Lab-on-Chip Diagnosis of Bacterial vs Viral Conjunctivitis

Pinkeye Project

Jin Wai GohXiaojun Sun

Aloysius Davin OetomoScott Simmons

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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

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System Layout

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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

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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]

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Electric Field and Velocity Profile

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Cell Trajectory

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Cell Culture Chamber

• Effective culture time Determine culture volume Depends on Co, substrate uptake rate, substrate diffusivity,

cell density, culture area + volume

• 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)

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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

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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.

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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