text: Nanofluidic devices have been built for application in chemistry, molecular biology and medicine. The main purposes to use nanofluidic devices are separation and measurement of solutions containing nanoparticles for drug delivery, gene therapy and nanoparticle toxicology on a micro-total-analysis system. An important advantage of micro- and nano-scaled systems is the small amount of sample or reagent used in analysis. This reduces the time required for sample processing. It is also possible to achieve analysis in an array, which further speeds up  processes and increases throughput of analysis.
  Nanochannels are utilized to achieve single-molecule sensing and diagnosis, as well as DNA separation. In many cases, nanofluidic devices are integrated within a microfluidic system to facilitate logic operation of fluids. The future of nanofluidic systems will be focused on several areas such as analytical chemistry and biochemistry, liquid transport and metering, and energy conversion.
  In nanofluidics, the valence numbers of the ions determines their net electrophoretic velocities. In other words, the velocity of an ion in the nano-channel is related not only to its ion mobility but also its ion valence. This enables the sorting function of nanofluidics, which cannot be done in a micro-channel. Therefore, it is possible to do sorting and separation for short strand DNA by using a nanochannel. For the single-molecule DNA application, the final goal is to sequence a strand of genomic DNA in a reproducible and precise result. Similar application can also be found in chromatography, or separation of various ingredients in the solution.
  Application also can be found in synthesis of fibers. Polymer fibers can be created by electrospinning the monomers at an interface between liquid and vacuum. An organized polymer structure is formed from a flow of monomers aligning on a substrate.
  There is also an attempt to bring nanofluidic technology into energy conversion. In this case, the electrical charged wall behaves as the stator, while the flowing solution as the rotor. It is observed that when the pressure-driven solvent flowing through a charged nanochannel, it can generate a streaming current and a streaming potential. This phenomenon can be used in electrical energy harvesting.
  Advances in nanofabrication techniques and concerns about energy shortage make people interested in this idea. The main challenge is to increase efficiency, which is now only a few percent, compared with efficiencies of up to about 95 per cent for standard rotational electromagnetic generators.