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Microelectrodes Connie Hong Dr. Valentine Vullev Department of Bioengineering University of California, Riverside Motivation Photolithography is costly and time consuming and requires a clean room Need for quick prototyping for sensors and electrodes Introduction Microfluidics is a fairly new application Emerging application is clinical pathology Goal: Non contact form of sensing Biosensors for bacteria and spores based on impedance spectrometry Introduction Reversibly adhered microfluidic chips used as a mask to create silver electrodes Replaces the current way of making electrodes: metal vapor deposition used in clean rooms or deep vacuum environments Fabrication “print and peel” Dextrose Glue Posts PDMS Tollen’s Reaction Channel design printed on poly styrene sheets Glass Silver Nitrate Silver electrode imprint Peel off PDMS Experimental Setup Fabricate metal wires to create electrodes for microfluidic devices Chemical deposition using Tollen’s reaction to create silver electrodes How profile of electrodes change based on flow rate using the profilometry Parameters of channels Separation 1000m Width 500m Results Distance Profilometry graphs Width 500μm, Separation 1500μm 7 1µL/min Flow Rate 2µL/min Height (µm) 6 5 4 3 2 1 0 0 500 1000 1500 Distance (µm) 2000 4µL/min Results Width 500μm, Separation 1000μm 10 Height (µm) 8 6 4 Flow Rate 1µL/min 4µL/min 2µL/min 4µL/min 2 0 0 200 400 600 800 1000 Distance (µm) 1200 1400 1600 Results Width 300, Separation 1500μm 10 Height (µm) 8 6 4 Flow Rate 1µL/min 2µL/min 2µL/min 4µL/min 2 0 0 500 1000 Distance (µm) 1500 2000 Improvements Treat glass with HF and sand paper to get better adhesion of silver To improve the height of the electrode, we will use copper electrodeposition. Silver paint, copper tape, and non conductive tape used on silver electrode. Placed in a CuSO4, HCl, and H2SO4 bath. Current based on the area of silver that is exposed to the solution. Improvements Improvements Copper electrode on sand papered glass 25 20 Height (um) Copper electrode 15 10 5 0 -5 0 500 1000 Distance (um) 1500 2000 Impedance Impedance spectroscopy reveals properties of materials We will use it to measure dielectric responses from various bacteria Test electrodes to see if they measure impedance across different media Impedance Use a simple model to do impedance analysis Model: R.E. Inductor Resistor Capitance W.E. Impedance in several media Medium 100mV 500mV 1000mV Air 3.989E-13 3.669E-13 3.630E-13 Water 4.730E-13 4.799E-13 4.843E-13 Tris* 4.249E-13 4.225E-13 4.226E-13 Subtilis** 4.305E-13 4.170E-13 4.133E-13 Sphaericus** 4.158E-13 4.180E-13 4.170E-13 4.217E-13 4.224E-13 E. coli** 4.430E-13 *Tris concentration is 2mM **bacteria is in 2mM Tris solution Conclusion The chips can be successfully made. The optimal channel that can be reproduced nonlithographically with our printer is 300 microns wide Slower flow rates tend to deposit more silver, creates taller electrodes. Best flow rate is 1L/min Copper electrodeposition greatly improves the height of the electrodes The electrodes are sensitive enough to detect small impedance differences in various media Future Goals Calculate capacitance for silver electrodes Develop method for the identification of bacteria and/or spores Non-contact method of sensing Acknowledgements Dr. Vullev Marlon Thomas Joseph Matthew Serrano Clift Dr. Vullev’s Lab James Lee Dr. Myung’s Lab Coordinators of BRITE