1. Flow cell design for WGM optical biosensor Yongqiang Yang BE8280 spring 2015

2. 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

3. 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

4. WGM optical biosensor system

5. 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.

6. Flow cell for the biosensor

7. Flow cell

8. 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

9. 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 (v o is very small). It is steady laminar flow and the gravity will be neglected. Equation of continuity

10. Flow profile Equation of motion with constant µ and ρ At r direction At ϴ direction Let

11. Flow profile Boundary conditions @r=R V r and V ϴ =0; @ r→∞ and

12. Flow profile Replace g with f BCs, @r→∞, f=1; @r→R, V r =V ϴ =0, f=0 Velocity around the microsphere

13. Flow profile Drag force on sphere Buoyant forceUneven pressure Skin force

14. Future work Use COMSOL Multiphysics Modeling Software to simulate the flow profile Design a flow cell for portable WGM optical biosensor

15. 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 techniques 2) Sensor (microsphere and tapered optic fiber) is interrogated in the microfluidic channel and is irreversible sealed 3) Before integrate the sphere in the microfluidic cannel the microsphere could be functionalized or just integrate a bare microsphere Sensor cell Sensor platform Laser system Waste collection Detector Pretreatment system Computer Injection port Quick connector to laser and detector system Quick connector to sample pretreatment system and waste collection Microsphe re and taper Microfluidi c cell and channels PDMS body Optic fiber

16. 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.