yang2011

M3P.057
OPTICAL-DRIVEN VORTEX AS A MICROPARTICLE CONCENTATOR
1
3
1
3*
4
S. M Yanl, T H Punde 2, Y. J. Chu , T M Yu , M H Liu , L. Hsu , and C. H Liu
1 Department ofElectrophysics, National Chiao Tung University, Taiwan, R.O.C.
2
Institute ofNanoEngineering and MicroSystems, National Tsing Hua University, Taiwan, R.O.C.
3
Department ofPower Mechanical Engineering, National Tsing-Hua University, Taiwan, R.O.C.
4
SINONAR Company, Taiwan, R.O.C
ABSTRACT
pattern. This optical-driven approach of controlling the
liquid is applied for microparticle concentration.
The light-driven optoelectronic vortex concept is
firstly reported in this article. Utilizing illuminating light
2. LIGHT-DRIVEN FLOW APPROACH
Operation principle of electroosmosis flow
image to manipulate the liquid flow direction without any
mechanic components is the feature of this design, named
as optoelectroosmosis flow (OEOF). With the simple
When the electrolyte is full of the micorchamber, the
organic
free cations are strongly attracted toward the surface and
photoconductive material, TiOPc, on the designed ITO
generate the electrical double layer (EDL). The term,
spin-coating
process
to
form
a
thin
pattern, the projected light pattern is able to generate
double, means it is formed by compact ions layer and
dynamic
diffuse ions layer which are different in the different
virtual
electrode
on
the
substrate
surface.
Besides, the non-uniform electric field distribution would
distribution of mobile. While the non-uniform electric
drive the ions moving with slip velocity. Furthermore,
field applies on EDL, the tangential component would
two light driven flows with different directions are able to
drive the ions in these regions. The velocity of these ions
form a clockwise or counter clockwise for microparticles
is named the slip velocity. The velocity of these ions is
concentration from non-illuminating toward illuminating
called the slip velocity, VHOF, which is defined by the
region. This convenient approach of light-driven flow and
Helmholtz-Smoluchowski equation. [5]
microparticle
concentration
without
any
mechanical
VEOF
component enlarge the scope of liquid manipulation field.
AD· PDL· Et
= -=--=-=-..:..
TJ
Where AD is the Debye length, PDL is the charge per
unit area of induced charge of the double layer, E/ is the
KEYWORDS
Optical-driven vortex, light-induced optoelectroosmosis
tangential component of the electric field and 11 is the bulk
flow,
liquid viscosity.
microparticle
concentration,
photoconductivity,
TiOPc
In
this
work,
photoconductive
1.
INTRODUCTION
"micro total analysis systems"
(J..lTAS) also called as
"lab-on-a-chip"
conductivity is increased and the charge transport this
layer to form a virtual electrode on the surface. It also
induces a non-uniform electric field distribution and the
sample transport following designed processes. Several
utilizing
different
tangential component of this electric field would generate
actuation
the ions slip velocity. Due to the virtual electrodes are
mechanisms and various micro electro mechanical system
induced by the illuminating pattern, the movement of
(MEMS) technologies have been reported. [2] Liquid
light region
pumping methods can be divides into two categories,
mechanic-displacement
based
based
micropumps
micropumps.
The
and
former
the
flow
integration
direction
of
EOF
A schematic diagram of the optical system used for
microparticle concentration is shown in
concentrator by using dynamic optoelectronic vortex
Fig. 1. A
mercury lamp provides the light source and projects it on
(OEV) approach wherein rotational direction and position
the digital micro mirror display (DMD) device. The
of the vortex could be manipulated easily by the optical
image on the DMD surface is control by a multi-touch
image. This method is based on an optoelectroosmosis
panel for convenient and intuitive flow manipulation and
flow (OEOF) concept [3] utilizing surface induced charge
the controlling interface is
photoconductive material,
programmed
with Flash
software (Adobe Systems Co., Ltd.). The reflected light
TiOPc[ 4], to drive the liquid by projecting light pattern.
pattern, which is the same as the image on DMD and
Without tuning the parameters, frequency and voltage, the
touch panel screen, is projected on the OEOF chip surface
flow direction can be manipulated by utilizing the light
978-1-4577-0156-6/11/$26.00 ©2011 IEEE
briefly,
System design
we demonstrate a microparticle
on the surface of a
able to modifY the
liquid pumping with light pattern.
the liquid. The latter applied external ac/dc to generate
slip
In
phenomenon and photoconductive material realizes the
uniform or non-uniform electric field for liquid driving.
article
is
immediately.
requires some components for active moving to disturb
In this
the
When the light image projects on TiOPc surface, it
systems have
been developed during the last few decades [1). Liquid
field-induced-flow
organic
define
material. A 500 nm TiOPc layer is placed on the electrode.
manipulation would be applied for chemical or biological
micropumps
the
to
modified by the light illuminating is the feature of this
Complex liquid handling techniques like pumping,
of
utilized
TiOPc,
non-uniform electric field. The conductivity would be
mixing, and reaction in
sorts
we
material,
and aligned to the designed indium tin oxide (ITO) pattern.
242
Transducers' 11, Beijing, China, June 5-9, 2011
A function generator (33120A, Agilent) is utilized to
G2 are the gap, 10 /lm. Therefore, the ratio of the electrode
supply the AC voltage. The experimental results were
and gap, Wl:Gl:W2:G2, is 3:1:5:1. Even so, this ratio is
observed and recorded by a charge-coupled device (CCD)
not good efficiency to pump the liquid. How to switch this
fixed ratio into high efficiency liquid pumping ratio is the
which was connected to the personal computer.
Multi-touch panel
feature of OEOF design.
rF�;;;;;;�iJ
�
�
Light
micromirror
Lens2
device
�
�
-
��
Lens1 Lamp
Figure 1. DEDF optical system design. A straight light powered
by UHP Hg Lamp through a pair of beam collimation focusing
is projected on the DMD surface and the light pattern is
reflected onto DEDF chip surface. The applied voltage and
frequency is controlled by a function generator and the DEDF
phenomenon is recorded by a charge-coupled device (CCD).
OEOF chip fabrication
o Pyrex
As the EOF principle described before, the virtual
f2j AZ4620
electrode on the TiOPc surface would generate ions
moving and surface slip velocity. The liquid is pumped
from
non-illuminating
However,
a
single
toward
light
illuminating
pattern
would
• ITO
�TiOPc
Figure. 2 The DEDF chip fabrication process. (a)�(d) The
lift-off process is utilized to define the ITO pattern position. (e)
A hardened thin TiDPc layer is fabricated on the ITO pattern
after spin-coating process and hot plat heating.
region.
generate
• Mask
a
symmetry liquid flow and they are neutralized to result in
zero net flow. Therefore, a pair of asymmetric electrodes
is designed to generate a net flow on the surface and a
series of these electrodes would enlarge the liquid
pumping effect.
The OEOF chip fabrication process is shown in Fig.#.
We utilize lift-off process to pattern the ITO image on the
glass. Firstly, the ITO electrode size and position are
defined with AZ4620 positive photoresist, Fig. 2(a)(b).
Next, a 2000 A thick ITO layer is deposited on a cleared
Pyrex-PR substrate by RF sputter system, Fig. 2(c).
Finally, acetone organic solvent is applied to remove the
AZ4620 layer. ITO pattern is fabricated on the Pyrex
substrate, Fig. 2(d). A thin TiOPc layer is spin-coated on
the substrate to cover the ITO pattern at 1500 rpm for 20 s.
After baking at 130°C for 30 min, the TiOPc structure is
hardened.
Fig. 3(a) shows the ITO pattern design which
consists of a pair comb-like electrodes with different
electrode width. A thin TiOPc layer, light blue color,
Figure 3 (a) A pair comb-like ITO pattern generates a series of
particular electrode sequence. (b) TiOPc layer thin 230nm
cover on ITO pattern. (c) WI and W2 are ITO electrodes and GI
and G2 are the gap between neighbor electrodes.
Operation principle
coated on the ITO pattern is shown in Fig.3 (b). The width
The key principle of OEOF is to transform a
of large and small ITO pattern is 30/lm and 70/lm. The
sequence of fixed ITO electrode into another sequence of
gap between each electrode is 10 /lm. In Fig.3(c), WI and
virtual electrode by utilizing the conductive property of
W2 are the ITO electrode, 30/lm and 70/lm, and Gl and
organic photoconductive material, TiOPc. As illustrated
243
in Fig. 4 (A), the overlapping area of the ITO pattern and
(a)
the light pattern determine the virtual electrode pattern on
the TiOPc surface. Without light pattern illuminating on
Os
(b)
the TiOPc layer, the charges are confined under the
photoconductivity material and on the ITO electrode.
2s
(c)
When the light pattern projected on the TiOPc surface, the
4s
TiOPc conductivity increases and the charges transport
(d)
through TiOPc layer to assemble and form the virtual
electrode to generate non-uniform
electric field.
In
suitable low ac frequency condition, this electric field
(e)
distribution would induce the surface charge to move with
slip velocity.
pattern to redefine the virtual electrode location. When
large ITO electrode, 50flm, and one-third of the small
direction and when the light pattern shifts 20flm in the
rightward direction, the virtual electrode sequence is
changed as shown in Fig. 4(B) and the flow direction is
reversed immediately.
I en
(b )
I I i I
12 s
(h)
ITO electrode, 30flm, the charge transforms on the
shown in Fig. 4(A), the liquid is pumped in the rightward
10 s
(g)
the 70flm wide light pattern covers the entire area of the
electrode. When the sequence of virtual electrode is as
8s
(t)
Following above principle, we can utilize light
photoconductive layer to form another sequence of virtual
6s
14 S
Figure 5. (a)�(h) Top view of DEOF chip. (a)�(d)A moving 20
f.lITl diameter polystyrene bead illustrates the rightward liquid
flow driven with DEDF. (e)�(h) We shift the light pattern
rightward 20 f.lITl and the virtual electrode sequence is reversed.
The leftward moving bead indicates that the charge
re-distribution reverses the flow direction.
The relationship between applied voltage and liquid
It' IT7 lit' FP1£
velocity is shown in Fig. 6. The applied ac voltage is
selected as 8, 8.5, 9, 9.5, and 10 voltage. Because the
microparticle is driven with slip flow, to measure the
I I !
microparticle velocity would estimate the liquid flow
speed. Accorrding to the measurement results, as the
Light pattern
applied ac voltage increases, it would generate larger
:=�:==���:;::--------��-------£:::��:�:�����=�:jf--
magnitude of non-uniform electric field and pump the
I I t' IT7 I I ! I 't' FP1£
+++++++++++++++
I�!
surface ions with faster slip velocity.
+++++++-++++++++
30
25
'"
"""-
E
S
Light pattern shift
Figure 4. The side view of DEDF chip. Utilizing light to
manipulate the liquid flow direction is the key technology.
(A) The illuminating region induces charge on the TiOPc
surface and the virtual electrode sequence makes the liquid
flow. (B) The rightward shift of the light pattern reverses the
virtual electrode sequence on TiDPc surface and the flow
direction.
''5
15
o
�
10
u.
o
o
5
7.5
8
9
8.5
9.5
10
10.5
Voltage (Vp.p.)
Figure 6. The DEDF velocity plotted against applied voltage (I/)
is fitted with v=KV2 where K is constant [6]. The increasing
applied voltage generates fast liquidflow velocity.
3. EXPERIMENT RESULTS
Light-driven liquid flow
The to and fro pumping
20
>
process of the liquid is
shown in Fig. 5. The light pattern is projected on the ITO
Microparticle concentration
pattern as above description, one-third of the small ITO
Utilizing the light pattern shift to reverse the liquid
electrode and entire large ITO electrode. The surface ions
flow
slip would drive the microparticle rightward, (a)�(d). As
direction,
it
also
provides
the
flexibility
to
manipulate the liquid as depicted in Fig. 7. As depicted in
the projecting light pattern shifts, the liquid pumping
the Fig. 7 (a), when the light pattern is aligned with the
direction is reversed immediately, (e)�(h). The processes
ITO pattern precisely, the liquid at the left and right half
demonstrate the convenience and flexibility of liquid
are driven in opposite direction leading to the formation
manipulation with light pattern.
of a vortex by the OEOF. Another feature of this
light-driven vortex is that the flow direction change is
244
immediate following the light pattern shifts without
left and right half are shifted and the micro particles are
concentrated at the center of clockwise vortex.
tuning any external ac conditions, voltage or frequency.
This
operation
makes
the
flow
manipulation
more
4. CONCLUSIONS
convenient.
The light-driven approach for liquid pumping has
Following the flow of counterclockwise vortex, the
microparticles spreaded on the chip are concentrated
been reported. The integration of photoconductivity
toward the center of the vortex which is the boundary of
material and patterned ITO glass realizes the method
left and right light pattern. When the left and right light
utilizing dynamic light pattern to manipulate the lquid
pattern parts are shifted to cover the suitable ITO region
flow in micro scale. In this article, we develop this
to make the left part liquid upward and right part liquid
concept and demonstrated the application of OEOF to
downward, the clockwise vortex is generated shown in
generate the optoelectronic vortex for concentration of
Fig. 7(b)
8flm size microparticles by using light image with good
control over the liquid flow manipulation.
ACKNOWLEDGEMENTS
This
project
was
financially sponsored
by
the
National Science Council (Grant No.98-2120-M-007003). We extend special thanks to the staff of the
Biophysical
University
Laboratory
and
the
at
National
Chiao
Micro-Systems
and
Tung
Control
Laboratory (MSCL) at National Tsing Hua University for
their assistance. We are also thankful to Prof. Hwan-You
Chang
o
o
ITO
0
D Virtual
Light pattern
Liquid flow
•
electrode
8
illustrates
the
application
of
OEV
[3] Shih-Mo Yang, Rong-Jhe Chen,Tung-Ming Yu,
Hang-Ping Huang, Long Hsu and Cheng-Hsien Liu,
"An adaptive bi-directional micro-pump by using
light-induced electroosmosis", Proc. MicroTAS 2010,
Netherlands, 3-7 October, 2010.
[4] Shih-Mo Yang et aI., "Dynamic manipulation and
Fig. 8(b) when we separate the right and the left part of
patterning
the light pattern with a distance, the region between two
driving
force
and
Hua
Engineering", J Fluids Eng. , 124, pp.384-392, 2002.
flows generate a counterclockwise vortex indicated by the
liquid
and
Tsing
"MEMS-micropumps: a review, Journal of Fluids
for
mobile 8flm diameter polystyrene beads. As observed in
no
Microbiology
National
T. "Microfluidic tools for cell biological research."
and right part is opposite, downward and upward. These
has
his
at
Nano Today 5, pp.28-47, 2010.
[2]N. T. Nguyen, X. Huang and T. K. Chuan,
optoelectronic flow. The direction of liquid flow at left
images
of
REFERENCES:
8(a) illustrates a counterclockwise vortex driven by
microparticles are concentrated in this area
staff
Laboratory
[1]Velve-Casquillas, G., Le Berre, M., Piel, M. & Tran, P.
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light
the
University for their support.
MicroparticIe
Figure 7. Top view of the chip with optoelectronic vortex. (A)
The alignment of ITO and light pattern makes the left halfand
the right half to pump the liquid in opposite directions and the
optoelectronic vortex is generated. (B) After shifting the light
pattern the direction of the vortex changes.
Fig.
and
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formation of vortex in clockwise. These processes mean
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the flow direction of vortex is able to be control only with
James and Valley, Justin K. and Hsu, Hsan-Yin and
projected light image.
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CONTACT
*Cheng-Hsien Liu, Tel: +886-3-5715131#33706;
Figure 8. Micropraticle concentration by light-driven
optoelectronic vortex. (A) A counterclockwise vortex is
generated at the border of the light pattern and 8 /fffl diameter
microparticles are concentrated. (B) The light patterns at the
[email protected]
Shih-Mo Yang, Tel: +886-3-5715131#33793;
[email protected]
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