Flow cell design for WGM optical biosensor

Yongqiang Yang BE8280 spring 2015

Research goal

• Develop a well designed flow cell for WGM optical resonator (bio)sensor.

• Facilitate the WGM optical resonator (bio)sensor in the real application

WGM optical biosensor

• WGM optical (bio)sensor is a portable, rapid, and label-free biosensor

• Recently, it has been used to detect proteins, DNA, nanoparticles, and pesticides at ultra-low (and biologically relevant) concentrations

WGM optical biosensor system

WGM optical biosensor

Flow out

Flow in

Flow cell

Sphere

Withdraw syringe pump

Injection syringe pump

If we use WGM optical resonator as a biosensor to detect biological activities in a aquarium environment, a well designed flow cell and flow system is necessary to deliver test solution to this functionalized microsphere.

Flow cell for the biosensor

Flow cell

Case analysis• WGM detection of 10 µg/mL lectin, injected at 0.1 mL/min at time 0, into

a PBS-filled microaquarium, in which a chitin-bioconjugated silica microsphere is submerged. The figure shows that the device is capable of performing WGM mode detection.– Assume the gap between the two cavity is 0.03 cm and the diameter of the water pillar

is 0.2 cm and the flow rate Q is 0.1 ml/min.– The diameter of sensor microsphere is 500 µm and the stem that hold the microsphere

is 100 µm.

PBS, lectin

Chitin bioconjugated microspheres in flow cell

Flow profile • Assume the flow is steady in side the water pillar • Comparing to the microsphere, the stem is smaller, we neglect it. We assume that there is

only microsphere in the water pillar• Average of the flow velocity in the water pillar is 0.05cm/sec. it is very slow flow• It is slow flow (vo is very small). It is steady laminar flow and the gravity will be

neglected.• Equation of continuity

Re 1ov D

22

1 1 1( ) ( sin ) ( ) 0

sin sinr

pr v v v

t r r r r

22

1 1( ) ( sin ) 0

sinrr v vr r r

Flow profile • Equation of motion with constant µ and ρ• At r direction

• At ϴ direction

• Let

22 2 2 2 2

21 1 2 2( ) (sin ) cot

sinr r r vv v vp

r vr r r r r r r r

22 2 2 2

1 1 1 1 2( ) ( ( sin ))

sin sinorv vvp

r vr r r r r r r r

( ) cos

( )sin

( )cos

r o

o

o

v v f r

v v g r

p p p r

Flow profile

• Boundary conditions • @r=R Vr and Vϴ=0; @ r→∞ and cosr ov v sinov v

22

22

2

2 2 2

2

2

1 1( cos ) ( sin cos ) 0( )

sin1 1

cos 2 2sin cos 0sin

2 20

2

2 4 4cos ( )

2

o o

o o

o

o

r v f v g continutyr r r

dfv r f r v g

r dr r

df f g

dr r rr df

g fdr

p d f df f gv r direction

r dr r dr r r

p d g dgv

r dr r d

2 2

2 2( )

g fdirection

r r r

Flow profile • Replace g with f

• BCs, @r→∞, f=1; @r→R, Vr=Vϴ=0, f=0

• Velocity around the microsphere

2 3 4 42 3

2 3 40( )

8

df d f d f r d fr r r continutydr dr dr dr

3432

1 4 1 2 3 43

3

3

3

3

2

3, ( 1, , , 0)

2 2

2 1, 1 cos

3 2

3 11 sin

4 4

2( ) cos

3

r o

o

o

CC R Rf C C r C C C C

r r

R RSo v v

r r

R Rv v

r r

v Rp p

R r

Flow profile

• Drag force on sphere

3

1( )

4cos cos 2 4

3

rr

o o

v vrr r r

Fz R g v R v R

Buoyant force Uneven pressure Skin force

Future work

• Use COMSOL Multiphysics Modeling Software to simulate the flow profile

• Design a flow cell for portable WGM optical biosensor

Portable WGM optical biosensor system 1) Injection port, to inject liquid or gas sample;2) Pretreatment system, includes valves, filters, separation (column), reservoir, pump, mixer and switch;3) Sensor platform, for installing the sensor cell and connecting the sensor cell to pretreatment system, waste collection, laser system and detector ;4) Sensor cell, installing a microsphere and a taper in a microfluidic channel. It has the optic fiber and flow tubing to connect the sensor platform. It could be specific and disposal; 5) Laser system, provide optic power to excite the microsphere; 6) Detector, receive the optic signal and convert to eclectic signal;7) Waste collection, collect waste samples;8) Computer and interfaces, control the pretreatment system, waste collection, laser system and detector, and translate the detector signal to readable information for operators.

Portable WGM optical biosensor

Sensor cell 1) Microfluidic channel , the microfluidic body and channel are fabricate by PDMS using the soft lithography techniques2) Sensor (microsphere and tapered optic fiber) is interrogated in the microfluidic channel and is irreversible sealed3) Before integrate the sphere in the microfluidic cannel the microsphere could be functionalized or just integrate a bare microsphere

Sensor cell

Sensor platformLaser

system

Waste collection

Detector

Pretreatment system

Computer

Injection port

Quick connector to laser and detector system

Quick connector to sample pretreatment systemand waste collection

Microsphere and taperMicrofluidi

c cell and channels

PDMS bodyOptic fiber

References• Dahmen, J. L., Yang, Y., Greenlief, C. M., Stacey, G., & Hunt, H. K. (2014). Interfacing

whispering gallery mode optical microresonator biosensors with the plant defense elicitor chitin. Colloids and Surfaces B: Biointerfaces, 122, 241-249.