Electrochemical Nonseparation
Binding/Immunoassays Based
On Solid-State Reversible
Polyion Selective Sensors
Katy Fordyce
Department of Chemistry
Corvallis, OR 97330
Mentor: Dr. Alexey Shvarev
Electrodes (ISEs)
~ Conduct current through a cell
~ Used to detect specific species
~ Applying new method
Advantages Over Old Methods
~ Nondestructive
~ Noncontaminating
~ Short response time
~ Can be designed for selectivity
~ Unaffected by color or turbidity
Species of Interest
1. Protamine
~ Avg. charge = +20
~ Peptide
~ Arginine Rich
NH2
NH
(CH 2 )3
O
NH2
+
NH
(CH 2 )3
O
NH
NH
NH2
NH
(CH 2 )3
NH
O
NH2
NH2
+
NH2
+
2. Trypsin
~ Peptidase
~ Specific for Arginine
How Trypsin Is Used
= Protamine
= Other Species
= Trypsin
•For more information about Cystic Fibrosis,
please visit www.cff.org
Basic SCE Design
• PVC body
• Graphite core
• Conducting polymer
~PEDOT
• Ion selective
membrane
~Hydrophobic
Cross Section View:
Membrane Composition: Important!
• Selectivity = Ion exchanger (DNNS+)
Membrane
SO 3
-
C 9H 19
C12H25
C 9H 19
C12H25
N
+
C12H25
C12H25
Tetradodecylammonium
Dinonylnaphthalenesulfonate
TDDA
H+ + DNNS-
How Do Reversible SCE’s Work?
1. Constant
Current
SCE
= Protamine ions
= Na+ ions
How Do Reversible SCE’s Work?
2. Stripping
Current
SCE
= Protamine ions
= Na+ ions
Question:
Can the method described earlier be used to
detect the enzyme activity of trypsin?
Research Goals:
1. Construct electrodes which are
selective for protamine
2. Test the electrodes in a trypsin
solution to monitor enzyme activity
Data Collection
Note: Both
graphs share
the same xaxis!
Measuring Trypsin Response
0.08
Protamine
0.07
Units / mL
0
10
30
50
0.06
E, V
0.05
Trypsin
0.04
0.03
0.02
Baseline
0.01
0.00
-0.01
0
100
200
300
Time, s
400
500
600
Calculating Trypsin’s Activity
Step 1. Convert potential
EXAMPLE
6
ln(A/A 0)
Step 2. The slope will
equal the k, the
reaction rate
Concentration
4
k
2
0
0
2
4
Time
6
In Summary
TDDA+ DNNS-
Membrane
Acknowledgements
~ Dr. Alexey Shvarev
~ Hasini Perera
~ Dr. Kevin Ahern
~ Group 4
~ The Howard Hughes
Medical Institute