A Disposable On-Chip Phosphate Sensor with Planar Cobalt Microelectrode on Polymer Substrate Zhiwei Zou,, Jungyoup Han, Am Jang*, Paul L. Bishop*, and Chong H. Ahn MicroSystems and BioMEMS Lab Department of Electrical and Computer Engineering and Computer ScienceS *Department of Civil and Environment Engineering, Cincinnati, OH 45221-0030, USA
Outline Introduction Device Concept and Design Fabrication Experiment Results Conclusions
Introduction Environment Phosphate is the major source of eutrophication of rivers and lakes. Agriculture Phosphate is an essential nutrient for all plants; phosphate fertilizer has been extensively used. Clinical diagnostics Phosphate concentration in human body is directly related to the diagnosis of several diseases.
Introduction Spectrophotometry Atomic Emission Spectrometry Standard phosphate measurement methods High accuracy Expensive instrument and long analysis time
Research Motivation Environmental applications Large scale field deployment Mass data collection Clinical applications Single-use and disposable Rapid detection Miniaturized Inexpensive Simplified Accurate Rapid
Enzyme materials Previous Approach Enzyme Based Biosensors Alkaline phosphatase, pyruvate oxidase, maltose phosphorylase, et al. Advantages High selectivity and sensitivity Limitations Enzyme materials are relative expensive and unstable. The sensor structure is relative complicated. H. Nakamura, M. Hasegawa, Y. Nomura, Y. Arikawa, R. Matsukawa, K. Ikebukuro, and I. Karube, Development of A Highly Sensitive Chemiluminescence Flow-Injection Analysis Sensor for Phosphate-Ion Detection using Maltose Phosphorylase, Journal of Biotechnology, Vol. 75, pp. 127-133, 1999.
Previous Approach Cobalt-Wire Electrode Xiao et al., (1995) first introduced cobalt metal as a phosphate-sensitive electrode material. Simplicity They showed that the metallic Co-wire has a selective potential response toward dihydrogen phosphate (H 2 PO 4-1 ) in the aqueous medium. Selectivity Sensitivity
Previous Approach Cobalt-Wire Electrode
Previous Work Microfabricated On-Chip Biosensors on Polymer Substrate Glucose permeable membrane Immobilized glucose oxidase Lactate Sensor Oxygen Sensor Glucose Sensor R OH 0.7 V R O + H + + e - Reference electrode Counter electrode RE Tyrosine WE Tyrosyl CE Glucose, lactate, and po 2 sensors e - CE RE M n+ M M M n+ 200 μm RE WE Hg CE Mercury droplet WE Insulin sensor Heavy metal ion sensor C. Gao, H.L.R. Rilo, P. Myneni, and C.H. Ahn, A New On-Chip Insulin Biosensor for Monitoring Dynamic Response of Human Islet Cells, Proceedings of the 8th International Conference on Miniaturized Systems in Chemistry and Life Sciences (microtas 2004), Malmo, Sweden, Sep. 26-30, 2004 X. Zhu, C. Gao, J.-W. Choi, P.L. Bishop, and C.H. Ahn, On-Chip Generated Mercury Microelectrode for Heavy Metal Ion Detection, Lab on a Chip, Vol. 5, pp. 212-217, 2005.
Previous Work Polymer Lab-on on-a-chip Cell Monitoring Chemical/Culture media loading channel Cultured Islet Cells On-Chip Insulin Biosensor Glucose Consumption 1 0.8 0.6 0.4 0.2 0 1 2 3 4 5 6 Days Unhealthy Cell Healthy Cell On-Chip Glucose Biosensor PDMS microfluidic system Islet Filtering pillars Captured islet Peak Current /na 1200 1000 800 600 400 200 0 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 Insulin Concentrations /um C. Gao, H.L.R. Rilo, P. Myneni, and C.H. Ahn, A New On-Chip Insulin Biosensor for Monitoring Dynamic Response of Human Islet Cells, Proceedings of the 8th International Conference on Miniaturized Systems in Chemistry and Life Sciences (microtas 2004), Malmo, Sweden, Sep. 26-30, 2004
Previous Work Polymer Lab-on on-a-chip Clinical Diagnostics Pouch Integration of pouch Calibration pouch Waste chamber Biosensor array 150 um POLYMER SUBSTRATE Biochemical sensor Optical transparency Biocompatibility Spray and screen printing Mass production Very low cost AIBN Pressure source Screen printing 200 um sproms (passive valve) Solid-propellant (AIBN) Microneedle Lateral metallic Integration of Metal needle microneedle AIBN heater Mold injection Rapid injection molding Techniques for MASS-PRODUCTION Cyclic Olefin Copolymer (COC) C.H. Ahn, J.-W. Choi, G. Beaucage, J. Nevin, J.-B. Lee, A. Puntambekar, and J.Y. Lee, "Disposable Smart Lab on a Chip for Point-of-Care Clinical Diagnostics" Proceedings of the IEEE, Special Issue on Biomedical Applications for MEMS and Microfluidics, Vol. 92, pp. 154-173, 2004.
Research Objectives Miniaturized on-chip phosphate sensor using planar cobalt microelectrodes on polymer substrate Measurement of both inorganic and organic phosphate in aqueous solutions Integrated with polymer microfluidic system to achieve disposable lab-on-a-chips Benefits Low cost, mass production, less analyte consumption, rapid detection, easy-to-use, long storage time, et al. High sensitivity and selectivity
Device Concept and Design Microfluidic chip Sensing chip Integrated biochip Electric contact
Device Concept and Design Microfluidic chip Inlet Outlet Sensing chip Automatic Pump-33 fluidic dual syringe system pump using micro-pump and micro-vales
Device Concept and Design Microfluidic chip O 2 O 2 P O 2 P Ag/AgCl Au E R 3CoO+2H 2 PO 4- +2H + Co 3 (PO 4 ) 2 +3H 2 O 2Co+O 2 2CoO P Co Au E W O 2 P Sensing chip Model 215 bench-top ph/mv meter BalanceTalk SL TM software
Fabrication Process Sensing Chip Ni COC Au Co S1818 SU-8 SU-8 patterning Au/Co evaporation and patterning Ni electroplating Co etching and patterning SU-8 removal Au etching Injection molding Ag/AgCl electroplating Standard microfabrication technology
Fabrication Process Microfluidic Chip Ni COC Au Co S1818 SU-8 SU-8 patterning Au/Co evaporation and patterning Ni electroplating Co etching and patterning SU-8 removal Au etching Injection molding Injection Mold process Ag/AgCl electroplating High throughput plastic micromachining
Fabrication Process Chip Bonding Ni COC Au Co S1818 SU-8 SU-8 patterning Au/Co evaporation and patterning Ni electroplating Co etching and patterning SU-8 removal Au etching Injection molding Ag/AgCl electroplating UV adhesive bonding
@ Fabricated Device WE WE Co Inlet Microchamber RE Ag/AgCl RE 500 µm Chip size: 1.5 cm 2 cm Electric contact Chamber volume: 2 µl Electrode: 200 µm 1.5 mm Outlet
Experiment Results Output potential vs. various KH 2 PO 4 concentrations -500-660 -550-680 Potential (mv) -600-650 -700-750 10-5 M 10-4 M 10-3 M Potential (mv) -700-720 -740-760 -780-800 10-2 M 0 100 200 300 400 500 Time (sec) -800-5 -4-3 -2 log [Concentration (M)] KH 2 PO 4 has been diluted to different concentrations using buffer solution. The buffer solution was made by potassium hydrogen phthalate (KHP) and KCl in de-ionized water at ph 5.0.
Experiment Results Time-dependent potential response in 10-5 M KH 2 PO 4 0-200 Potential (mv) -400-600 -800 0 5 10 15 20 25 30 35 Time (min) The proposed on-chip sensor presents a steady-state response for more than 30 minutes in 10-5 M KH 2 PO 4 solution, which is sufficient for disposable sensor applications.
Experiment Results Output potential vs. various organic phosphate concentrations -450-450 -480-480 Potential (mv) -510-540 -570-600 -630 Potential (mv) -510-540 -570-600 -630-660 -5-4 -3-2 log[concentration (M)] -660-5 -4-3 -2 log[concentration (M)] Adenosine 5'-triphosphate (ATP) Adenosine 5'-diphosphate (ADP) ATP and ADP have been diluted to different concentrations using buffer solution. The buffer solution was made by potassium hydrogen phthalate (KHP) and KCl in de-ionized water at ph 5.0.
Experiment Results Reproducibility of the fabricated sensor -700-600 RSD = 0.6% -1000 RSD = 2.5% and 2.1% KH 2 PO 4 ATP Potential (mv) -500-400 -300-200 -100 Potential (mv) -800-600 -400-200 0 0 2 4 6 8 10 Number of injection 0 1 2 3 4 Sensor number Potential responses to ten times repeated injections of 10-3 M ADP to the same phosphate sensor Chip-to-chip deviation of four different phosphate sensors in measuring 10-3 M KH 2 PO 4 and 10-3 M ATP
Conclusions Anew on-chip phosphate sensor using planar cobalt micro electrodes has been designed and fabricated. The feasibility of using the proposed sensor to monitor both inorganic and organic phosphate has been presented. Can be quickly fabricated with low cost and high yield compared to the bulk cobalt-wire based phosphate sensor, while still keeping the good performance. Fully integrated with polymer microfluidic system and can be easy developed as multi-analyte polymer lab-on-a-chips. Especially suitable for the large-scale field deployment for mass environmental data collections and disposable point-ofcare testing (POCT) in clinical diagnostics.
Acknowledgements Financial support NIH-P021-L684 Technical assistance Mr. Ron Flenniken Institute for Nanoscale Science and Technology (INST) at the