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Holes have always found use for a variety of reasons. You can grow things in them (like plants), pour things in them (like concrete), and use them to store things (like garbage or treasure). So, is it any surprise that nanometer-sized holes have found some interesting uses in nanotechnology? By definition, a nanoporous material has many deep pores with diameters in the nanometer scale.
Nanopores can be fabricated by either a top-down or bottom-up approach. As usual, the top-down approach is steadier but ultimately limited in density by the diffraction limits of lithography. The bottom up approach is quickly become the more important one as researchers have recently developed a very reliable technique. The key to making the bottom-up approach feasible was in finding a way to control the diameter of the pores. Since a bottom up approach required self-assembly of nanotubes, there wasn't as much control over distribution of diameters. Recently, researchers at Sandia National Laboratories found that they could use UV light to tune the diameter of the self-assembled nanopores. This discovery could lead to a number of exciting applications that we will now discuss.
For one thing, a nanoporous material would be an ideal storage source for fuels or batteries. Nanopores represent the ultimate in matter storage density while at the same time demonstrating high strength and durability. Many exciting new ideas are focused on using nanoporous materials for hydrogen fuel cell storage.
In the medical sciences, a single nanopore could be tuned to the diameter of a DNA strand. This would act as a filter for DNA and would also allow researchers to analyze the entire length of the DNA strand in sequence.
Speaking of filters, nanoporous materials could finally unlock the most sought after filter of all time: the oxygen-nitrogen separator. For many years, industry experts in the field of air filtration have spent millions of dollars trying to pull oxygen directly out of our ambient atmosphere. This would save so much money compared to chemical oxygen synthesis that it's not even funny.
With the new spate of highly controllable self-assembled nanopores, researchers are promising the kind of precision that would make this kind of filter happen. To give you an idea of the precision required, consider that the difference in diameter between oxygen and nitrogen is only 0.2 angstroms!
In a final note, nanoporous silicon has been recently made to emit light. This was a huge discovery because silicon is an indirect bandgap material that normally doesn't radiate light. If we could ever build a laser from silicon (instead of GaAs) electronics-photonics applications would be a lot more efficient.