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TRACK 3 TRACK 3 Technical Program

according to a sixth-order Landau potential. Fitting parameters indicate the at a concept quite analogous to that of “access resistance” of pores but in
transition is second order at a = 0.5, and passes through a tricritical point, the context of resistance to electroosmotic flow under the influence of an
becoming first order for a >> 1. A simple scaling of the fitting parameters with applied voltage. We perform full numerical simulations of the underlying
allows full collapse of the experimental data. This instability can be used to continuum equations to obtain numerical results to check our theoretical
drive enhanced mixing at the moderate Re that can be achieved in microflu- deductions. An appropriate generalization to a large number of holes in
idic devices and we show that further mixing enhancement can be achieved the membrane should result in a theory of membrane transport based on
by patterning the surfaces of the channel walls. The effect of adding a small membrane microstructure. Similarly, consideration of oscillating pressure
concentration (~0.01 wt%) of high molecular weight polymer is to reduce the and electric fields should lead naturally to calculations of dynamic mobility
value of Rec in comparison to the Newtonian solvent. and a fundamental understanding of electroseismic and seismoelectric
phenomena that have many novel applications ranging from imaging of bio-
logical tissues to remote sensing in hydrogeology. These are some areas of
potential future development.
3-2
FLOW AND TRANSPORT DEVICES II 12:00pm Nano Fountain Probe Technology for In Vitro Single
Cell Studies
Hidalgo 11:30 AM - 1:00 PM
Technical Presentation. NEMB2016-5923
Session Organizer: Horacio Espinosa, Northwestern University,
Evanston, IL, United States Horacio Espinosa, Northwestern University, Evanston, IL, United
States, Ruiguo Yang, Mark Duncan, iNfinitesimal LLC, Skokie, IL,
11:30am Electrokinetic Flows through Nanopores United States

Keynote. NEMB2016-5919 We present a broadly-applicable microfluidic technology, the Nanofountain
Probe (NFP), for single cell delivery of biomolecules and functional nanopar-
ticles. The NFP is a scanning probe nanodelivery tool that makes use of on-
Sandip Ghosal, Northwestern University, Evanston, IL, United chip fluid reservoirs and integrated microchannels to deliver liquid solutions
States, Mao Mao, COMSOL, Burlington, MA, United States, John to sharp-apertured dispensing tips [1,2,3]. The unique tip geometry allows for
Sherwood, DAMTP, Cambridge University, Cambridge, Cam- both sub-100-nm nanopatterning on substrates for subsequent cell culture,
bridgeshire, United Kingdom as well as direct biomolecular delivery inside cells with minimum invasive-
ness [4,5]. In this presentation we will articulate the working principles and
Transport of small ions or polymers through pores in membranes ranging demonstrate the in vitro single cell transfection of biomolecules (DNA, RNA,
in diameter from a few to a few hundred nanometers play an important plasmids) [5]. Applications including temporal delivery of RNA molecular
role in the biology of the cell as well as in nanotechnology. Examples of beacons for single cell live analysis [6] and gene editing with CRISPR/Cas9
the former include ion channels in membranes that are responsible for will be presented. Likewise, the use of the NFP technology in the generation
nerve impulse propagation, the transport of protein precursors through of cell lines that eliminate limited dilution will be illustrated.
pores in the mitochondrial membrane, the movement of mRNA out of the
nucleus of Eukaryotic cells through pores in the nuclear membrane etc. The presentation will close with a discussion of the impact of microfluidic
Important examples of the latter are nanopore based fast DNA sequencing technology in applications such as single cell manipulation and analysis,
using the Coulter counter principle, insertion of foreign bodies into cells by stem cell research, and drug screening.
electroporation and Scanning Ion Conductance Microscopy. In all of these
applications electrophoresis of charged particles through small pores is a [1] N. Moldovan, et al., J. Micromech. Microeng. 16, 10, 2006.
dominant theme. However, recent work has shown that the hydrodynamic [2] N. Moldovan, et al., JMEMS, 15, 2006.
flow generated by electroosmotic effects greatly influence the nature of [3] O. Loh, et al., PNAS, 105, 43, 2008.
these transport processes. Such transport problems span a range of scales [4] O. Loh, et al., Small, 5, 14, 2009.
from the molecular to the continuum: the smallest biological pores (e.g. ion [5] W. Kang, et al., Nano Letters, 13, 6, 2013.
channels) are barely larger than water molecules themselves and can only [6] J.P. Giraldo-Vela, et al., Small, 11, 20, 2015.
be understood in terms of a discrete molecular level representation. How-
ever, in most of the applications in nanotechnology where pores are in the 12:20pm A Microfluidic Rectifier Enabling Zero Backflow in the
range of 5-1000 nm, the continuum model of electrokinetics that combine Pulsatile Flow Regime
Stoke’s Flow with the Nernst-Planck-Poisson model of ion transport is fairly
effective, at least to a first approximation. Here we will explore some recent Technical Presentation. NEMB2016-6009
experimental work on observing very small scale flows through nanopores
and attempt to understand such effects from fundamental studies using a
sequence of models that employ the continuum electrokinetic picture. The Vladimir Coltisor, Texas Tech University Department of Mechanical
first and simplest of such models is that of a single circular hole in an insu- Engineering, Lubbock, TX, United States, Lee-Woon Jang, Depart-
lating membrane of fixed constant surface charge density. The membrane ment of Mechanical Engineering/Texas Tech University, Lubbock,
separates two chambers filled with an electrolyte across which an electric TX, United States, Jungkyu Kim, Texas Tech University, Lubbock,
voltage has been applied. Potentials are assumed low compared to the TX, United States
Boltzmann scale so that the Debye-Hückel approximation is permissible.
The relevant parameters here are the ratio of the hole radius to the Debye Many microfluidic pumps use pulsatile flow to deliver discrete volumes to
length usually a very large quantity that nevertheless could be of order uni- specific target locations. Backflow within pulsatile microfluidic pumps can
ty for nanopores, and some measure of the dimensionless surface charge. have an adverse effect on droplet generation and causes unwanted mixing
For this problem we show that one can calculate explicitly the electro-os- due to breakdown in laminar flow boundaries. A fluidic diode would provide
motic flow rate per unit applied voltage and this quantity has a nontrivial a rectifying effect and restrict backflow allowing for a much more precise
nonlinear dependence on the ratio of pore radius to Debye length. We flow pattern. Fluidic rectifying structures have been proposed in the past
then construct an approximate theory for a circular pore in a membrane however, many of them work at high Reynolds numbers. Microfluidic rec-
of finite thickness. For membrane thicknesses that are large compared to tifiers tend to be for continuous flow and pulsatile flow diodes tend to be
pore radius we recover the standard result for flow through infinitely long mostly lifting gate structures and flap structures. None of these structures 33
channels whereas our result reduces to that of the zero thickness mem- eliminate backflow completely. We developed a fluidic rectifier comprised
brane considered earlier in the opposite limit of thin pores. Thus, we arrive