Ionic current modulation of gate inserted nanopores

Abstract

Abstract

Recent nanotechnology field in the past few years has accomplished a great development in bringing ion devices down to nanometer scale which as a result, the nanometer scale devices can open a new field called Nanofluidics. Nanofluidics is the study of behaviors, manipulation and control of matters that are confined to structures of nanometer scale in fluid environments. In diverse nanofluidic areas, especially, ion devices such as nanopores and nanochannel have great attentions owing to its possibility for bio/chemical analysis or sensing as platform devices. The ion devices can deal with many bio molecules or nanoparticles because nanopores and nanochannels can be worked in liquid environments in which such molecules or particles stabilized. The two representative ion devices, nanopores and nanochannels, have several difference in geometries and characteristics. Nanochannel generally has nanometer dimension in channel cross section while the length scale is about few hundreds micro meters, so the nanochannel has a large aspect ratio. Also, nanochannels have array structures of dozens of channels and are integrated with micro channels. Usually, the nanochannel structures show better properties in ionic current rectification, also, because of the large aspect ratio, threadlike molecules such as DNA can be stretched out along the channel. On the other hand, nanopores have relatively thin thickness, less than 100nm scale with sub 10nm scale pore. In addition, the nanopore device has a membrane structure which separate reservoir into cis- and trans-chamber. The nanopore is located on the membrane and molecules and ions pass through the pore. Compare to channel structure, nanopore is relatively easy to fabricate. Also, a single nanopore can be utilized for single molecule analysis. One of important issues in such ion devices is to understand transport phenomena of ions, molecules or nanoparticles because understanding on transports, makes it possible to manipulate and control target molecules. Analogous to semiconductor devices, preferential ion flux can be achieved in nanofluidic devices and the ionic current rectification is caused by so called symmetry breaking of the nanofluidic system such as structure or ion concentration in ion channels. Ionic current rectification is regarded as the way of delivery of ions, particles and bio-molecules in selectively. Therefore, study on good rectifying devices is very important. In this thesis, we suggest a fabrication method of nanopore which is characterized as all around gate structure and a very long ion channel for highly effective ionic current rectification. In order to enhance the rectification effect, we combine the nanopores with channel like structures which as a result, our nanopore is relatively very thick compare to general nanopore devices. The reason why we combine the two structures is that as mentioned above, channel shape shows better rectifying property. Also, we fabricate the nanopore that has size difference between top and bottom pore, and the asymmetrically located gate electrode around small pore region because device asymmetry is important for rectification. The rectifying characteristic of our device will be demonstrated throughout this thesis. We expect our nanopores can give a good contribution to nanofluidic communities, since it can provide highly effective gate controllability on the ion transport.