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Electrokinetics in
Micro- and Nano-fluidics
Gilad Yossifon
Technion – Israel Institute of Technology, Faculty of Mechanical Engineering, Micro- and Nano-Fluidics Laboratory
Micro- and Nano-fluidics
Structures of m/nm scale
Devices (pumps, valves, mixers, etc.)
Advantages:
• Reduced consumption of reagents
• Reduced power consumption
• Shorter reaction times
• Parallel processing
• Batch fabrication
• Integrated systems (Lab-on-a-chip)
• Portable devices
• New concepts / functionalities
• Surface force rules
Surface force (e.g. tension, viscous friction)
Volume force (e.g. weight, buoyancy, inertial)
• Viscosity rules
Low Reynolds number:
Laminar flow (no turbulence),
No inertia effects
• Diffusion rules ( )
Low Peclet number:
Mixing through diffusion
Re 1cos
inertia VL
vis ity
Schulte et al., 2002
mm
m
2300Re
Re 1
2
e 1convection L D LV
Pdiffusion L V D
2t L D
1surface force A
volume force V L
Why Electrokinetics ?
• Large pressure gradients:
• Electro-osmotic flow:
2
12pU
L h
Yeast cells
Li et al., 1997
40m
0 f
E U
Helmholtz-
Smoluchowski
slip velocity
h
Why Electrokinetics ?
Electric-Double-Layer (EDL)
• Electrolyte (dissolved ions)
• EDL - screens surface charge
• Diffuse layer - mobile ions, net charge
( )
01 cD
mMfornmD 1001.01001.0~
- -
- - - - - - -
-
-
-
-
+
+
+
+
+
+
+ +
+
+
+
+
+ +
+ +
+
+
Compact
layer Diffuse layer
Slip plane
x
ic
x
0c
c
c
+
+
+
Bulk solution
-
-
-
+
+
+
-
+
+
+
-
-
Electro-Osmosis Flow (EOF)
• Electrostatic body force ( )
• Diffuse layer drag fluid along
the wall
Eel
• Outside EDL: EU
Helmholtz-Smoluchowski
slip velocity
y
U
Slip plane
Non-Linear EOF in Microfluidics
Increasing field intensity Yossifon, Frankel & Miloh, Phys. Fluids (2006)
Eckstein, Yossifon, Seifert & Miloh, J. Colloid Interface Sci. (2009)
Linear EOF Non-linear EOF
)(~ 2
0 aEO||v Eveq )(~ 0aEOi
Zehavi & Yossifon, Phys. Fluids (submitted)
E E
Induced-charge electrophoresis
(ICEP)
Induced-charge electroosmosis
(ICEO)
Induced Charge Electro-Phoresis (ICEP)
Squires & Bazant, J. Fluid Mech (2004)
Boymelgreen & Miloh, Phys. Fluids, (2011)
T. M. Squires and M. Z. Bazant,
J. Fluid Mech(2006)
2orbitr m 25.6orbitr m
Experimental pathlines
Boymelgreen, Yossifon, Park, & Miloh, Phys. Rev. E, 89, 011003 (2014)
E E
T. M. Squires and M. Z. Bazant,
J. Fluid Mech(2006)
Comparison to a kinematic model
Boymelgreen, Yossifon, Park, & Miloh, Phys. Rev. E, 89, 011003 (2014)
Dielectrophoresis - movement of neutral matter caused
by polarization effects in a non-uniform electric field
Medium polarizability < Particle Polarizability
Positive DEP (pDEP)
Particle is attracted to high electric fields
Negative DEP (nDEP)
Particle is repelled from high electric fields
Medium polarizability > Particle polarizability
F1 F2
FDEP
- - -
+
+ +
- - -
+
+ +
- -
+ +
F2 F1
FDEP
E E
Dielectrophoresis (DEP)
Particles
40µm
40µm
f=50 kHz
f=10 MHz
Particles move towards
high electric fields
Particles are repelled from
high electric fields
Electric field Simulation
A
B
Morgan et al., J. Phys. D: Appl. Phys. 33, 632 (2000)
FD
EP
Frequency (Hz)
0
Cross-over frequency
(COF)
Quadrupole electrode array
Inlet Outlet
2mm
Flow
35µm
Glass slide
PDMS
Electrodes
Experimental setup
Rozitsky, Fine, Dado, Nussbaum-Ben-Shaul, Levenberg & Yossifon, Biomed. Microdevices 15, 859 (2013)
Trapping Measurements
Flow
Fibroblasts (f=2MHz)
in
outin
J
JJTrapping
%
Measurement method
Rozitsky, Fine, Dado, Nussbaum-Ben-Shaul, Levenberg & Yossifon, Biomed. Microdevices 15, 859 (2013)
-50
0
50
100
10 100 1000 10000 100000 1000000
Freq (kHz)
Nor
mal
ized
For
ce
HUVEC
HUVEC - model
-50
0
50
100
10 100 1000 10000 100000 1000000
Freq (kHz)
Nor
mal
ized
For
ce
mES
mES - model
-50
0
50
100
10 100 1000 10000 100000 1000000
Freq (kHz)
Nor
mal
ized
For
ce
HNDF
HNDF - model
σcyto [μS/cm] σmem [μS/cm] Cell type
2240 0.16 HNDF
3750 0.26 HUVEC
3970 0.78 mESCs
8760 2.92 *hES
Curve fitting – cells
Rozitsky, Fine, Dado, Nussbaum-Ben-Shaul, Levenberg & Yossifon, Biomed. Microdevices 15, 859 (2013)
16
Why Nanofluidics ?
• Ion separation
• Electro-chemo-mechanical energy conversion
• Desalination / water purification
d ~ 50 nm +
+
+
+
+ +
+ - - +
+ +
+ +
+ +
+ +
+ -
- - -
- - +
-
-
Microchannel Nanochannel
+ +
+ +
- - - - - - -
- - - - - - -
• EDLs overlap ion permselectivity (membranes / ion-channels)
-
-
-
+ +
+
+
+ +
+ +
+ +
+ +
+ +
+ +
+ +
+ +
+ - - - - - - -
+
+
+ +
+
+
+ ~100 μm ~ 100 nm
d ~ 50 nm
- - - - - - -
+ -
Pressure gradient
+ -
Pressure gradient
+
17
• Concentration-polarization
Pre-concentration (106-fold !)
• Nanofluidic electronics (diode,
field-effect transistor)
• Artificial ion-channels
• EDLs overlap ion permselectivity (membranes / ion-channels)
Nanochannel
+ +
+
+
+ +
+ +
+ +
+ +
+ +
+ +
+ +
+ +
+ - - - - - - -
+
+
+ +
+
+
+ ~ 100 nm
d ~ 50 nm
- - - - - - - +
- +
Electric field anode
+
cathode
-
Depletion
layer
Enrichment
layer C0
-
-
- -
- + + +
+
+
cathode
-
anode
+
Why Nanofluidics ?
Yossifon, Chang & H.-C. Chang,
Phys. Rev. Lett. (2009) An ion channel
Some Practical Implementations
Chun et al., 2007
Wang et al., Anal. Chem. (2005)
Kim et al., Nature Nanotech. (2010)
Mixing Biomolecule
preconcentration
Desalination
Anomalies in Nanofluidics
0
25
50
75
100
0 10 20 30 40
Voltage (V)
Cu
rren
t (n
A)
1 mM
0.03 mM
Ohmic limiting Overlimiting
Nonlinear IV curve
Enrichment-depletion and
Pattern formation Interchannel communication
Nanocolloid-nanoslot interaction
Yossifon, Mushenheim, Chang & H.-C. Chang,
Phys. Rev. E (2009)
Chang & Yossifon, Biomicrofluidics (2008)
Yossifon & Chang, Phys. Rev. Lett. (2008)
Yossifon, Mushenheim & Chang, Euro. Phys. Lett. (2010) Yossifon, Chang & H.-C Chang,
Phys. Rev. Lett. (2009)
Yossifon & Chang, Phys. Rev. E (2010)
Secondory overlimiting
transition Field-Focusing Effect Yossifon, Mushenheim & Chang,
Phys. Rev. E (2010)
Non-Linear I-V
0
25
50
75
100
0 10 20 30 40
Voltage (V)
Cu
rre
nt
(nA
)
1 mM
0.03 mM
Ohmic limiting Overlimiting
Yossifon & Chang, Phys. Rev. Lett. (2008)
Yossifon, Mushenheim, Chang & H.-C. Chang, PRE (2009)
cathode
Nanochannel
+ +
+
+
+ +
+ +
+ +
+ +
+ +
+ +
+ +
+ +
+ - - - - - - -
+
+
+ +
+
+
+ ~ 100 nm
d ~ 50 nm
- - - - - - - +
- +
Electric field anode
+
cathode
-
Depletion
layer
Enrichment
layer C0
-
-
- -
- + + +
+
+
Rubinstein & Sthilman, J. Chem. Soc. (1979)
ILimiting
Levich (1962)
• EDLs overlap ion permselectivity (counterions)
• Concentration-polarization
• Limiting current overlimiting current
• Overlimiting current high throughput of ion transport
• Depletion layer thickness selection mechanism ?
Experimental setup
• Nano-slot: h=190nm deep (W>>h) Pseudo-1D
• Solutions: DI, KCl solution (10M-1mM), Rhodamine (10M)
• Colloids: 1m negatively charged fluorescent polystyrene
beads (0.02% vol.)
Nanoslot Glass Micro-
chamber
1 mm
1 mm
Electrodes
Top-view
Side-view
d=0.5 mm
3 m
m
h=190 nm
W=
2.5
mm
Permselective
membrane
Bulk
region
Rubinstein & Zaltzman, PRE (2000)
+ -
Micro-Vortices & Colloid Dynamics Voltage sweep (low ionic concentrations)
+ -
Increase of voltage Ohmic /
Limiting Over-limiting
c0=100M
Green & Yossifon & Chang, Phys. Rev. E, 87, 033005 (2013)
Eliminating the Limiting Resistance Region
Yossifon, Mushenheim & Chang, PRE (2010)
W= 0.05 mm W = 2.5 mm
W
0
2
4
6
8
10
0 5 10 15 20
Voltage (V)
No
rma
lize
d c
urr
en
t (A
/S)
2.5 mm
1 mm
0.5 mm
0.05 mm
י
f
cczF
0
2 )~~(~
0~~~
c
RT
DzFcD
0~
)~~(~~' 2 cczFpu
0~ u
En
Et
3D Geometric Field Focusing
Green & Yossifon, Phys. Rev. E (2013)
3D and 3 Layers Micro-Nano-Micro device
Green & Yossifon, Phys. Rev. E (submitted)
High voltage (Overlimiting) current rectification
• Symmetric electro-chemical potential, Asymmetric entrance
geometry
(+) (-)
(-) (+)
forward
reverse
reverse
forward
• Ohmic: R = Iforward / Ireverse = 1
• Over-limiting: R > 1
• R increases with decreasing C
• R increases with V
1 mm 3 X 3 mm
2.3 X 3 mm
Ohmic Over-limiting
30 V
Yossifon, Chang & H.-C Chang, Phys. Rev. Lett. (2009)
EIS of Microchannel-Nanochannel
Interface Devices
Schiffbauer, Park & Yossifon, Phys. Rev. Lett. (2013)
Schiffbauer & Yossifon, Phys. Rev. E 86, 056309 (2012)
EIS of Microchannel-Nanochannel
Interface Devices
Schiffbauer, Liel & Yossifon, Phys. Rev. E (submitted)
Schiffbauer & Yossifon, Phys. Rev. E (submitted)
Nanoslot impedance sensor
~
P. Musenheim, S. Basuray, G. Yossifon, S. Senapati and H.-C. Chang,
A Nanoslot DNA Sensor for Quantitative Real-Time PCR, US Patent application CU8651.
Summary Ion-permselectivity (ion-channel, membrane)
Non-linear electrokinetic effects:
Concentration-polarization preconcentration
Overlimiting current high ionic flux throughput
Vortex instability mixing
Current rectification nanofluidic diode
Interchannel cross-talk synergy effect, multi-target sensing
Nanocolloid-nanoslot interaction additional transitions in the IV
curve
Future directions: optimum nanochannel array separation,
nanocolloid-nanochannel interaction
Acknowledgements
Questions ?
