Feb 23, 2012
Electronic sensitivity to internal electrolyte composition revealed in semiconducting SWCNT
Carbon nanotubes (CNTs) are high-performance one-dimensional electronic materials with a large surface-to-volume ratio, which makes them a great candidate for chemical and biological sensors. Also, in recent years, the material's hollow structure has been employed as a nanochannel to rapidly transport a variety of ions and molecules, in gas and liquid phases. It is appealing to combine the nanoelectronic and nanofluidic advantages of CNTs into one unit – a nanoelectrofluidic device. Integration would enable CNTs to function as both a fluid conduit and an electrical detector simultaneously. The high electronic sensitivity of CNTs could then be used to probe the transport dynamics of fluid, ions and small molecules in sub-2 nm channels – a regime that has much to offer experimentalists. In addition, such a device may lead to new types of CNT sensors with enhanced sensitivity and selectivity.
Recently, a prototype device based on a semiconducting single-walled CNT (SWCNT) with nanofluidic and electronic field effect transistor (FET) functionality has been built. The internal wetting of semiconducting SWCNTs by pure water significantly modifies the FET characteristics. The device has also been utilized to acquire the average speed of water molecules when moving inside a semiconducting SWCNT.
Now, scientists at Arizona State University and Florida International University have investigated these effects in more detail – examining the electronic sensitivity of SWCNTs to internal electrolyte composition. In the systematic study, the researchers looked at the electrical response of a SWCNT when its interior was exposed to aqueous solutions with various ion concentrations, pH and ion species. High sensitivity was observed for the devices made with semiconducting SWCNTs.
These electronic responses are very different to those recorded when the analyte contacts the external surface of SWCNT. It's likely that this sensitivity is due to the strong interaction between the electrolyte components and the highly curved crystalline inner surface of the carbon nanotube in an extremely confined space.
The work is a continuation of previous studies of single SWCNTs as nanofluidic devices and takes the team a step closer to its goal of a functional nanoelectrofluidic device. In the future, the group plans to use the same device geometry to examine the electronic response of charged small molecules passing through a semiconducting SWCNT.
The researchers presented their results in the journal Nanotechnology.
About the author
The study was conducted by researchers from Arizona State University (ASU) and Florida International University (FIU), US. The work was mainly funded by the DNA sequencing technology program of the National Human Genome Research Institution (NHGRI). Di Cao is a PhD student in physics at ASU. He fabricated the devices and carried out measurements, along with Pei Pang, also a PhD student in physics at ASU. Hao Liu, a PhD student in chemistry at ASU, made contributions in the CNT growth and microfluidic device fabrication. Prof. Jin He is an assistant research professor at ASU and, since 2011, an assistant professor at FIU. He has a strong interest in nanobiotechnology, molecular electronics and single molecule biophysics. Prof. Stuart Lindsay is a Regents' Professor and the director of the single molecule biophysics center at the Biodesign institute at ASU. Profs. He and Lindsay guided the project.