Modelling and development of droplet generation method for magnetically actuated digital ...

146 Pages·2017·22.9 MB·English

Modelling and development of droplet
generation method for magnetically actuated
digital microfluidics
by
Timothy James Hutama
A thesis submitted to the
Department of Chemistry
in conformity with the requirements for
the degree of Master of Science
Queen’s University
Kingston, Ontario, Canada
September 2017
Copyright © Timothy James Hutama, 2017
Abstract
Digital microfluidics is useful in miniaturizing different types of biological tests due
to an ability to perform multiple operations on a single chip with a single common
geometry. However, one of the largest problems in using digital microfluidics has
been biofouling during these processes, a phenomenon which is exacerbated when
using electric fields for fluid manipulation. Magnetic microfluidics is an alternative
actuation mechanism, which does not have this same limitation. However, until
recently it has been impossible to create drops, which can also be subsequently moved
to perform multiple step analyses. In this thesis, a method for creating drops on
superhydrophobic surfaces using magnetic force as the primary actuation mechanism
is outlined.
Using numerical simulations in Comsol Multiphysics, the method was explored to
determine several of the limitations of the system, including the minimum actuatable
volume (5 µL). Additionally, the flow within the drops was explored to obtain a better
understanding of the experimental results. Experimental validation of the results fol-
lowed, and it was found that the system showed a 1-to-1 linear change in drop volume
relative to expected dispensed volume, verifying the theoretical model. Experimental
validation found that the error of the system is constant over any dispensed volume
at ±0.5-0.6 µL.
i
The method was applied to miniaturize a standard test for hard water determina-
tion, a complexometric EDTA titration. The results from a specially designed chip
are compared to a titration of a 10 mL volume of the same sample and two were found
to be equal within error (100-170 ppm for the chip, 124 ± 2 ppm for the standard
method). The water hardness estimate from the chip was further improved upon by
image analysis, and the range narrowed to 120 ± 10 ppm, again within the same error
asthestandardmethod. Togetherwiththetheoreticalanalysis, thisresultverifiesthe
practicality of the method for analytical operations. Finally, preliminary work into
making the magnetic droplet manipulation method more general was conducted, and
it was found to be possible to create chips which utilize any combination of droplet
mixing, merging, moving, and splitting.
ii
Co-Authorship
All the work contained in this thesis was carried out by the author under the guidance
of Dr. Richard D. Oleschuk at the department of Chemistry of Queen’s University at
Kingston. Portions of this thesis have been previously published in refereed journals
as the following paper:
Hutama, T.J; Oleschuk, R.D. Lab Chip 2017. 17, 2640-2649
iii
Acknowledgements
I would like to thank my supervisor Dr. Richard Oleschuk for his support and guid-
ance. I also want to thank the members of my committee, Dr. Guojun Liu and Dr.
Stephen Brown, for their advice and suggestions, and I thank everyone in the group,
Dr. Kyle Bacchus, Prashant Agrawal, Bidur Ghimire, Matthias Hermann, David
Simon, and Xilong Yuan for their support.
I would also like to acknowledge the financial support from the Natural Sciences
andEngineeringResearchCouncilofCanada(NSERC)whosegrantshaveenabledthe
purchase of the material utilized in this thesis and the support of CMC microsystems
whose networked COMSOL licences have enabled the finite element modelling used
in this thesis.
I would also like to thank my friends, especially Shervonne, Derek, James, Lisa,
Robert, and Zachary for their humour and continued encouragement to study and
enjoy the chemical sciences and my family whose support have made it possible to
continue in my research.
iv
Contents
Abstract i
Co-Authorship iii
Acknowledgements iv
Contents v
List of Tables ix
List of Figures x
List of Abbreviations xii
Chapter 1: Introduction 1
1.1 Microfluidics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.2 Digital Microfluidics . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.2.1 Digital Microfluidic Actuation Methods . . . . . . . . . . . . . 5
1.2.1.1 Surface Tension . . . . . . . . . . . . . . . . . . . . . 5
1.2.1.2 Electrowetting . . . . . . . . . . . . . . . . . . . . . 9
1.2.1.3 Magnetic Actuation . . . . . . . . . . . . . . . . . . 14
v
1.2.2 Droplet Generation Methods . . . . . . . . . . . . . . . . . . . 19
1.2.2.1 Electronic Methods . . . . . . . . . . . . . . . . . . . 22
1.2.2.2 Physical Methods . . . . . . . . . . . . . . . . . . . . 26
1.3 Device Fabrication Methods . . . . . . . . . . . . . . . . . . . . . . . 31
1.3.1 Traditional Fabrication Methods . . . . . . . . . . . . . . . . . 32
1.3.2 3D Printing . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
1.4 Motivation and Objectives . . . . . . . . . . . . . . . . . . . . . . . . 36
Chapter 2: Materials and Methods 39
2.1 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
2.2 3D Printing and Chip Design . . . . . . . . . . . . . . . . . . . . . . 42
2.2.1 Design of the Splitting Assessment Chip . . . . . . . . . . . . 45
2.2.2 Design of the EDTA Titration Chip . . . . . . . . . . . . . . . 48
2.2.3 Design of the Generalized Actuation Chip . . . . . . . . . . . 50
2.3 Numerical Simulations . . . . . . . . . . . . . . . . . . . . . . . . . . 53
2.3.1 Simulation Model Design . . . . . . . . . . . . . . . . . . . . . 54
2.3.2 Starting and Boundary Conditions . . . . . . . . . . . . . . . 57
2.3.2.1 Simulation 1: Well filling Simulation Without Hy-
drophillic Patch . . . . . . . . . . . . . . . . . . . . . 58
2.3.2.2 Simulation2: WellfillingSimulationWithHydrophillic
Patch . . . . . . . . . . . . . . . . . . . . . . . . . . 59
2.3.2.3 Simulation 3: Demonstrating Droplet Splitting After
Well Filling . . . . . . . . . . . . . . . . . . . . . . . 60
2.4 Physical Validation of Numerical Simulations . . . . . . . . . . . . . . 61
2.4.1 Volume Determination . . . . . . . . . . . . . . . . . . . . . . 62
vi
2.4.2 EDTA Titration and Validation of On-chip Titration . . . . . 63
2.4.3 General Application Volume Limit Determination . . . . . . . 66
Chapter 3: DropletGenerationUsingOnlyMagneticForcebyTopol-
ogy Assisted Dispensing 67
3.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67
3.2 Computational Fluid Dynamics . . . . . . . . . . . . . . . . . . . . . 67
3.2.1 Probing the Necessity of a Hydrophilic Patch . . . . . . . . . 68
3.2.2 The Droplet Splitting Mechanism . . . . . . . . . . . . . . . . 74
3.3 Experimental Validation . . . . . . . . . . . . . . . . . . . . . . . . . 79
3.3.1 Splitting Mechanism Validation and Volume Correlation . . . 79
3.3.2 Method Reproducibility . . . . . . . . . . . . . . . . . . . . . 83
3.3.3 Extent of Permissible Liquids . . . . . . . . . . . . . . . . . . 85
3.4 Method Automation . . . . . . . . . . . . . . . . . . . . . . . . . . . 87
3.5 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89
Chapter 4: Doing Chemistry with Magnetic Microfluidics 91
4.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91
4.2 EDTA Titration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91
4.2.1 Water Hardness Range Determination . . . . . . . . . . . . . 92
4.2.2 Cell Phone Analysis . . . . . . . . . . . . . . . . . . . . . . . 94
4.3 Generalized Actuation Chip . . . . . . . . . . . . . . . . . . . . . . . 102
4.3.1 Design and Operation . . . . . . . . . . . . . . . . . . . . . . 102
4.3.2 Limits of Actuation . . . . . . . . . . . . . . . . . . . . . . . . 105
4.4 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107
vii
Chapter 5: Summary and Conclusions 108
Bibliography 111
Appendix A: Test Chip Designs 127
Appendix B: Automation Code 129
viii
List of Tables
2.1 Titration chip well volumes as experimentally determined and corre-
sponding endpoint at which the indicator changes colour. . . . . . . . 50
ix