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 PDMS Silver electrode imprint Channel design printed on poly styrene sheets Glass Silver Nitrate Dextrose Peel off PDMS Glue Posts Tollen’s Reaction “print and peel”

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 Width 500  m Separation 1000  m

Results Profilometry graphs Width 500μm, Separation 1500μm Distance

Results Width 500μm, Separation 1000μm

Results Width 300, Separation 1500μm

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 CuSO 4, HCl, and H 2 SO 4 bath. Current based on the area of silver that is exposed to the solution.

Improvements

Improvements Copper electrode on sand papered glass

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. InductorResistorCapitance W.E.

Impedance in several media Medium100mV500mV1000mV Air3.989E E E-13 Water4.730E E E-13 Tris*4.249E E E-13 Subtilis**4.305E E E-13 Sphaericus**4.158E E E-13 E. coli**4.430E E E-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 1  L/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