Transcript Microelectrodes - University of California, Riverside

Microelectrodes
Connie Hong
Dr. Valentine Vullev
Department of Bioengineering
University of California, Riverside
Motivation
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Photolithography is
costly and time
consuming and
requires a clean room
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Need for quick
prototyping for sensors
and electrodes
Introduction
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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
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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
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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 1000m
Width 500m
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
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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
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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
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Use a simple model to do impedance
analysis
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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
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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
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Calculate capacitance for silver electrodes
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Develop method for the identification of
bacteria and/or spores
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Non-contact method of sensing
Acknowledgements
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Dr. Vullev
Marlon Thomas
Joseph Matthew Serrano Clift
Dr. Vullev’s Lab
James Lee
Dr. Myung’s Lab
Coordinators of BRITE