Anthony B. Hmelo

Nanofluidics

Chemical reactions and biological processes often occur in a fluid environment, since the mobility of fluids offers many advantages for processes requiring transport and mixing. Indeed basic biological and neurological signals arise from ion transport in fluids through nanoscale channels. This project investigates the properties of fabricated nanofluidic structures, specifically lab-on-a-chip devices. In these devices, sample transport and delivery through nanometer-dimension channels is precisely controlled using electrokinetic forces to drive and valve the flow of an electrolyte buffer solution. At 100 nm such channels may be used as biochips or other chemical transport systems. At 10 nm and smaller fundamental questions arise as to the mechanisms of fluid transport, sidewall interactions, and double layer effects. As we approach the ultimate goal of 2 nm channels, comparable to the diameter of a single DNA molecule, conformal control and molecular scale characterization may be possible.

FIB Milling of Nanochannels in Silicon

100 nm Channels in Silicon

Our approach for nanochannel fabrication utilizes a Focused Ion Beam (FIB) microscope to modify conventional microfluidic devices for functionality on the nanometer scale. In the example shown below (image on the top) a micron scale fluidic network has been previously prepared by photolithographic etch in silicon. We have fabricated redundant 100 nm channels interconnecting two microscale fluidic pathways, using a focused Ga ion beam to selectively remove material with 10 nm resolution. Enclosed fluidic channels are subsequently achieved by bonding a transparent glass lid to the substrate. To test the transport properties of the nanochannels a fluorescent dye such as 25 mM Rhodamine B-base in a 10 mM sodium borate buffer solution is introduced and induced to flow in the fluidic network. The fluorescent signal in the redundant nanochannels (image on the bottom) confirms that we are able to drive flow between microchannels though the nanochannel pathways. Narrower features may be achieved though molecular coatings or oxidation of nanochannel walls.

Read more:
J.P. Alarie, A.B. Hmelo, S.C. Jacobson, A.P. Baddorf, L. Feldman, and J.M. Ramsey, Fabrication and Evaluation of 2D Confined Nanochannels, in Micro Total Analysis Systems 2003, Volume 1, M.A. Northrup, K.F. Jensen, and D.J. Harrison, eds., Transducers Research Foundation, Cleveland Heights, Ohio, (2003), 9-12.