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http://www.diva-portal.org
Postprint
This is the accepted version of a paper presented at
Acoustofluidics 2016, Kongens Lyngby, Denmark,September 22-23
2016.
Citation for the original published paper:
Fornell, A., Nilsson, J., Jonsson, L., Periyannan Rajeswari, P.,
Joensson, H. et al. (2016)Particle enrichment in two-phase
microfluidic systems using acoustophoresis.In:
N.B. When citing this work, cite the original published
paper.
Permanent link to this
version:http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-309851
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Particle enrichment in two-phase microfluidic systems using
acoustophoresis Anna Fornell1, Johan Nilsson1, Linus Jonsson1, Prem
Kumar Periyannan Rajeswari2, Haakan N. Joensson2 and Maria Tenje1,3
1Dept. Biomedical Engineering, Lund University, Lund, Sweden
E-mail: [email protected] 2Div. Proteomics and
Nanobiotechnology, Science for Life Laboratory, KTH Royal Institute
of Technology, Stockholm, Sweden 3Engineering Sciences, Science for
Life Laboratory, Uppsala University, Uppsala, Sweden Introduction
Droplet microfluidics provides a tool to create confined and
discrete reaction chambers for biological and chemical experiments
at high throughput [1]. The method has attracted special interest
for single-cell studies since it is possible to encapsulate single
cells inside droplets. This makes it possible to create more
sensitive analysis of cells since the results arise from a
particular cell and is not the average response of thousands of
cells [2]. To miniaturize biological assays using droplets the same
processes and steps performed in standard protocols have to be
integrated on microfluidic chips. Here, we present a method to
concentrate particles in droplets by combing acoustic particle
focusing inside droplets with a trident shaped droplet split, and
we report ten times higher concentration of particles in the center
daughter droplets compared with the side daughter droplets when
ultrasound is applied [3]. Experimental An illustration of the
developed concept for particle enrichment inside droplets and a
photograph of the fabricated acoustofluidic device are shown in
figure 1. The microfluidic channels were wet-etched on a silicon
wafer and sealed by anodic bonding of a 1.1 mm thick glass lid.
Aqueous droplets with polystyrene microparticles (5 µm) were
generated in a continuous organic phase (olive oil). All liquid
flows were controlled by syringe pumps. A piezoelectric transducer
was glued on the silicon side of the chip. To achieve particle
focusing inside the droplets the transducer was actuated with a
frequency matched to create λ/2-resonance in the main channel.
After the particle focusing step each droplet was split into three
daughter droplets in a trifurcation. The performance of the system
was evaluated by measuring the concentration of particles in the
center and side daughter droplets using a Coulter Counter. To
demonstrate the possibility to manipulate cells inside droplets and
show the suitability of the system for biological applications, red
blood cells were encapsulated and manipulated inside the
droplets.
Figure 1: Left: Illustration of the concept for acoustic
particle enrichment inside droplets. Aqueous droplets containing
particles are generated. The applied acoustic field moves the
particles to the pressure node in the center of the droplets, and
finally each droplet is split into three daughter droplets at a
trifurcation. Right: Photograph of the microfluidic chip for
particle enrichment in droplets. Channel width x channel height 435
µm x 165 µm. Results At λ/2-resonance (1.8 MHz, 25 Vpk-pk) the
particles inside the droplets were moved to the center of the
droplets. The droplets were transported downstream to a
trifurcation where each droplet was split into three daughter
droplets with approximately the same size (25-28 nl). When
ultrasound was applied the majority of the particles were enriched
in the center daughter droplets as seen in figure 2.
Ultrasonic transducer
Water
Oil
Oil Flow
1 2 3 41 Droplet generation2 Particle encapsulation3 Acoustic
focusing4 Droplet splitting
2 cm
Piezo
Droplet split
Droplet generation
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Figure 2: Particle enrichment in droplets. Without ultrasound
(left photograph) the particles are positioned in the entire main
droplet resulting in particles in all daughter droplets after the
droplet split. When ultrasound is applied (right photograph) the
particles are directed to the center daughter droplet during the
splitting step resulting in particle enrichment.
The concentration of particles in the daughter droplets after
the acoustic focusing step and the droplet split is presented in
figure 3. When ultrasound was applied the concentration of
particles in the center daughter droplets was more than ten times
higher than in the side daughter droplets. In the control
experiment without ultrasound only a small concentration difference
was observed between the center and side daughter droplets. Figure
3: Concentration of
particles with and without ultrasound during the droplet split.
Experiments were performed three times (n=3) with data acquisition
in triplicates. Error bars represent ± standard deviation.
To investigate the possibility to use the described method for
droplet based cell assays, red blood were encapsulated inside the
droplets. When ultrasound was applied to the system the cells were
found to be immediately moved to the center of the droplets, see
figure 4. Figure 4: Acoustic focusing of
red blood cells in droplets. At application of ultrasound the
cells were positioned to the center of the droplet (right photo).
It was also observed that the droplet interface was slightly
deformed by the ultrasound.
Conclusion We have developed a method to enrich particles inside
droplets by combining acoustic focusing with a trident shaped
droplet split. 89% of the particles were collected in the center
daughter droplets when 2/3 of the original droplet volume was
removed. It was also shown that the method can be used to
manipulate red blood cells inside droplets. These results opens up
for novel droplet based assays that are not possible to perform
today. References [1] R. Seemann, M. Brinkmann, T. Pfohl and S.
Herminghaus, Rep Prog Phys, 75, 16601 (2012). [2] D. Di Carlo and
L. P. Lee, Anal. Chem., 78, 7918–7925 (2006). [3] A. Fornell, J.
Nilsson, L. Jonsson, P. K. Periyannan Rajeswari, H. N. Joensson and
M. Tenje, Anal. Chem., 87, 10521–10526 (2015).
Ultrasoundoff Ultrasoundon
FocusedparticlesRandomlydistributedparticles
Ultrasoundoff Ultrasoundon
Randomlydistributedcells Focusedcells
With ultrasound0
3
6
9
12
15
Conc
entr
atio
nx1
06 p
artic
les/
ml
Orig
inal
Side
Cent
er
Orig
inal
Cent
er
Side
Without ultrasound
ENRICHMENT
