Nanofluidics


Nanofluidics is the study of fluids contained within structures with dimensions in the nanometer range. It is a growing field due to its usefulness in particle analysis and small sample size requirements. The research conducted in our group explores ways in which nanofluidics and optics can be combined for biomedical applications, such as analyzing blood for disease and its component particles. 

We have developed a process using photolithography and sacrificial cores to etch small channels in silicon dioxide deposited on silicon wafers. The height of these channels (a few nanometers tall) are an order of magnitude smaller than the length and width of the structure, creating a planar like shape in which fluids can enter and be analyzed. 

When working with nanofluidics, issues such as the flow of the liquid, filling mechanisms, and particle detection are much different than they are at the macro or even micro size range. Research is being conducted to discover how fluid physics works at the nano level. 

Using nanofluidic structures our group has developed a trapping method used for isolating and analyzing nanoparticles within sample solutions. These solutions contained plasticbeads with diameters of 120 nm and 30 nm, as well as HSV-1 and HBV virus capsids whose diameter closely resemble those of the beads. By changing the dimensions of the channel, one can isolate beads of a certain size by creating passages whose heights are smaller than the diameter of the particle being analyzed. Then, by exciting a fluorescent signal used to identify the particle, one can identify if such particles are within the given sample, as they will create a band of light within the channel at the trap location. In addition to passive traps which have channel heights rigidly set during their fabrication, we are developing active traps in which their dimensions can be changed dynamically using electrostatic forces. 

In addition to the filtration process, much effort has gone into studying how the channels are filled, and in the development of pumps that would allow for more uniform flow of the fluid within the channel. As the size of the channels decrease, the liquid’s behavior resembles less and less the behavior predicted by conventional models and equations (such as the Washburn equation on capillary force). Our group is researching the effect these factors have on the shape of the meniscus formed within the channel, as its shape and flow rate may affect the effectiveness of the trapping method before mentioned. 

Also, alternative pumping methods are being evaluated to find a way in which the flow of the liquid will be more uniform. Mechanical pumps are ineffective for our purposes as they cause the liquid to pulse rather than flow. Additionally, they can be destructive to the particles being analyzed. Capillary action and electro-osmotic pumps are being studied as possible alternatives to mechanical pumps. 


Figure 1


Figure 2


Figure 3


Publications

  1. "Effects of surfactant addition and alternating current electrophoretic oscillation on size fractionation of nanoparticles using channels with three different height segments", Jie Xuan, Mark N. Hamblin, John M. Stout, H. Dennis Tolley, Adam T. Woolley, Aaron R. Hawkins, and Milton L. Lee, Journal of Chromotography A 1218, 9102-9110, (2011).
  2. "Capillary Flow in Sacrificially-etched Nanochannels", Mark N. Hamblin, Aaron R. Hawkins, Dallin Murray, Daniel Maynes, Milton L. Lee, Adam T. Woolley, H. Dennis Tolley, Biomicrofluidics 5, 021103, (2011).
  3. "Selective trapping and concentration of nanoparticles and viruses in dual-height nanofluidic channels", Mark N. Hamblin, Jie Xuan, Daniel Maynes, H. Dennis Tolley, David M. Belnap, Adam T. Woolley, Milton L. Lee, and Aaron R. Hawkins, Lab on a Chip 10, 173-178, (2010).