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Ultrafast microfluidic droplet sorter extension work Kong, Luke; Wu, Samuel 2012

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Ultrafast Microfluidic Droplet Sorter Extension Work  Luke	
  Kong Samuel	
  Wu Project	
  Sponsor: Dr.	
  Carl	
  Hansen Project	
  Mentors: Tim	
  Leaver Adam	
  Quiring ENPH	
  459	
   Engineering	
  Physics The	
  University	
  of	
  BriLsh	
  Columbia April	
  2,	
  2012 Project	
  Number	
  1209 !  ExecuLve	
  Summary This	
  project	
  builds	
  on	
  work	
  done	
  by	
  a	
  previous	
  APSC	
  459	
  group,	
  who	
  developed	
  fluorescence-­‐ based	
  droplet	
  sorLng	
  device	
  similar	
  to	
  that	
  described	
  by	
  AgresL	
  et	
  al.	
  up	
  to	
  the	
  point	
  where	
  it	
   could	
  detect	
  the	
  fluorescence	
  of	
  droplets	
  up	
  to	
  a	
  rate	
  of	
  1kHz.	
  	
  However,	
  it	
  was	
  unable	
  to	
  sort	
   droplets;	
  this	
  project	
  sought	
  to	
  add	
  droplet	
  sorLng	
  funcLonality	
  to	
  their	
  microfluidic	
  chip	
  de-­‐ sign. Our	
  project	
  aimed	
  to	
  demonstrate	
  droplet	
  actuaLon	
  with	
  use	
  of	
  the	
  exisLng	
  experimental	
   setup.	
  	
  This	
  consisted	
  of	
  three	
  main	
  objecLves: 1. Model	
  effect	
  of	
  electrode	
  design	
  and	
  geometry	
  on	
  droplet	
  actuaLon	
  using	
  finite-­‐ element	
  analysis	
  (implemented	
  in	
  COMSOL).	
  	
   2. Demonstrate	
  actuaLon	
  of	
  droplets,	
  redesigning	
  microfluidic	
  chip	
  if	
  necessary. 3. OpLmize	
  setup	
  towards	
  droplet	
  sorLng	
  at	
  speeds	
  on	
  the	
  same	
  order	
  (1-­‐2	
  kHz)	
  as	
  exist-­‐ ing	
  work	
  (AgresL,	
  2010). Using	
  COMSOL	
  we	
  determined	
  the	
  factors	
  that	
  will	
  most	
  strongly	
  affect	
  the	
  dielectrophoreLc	
   force	
  on	
  a	
  droplet	
  in	
  a	
  channel.	
  	
  From	
  these	
  results	
  we	
  redesigned	
  the	
  droplet	
  sorter	
  chip	
  from	
   the	
  previous	
  group	
  and	
  fabricated	
  chips	
  with	
  a	
  new	
  electrode	
  design	
  (microfluidic	
  channels	
  to	
   be	
  filled	
  with	
  low-­‐melLng-­‐point	
  alloy).	
  	
  We	
  then	
  went	
  on	
  to	
  demonstrate	
  droplet	
  redirecLon	
  at	
   a	
  rate	
  of	
  at	
  least	
  100Hz.	
  	
   Although	
  droplet	
  redirecLon,	
  the	
  main	
  focus	
  of	
  this	
  project,	
  was	
  successfully	
  demonstrated,	
   much	
  work	
  remains	
  to	
  be	
  done	
  on	
  this	
  project.	
  	
  The	
  redirecLon	
  needs	
  to	
  be	
  coupled	
  to	
  the	
  pre-­‐ vious	
  459	
  group’s	
  droplet	
  detecLon	
  setup	
  in	
  order	
  for	
  controlled	
  droplet	
  actuaLon.	
  	
  	
  Recom-­‐ mendaLons	
  were	
  made	
  about	
  electrode	
  fabricaLon,	
  droplet	
  transfer	
  from	
  generator	
  to	
  sorter	
   and	
  high	
  voltage	
  switching.	
    !  Table of Contents 1.0 Introduction!  1  2.0 Discussion!  4  2.1 Dielectrophoresis!  4  2.2 High-Voltage Switching!  4  2.3 Modeling!  5  2.3.1 The Construct!  5  2.3.2 Finite Element Analysis!  6  2.3.4 Computation!  7  2.3.5 Optimization!  8  2.4 Sorter Chip Design! 2.4.1 List of Modifications!  10  2.4.2 Design Description!  10  2.5 Sorter Chip Fabrication!  13  2.5.1 Fabrication!  13  2.5.2 Results!  13  2.6 Electrode Fabrication!  14  2.6.1 Procedure!  14  2.6.2 Results!  15  2.7 Electrode Characterization! 2.7.1 Procedure! !  10  16 16  2.7.2 Results!  2.8 Switch Characterization!  17 18  2.8.1 Procedure!  18  2.8.2 Results!  19  2.9 Droplet Actuation!  21  2.9.1 Procedure!  22  2.9.2 Results!  22  Conclusions!  24  3.0 Project Deliverables!  25  3.1 List of Deliverables!  25  3.2 Financial Summary!  25  4.0 Recommendations!  26  4.1 Electrode Fabrication!  26  4.2 Droplet Re-injection!  27  4.3 HV switching!  28  5.0 Appendices!  !  29  Appendix A: Fabrication Protocols!  29  A.1 Wafer Fabrication Procedure!  29  A.2 Wafer Fabrication Protocols!  30  A.3 PDMS Chip Fabrication!  32  Appendix B: SOP for generating droplets for use with 30um channel width sorter chips.! 33 Appendix C: HV Switch design by the UBC PHAS E-LAB!  34  Appendix D: Electrode alloy quotes!  36  6.0 References!  !  38  Table of Figures/Tables 1	
    Fig.	
  1.	
  Diagram	
  of	
  microfluidic	
  droplet	
  sorter  6	
    Fig.	
  2.	
  Basic	
  construct	
  of	
  COMSOL	
  electrode	
  model  7	
   8	
    Fig.	
  3.	
  Mesh	
  for	
  COMSOL	
  electrode	
  model 2 Fig.	
  4.	
  Y-­‐Z	
  slice	
  study	
  of	
   ∇ E halfway	
  through	
  oil	
  channel	
  in	
  x	
  direcLon.  11	
    Fig.	
  5.	
  AutoCAD	
  drawing	
  of	
  droplet	
  sorter	
  chips.  12	
    Fig.	
  6.	
  Flat	
  (top)	
  and	
  sharp	
  (bofom)	
  electrode	
  designs.  14	
    Fig.	
  7	
  Electrode	
  channels	
  following	
  injecLon	
  of	
  GaIn  16	
    Fig.	
  8.	
  Diagram	
  of	
  setup	
  for	
  electrode	
  characterizaLon.  17	
    Fig	
  9.	
  Electrode	
  voltages	
  when	
  a	
  0-­‐5V	
  square	
  wave	
  is	
  applied  18	
    Fig.	
  10.	
  SchemaLc	
  for	
  connecLng	
  HV	
  supply	
  to	
  electrodes  19	
    Fig	
  11.	
  Switch	
  output	
  when	
  10V	
  signal	
  is	
  applied	
  to	
  input	
    19	
    Fig.	
  12.	
  Switch	
  output	
  when	
  75V	
  signal	
  is	
  applied	
  to	
  input  20	
    Fig.	
  13.	
  Switch	
  output	
  measured	
  by	
  high-­‐voltage	
  probe	
  when	
  300V	
  signal	
  is	
  applied  21	
    Fig.	
  14.	
  Droplet	
  generaLng	
  device	
  generated	
  by	
  previous	
  APSC	
  459	
  group  22	
    Fig.	
  14.	
  Demonstrated	
  droplet	
  redirecLon  11	
    Table	
  1:	
  Droplet	
  Sorter	
  Design	
  SpecificaLons  13	
    Table	
  2:	
  Photoresist	
  specificaLons  !  1.0 Introduction 	
    Our	
  ever-­‐growing	
  understanding	
  of	
  biology	
  allows	
  us	
  to	
  manipulate	
  and	
  engineer	
  bio-­‐  logical	
  systems	
  in	
  novel	
  ways,	
  with	
  such	
  fields	
  as	
  syntheLc	
  biology	
  and	
  protein	
  engineering.	
  As	
   biology	
  operates	
  on	
  small	
  scales	
  (proteins	
  to	
  cells)	
  and	
  across	
  large	
  orders	
  of	
  magnitudes	
  (tril-­‐ lions	
  of	
  molecules/cells),	
  effecLve	
  assaying	
  techniques	
  are	
  essenLal	
  for	
  successful	
  experimen-­‐ taLon	
  and	
  validaLon.	
  	
  Screening,	
  however,	
  is	
  olen	
  a	
  rate-­‐limiLng	
  step	
  in	
  both	
  Lme	
  and	
  re-­‐ sources. 	
    ExisLng	
  macro-­‐assaying	
  methods	
  involving	
  microwell	
  plates,	
  when	
  automated	
  roboL-­‐  cally,	
  can	
  achieve	
  processing	
  speeds	
  of	
  ~1	
  Hz,	
  but	
  this	
  does	
  not	
  allow	
  for	
  treatment	
  of	
  individual 	
   cells	
  (AgresL	
  et	
  al.,	
  2010).	
   	
    OpLmally,	
  it	
  is	
  desired	
  to	
  be	
  able	
  to	
  manipulaLng	
  individual	
  cells	
  in	
  a	
  high	
  throughput	
    manner,	
  requiring	
  technology	
  capable	
  of	
  operaLng	
  on	
  small	
  size	
  scales.	
  	
  EncapsulaLon	
  of	
  bio-­‐ material	
  within	
  droplets	
  provides	
  such	
  a	
  planorm,	
  allowing	
  for	
  treatment	
  within	
  a	
  unique	
  picoli-­‐ tre	
  scale	
  microenvironment.	
  	
  Each	
  droplet	
  could	
  potenLally	
  be	
  experimented	
  upon	
  individually,	
   able	
  to	
  be	
  split	
  and	
  merged	
  with	
  other	
  droplets	
  (Griffiths	
  &	
  Tawfik,	
  2006).	
  	
    Fig.	
  1Diagram	
  of	
  microfluidic	
  droplet	
  sorter.	
  	
  Fluorescent	
  droplets	
  are	
  seen	
  here	
  as	
  light-­‐colored	
  spheres,	
  non-­‐ fluorescent	
  drops	
  as	
  dark.	
  (AgresL	
  et	
  al.,	
  2010)	
    	
    Sponsored	
  by	
  Dr.	
  Carl	
  Hansen	
  (UBC	
  Centre	
  for	
  High-­‐Throughput	
  Biology),	
  this	
  project	
    aims	
  to	
  replicate	
  a	
  droplet	
  sorter	
  developed	
  by	
  AgresL	
  et	
  al.	
  	
  They	
  were	
  able	
  to	
  sort	
  droplets	
   !  1  into	
  one	
  of	
  two	
  channels	
  by	
  applying	
  a	
  voltage	
  across	
  two	
  electrodes,	
  creaLng	
  a	
  non-­‐uniform	
   electric	
  field	
  and	
  a	
  subsequent	
  dielectrophoreLc	
  force	
  on	
  the	
  droplet.	
  	
  	
   	
    If	
  successful,	
  this	
  device	
  could	
  be	
  applied	
  towards	
  directed	
  evoluLon	
  or	
  digital	
  PCR	
  ex-­‐  periments,	
  potenLally	
  reducing	
  Lme	
  and	
  reagent	
  costs	
  by	
  several	
  orders	
  of	
  magnitude.	
  	
   The	
  project	
  objecLve,	
  as	
  stated	
  by	
  the	
  project	
  sponsor	
  Carl	
  Hansen: “Add	
  droplet	
  sorLng	
  funcLonality	
  to	
  the	
  microfluidic	
  chip.	
  This	
  should	
  be	
  accomplished	
  by	
   adding	
  an	
  electrode	
  upstream	
  of	
  a	
  juncLon	
  leading	
  to	
  two	
  collecLon	
  channels.	
  By	
  using	
  the	
   electrode	
  to	
  apply	
  an	
  electric	
  field	
  across	
  the	
  channel,	
  droplets	
  could	
  be	
  sorted	
  into	
  one	
  of	
   the	
  two	
  channels.	
  The	
  group	
  would	
  be	
  required	
  to	
  research	
  and	
  design	
  the	
  electrodes	
  (as	
   well	
  as	
  selecLng	
  a	
  suitable	
  fabricaLon	
  technique)	
  as	
  well	
  as	
  the	
  switching	
  electronics.	
  This	
   objecLve	
  could	
  involve	
  modeling	
  in	
  COMSOL	
  and	
  microfabricaLon	
  of	
  test	
  devices.” In	
  addiLon,	
  we	
  had	
  three	
  self-­‐formed	
  project	
  objecLves: 1.	
  Model	
  electrode	
  design	
  with	
  COMSOL	
   We	
  will	
  model	
  the	
  effect	
  of	
  electrode	
  design	
  on	
  actuaLon	
  of	
  droplets	
  using	
  COMSOL	
   (finite-­‐element	
  analysis).	
  	
  Varying	
  different	
  factors	
  (electrode	
  posiLon,	
  geometry,	
  AC	
  vs.	
   DC	
  field,	
  field	
  strength),	
  we	
  will	
  produce	
  an	
  evaluaLon	
  for	
  the	
  electrode	
  design	
  which	
  will	
   exert	
  the	
  maximum	
  dielectrophoreLc	
  force	
  on	
  a	
  25	
  μm-­‐diameter	
  droplet.	
   2.	
  Demonstrate	
  droplet	
  actuaLon. We	
  will	
  demonstrate	
  actuaLon	
  of	
  droplets	
  using	
  the	
  electrode	
  design	
  chosen	
  from	
  the	
   modelling,	
  redesigning	
  the	
  microfluidic	
  chip	
  if	
  necessary.	
  	
  SorLng	
  will	
  be	
  performed	
  at	
  1Hz	
   at	
  this	
  stage,	
  as	
  demonstraLng	
  that	
  actuaLon	
  is	
  controllable	
  and	
  reproducible	
  is	
  the	
  main	
   focus	
  of	
  this	
  objecLve.  !  2  3.	
  OpLmize	
  droplet	
  sorLng. Improve	
  experimental	
  setup	
  towards	
  sorLng	
  at	
  speeds	
  on	
  the	
  same	
  order	
  (1-­‐2	
  kHz)	
  as	
  ex-­‐ isLng	
  work	
  (AgresL,	
  2010).  	
    This	
  report	
  will	
  outline	
  the	
  theory	
  used,	
  the	
  methods	
  and	
  results	
  of	
  various	
  experiments,	
    issues	
  encountered,	
  as	
  well	
  as	
  conclusions	
  and	
  recommendaLons	
  for	
  future	
  developments	
  re-­‐ garding	
  this	
  project.	
  	
  This	
  report	
  aims	
  to	
  convey	
  project	
  findings	
  to	
  the	
  project	
  sponsor,	
  Carl	
   Hansen,	
  his	
  lab	
  personnel	
  and	
  the	
  Engineering	
  Physics	
  Project	
  Lab.  !  3  2.0 Discussion 2.1 Dielectrophoresis 	
    ParLcles	
  present	
  in	
  an	
  applied	
  electric	
  field	
  exhibit	
  polarizaLon;	
  when	
  placed	
  in	
  a	
  non-­‐  uniform	
  electric	
  field,	
  the	
  parLcle	
  will	
  be	
  subject	
  to	
  a	
  dielectrophoreLc	
  force.	
  	
  Depending	
  on	
  a	
   difference	
  in	
  electric	
  properLes	
  (i.e.	
  dielectric	
  constant),	
  a	
  water	
  droplet	
  present	
  in	
  an	
  oil	
  will	
   move	
  towards	
  an	
  area	
  of	
  higher	
  electric	
  field,	
  experiencing	
  a	
  force	
  given	
  by	
  the	
  following	
  rela-­‐ Lon	
  (Ahn	
  et	
  al.,	
  2006):  2 FDEP = 4π r 3∇ E 	
    Dielectrophoresis	
  is	
  the	
  actuaLon	
  mechanism	
  for	
  sorLng	
  droplets.	
  	
  However,	
  if	
  a	
  DC	
    voltage	
  is	
  applied	
  screening	
  effects,	
  where	
  the	
  environment	
  around	
  a	
  polarized	
  parLcle	
  polar-­‐ izes	
  in	
  the	
  opposite	
  direcLon	
  to	
  offset	
  the	
  charge	
  accumulaLon,	
  reduce	
  the	
  effecLve	
  electric	
   field.	
  	
  This	
  can	
  be	
  negated	
  by	
  applying	
  an	
  AC	
  signal	
  on	
  the	
  order	
  of	
  20kHz	
  (AgresL	
  et	
  al.,	
  2010).	
  	
   Thus,	
  a	
  high	
  voltage	
  20kHz	
  AC	
  signal	
  of	
  at	
  least	
  1kV	
  across	
  the	
  electrodes	
  is	
  desired.  2.2 High-Voltage Switching To	
  produce	
  a	
  HV	
  AC	
  signal,	
  a	
  suitable	
  switching	
  mechanism	
  was	
  required	
  to	
  handle	
  voltages	
  of	
   at	
  least	
  1kV.	
  	
  The	
  voltage	
  itself	
  is	
  provided	
  by	
  a	
  PS325	
  2500V-­‐25W	
  high	
  voltage	
  power	
  supply	
   made	
  by	
  Stanford	
  Research	
  Systems,	
  Inc. 	
    A	
  solid	
  state	
  switch	
  from	
  Behlke	
  meeLng	
  technical	
  requirements	
  (HTS	
  61-­‐03-­‐GSM	
  -­‐	
  rise/  fall	
  Lme	
  of	
  10ns,	
  maximum	
  operaLng	
  frequency	
  of	
  2.5MHz)	
  was	
  idenLfied	
  and	
  subsequently	
   ordered,	
  but	
  due	
  to	
  a	
  number	
  of	
  complicaLons	
  on	
  part	
  of	
  the	
  company	
  we	
  were	
  not	
  able	
  to	
  ob-­‐ tain	
  the	
  switch	
  (Behlke,	
  2012).	
  	
  A	
  switch	
  designed	
  and	
  constructed	
  by	
  the	
  PHAS	
  E-­‐LAB	
  was	
  for-­‐ tunately	
  able	
  to	
  be	
  obtained	
  from	
  Pavel	
  Trochtchanovitch	
  (E-­‐LAB	
  manager).	
  	
  This	
  switch	
  is	
   !  4  driven	
  by	
  a	
  0-­‐5V	
  signal	
  and	
  can	
  handle	
  switching	
  voltages	
  of	
  up	
  to	
  3kV.	
  	
  A	
  schemaLc	
  of	
  the	
   switch	
  can	
  be	
  found	
  in	
  Appendix	
  C. 	
    The	
  electrodes	
  were	
  characterized	
  in	
  order	
  to	
  determine	
  if	
  they	
  possessed	
  any	
  parasiLc	
    capacitance	
  which	
  would	
  limit	
  the	
  maximum	
  frequency	
  of	
  the	
  applied	
  AC	
  signal.	
  	
  The	
  switch	
   was	
  characterized	
  to	
  determine	
  performance	
  with	
  our	
  system.  2.3 Modeling 	
    The	
  cell 	
  sorter	
  system	
  is 	
  modeled	
  on	
  COMSOL	
  MulLphysics	
  solware	
  prior	
  to	
  its 	
  fabrica-­‐ 2 Lon.	
   The	
   governing	
  formula	
  for	
   the	
   dielectrophoreLc	
   force:	
   FDEP = 4π r 3∇ E 	
  is	
  a 	
  funcLon	
  of	
   the	
  gradient	
  of	
  the	
  electric	
  field	
  squared.	
   The	
  goal	
  is 	
  to	
  opLmize	
  the	
  system	
  on	
  the 	
  solware 	
  to	
   2 maximize	
   ∇ E .  2.3.1 The Construct 	
    This 	
  system	
  contains	
  three 	
  important	
  components:	
   Component	
  1	
  being	
  the	
  oil	
  channel,	
    where	
  the 	
  droplets 	
  travel;	
  Component	
  2	
  represents 	
  the	
  ground	
   electrode;	
  Component	
  3	
  is 	
  the	
   high	
  voltage	
  electrode.	
   These	
  three	
  components 	
  are	
  in	
  the	
   same	
   x-­‐y	
   plane.	
   Above	
   this	
  plane,	
   lies	
  the	
  PDMS	
  top,	
  and	
  the	
  glass	
  base	
  is	
  sefled	
  below	
  it.	
    !  5  Fig. 2. Basic construct of COMSOL electrode model  	
    There	
  are	
  a 	
  few	
  parameters 	
  to	
  be	
  tested	
  in	
  this	
  stage.	
  By	
  speculaLon,	
  the	
  most	
  influen-­‐  Lal	
   parameter	
   would	
   be 	
  the	
  distance	
   between	
   the	
   electrodes 	
   and	
   the 	
  oil	
   channel 	
  in	
   the	
   x-­‐ direcLon	
  (d1).	
   Secondary	
  concerns	
  are 	
  the	
  distance 	
  between	
  the	
  electrodes	
   in	
  the	
  y-­‐direcLon	
   (d2),	
  and	
  the	
  thickness	
  of	
  the	
  electrodes	
  (d3).	
    2.3.2 Finite Element Analysis 	
    The	
  modeling	
  process 	
  provides 	
  a 	
  wide	
  range	
  of	
  accuracies.	
   COMSOL	
  basically	
  breaks 	
  this	
    system	
  into	
  tens	
  or	
  hundreds	
  of	
  thousands	
  of	
   tetrahedrons	
  and	
  analyze	
  each	
  element	
  individu-­‐ ally.	
   To	
  achieve 	
  an	
  accurate	
  esLmate,	
   it	
   is 	
  necessary	
   to	
  have	
   a 	
  higher	
   density	
   near	
   the	
  elec-­‐ trodes 	
  and	
  the 	
  oil	
  channel,	
  whereas 	
  the	
  states 	
  of	
  the	
  regions 	
  far	
  away	
  do	
  not	
   contribute	
  much	
   to	
  the	
  accuracy	
  of	
  the	
  calculaLon.	
  The	
  system	
  is	
  therefore	
  broken	
  down	
  in	
  this	
  manner:  !  6  Fig.	
  3.	
  Mesh	
  for	
  COMSOL	
  electrode	
  model  2.3.4 Computation 	
    Although	
  the	
  enLre	
  system	
  is 	
  analyzed,	
  it	
  is 	
  only	
  the	
  region	
  near	
  the	
  oil	
  channel 	
  is	
  of	
  in-­‐  terest.	
  Therefore,	
  a 	
  y-­‐z	
  study	
  plane 	
  cusng	
  through	
  the 	
  oil	
  channel 	
  is 	
  created	
  to	
  display	
  the	
  in-­‐ formaLon	
  in	
  a	
  more	
  clarified	
  style:  !  7  2 Fig.	
  4.	
  Y-­‐Z	
  slice	
  study	
  of	
   ∇ E halfway	
  through	
  oil	
  channel	
  in	
  x	
  direcLon. 	
    In	
   the	
   figure 	
  above,	
   the	
   colours 	
  represent	
   the	
   strength	
   of	
   the	
  divergence 	
  of	
   E-­‐norm	
    squared	
  in	
   the	
  x-­‐direcLon.	
   The 	
  colour	
   darkens 	
   as 	
  the	
  strength	
  increases,	
   as	
   indicated	
  by	
   the	
   scale	
  bar.	
   The	
  maximum	
  value	
  occurs	
  in	
  the	
  area	
  of	
  the	
  oil	
  channel	
  perpendicular	
  to	
  the 	
  signal	
   electrode.  2.3.5 Optimization 	
    The	
  task	
  now	
  is	
  to	
  vary	
   electrode	
  spacing	
   and	
  opLmize 	
  this	
  parameter.	
  The 	
  procedure	
    involves 	
  manually	
   decrement	
   the	
  value 	
  of	
   a 	
  parameter	
   that	
   determines 	
  d1,	
   starLng	
  from	
  the	
   original 	
  distance 	
  used	
  in	
  the	
  previous	
   group’s 	
  design.	
  Aler	
   plosng	
   the 	
  results 	
  on	
  Excel,	
   it	
   is	
   concluded	
  that	
  the	
  gradient	
  increases	
  as	
  d1	
  decreases.  !  8  2 Fig.	
  5.	
  Plot	
  of	
   ∇ E 	
  as	
  a	
  funcLon	
  of	
  electrode	
  spacing	
  d1  According	
  to	
  the	
  data,	
  the	
  gradient	
  strength	
  increased	
    	
  Lmes,	
  as	
  d1	
  is	
  decreased	
  to	
  a 	
  fourth	
   2 of	
  its	
  original	
  value.	
  	
  The	
  eventual	
  best	
  result	
  obtained	
  is	
   d1 = 7 µ m giving	
   ∇ E = 3.77 × 1011 .	
    	
    The	
  absolute 	
  potenLal 	
  difference	
  is 	
  at	
   500	
  V,	
  in	
  DC	
  sesng.	
   	
  The 	
  secondary	
  parameters	
    are	
  then	
  tested,	
  and	
  they	
  demonstrated	
  lifle	
  contribuLon	
  to	
  the	
  gradient	
  strength.	
  Due	
  to	
  fab-­‐ ricaLon	
  limitaLons,	
   these	
  parameters 	
  are 	
  given	
  rather	
  modest	
  values,	
  which	
  will	
  be 	
  elaborated	
   upon	
  in	
  the	
  next	
  secLon	
  of	
  this	
  report.  !  9  2.4 Sorter Chip Design 	
    The	
  chip	
  design	
  is 	
  inherited	
  from	
  the 	
  AutoCAD	
  file	
  drawn	
  by	
  the 	
  previous 	
  group.	
  The	
  de-­‐  sign	
  demonstrated	
  a 	
  close	
  resemblance 	
  to	
  the 	
  original 	
  design	
  by	
  AgresL	
  et	
  al.	
  However,	
  criLcal	
   changes 	
  are 	
  applied	
  according	
   to	
  the 	
  COMSOL	
  model 	
  to	
  maintain	
  consistency.	
   	
  The 	
  AutoCAD	
   file	
  can	
  be	
  found	
  on	
  the	
  USB	
  sLck	
  included	
  with	
  this	
  report.  2.4.1 List of Modifications 1. Channels	
  for	
  the	
  electrodes	
  are	
  added 2. Inlets 	
  and	
  outlets	
  are	
  added	
  to	
  allow	
  the	
  liquid	
  form	
  of	
  the	
  metal 	
  alloy	
  to	
  flow	
  into	
  the	
   channels	
  and	
  solidify 3. Replaced	
  the	
  second	
  design	
  with	
  the	
  current	
  design	
  to	
  have 	
  in	
  total	
  8	
  similar	
   chips 	
  on	
  a	
   single	
  wafer  2.4.2 Design Description 	
    One	
  silicone 	
  wafer	
   is 	
  able	
  to	
   hold	
  designs	
  for	
  eight	
   PDMS	
  chips.	
   Four	
   different	
  designs	
    are	
  used,	
  resulLng	
  in	
  two	
  chips 	
  per	
   design.	
   	
   Therefore,	
  some 	
  less	
  opLmal 	
  designs 	
  are	
  included	
   in	
  the 	
  intenLon	
  of	
  result	
  comparison.	
  The	
  core	
  design,	
  inherited	
  from	
  the	
  COMSOL	
  model 	
  plus	
   three	
  other	
  variaLons	
  make 	
  up	
   the	
  four	
   designs.	
   Due 	
  to	
  fabricaLon	
  limitaLons,	
  the 	
  parameter	
   d1	
  as	
  described	
  in	
  SecLon	
  3,	
  has	
  been	
  increased	
  to	
   10 µ m .  !  10  Fig.	
  5.	
  AutoCAD	
  drawing	
  of	
  droplet	
  sorter	
  chips. Table	
  1:	
  Droplet	
  Sorter	
  Design	
  SpecificaLons Design 1 2 3 4  d1 (μm) 10 10 20 10  !  11  d2 (μm) 72 142 72 110  	
    As 	
  stated	
  in	
  the 	
  Table	
  3.01,	
   d1	
  in	
  the	
  third	
  design	
  is 	
  twice 	
  the	
  magnitude	
  of	
  the 	
  others.	
  It	
    is 	
  to	
  confirm	
  the	
  results 	
  predicted	
  by	
  computer	
  modeling	
  discussed	
  in	
  SecLon	
  4.	
  The	
  fourth	
  de-­‐ sign	
  is 	
  rather	
  unconvenLonal.	
  It	
   is 	
  suspected	
  that	
  the 	
  electrode	
  with	
  a 	
  sharp	
  end	
  may	
  produce	
  a	
   more	
  powerful	
  electric	
   field.	
  This	
  idea 	
  is	
  then	
  implemented	
  in	
   the	
   AutoCAD	
  design	
  for	
  tesLng	
   purposes.  Fig.	
  6.	
  Flat	
  (top)	
  and	
  sharp	
  (bofom)	
  electrode	
  designs.  !  12  2.5 Sorter Chip Fabrication 2.5.1 Fabrication 	
    FabricaLon	
   was 	
  performed	
   with	
   the 	
  microfabricaLon	
  faciliLes 	
  in	
   the	
   NCE	
   cleanroom,	
    UBC.	
  The	
  process	
  took	
  in	
  total	
  4	
  days.	
  Detailed	
  protocols	
  can	
  be	
  found	
  in	
  Appendix	
  A.  2.5.2 Results 	
    Two	
   wafers	
  were	
  fabricated	
  and	
  the 	
  specificaLons	
  listed	
   in	
  Table	
  4.01.	
   	
   VariaLons 	
  in	
    channel 	
  height	
  occurred	
  due	
   to	
  slight	
   differences 	
  in	
  UV	
   exposure	
  Lme 	
  and	
  fabricaLon	
  errors	
   (missing	
  UV	
  filter,	
  etc.). Table	
  2:	
  Photoresist	
  specificaLons Wafer 1 Output Channel Oil Channel Electrode  Height (μm) 130 40 40  Width (μm) 180 30 30  Wafer 2 Output Channel Oil Channel Electrode  Height (μm) 142 50 50  Width (μm) 185 30 30  !  13  2.6 Electrode Fabrication 	
    The	
  previous	
  group	
  fabricated	
  electrodes	
  with	
  etched	
  chrome	
  placed	
  below	
  the	
  PDMS	
    sorter	
  chip,	
  contrary	
  to	
  what	
  was	
  done	
  in	
  the	
  AgresL	
  paper,	
  where	
  channels	
  were	
  formed	
   alongside	
  that	
  of	
  the	
  sorter	
  and	
  filled	
  with	
  a	
  low-­‐melLng	
  point	
  solder.	
  	
  We	
  opted	
  to	
  follow	
  the	
   method	
  in	
  the	
  AgresL	
  paper,	
  adding	
  channels	
  to	
  the	
  previous	
  sorter	
  chip	
  design. 	
    Several	
  low-­‐melLng-­‐point	
  alloys	
  were	
  considered,	
  but	
  due	
  to	
  price,	
  eutecLc	
  Gallium	
  In-­‐  dium	
  was	
  chosen.	
  	
  As	
  it	
  is	
  liquid	
  at	
  room	
  temperature,	
  it	
  can	
  be	
  injected	
  into	
  the	
  channel	
  inlets	
   with	
  a	
  syringe.	
  	
  Quotes	
  from	
  Indium	
  and	
  AIM	
  Solder	
  can	
  be	
  found	
  in	
  Appendix	
  D.  2.6.1 Procedure 	
    The	
  liquid	
  GaIn	
  is	
  withdrawn	
  into	
  a	
  1mL	
  syringe	
  and	
  injected	
  into	
  the	
  one	
  of	
  the	
  elec-­‐  trode	
  channel	
  inlets.  !  14  2.6.2 Results  Fig.	
  7	
  Electrode	
  channels	
  following	
  injecLon	
  of	
  GaIn 	
    GaIn	
  seemed	
  to	
  flow	
  well	
  through	
  the	
  PDMS	
  channels,	
  requiring	
  only	
  minimal	
  back	
    pressure	
  applied	
  to	
  the	
  syringe.	
  	
  It	
  adheres	
  well	
  to	
  the	
  channel	
  walls	
  and	
  fills	
  the	
  channel	
  com-­‐ pletely	
  with	
  no	
  problems	
  at	
  corners	
  or	
  air	
  bubbles	
  without	
  any	
  need	
  of	
  priming.	
  	
   	
    However,	
  due	
  to	
  high	
  surface	
  tension	
  forces,	
  upon	
  removal	
  of	
  syringe	
  from	
  electrode	
    channel	
  inlet	
  a	
  large	
  amount	
  of	
  GaIn	
  will	
  spill	
  out.	
  	
  As	
  it	
  does	
  not	
  spread	
  out	
  over	
  a	
  surface	
  at	
   room	
  temperature,	
  the	
  majority	
  can	
  be	
  withdrawn	
  back	
  into	
  the	
  syringe	
  and	
  the	
  residue	
  can	
  be	
   cleaned	
  off	
  by	
  water	
  or	
  HFE-­‐7500	
  oil,	
  but	
  it	
  cannot	
  be	
  removed	
  completely.	
  	
  	
    !  15  2.7 Electrode Characterization 	
    Electrodes	
  were	
  tested	
  to	
  determine	
  their	
  ability	
  to	
  conduct	
  an	
  AC	
  signal	
  by	
  determining	
    the	
  RC	
  Lme	
  constant.	
  This	
  Lme	
  constant	
  was	
  assumed	
  to	
  be	
  independent	
  of	
  the	
  voltage	
  applied	
   (resistance	
  and	
  capacitance	
  being	
  properLes	
  of	
  the	
  material).	
  	
    2.7.1 Procedure  pro  be  Fig.	
  8.	
  Diagram	
  of	
  setup	
  for	
  electrode	
  characterizaLon. 1. A	
  0-­‐6V	
  square	
  wave	
  was	
  applied	
  with	
  the	
  NI	
  DAQ	
  card	
  to	
  the	
  signal	
  electrode	
  inlet	
  and	
   the	
  output	
  signal	
  measured	
  at	
  the	
  signal	
  electrode	
  outlet.	
  	
   2. Square	
  waves	
  at	
  200Hz,	
  20kHz	
  and	
  1MHz	
  were	
  applied	
  to	
  the	
  electrode	
  inlet	
  and	
  the	
   Lme	
  constant	
  was	
  measured	
  using	
  the	
  OSCILLOSCOPE	
  to	
  be	
  the	
  Lme	
  taken	
  for	
  the	
  volt-­‐  1 age	
  at	
  the	
  electrode	
  outlet	
  to	
  reach	
   of	
  its	
  original	
  value	
  at	
  the	
  falling	
  edge. e  !  16  2.7.2 Results  Fig	
  9.	
  Electrode	
  voltage	
  (yellow)	
  when	
  a	
  0-­‐5V	
  square	
  wave	
  (200Hz,	
  20kHz,	
  1MHz	
  lel	
  to	
  right)	
  is	
   applied	
  (blue) 	
    The	
  Lme	
  constant	
  at	
  the	
  signal	
  electrode	
  was	
  measured	
  to	
  be	
  30ns	
  at	
  each	
  applied	
  fre-­‐  quency,	
  while	
  that	
  of	
  the	
  applied	
  TTL	
  signal	
  was	
  25ns.	
  	
  The	
  electrode	
  signal	
  closely	
  follows	
  the	
   applied	
  voltage	
  waveform,	
  suggesLng	
  that	
  maximum	
  switching	
  frequency	
  across	
  the	
  electrodes 	
   is	
  limited	
  by	
  the	
  applied	
  signal,	
  not	
  necessarily	
  by	
  the	
  electrode’s	
  capacitance.	
  	
   	
    This	
  suggests	
  a	
  maximum	
  frequency	
  of	
  at	
  least	
  33MHz,	
  well	
  above	
  that	
  of	
  the	
  desired	
    20kHz.	
  	
  The	
  maximum	
  should	
  theoreLcally	
  be	
  even	
  higher,	
  since	
  the	
  electrode	
  Lme	
  constant	
   seemed	
  to	
  be	
  dependent	
  on	
  the	
  signal	
  Lme	
  constant.  !  17  2.8 Switch Characterization The	
  switch	
  was	
  characterized	
  to	
  determine	
  performance	
  with	
  our	
  system.	
  	
    2.8.1 Procedure  pro  be  0V-5V TTL Signal  Fuse HV Switch  HV Supply  + =  Fig.	
  10.	
  SchemaLc	
  for	
  connecLng	
  HV	
  supply	
  to	
  electrodes 1. A	
  10V	
  signal	
  (from	
  HV	
  source)	
  was	
  applied	
  to	
  the	
  electrodes	
  at	
  400Hz,	
  1kHz,	
  20kHz	
  and	
  the	
   switch	
  output	
  measured	
  on	
  the	
  scope. 2. A	
  75V	
  AC	
  signal	
  was	
  applied	
  to	
  the	
  electrodes	
  at	
  800Hz,	
  1kHz	
  and	
  20kHz	
  and	
  the	
  switch	
  out-­‐ put	
  measured. 3. 50V,	
  100V,	
  200V	
  and	
  300V	
  were	
  applied	
  to	
  the	
  switch	
  and	
  the	
  output	
  measured	
  with	
  a	
  high-­‐ voltage	
  probe	
  (which	
  reduces	
  a	
  voltage	
  by	
  1220x	
  to	
  be	
  readable	
  on	
  the	
  scope).	
  	
  Due	
  to	
  some	
   yet	
  unknown	
  reason,	
  the	
  high-­‐voltage	
  probe	
  was	
  only	
  able	
  to	
  make	
  measurements	
  when	
  a	
   regular	
  scope	
  probe	
  was	
  also	
  afached	
  to	
  the	
  switch	
  output,	
  therefore	
  only	
  voltages	
  up	
  to	
   300V	
  (maximum	
  raLng	
  for	
  the	
  regular	
  probe)	
  were	
  able	
  to	
  be	
  tested. !  18  2.8.2 Results  Fig.	
  11.	
  Switch	
  output	
  (blue)	
  with	
  10V	
  signal	
  applied	
  at	
  input	
  (yellow)	
  at	
  400Hz,	
  1kHz	
  and	
  20kHz	
   lel	
  to	
  right 	
    Output	
  signal	
  exhibits	
  a	
  long	
  fall	
  Lme,	
  which	
  results	
  in	
  the	
  signal	
  being	
  clipped	
  starLng	
    at	
  around	
  500Hz.	
  	
  At	
  20kHz	
  the	
  voltage	
  is	
  similar	
  to	
  that	
  of	
  a	
  DC	
  voltage	
  signal.  Fig.	
  12.	
  Switch	
  output	
  (blue)	
  with	
  75V	
  signal	
  applied	
  at	
  input	
  (yellow)	
  at	
  1kHz	
  and	
  20kHz	
  lel	
  to	
   right  !  19  Fig.	
  13.	
  Switch	
  output	
  measured	
  by	
  high-­‐voltage	
  probe	
  (purple)	
  and	
  regular	
  oscilloscope	
  probe	
   (blue)	
  when	
  300V	
  signal	
  is	
  applied	
  at	
  450Hz	
  and	
  20kHz 	
    The	
  output	
  when	
  75V	
  and	
  300V	
  is	
  applied	
  exhibits	
  a	
  similar	
  behavior	
  to	
  that	
  of	
  10V,	
  with	
    the	
  falling	
  edge	
  clipping	
  upwards	
  unLl	
  it	
  is	
  similar	
  to	
  a	
  DC	
  signal	
  at	
  20kHz.	
  	
  The	
  switch	
  can	
  there-­‐ fore	
  be	
  operated	
  in	
  AC	
  up	
  to	
  1kHz	
  before	
  clipping	
  becomes	
  a	
  large	
  factor	
  and	
  operaLng	
  the	
   switch	
  at	
  20kHz	
  can	
  let	
  us	
  mimic	
  a	
  DC	
  signal.  !  20  2.9 Droplet Actuation 	
    Droplets	
  were	
  formed	
  using	
  the	
  exisLng	
  implementaLon	
  (Fig.	
  2);	
  a	
  PDMS	
  device	
  con-­‐  nected	
  to	
  input	
  syringe	
  pumps	
  coflows	
  HFE-­‐7500	
  oil	
  with	
  3%	
  w/w	
  PFPE-­‐PEG	
  block	
  copolymer	
   surfactant	
  (to	
  prevent	
  droplet	
  coalescence)	
  to	
  disperse	
  the	
  aqueous	
  droplets	
  at	
  the	
  flow-­‐ focusing	
  juncLon	
  (inset).	
  	
  These	
  droplets	
  were	
  then	
  collected	
  in	
  a	
  microcentrifuge	
  tube	
  from	
   the	
  output	
  port	
  and	
  re-­‐injected	
  into	
  the	
  sorLng	
  device	
  (Mulholland	
  et	
  al.,	
  2011).  Fig.	
  14.	
  Droplet	
  generaLng	
  device	
  generated	
  by	
  previous	
  APSC	
  459	
  group	
  (Mulholland	
  et	
  al.,	
   2011). The	
  sharp	
  and	
  flat	
  electrode	
  designs	
  were	
  tested	
  at	
  a	
  range	
  of	
  voltages	
  and	
  applied	
  frequencies,	
   with	
  actuaLon	
  detected	
  t	
  30	
  fps	
  by	
  the	
  CCD	
  camera	
  setup	
  developed	
  by	
  the	
  previous	
  459	
   group.	
  	
  The	
  high-­‐voltage	
  source	
  is	
  connected	
  to	
  the	
  switch	
  via	
  a	
  high-­‐voltage	
  connector	
  and	
  the	
   switch	
  is	
  driven	
  by	
  a	
  0-­‐5V	
  TTL	
  signal	
  from	
  the	
  NI	
  DAQ	
  board.	
  	
  The	
  switch	
  output	
  is	
  connected	
  to	
   the	
  signal	
  electrode	
  through	
  a	
  200mA	
  fuse	
  and	
  the	
  ground	
  electrode	
  is	
  connected	
  to	
  ground.	
  	
    !  21  2.9.1 Procedure 1. 30um	
  droplets	
  were	
  formed	
  using	
  20-­‐67-­‐31	
  (D1-­‐D2-­‐Height)	
  droplet	
  generator	
  chip	
  flowing	
   HFE-­‐7500	
  with	
  3%	
  w/w	
  RainDance	
  surfactant	
  at	
  250uL/hr	
  and	
  deionized	
  water	
  at	
  25uL/hr. 2. Droplets	
  were	
  withdrawn	
  into	
  a	
  1mL	
  syringe	
  and	
  re-­‐injected	
  into	
  the	
  sorter	
  chip	
  with	
  sharp	
   electrode	
  design	
  at	
  10uL/hr	
  with	
  an	
  accompanying	
  oil	
  flow	
  rate	
  of	
  100uL/hr. 3. A	
  HV	
  AC	
  signal	
  was	
  applied	
  to	
  electrodes	
  via	
  switch	
  at	
  500V,	
  1000V,	
  2000V,	
  2500V	
  with	
  fre-­‐ quencies	
  500Hz,	
  1kHz,	
  20kHz.	
  	
   An	
  SOP	
  for	
  generaLng	
  droplets	
  used	
  with	
  this	
  test	
  can	
  be	
  found	
  in	
  Appendix	
  B.  2.9.2 Results  Fig.	
  15.	
  Demonstrated	
  droplet	
  redirecLon	
  with	
  1000V/20kHz	
  applied	
  signal	
  (lel)	
  and	
  when	
  sig-­‐ nal	
  was	
  turned	
  off	
  (right)	
  -­‐	
  1000V-­‐20kHz.avi 	
    Droplet	
  redirecLon	
  was	
  not	
  able	
  to	
  be	
  demonstrated	
  with	
  the	
  flat	
  electrode	
  designs	
  but	
    it	
  was	
  demonstrated	
  with	
  the	
  sharp	
  electrode	
  design	
  (see	
  data	
  files	
  in	
  USB	
  key	
  included	
  with	
   report).	
  	
  Due	
  to	
  the	
  frame	
  rate	
  of	
  the	
  camera	
  (30	
  fps),	
  we	
  could	
  not	
  ascertain	
  the	
  rate	
  of	
  drop-­‐ let	
  actuaLon.	
  	
  Slowing	
  down	
  the	
  video,	
  the	
  droplet	
  flow	
  rate	
  is	
  esLmated	
  to	
  be	
  on	
  the	
  order	
  of	
   at	
  least	
  100Hz.	
  	
  Not	
  all	
  droplets	
  were	
  observed	
  to	
  flow	
  uniformly	
  into	
  one	
  channel,	
    !  22  	
    There	
  was	
  no	
  noLceable	
  difference	
  in	
  performance	
  of	
  droplet	
  redirecLon	
  when	
  the	
  ap-­‐  plied	
  signal	
  operated	
  at	
  500Hz,	
  1kHz	
  or	
  20kHz.	
  	
  Here	
  20kHz	
  is	
  assumed	
  to	
  be	
  similar	
  to	
  a	
  DC	
   voltage,	
  since	
  the	
  output	
  signal	
  has	
  been	
  significantly	
  clipped	
  high.	
  	
  To	
  determine	
  the	
  effect	
  of	
  a 	
   higher	
  frequency	
  AC	
  signal	
  (20kHz),	
  a	
  more	
  suitable	
  switch	
  is	
  required. 	
    With	
  polydispersity	
  in	
  the	
  re-­‐injected	
  droplets,	
  when	
  500V	
  was	
  applied	
  the	
  chip	
  was	
    able	
  to	
  sort	
  smaller	
  droplets	
  (30um	
  diameter)	
  while	
  not	
  drawing	
  in	
  larger	
  droplets	
  (45um	
  di-­‐ ameter).	
  	
  	
  	
  This	
  suggests	
  an	
  applicaLon	
  where	
  a	
  conLnuously	
  applied	
  voltage	
  could	
  act	
  as	
  a	
  filter	
   to	
  sort	
  droplets	
  based	
  on	
  size. 	
    Videos	
  of	
  all	
  cases	
  tested	
  can	
  be	
  found	
  on	
  the	
  USB	
  sLck	
  included	
  with	
  this	
  report.  !  23  2.0 Conclusions 	
    This	
  project	
  sought	
  to	
  add	
  droplet	
  redirecLon	
  to	
  a	
  microfluidic	
  sorter	
  chip	
  developed	
  by	
    a	
  previous	
  APSC	
  459	
  group.	
  	
  An	
  technique	
  for	
  fabricaLng	
  electrodes	
  was	
  determined,	
  adding	
   addiLonal	
  microfluidic	
  channels	
  upstream	
  of	
  a	
  juncLon	
  leading	
  to	
  the	
  collecLon	
  channels	
  and	
   filling	
  them	
  with	
  low-­‐melLng-­‐point	
  alloy.	
  	
  Electrode	
  designs	
  were	
  modeled	
  in	
  COMSOL	
  and	
  the	
   previous	
  group’s	
  sorter	
  chip	
  redesigned	
  accordingly	
  to	
  include	
  the	
  most	
  effecLve	
  designs.	
  	
   	
    A	
  high-­‐voltage	
  switch	
  was	
  obtained	
  from	
  the	
  PHAS	
  E-­‐LAB,	
  though	
  it	
  can	
  only	
  switch	
  high	
    voltages	
  at	
  a	
  maximum	
  of	
  1kHz,	
  much	
  less	
  than	
  the	
  desired	
  frequency	
  of	
  20kHz.	
  	
  A	
  few	
  meth-­‐ ods	
  of	
  increasing	
  this	
  switching	
  frequency	
  were	
  suggested	
  by	
  the	
  PHAS	
  E-­‐LAB	
  and	
  included	
  in	
   the	
  recommendaLons.	
   	
    Droplet	
  actuaLon	
  was	
  demonstrated	
  on	
  the	
  order	
  of	
  100Hz	
  with	
  an	
  applied	
  voltage	
  sig-­‐  nal	
  between	
  500V	
  -­‐	
  2500V	
  AC	
  with	
  a	
  frequency	
  range	
  of	
  0-­‐1kHz.	
   	
    In	
  order	
  to	
  afain	
  fluorescence-­‐based	
  droplet	
  sorLng	
  at	
  appreciable	
  speeds	
  (1-­‐2kHz),	
    more	
  work	
  is	
  required	
  in	
  the	
  following	
  areas: 1. ActuaLon	
  needs	
  to	
  be	
  coupled	
  to	
  the	
  first	
  APSC	
  459	
  group’s	
  droplet	
  detecLon	
  system.	
  	
   The	
  LabVIEW	
  scripts	
  would	
  need	
  to	
  be	
  modified	
  and	
  extended	
  to	
  drive	
  the	
  HV	
  switch. 2. A	
  new	
  HV	
  switch	
  which	
  could	
  operate	
  in	
  the	
  20kHz	
  range	
  would	
  need	
  to	
  be	
  sourced	
  or	
   the	
  current	
  switching	
  setup	
  improved.	
  	
  The	
  effect	
  of	
  a	
  high-­‐frequency	
  high-­‐voltage	
  sig-­‐ nal	
  would	
  then	
  need	
  to	
  be	
  tested. 3. Droplet	
  generator-­‐sorter	
  coupling	
  would	
  need	
  to	
  be	
  improved	
  to	
  increase	
  control	
  over	
   droplet	
  speed	
  in	
  the	
  sorter	
  chip.  !  24  3.0 Project Deliverables 3.1 List of Deliverables Deliverable  Medium  Details Finite-­‐element	
  analysis	
  of	
  different	
  electrode	
    COMSOL	
  Models Droplet	
  ActuaLon Microfluidic	
  design Microfluidic	
  chips  Electronic Electronic Electronic Physical  designs Videos	
  of	
  droplet	
  actuaLon	
  (video)	
   AutoCAD	
  file	
  with	
  modified	
  chip	
  design Microfluidics	
  chips	
  with	
  electrode	
  channels  Photolithographic	
  masks  Physical  Mask	
  fabricated	
  during	
  project  Photoresist	
  molds  Physical  Molds	
  fabricated	
  during	
  project Was	
  borrowed	
  from	
  Pavel,	
  but	
  he	
  can	
  help	
    HV	
  switch Log	
  Books RecommendaLon	
  Report  Physical construct	
  copies Paper Records	
  of	
  meeLngs,	
  rough	
  work Paper/Electronic Submifed	
  aler	
  project	
  is	
  finished.  PresentaLon  In	
  Person  Given	
  aler	
  project	
  is	
  finished.  3.2 Financial Summary  #  DescripLon  Quan-­‐ Lty  Vendor  Cost	
  ($	
   CAD)  1  EutecLc	
  Gallium	
  In-­‐ dium  1  Sigma-­‐Aldrich 80.30  SKU-­‐pack	
  size: 495425-­‐5G Total 80.30  !  25  Purchased	
   by  To	
  be	
   funded	
  by  Hansen	
   Lab  Hansen	
   Lab  4.0 Recommendations 4.1 Electrode Fabrication 	
    Currently	
  electrodes	
  are	
  fabricated	
  by	
  injecLng	
  eutecLc	
  Gallium-­‐Indium	
  (melLng	
  point	
    15.7	
  oC)	
  into	
  the	
  electrode	
  channels.	
  	
  This	
  is	
  done	
  easily	
  with	
  a	
  1mL	
  syringe,	
  but	
  there	
  are	
  sev-­‐ eral	
  drawbacks: 1. GaIn	
  is	
  toxic	
  and	
  can	
  cause	
  severe	
  skin	
  burns,	
  making	
  fabricated	
  electrodes	
  more	
  diffi-­‐ cult	
  to	
  handle.	
  	
  It	
  is	
  also	
  difficult	
  to	
  clean	
  off	
  surfaces. 2. GaIn	
  is	
  difficult	
  to	
  inject	
  –	
  flowing	
  the	
  GaIn	
  through	
  30um-­‐wide	
  channels	
  requires	
  a	
  large	
   enough	
  back	
  pressure	
  such	
  that	
  removal	
  of	
  the	
  syringe	
  from	
  the	
  channel	
  inlet	
  will	
  re-­‐ lease	
  a	
  large	
  amount	
  of	
  GaIn	
  from	
  the	
  syringe.	
  	
  Not	
  only	
  a	
  waste	
  of	
  material,	
  even	
  when	
   cleaned	
  off	
  the	
  PDMS	
  remains	
  slightly	
  opaque,	
  reducing	
  image	
  quality	
  with	
  the	
  opLcal	
   system. 3. The	
  HV	
  and	
  ground	
  voltages	
  are	
  connected	
  to	
  the	
  electrode	
  channel	
  by	
  directly	
  inserLng	
   a	
  header	
  pin	
  into	
  an	
  electrode	
  channel,	
  which	
  causes	
  the	
  GaIn	
  near	
  the	
  oil	
  channel	
  to	
   shil	
  and	
  pull	
  away	
  if	
  the	
  pins	
  are	
  inserted/removed.	
  	
  This	
  affects	
  the	
  uniformity	
  of	
  the	
   electric	
  field	
  generated. 4. GaIn	
  will	
  expand	
  and	
  contract	
  readily	
  with	
  changes	
  in	
  temperature.	
  	
  Bringing	
  the	
  chip	
   into	
  an	
  environment	
  warmer	
  than	
  that	
  in	
  which	
  it	
  was	
  made	
  will	
  cause	
  the	
  GaIn	
  to	
  spill	
   out	
  of	
  the	
  electrode	
  channel	
  outlets	
  as	
  well	
  as	
  pull	
  away	
  from	
  the	
  walls.	
  	
  If	
  the	
  header	
   pins	
  have	
  been	
  afached	
  to	
  the	
  chip	
  via	
  an	
  adhesive,	
  this	
  expansion	
  will	
  cause	
  the	
  adhe-­‐ sive	
  to	
  lil	
  from	
  the	
  chip. 	
    Use	
  of	
  a	
  low-­‐melLng	
  point	
  alloy	
  whose	
  melLng	
  point	
  is	
  above	
  room	
  temperature	
  (60-­‐  70oC)	
  could	
  easily	
  address	
  all	
  these	
  concerns.	
  	
  Of	
  the	
  alloys	
  invesLgated,	
  Wood’s	
  alloy	
  seems	
  to	
   be	
  the	
  most	
  feasible	
  in	
  terms	
  of	
  cost	
  ($92.22	
  from	
  City	
  Chemical	
  LLC	
  as	
  opposed	
  to	
  $355	
  for	
  In-­‐ dalloy	
  19	
  from	
  Indium	
  for	
  the	
  minimum	
  order).	
  	
  This	
  project	
  would	
  only	
  require	
  a	
  minimal	
   amount	
  and	
  the	
  PHAS	
  E-­‐LAB	
  has	
  agreed	
  to	
  purchase	
  any	
  excess	
  Wood’s	
  Alloy.	
  	
   !  26  4.2 Droplet Re-injection 	
    Droplet	
  re-­‐injecLon	
  into	
  the	
  sorter	
  chip	
  is	
  difficult	
  and	
  erraLc	
  using	
  syringe	
  pumps.	
  	
  Sev-­‐  eral	
  concerns	
  came	
  up: 1. Droplets	
  must	
  be	
  withdrawn	
  from	
  an	
  external	
  container	
  using	
  a	
  syringe.	
  	
  This	
  causes	
  some	
   droplets	
  to	
  be	
  lel	
  as	
  residue	
  in	
  the	
  container	
  as	
  well	
  as	
  risks	
  having	
  some	
  droplets	
  coalesce	
   when	
  drawn	
  through	
  the	
  syringe	
  Lp. 2. Back	
  pressure	
  during	
  re-­‐injecLon	
  is	
  difficult	
  to	
  control,	
  complicated	
  by	
  relaLvely	
  long	
  tubing	
   between	
  the	
  syringe	
  pump	
  and	
  the	
  chip	
  with	
  changes	
  in	
  height.	
  	
  Olen	
  Lmes	
  it	
  was	
  necessary	
   to	
  apply	
  a	
  large	
  back	
  pressure	
  then	
  switch	
  it	
  off	
  and	
  have	
  the	
  residual	
  pressure	
  drive	
  the	
   droplets	
  in	
  order	
   3. Droplets,	
  being	
  less	
  dense	
  than	
  the	
  HFE-­‐7500	
  oil	
  environment	
  are	
  posiLvely	
  buoyant	
  and	
  will	
   clump	
  at	
  the	
  highest	
  point	
  in	
  a	
  loop	
  of	
  tubing.	
  	
  This	
  requires	
  a	
  larger	
  back	
  pressure	
  to	
  drive	
   droplets	
  and	
  results	
  in	
  the	
  droplet	
  injecLon	
  speed	
  being	
  someLmes	
  unpredictable. 	
    The	
  system	
  in	
  the	
  AgresL	
  paper	
  has	
  both	
  droplet	
  generator	
  and	
  sorter	
  on	
  the	
  same	
  chip;	
    droplets	
  are	
  formed	
  and	
  flow	
  through	
  a	
  stretch	
  of	
  polyetheretherketone	
  tubing	
  directly	
  to	
  the	
   sorter.	
  	
  Having	
  an	
  integrated	
  generator/sorter	
  chip	
  would	
  address	
  some	
  of	
  the	
  issues	
  surround-­‐ ing	
  re-­‐injecLon.  !  27  4.3 HV switching 	
    Currently,	
  the	
  maximum	
  operaLng	
  frequency	
  of	
  the	
  switch	
  provided	
  by	
  the	
  PHAS	
  E-­‐LAB	
    is	
  approximately	
  1kHz	
  at	
  best,	
  due	
  to	
  the	
  large	
  Lme	
  constant	
  of	
  the	
  signal	
  output.	
  	
  In	
  order	
  to	
   properly	
  test	
  dielectrophoresis	
  with	
  a	
  HV	
  AC	
  signal	
  (on	
  the	
  order	
  of	
  20kHz	
  or	
  greater),	
  an	
  alter-­‐ naLve	
  switching	
  method	
  is	
  required.	
  	
  Pavel	
  Trochtchanovitch	
  from	
  the	
  PHAS	
  E-­‐LAB	
  has	
  several	
   alternaLves	
  which	
  could	
  be	
  explored: 1. Using	
  a	
  second	
  switch	
  to	
  sink	
  current	
  from	
  the	
  signal	
  electrode	
  as	
  soon	
  as	
  the	
  first	
   switch	
  is	
  turned	
  off.	
  	
  This	
  would	
  involve	
  an	
  addiLonal	
  interface	
  circuit	
  which	
  prevents	
   the	
  two	
  switches	
  from	
  being	
  turned	
  on	
  at	
  the	
  same	
  Lme,	
  with	
  some	
  tunable	
  “dead-­‐ Lme”	
  between	
  when	
  the	
  operaLon	
  of	
  the	
  switches.	
  	
  Of	
  course,	
  this	
  dead-­‐Lme	
  will	
  be	
  a	
   limiLng	
  factor	
  on	
  the	
  maximum	
  operaLng	
  frequency	
  of	
  the	
  dual-­‐switch	
  setup. 2. Building	
  a	
  switching	
  circuit	
  from	
  gate	
  drivers	
  instead	
  of	
  opto-­‐isolaters.	
  	
  This	
  design	
   would	
  be	
  limited	
  to	
  ±	
  600V,	
  so	
  a	
  bipolar	
  HV	
  source	
  would	
  be	
  required.  !  28  5.0 Appendices Appendix A: Fabrication Protocols A.1 Wafer Fabrication Procedure 1. Clean the surface of the silicone wafer a. Pour IPA solution onto both sides of the silicone wafer b. Use nitrogen gas to dry the wafer 2. Pour photoresist onto the wafer 3. Set wafer on the spin-machine a. Turn on the vacuum and ensure the wafer is secured b. Set up the protocol 4. Start the spin-machine and wait 5. Bake the wafer in the oven 6. Ultraviolet exposure a. Attach the mask on a glass slide b. Place wafer in the frame c. Line up the wafer with the mask using the microscope 7. Expose the wafer in ultraviolet 8. Develop the wafer a. Pour the developer in a container b. Place the wafer in the liquid and rinse c. In a separate container, rinse the wafer again with the same developer 9. Bake the wafer in the oven 10. Examine the wafer under a microscope to make sure no unwanted dust particles are present 11. Measure the height of the oil channel  !  29  A.2 Wafer Fabrication Protocols Name: Date: Photoresist: Previous layers: Spin speed and time  Adam Q / Luke 07-Feb-12 SU-8 3050 Lot# 11040263 Expiriry 5/1/2012 Should have done IPA coating before resist 500rpm spread cycle for 10s, 3250 rpm for  Pre-bake (time and temperature) Exposure time: Post-bake time: Developer: Development time: Solvent to wash off developer: Hardbrake: Thickness (using alpha-step) Other notes:  30 seconds 95 C 15 min 9s w/ filter 1-5-1 65-95-65 SU8 Developer 2 min IPA Ramp to 120C, hold 10 mins, ramp down 37-40 (μm) Some of the electrodes are touched the oil channel. May be the result of underdeveloping  Name: Date: Photoresist: Previous layers: Spin speed and time Pre-bake (time and temperature) Exposure time: Post-bake time: Developer: Development time: Solvent to wash off developer: Hardbrake: Thickness (using alpha-step)  Adam Q / Luke / Sam 07-Feb-12 SU-8 100 (lot 11080530, exp 9/1/2012) Su8 3050 500 rpm for 30s, 1600 rpm for 50s 65 for 20 min, 95 for 50 min, 65 for 5 min 26 sec with filter n/a SU8 developer 8 min Ipa None n/a  !  30  Other notes:  Forgot to tape over alignment marks on previous layer so alignment was very difficult  Name: Date: Photoresist: Previous layers: Spin speed and time Pre-bake (time and temperature) Exposure time: Post-bake time: Developer: Development time: Solvent to wash off developer: Hardbrake: Thickness (using alpha-step) Other notes:  Adam Q / Luke / Sam 09-Feb-12 SU-8 100 (lot 11080530, exp 9/1/2012) SU8 3050, SU8 100 (removed) 500 rpm for 30s, 1600 rpm for 50s 65 for 20 min, 95 for 50 min, 65 for 5 min 26 sec with filter 65 for 2 min, 95 for 12 min, 65 for 2 min SU8 developer 8 min IPA None 130μm  !  31  A.3 PDMS Chip Fabrication 1. Use TCMS to remove moisture from silicone wafers under a fume hood 2. Make a foil dish for each wafer 3. Place each wafer in foil dish 4. Apply PDMS cleaning layer to remove any particles a. Mix PDMS using 10:1 ratio of RTV A:B with 20g A and 2g B per wafer b. Mix in centrifuge (1 minute mix plus 2 minute degas) c. Pour onto wafer 5. Bake at 80C for 25 minutes 6. Remove cleaning layer a. Cut along edge of water using a scalpel b. Peel off PDMS 7. Apply thicker PDMS layer a. Mix PDMS using 10:1 ratio of RTV A:B with 50g A and 5g B per wafer b. Mix in centrifuge (1 minute mix + 2 minute degas) c. Pour onto wafer 8. Place PDMS with wafers in a vacuum chamber for 1 hour a. Bubbles will form, so alternate at beginning between vacuum and atmospheric pressure to ensure PDMS will not bubble over sides of foil dish b. After bubbling subsides, wafers can be left in vacuum chamber for the remainder of the hour 9. Bake at 80C for 1 hour 10. Punch holes for channel inlets and outlets  !  32  Appendix B: SOP for generating droplets for use with 20-67-16 (D1D2-Height) droplet generator chip. 1. Flush	
  droplet	
  generator	
  with	
  disLlled	
  water. 2. Check	
  for	
  presence	
  of	
  debris;	
  if	
  present,	
  flush	
  again	
  with	
  water. 3. Set	
  up	
  syringe	
  pumps a. Withdraw	
  disLlled	
  water	
  and	
  HFE-­‐7500	
  oil	
  with	
  3%	
  w/w	
  Raindance	
  surfactant	
   into	
  1mL	
  syringe. b. Afach	
  tubing	
  long	
  enough	
  to	
  reach	
  generator	
  chip	
  to	
  end	
  of	
  syringes;	
  inject	
  liq-­‐ uid	
  to	
  Lps	
  of	
  tubing. c. Connect	
  tubing	
  to	
  appropriate	
  inlets. d. Set	
  syringe	
  diameter	
  (4.83mm	
  if	
  using	
  1mL	
  syringe). e. Set	
  flow	
  rate	
  to	
  25uL/hr	
  for	
  water,	
  250uL/hr	
  for	
  oil. 4. Turn	
  on	
  pump	
  for	
  water,	
  ensuring	
  that	
   5. Aler	
  5	
  min,	
  turn	
  on	
  pump	
  for	
  oil. 6. With	
  generator	
  outlet	
  open,	
  use	
  opLcal	
  setup	
  and	
  LabVIEW	
  program	
  to	
  ensure	
  that	
  cor-­‐ rectly	
  sized	
  droplets	
  are	
  being	
  outpufed. 7. Afach	
  a	
  short	
  piece	
  of	
  tubing	
  to	
  generator	
  outlet	
  and	
  redirect	
  droplets	
  into	
  a	
  micro-­‐ centrifuge	
  tube	
  (or	
  container	
  of	
  choice)	
  for	
  storage.  !  33  Appendix C: HV Switch design by the UBC PHAS E-LAB  !  34  	
    The	
  switch	
  transistors	
  Q1	
  and	
  Q2	
  are	
  driven	
  by	
  an	
  applied	
  TTL	
  signal	
  (0-­‐5V),	
  opLcally	
  iso-­‐  lated	
  with	
  U1.	
  	
  The	
  signal	
  is	
  propagated	
  through	
  to	
  the	
  3N400S	
  high-­‐voltage	
  MOSFET	
  whose	
   drain-­‐to-­‐source	
  voltage	
  is	
  rated	
  as	
  being	
  up	
  to	
  4kV.	
  	
  The	
  MOSFET	
  begins	
  to	
  conduct	
  when	
  the	
   gate-­‐to-­‐source	
  voltage	
  exceeds	
  2~4V,	
  resulLng	
  in	
  the	
  voltage	
  at	
  P5/P6	
  being	
  the	
  same	
  as	
  that	
  at	
   P1/P2.	
  	
  C2	
  has	
  been	
  removed	
  to	
  allow	
  for	
  faster	
  switching.  !  35  Appendix D: Electrode alloy quotes AIM Solder  Gmail - Low melting-point solder quote.  12-04-02 7:37 AM  Samuel Wu <samuelwu90@gmail.com>  Low melting-point solder quote. Gaby Melki <gmelki@aimsolder.com> To: Samuel Wu <samuelwu90@gmail.com> Cc: Claude Carreau <ccarreau@aimsolder.com>  Wed, Feb 29, 2012 at 11:28 AM  Hello, Following is the quote for the solder wire you requested: Alloy: 49Bi/21In/18Pb/12Sn Diam.: 0.030" Min qty: 10 feet Price: $45.90/ft Lead time : 10 working days or sooner FOB : Montreal Terms: COD Regards, Gaby Melki Customer Service Manager AIM Metals & Alloys L.P. Tel : 514- 494-5502 * 800-361-0783 Fax: 514- 494-6133 * 800-363-7754 gmelki@aimsolder.com www.aimsolder.com “Solder Plus Support” From: Samuel Wu [mailto:samuelwu90@gmail.com] Sent: Wednesday, February 29, 2012 12:56 PM To: Gaby Melki Subject: Low melting-point solder quote. [Quoted text hidden]  https://mail.google.com/mail/u/0/?ui=2&ik=288eee50d0&view=pt&q=solder&qs=true&search=query&msg=135ca9579228772c  !  36  Page 1 of 1  Indium  QUOTATION Page: ICA Contact: Customer RFQ #: Quote Date: Expiration Date: Terms: Delivery Terms:  Customer: 9027944 Samuel W. University of British Columbia Dept. of Physics AMPEL, Room 245 2355 East Mall Vancouver BRC V6T 1Z4 Canada Phone: 604-961-1530  1 ble  02/23/12 03/02/12 Prepay (c/card Free car Utica, NY Customer Currency: US$ US Dollar ICA Territory: BritColm ICA Estimate: E016093  ________________________________________________________________________________ Item / Description  Quantity  Ind#19 Solder Wire  UM  Unit Price  28.000  .030" dia. wire  12.71000  Net Amount  355.88  GM  Min. order 28gm @ $12.71/gm lead time: estimated 12-15 working days after ARO single release  Sale Amount:  355.88  USA Tax: GST/VAT: Misc: Total Amount:  0.00 0.00 0.00 355.88  Please contact us immediately to discuss any issues with this correspondence. Thank you for your business.  ISO 9001 REGISTERED Y002-007.RVF 10 FEB 2011  !  37  6.0 References AgresL,	
  J.	
  J.,	
  AnLpov,	
  E.,	
  Abate,	
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  Ahn,	
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  Baret,	
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  Marquez,	
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  et	
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   (2010).	
  Ultrahigh-­‐throughput	
  screening	
  in	
  drop-­‐based	
  microfluidics	
  for	
  directed	
  evoluLon.	
   Proceedings	
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  107(9),	
   4004-­‐9.	
  NaLonal	
  Acad	
  Sciences.	
  doi:10.1073/pnas.0910781107 Ahn,	
  K.,	
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  Hunt,	
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  Westervelt,	
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  M.,	
  Link,	
  D.	
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  Weitz,	
  D.	
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  (2006).	
  Dielectro-­‐ phoreLc	
  manipulaLon	
  of	
  drops	
  for	
  high-­‐speed	
  microfluidic	
  sorLng	
  devices.	
  Applied	
  Physics	
   Le=ers,	
  88(2),	
  024104.	
  doi:10.1063/1.2164911 Behlke.	
  Fast	
  High	
  Voltage	
  Transistor	
  Switch:	
  61-­‐31-­‐GSM	
  -­‐	
  Datasheet.	
  Retrieved	
  April	
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  2012	
  	
   	
   from	
  Behlke	
  website:	
  hfp://www.behlke.de/pdf/61-­‐03-­‐gsm.pdf  Griffiths,	
  A.	
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  &	
  Tawfik,	
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  (2006).	
  Miniaturising	
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  Trends	
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  doi:10.1016/j.Lbtech.2006.06.009 Mulholland,	
  B.,	
  da	
  Costa,	
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  Ultrafast	
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