Particle Separation and Chemical Gradient Control via Focused Travelling Surface Acoustic Waves (F-TSAW)

1. Ghulam Destgeer
Particle Separation and Chemical Gradient Control
via
Focused Travelling Surface Acoustic Waves (F-TSAW)
Flow Control Laboratory, Department of Mechanical Engineering
2013.06.10

2. 2
Contents
• Introduction
• Theory
• Device design and fabrication
• Experimental setup
• Results
• Summary

3. Introduction
Surface acoustic wave

4. 4
Particle separation
• The isolation and separation of micro
particulate materials in a continuous
flow are required for chemical
syntheses and biological analyses.
• The separation and sorting of cells are
critical in a variety of biomedical
applications including:
i. Diagnostics
ii. Therapeutics
iii. Cell biology
<Lee et al., 2010, Lab Chip> <Daniel et al., 2010, Anal Bioanal Chem>
Huang’s group
Sung’s group

5. 5
Particle manipulation by SSAW
• Particle separation:
– Particle diameter: 0.87μm (Red), 4.16μm (Green)
• Experimental parameters:
– Frequency: 12.6MHz
– Power: 15-22dBm (30-160mW)
– Flow rate: 0.6-2μl/min
<Shi et al., 2009, Lab Chip>

6. 6
Chemical gradient control
• Most methods are capable of
generating linear chemical
gradient profiles in a static
manner.
• Generating pulsatile chemical
gradients in microfluidic devices
has important implications for
the characterization of dynamic
biological and chemical
processes.
• Dynamic temporal control of
chemical gradients is required.
<Ahmed et al., 2013, Lab Chip> <Daniel et al., 2006, Anal. Chem.> <Seidi et al., 2011, Biomicrofluidics>

7. 7
Chemical gradient control by oscillating bubbles
• Chemical solutions:
– Dextran-FITC (stimulant)
– Phosphate buffered saline(buffer)
• Input voltage and frequency:
– 12-16Vpp and 30kHz
<Ahmed et al., 2013, Lab Chip>

8. 8
Objective
• (a) Device schematic (b) Particle separation
• (c) Chemical gradient control and uniform micromixing
• (d) F-TSAW amplitude (e) Fabricated device

9. Theory

10. 10
Acoustic radiation force on compressible spheres
For TSAW:
<Yosioka & Kawasima, 1955, Acoustica>
𝐸 𝑎𝑐 = (4π𝑓𝑢)2
𝜌 𝑓 𝐴 2
=
2(4π𝑓𝑢)2
𝑘2
= 8(𝑐𝑢)2𝐴 2
=
2 𝐸 𝑎𝑐
𝑘2 𝜌 𝑓
where, 𝐸 𝑎𝑐 is acoustic energy density, 𝑢 is SAW amplitude, 𝑘 = 2π
λ is
wavenumber, 𝑐 is speed of sound on wafer surface, 𝑓 is the frequency of SAW, Pin
is the input power and V is the input voltage.
where, 𝛼 =
𝜌 𝑓
𝜌 𝑝
, 𝛽 =
𝑐 𝑓
𝑐 𝑝
, R is radius of μ-particles & A is complex amplitude
of the velocity potential.
𝐹 𝑇𝑆𝐴𝑊 = 2𝜋𝜌 𝑓 𝐴 2(𝑘𝑅)6φ 𝑇𝑆𝐴𝑊
φ 𝑇𝑆𝐴𝑊 =
1 −
𝛼 2 + 𝛼 𝛽2
3
2
+
2 1 − 𝛼 2
9
(2 + 𝛼)2
TSAW
Flow
𝐹 𝑇𝑆𝐴𝑊 ~ 𝑉2
𝑓6
𝑅6
~ Pin 𝑓6
𝑅6

11. 11
F-TSAW amplitude
• Acoustic wave amplitude is estimated as:
• Acoustic wave amplitude qualitative measure:
𝑢(𝑥, 𝑧) ≈
1
𝑍1/4
−∞
+∞
𝐺 𝑡 exp 𝑗 𝑡4
+𝑍′
𝑡2
+𝑋′
𝑡 𝑑𝑡
𝑍′
=
(0.145𝑍 − 𝑅𝑘0/2)
4.98𝑍
𝑋′ =
−𝑋
4
4.98𝑍
𝑡 =
4
4.98𝑍𝐾1 𝑍 = 𝑘0 𝑧 𝑋 = 𝑘0 𝑥 𝐾1 = 𝑘1/𝑘0
<Fang and Zhang, 1989, IEEE Transactions on Ultrasonic> <Wu et al., 2005, IEEE Transactions on Ultrasonic>
Wu et al. 2005 Calculated
θ
R
A A’

12. 12
F-TSAW amplitude
5R 5R 5R
5R 5R 5R
5R 5R 5R
AmplitudeAmplitudeAmplitude
AmplitudeAmplitudeAmplitude
AmplitudeAmplitudeAmplitude

13. 13
F-TSAW amplitude
Frequency(MHz)

14. 14
SAW amplitude calculation
F 𝑇𝑆𝐴𝑊~ (Eac/k2) (kR)6φ 𝑇𝑆𝐴𝑊
E 𝑎𝑐~ u2 f2 ρ
Energy density (Eac) – J/m3
SAW displacement (u) – nm
Frequency (f) – MHz
Density (ρ) – kg/m3
Wave number (k) – (μm)-1
Particle radium (R) – (μm)
Constant (φ)
Contour plots of SAW displacement square (u2) – m2
Top – f =133.3MHz
Bottom – f = 40.0MHz
x
z

15. Device design and fabrication

16. 16
F-TSAW device design
• Two salient features: (i) unidirectional (ii) focused
• Interdigitated transducer(IDT): Two interlocking
comb-shaped metallic electrodes on top of a
piezoelectric substrate.
• Frequency of applied AC signal = frequency of
SAW (fSAW)
– fSAW = c/λ, c is speed of sound in the piezoelectric
substrate
Maximum energy is
transmitted in the
forward direction.
Very little energy is transmitted
in the backward direction.
SAW
λ
λ/8
λ/43λ/16
SAW
Unidirectional transducer
λλ/4
SAW SAW
IDT
F-TSAW amplitude by
a focusing transducer

17. 17
Fabrication of micro-chip

18. 18
Microfluidic channels
150µm 500µm200µm
1st 2nd 3rd

19. 19
Focused IDTs
40MHz 133.3MHz
1st 2nd

20. Experimental setup

21. 21
Experiment schematic
Signal generator, N5181A [3GHz]
μ-pump, neMESYS
Microscope, BX51
Camera, DP26
Power amplifier, ZHL-1-2W
DC power supply, E3634A
Micro
Chip
PDMSLiNbO3
Au electrodes

22. 22
Experimental setup
Power supply
Amplifier
Signal generator
Microscope
Microchip
Micropump
Display screen
Oscilloscope
Camera

23. Results

24. 24
Experimental parameters
PARAMETERS Device #1 Device #2 Device #3 Device #4
Frequency (MHz) 40 133.3 133.3 133.3
Input power 0.25µW 0.45mW 0.07mW ---
After amplification 0.175mW 275mW 63mW 60–200mW
Radius of FUT (mm) 6 4 4 4
Distance from FUT
to microchannel
1.25R 2.5R 2.5R 2.5R
µ-channel
cross section (µm×µm)
150×110 150×45 200×40 500×90
Particles diameter (µm) 30 and 10 10 and 3 10 and 3 ---
Fluid/media DI water DI water DI water
DI water,
rhodamine
Total flow rate (µl/hr) 50 150 100 100
Average velocity (mm/s) 0.84 6.17 3.5 0.6
Function
Particle
Separation
Particle
Separation
Particle
Separation
Gradient
Generation
Names CAPS-1 CAPS-2 CAPS-3 CAGG
*CAPS: Cross-type Acoustic Particle Separator
*CAGG: Cross-type Acoustic Gradient Generator

25. 25
CAPS-1: Particle trajectory and separation
• Experimental conditions:
– Frequency (f): 40MHz (Low)
– Input power: 725µW
– Flow rate (Q): 50μl/h (0.84mm/s)
– μ-channel cross-section: 150x110μm
– μ-particles diameter: 10, 30μm
• Equation of particle motion:
• Acoustic radiation force:
• Stokes drag force:
• Particle trajectory:
– Left figure: Theoretical
– Center figure: Experimental
• Particle separation on right
𝑚 𝑧 = 𝐹 𝑇𝑆𝐴𝑊 − 𝐹 𝐷
𝐹 𝑇𝑆𝐴𝑊 = 4π𝐸 𝑎𝑐 𝑘4 𝑅6φ 𝑇𝑆𝐴𝑊
𝐹 𝐷 = 6πη𝑅 𝑧

26. 26
CAPS-2: Particle trajectory and separation
• Experimental conditions:
– Frequency (f): 133.3MHz (High)
– Input power: 1.36W
– Flow rate (Q): 150μl/h
(6.17mm/s)
– μ-channel cross-section:
150x45μm
– μ-particles diameter: 10, 3μm
• (a) Schematic diagram of a
PDMS microchannel.
• (b-c) Once the TSAW was
turned ON, a distinct
separation distance could be
observed.
• (d) Trajectory followed by a 10
µm particle influenced by
acoustic streaming.

27. 27
CAPS-3: Particle trajectory and separation
• Experimental conditions:
– Frequency: 133.3MHz
– Input power: 225mW
– μ-channel cross-section:
• h x w: 40 x 200 μm
– Flow rate (Q):
• Sample+ Sheath: 25μl/h + 75μl/h = 100μl/h
• Average speed: 3.5mm/s
– μ-particles diameter: 3μm and 10μm
• Left: TSAW OFF, all the particles flowing
together with the laminar flow.
• Right: TSAW ON, larger particles are
pushed towards the opposite wall
resulting in separation

28. 28
Particle separation efficiency
• (a) TSAW OFF: all of the particles are
collected at the same outlet
• (b) TSAW ON: 3µm particles are
collected at same outlet whereas
almost 100% of the 10µm particles
passed through a separate outlet.
(a) (b)

29. 29
CAPS-3: Particle deflection vs. input power
• Flow rate is kept constant:
– Sheath + Sample = 80 + 20 = 100 µlh-1

30. 30
CAPS-3: Deflection vs. input power and flow rate
• For particles with diameter 10µm:

31. 31
CAPS-3: Deflection (µm) vs. Input Power (mW)

32. 32
CAGG
• Acoustic streaming flow induced
via F-TSAW
• Flow is traced by 1µm polymer
microspheres dispersed in DI
water.
• On smaller particles, drag force is
dominant compared to acoustic
radiation force.
• Three microchannels 150µm x
45µm, 200µm x 40µm and 500µm
x 90µm from left to right,
respectively, are tested.
• Microchannel 500µm x 90µm can
produce strong and large vortices
appropriate for mixing and
gradient control.
F-TSAW
F-TSAW

33. 33
Chemical gradient control and micromixing
• Acoustic streaming flow
– Generate chemical gradient
– Uniformly mix fluids.
• Microchannel
– w×h: 500µm×90µm
• Flow rate: 100µl/h (0.6mm/s)
– Fluid 1: rhodamine: 50µl/h
– Fluid 2: DI water: 50 µl/h
• Power input
– Gradient control: 60–200mW (18–
23dBm)
– Uniform mixing: 800mW (29dBm)

34. 34
Chemical gradient control and micromixing

35. 35
Summary
• Four types of devices are tested:
– First three are Cross-type Acoustic Particle Separator (CAPS)
– Fourth is Cross-type Acoustic Gradient Generator (CAGG)
• A single micro-chip is capable to be used as CAPS or CAGG
• Particles are successfully separated with efficiency close to
100%:
– 10μm particles from 3μm and 30μm particles from 10μm
• Particle deflection is plotted against input power which
shows:
– 3μm, 7μm and 10μm are separated
• Low amplitude and high frequency (40 and 133.3MHz) waves
are used.
• Chemical gradient control and uniform mixing is also shown
using F-TSAW without trapping any micro-bubble.

36. THANK YOU FOR YOUR ATTENTION!!!