Designed a chip that separates bacteria from teardrop using dielectrophoresis and cultures bacteria to an effective concentration for antibiotic sensitivity testing.

1. Pinkeye Project
Jin Wai Goh
Xiaojun Sun
Aloysius Davin Oetomo
Scott Simmons

2. 2
Background
• Pinkeye is caused by bacteria and viruses
• Current diagnosis methods are slow and require training
• Our design has these factors in mind:
– Deliver results in less than 24 hours
– Require minimal training
– Simple/inexpensive to manufacture
– Long shelf life

3. 3
System Layout

4. 4
Sample Collection
• Allow ~10 teardrops (~50 µL) to fall into a syringe
• Place syringe into syringe pump
• Connect syringe pump to the PinkeyeDetect device via PTFE tube
• Pump at a rate of 30 µL/hr

5. 5
Simulation of Bacteria Separation
〈FDEP〉=πa3εmRe{K}∇|Erms|2
Frequency of the electric field 1000[kHz]
"Fluid medium conductivity" 0.12 [S/m]
"Fluid relative permittivity" 78
"Fluid density" 1000[kg/m^3]
"Fluid dynamic viscosity" 1e-3[Pa*s]
"Particle density (RBCs and bacteria)" 1050[kg/m^3]
"Particle diameter: bacteria (gram-positive)" 1.8[um]
"Particle diameter: RBCs" 8 [um]
"Particle conductivity: bacteria (gram-positive)" 0.25[S/m]
"Particle conductivity: RBCs" 0.31[S/m]
"Particle relative permittivity: bacteria (gram-positive)" 20
"Particle relative permittivity: RBCs" 59
"Shell electrical conductivity: bacteria (gram-
positive)" 1e-6[S/m]
"Shell electrical conductivity: RBCs" 1e-6[S/m]
"Shell relative permittivity: bacteria (gram-positive)" 6
"Shell relative permittivity: RBCs" 4.44
"Shell thickness: bacteria (gram-positive)" 4[nm]
"Shell thickness: RBCs" 9[nm]

6. 6
Electric Field and Velocity Profile

7. 7
Cell Trajectory

8. 8
Cell Culture Chamber
• Effective culture time  Determine culture volume
 Depends on Co, substrate uptake rate, substrate diffusivity,
cell density, culture area + volume
𝑫𝒂 =
𝑲𝒎 × 𝒉 × 𝝈
𝑫 × 𝑪 𝒐
• Fabricated through replica molding and photolithography.
• PDMS was used because:
 Non-toxic
 Gas permeable
 Excellent optical properties (low autofluorescence &
transparency)
• Bacteria inflow ~ 1.2X106 μm/s (require ~ 3X culture medium)
 Total volume ~ 4.8X106 μm/s
 179μm x 179μm x 150μm (L x W x h)

9. 9
Mueller Hinton Broth (MHB)
• 0.3g/mL beef extract
• 0.0175 g/mL casamino acid
• 0.0015 g/mL starch
• Non-selective (grow all bacteria present equally)
• Starch absorbs toxins released from bacteria so it doesn’t interfere
with antibiotic testing
• Loose agar  better diffusion

10. 10
TWIST Valves
• Designed by Weibel et al.
• Stainless steel screws bonded to PDMS channel
• Elastic modulus PDMS (2.4 mPa; 360 psi)
 Filling compartments produces pressure that later drives inflow/outflow of fluids.
 Hand-operated, cheap, seals chamber indefinitely.

11. 11
Antibiotic Sensitivity Testing
• Based on SBM method
• Concentration gradient generated through mixing channels (low fluid
resistance) that are sandwiched between resistance adjustment
channels (high fluid resistance)
• Freeze-dried antibiotic matrix
• MIC determination in 3 hr