Nanofluidic systems

The nature of the liquid in contact with a surface is also very important, with respect to boundary conditions. Although slip has long been observed for highly non-Newtonian, viscoelastic liquids such as polymer flows and extrusions, many recent studies have reported slippage of Newtonian liquids under a variety of experimental conditions. This clearly indicates that care must be taken when modeling any type of micro- or nanofluidic system, no matter which liquid is employed. 

Most importantly, reaction rates in nanofluidic systems can be controlled both by shape and volume changes. The important interplay between chemical reactions and geometry has been conceptualized within a theoretical framework for ultra-small volumes and tested on a number of experimental systems, opening pathways to more complex, dynamically compartmentalized ultra-small volume reactors, or artificial model cells, that offer more detailed understanding of cellular kinetics and biophysical phenomena, such as macromolecular crowding. 

The major application of dielectrophoresis in micro- and nanofluidic systems continues to be the manipulation of particles and cells. Popular applications include particle trapping, dielectrophoretic microsystems, traveling wave dielectrophoresis, and determination of cell dielectric properties. The specific dielectrophoretic techniques used in existing applications are too numerous to cover in this entry. This entry does provide a brief overview of some of the established manipulation techniques. 

Nanofluidic Systems with Overlapped Double Layers... 

Nearly all the analytical derivations above have explicitly assumed that the system is sufficiently large that there exists a region far away from the surface where the double layer vanishes, and both pe and / go to zero. In nanofluidic systems, however, the channel height, h, is commonly on... 

Fluid flow in small devices acts differently from those in macroscopic scale. The Reynolds number (Re) is the most often mentioned dimensionless number in fluid mechanics. The Re number, defined by pf/L/p, represents the ratio of inertial forces to viscous ones. In most circumstances involved in micro- and nanofluidics, the Re number is at least one order of magnitude smaller than unity, ruling out any turbulence flows in micro-/nanochannels. Inertial force plays an insignificant role in microfluidics, and as systems continue to scale down, it will become even less important. For such small Re number flows, the convective term (pu Vu) of Navier-Stokes equations can be dropped. Without this nonlinear convection, simple micro-/ nanofluidic systems have laminar, deterministic flow patterns. They have parabolic velocity... 

Nanofluidic systems are integrated microdevices with at least one component in the devices having length scales in the range of one to hundreds of... 

It is worth noting that there is still debate on whether nanofluidic systems should be strictly used for systems with channels of tens of nanometers or smaller in all cross-sectional dimensions or they can include systems with microsized chaimels that contain nanoHter volumes. The definition here emphasizes the comparable sizes of channels with nanoscale physical length scales, which may lead to interesting phenomena and applications. 

To date, nanofluidic single-molecule detection has been done in two ways. One takes the advantage of the comparable size of nanochannels and macromolecules and detects the modulation of ion current through a nanochannel or a nanopore when an individual macromolecule enters the nanochannel/nanopore. This method is well known as resistive-pulse sensing or the Coulter principle. The other uses a nanochannel as a confined region to limit the number of molecules inside the nanochannel and uses other methods such as optical microscopy to sense a single molecule inside the nanochannel. Both approaches have demonstrated successful detection of single molecules inside nanofluidic channels. However, to date, only a few examples for each approach have been reported since nanofluidic systems have been developed only within the last decade. 

These nanopores were not fabricated in batches but made individually in expensive tools, and the fluid cells at each side of the nanopore are bulk fluid cells, which may consume a significant amount of sample. Efforts of making on-chip nanofluidic systems for single-molecule detection based oti the same principle started with a 3 pm long, 200 nm in diameter PDMS nanochannel on a glass substrate [3]. The channel size (200 nm) is much larger than a typical nanopore (<10 nm) due to the limitation of... 

Nanofluidic systems constructed for fluorescent single-molecule detection are relatively simple with nanochannels connected to... 

Nanofluidic systems are also ideally suitable for certain single-molecule detection techniques such as total internal reflection fluorescence (TIRF) microscopy. TIRF utilizes evanescent waves, which are generated by total internal reflection of a laser beam, to excite the fluorescence signal, and since evanescent waves decay exponentially, the molecule of interest must locate to the close proximity of the interface of the glass and liquid. Nanofluidic systems confine molecules of interest in nanochannels, which is well in the evanescent field of TIRF microscopy. 

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