filling speed could be noted, which might be attributed to the electroviscous effects and stronger surface influences over nanoscopic length scales. Future efforts need to be directed to develop more rigorous mathematical models to predict the quantitative trends of capillary fiUing in nanofluidic channels to resolve these issues. 

The fast development of nanotechnology will lead to the emergence of nanofluidic technology. It is expected that the transport of irais and macromolecules and the cmitrol of liquid in nanofluidic channels and structures will stfll likely involve the use of an electrical field. This wfll open a completely new territoiy for nanofluidic-based electroldnetic phenomena which wfll be the main focus of the next decade of research. 

For the future work, elastomer tunable optofluidic devices are expected to extend into the nano-optics or nanofluidic fields. Several tunable nano-optical antenna devices fabricated on a stretchable PDMS substrate have been demonstrated recently. Combining elastomer-based micro/nano-devices with nanoplasmonic elements can be interesting for molecule-level imaging and spectroscopy. A tunable elastic nanofluidic channel was demonstrated recently on a PDMS chip for nanoparticle separation and molecule trapping [12]. One of the challenges of PDMS-based tunable nano-devices is to realize the high accuracy in control. High-precision control of PDMS-based tunable structures could be realized by very fine pneumatic actuation or connection to a piezo-actuator. 

Stein D, Kruithof M, Dekker C (2004) Surface-charge-govemed ion transport in nanofluidic channels. Phys Rev Lett 93(3) 035901-l-035901-4... 

In the microfluidic and nanofluidic channels, the flow field is laminar and thus the Stokes equations (Eq. 8) along with the continuity equation (Eq. 9) should be solved in order to find the velocity of the flow field. In the Stokes equation, the term... 

Single-molecule denaturation mapping of DNA in nanofluidic channels. Proc Natl Acad Sci U S A 107(30) 13294-13299... 

Daiguji H, Yang PD, Szeri AJ, Majumdar A (2004) Electrochemomechanical energy conversion in nanofluidic channels. Nano Lett 4(12) 2315-2321... 

Electrophoretic Transport in Nanofluidic Channels, Fig. 1 Schematic of a nanocharmel for electrophoretic transport... 

Kamik R, Castelino K, Duan C, Majumdar A (2006) Diffusion-limited patterning of molecules in nanofluidic channels. Nano Lett 6(8) 1735... 

When the EDL interaction occurs in nanofluidic channels, a traditional bulk ionic concentration does not even exist. The local electroneutrality may never be obtained at the middle of channel for these cases. People have found the counterion enrichment when the EDL overlap occurs in the nanochannels. A few methods have been proposed to determine the effective bulk ionic concentration in nanochannels. A reasonable determination for the effective bulk ionic concentration with double-layer interactions in nanochannels requires (i) to reflect the dominating ions effects on transport and (ii) to transform to the traditional bulk concentration automatically when the double-layer interaction vanishes. Based on these requirements, we present a new enrichment coefficient, a, to calculate the... 

The notion of depth of focus is important in microfluidic and nanofluidic studies, because it influences the spatial resolution of the measurement. Let us consider a microfalaicated channel with a channel depth of d, in which fluorochrome molecules are being contained and measured. If Z > d, then all the fluorochrome molecules are always in focus, and they all are imaged clearly in the optical detector. Consequently, in microfluidic channels, where the fluorochrome molecules are typically much smaller than the channel depth d, the position of the fluorochrome molecules along the channel depth cannot be resolved anymore. Hence, multiple molecules that are positioned near each other cannot be distinguished from each other, and three-dimensional measurements (for instance, to characterize the transport of fluid inside such channels) cannot be performed. In nanofluidic channels, however, where the fluorochrome sizes are more similar to the channel depth d, the measurements can be described as a quasi-2D problem, and it is not required anymore to resolve along the channel depth. 

Compared to macroscale fluidic channels, the surface-to-volume ratio in microfluidic and nanofluidic channels is significantly larger, and consequently the physical effects caused by channel surfaces become more prominent. Therefore, it also becomes increasingly important to understand microfluidic and nanofluidic phenomena at these surfaces. A particular fluorescence... 

To be able to design devices based on microfluidics and nanofluidics, it is crucial to quantitatively visualize the flow of fluids in the microfluidic and nanofluidic channels. There have been many flow visualization methods being developed for macroscale fluid flow (e.g., hot-wire anemometry), but most of them are not suitable for micro- and nanoscale measurements because they are too intrusive for micro- and nanoscale fluid flows [3]. Fluorescence measurements are very suitable for quantitatively visualizing flow in micro- and nanoscales, because it is nonintrusive and it allows for measurements with a high spatial resolution. 

As we go from microfluidics to nanofluidics and the sizes of tracer particles are more and more reduced to the limit of a single-molecule of fluo-rochromes, the distinction between the scalar-based and particle-based methods becomes obsolete [3, 4], In turn, the small dimensions of the microfluidic and nanofluidic channels also allow for increased sensitivity in the fluorescence detections the background signal (caused by sample impurities and scattered photons) scales linearly with the size of the detection volume, while the fluorescence signal of each fluoro-chrome single-molecule is independent of the detection volume. 

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