An Optical MEMS Sensor for On-chip Catechol Detection

This thesis reports the successful design, fabrication and testing of an optical MEMS sensor for the detection of the toxic phenol, catechol. Catechol’s presence in food and drinking water posses a health concern due to its harmful effects on cell respiration. By-products of catechol oxidation have demonstrated increased absorbance changes in a chitosan film in the UV and near UV range. Our reported sensor utilizes patterned SU-8 waveguides and a microfluidic channel to deliver catechol samples to an electrodeposited chitosan film for absorbance measurements at 472 nm…

Contents

1 Introduction and Motivation
1.1 Traditional Biophotonics Techniques
1.1.1 Fluorescence
1.1.2 Bioluminescence
1.1.3 Absorbance
1.2 Catechol Detection
1.2.1 Phenols
1.2.2 Electrochemical Detection
1.2.3 Optical Detection
1.3 Lab-on-a-Chip Devices
1.3.1 MEMS Technology
1.3.2 Optical Integration in MEMS
1.3.3 Microfluidics
1.4 Biofunctionalization
1.4.1 Traditional Techniques
1.4.2 Chitosan Patterning Techniques
1.4.3 Amine conjugation
2 Device Design
2.1 Design Iterations
2.1.1 Previous Researce
2.1.2 Absorbance Test Chip Design
2.1.3 Final Microfluidic Design
2.2 Waveguides
2.2.1 Materials
2.2.2 Light Propagation and Loss
2.2.3 Facet Roughness
2.3 Channel Design
2.4 Electrode Design
2.4.1 Cr/Au Electrodes
2.4.2 Indium Tin Oxide (ITO) Sidewall
2.5 Fiber Clamp Structures
3 Device Fabrication
3.1 Process Flow
3.2 Electrode Patterning
3.3 SU-8 Recipe Development
3.3.1 SU-8 Uniformity
3.3.2 SU-8 Adhesion
3.4 ITO Patterning
3.4.1 AZ9245 Sidewall Profile
3.4.2 ITO Conductivity
3.5 Die-level Processes
3.5.1 Chitosan Deposition
3.5.2 PDMS Bonding
3.5.3 Optical Fiber Preparation
4 Testing and Results
4.1 Slide Absorbance
4.1.1 Testing Apparatus
4.1.2 Slide Absorbance Results
4.2 MEMS Sensor Testing
4.2.1 Testing Apparatus
4.2.2 Total Optical Loss
4.2.3 Preliminary Optical Testing
4.2.4 Catechol Detection Results
5 Discussion
5.1 Data Discrepancies
5.1.1 Electrode Area Variations
5.1.2 Flow Rate Dependence
5.1.3 Metal Contamination
5.2 Sensor Comparison
6 Conclusion & Future Work
APPENDIX
REFERENCES

Author: Dykstra, Peter Hume

Source: University of Maryland

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