Title: Electrochemical Analysis of SelfAssembled Monolayer SAM on a Gold Electrode Surface
1Electrochemical Analysis of Self-Assembled
Monolayer (SAM) on a Gold Electrode Surface
- Gerald D. McEwen
- BIE 7870
- February 7, 2008
2Objectives
BIE 7870
02/07/2008
- Utilize electrochemical techniques to analyze DNA
on a gold electrode surface - Calculate specific electrochemical parameters
- Look at the possibility of a lab-on-a-chip
design
3Outline
BIE 7870
02/07/2008
- Introduction
- Background
- Materials and Methods
- Results
- Discussion
- Summary
- Conclusions
- Future Work
4Introduction
BIE 7870
02/07/2008
- Cryptosporidium parvum, a waterborne protozoan
parasite, can cause debilitating to
life-threatening illness when introduced to the
human gastrointestinal system 1. - The World Health Organization recognizes C.
parvum as a significant global health threat to
humans 2.
Sporulated oocysts, containing 4 sporozoites, are
excreted by the infected host through feces and
possibly other routes such as respiratory
secretions . Transmission of Cryptosporidium
parvum and C. hominis occurs mainly through
contact with contaminated water (e.g., drinking
or recreational water). Many outbreaks in the
United States have occurred in waterparks,
community swimming pools, and day care centers.Â
Zoonotic and anthroponotic transmission of C.
parvum and anthroponotic transmission of C.
hominis occur through exposure to infected
animals or exposure to water contaminated by
feces of infected animals . Following
ingestion (and possibly inhalation) by a suitable
host , excystation occurs.
http//www.dpd.cdc.gov/dpdx/HTML/Cryptosporidiosis
.asp?bodyFrames/A-F/Cryptosporidiosis/body_Crypto
sporidiosis_page1.htm
5Introduction contd
BIE 7870
02/07/2008
- In 1993, C. parvum caused illness in greater than
400,000 people and caused 104 deaths in Milwaukee
3 - More recently an outbreak in Utah had a record
1,600 cases for the summer months 4 - Environmental Protection Agency (EPA) estimates
that 155 million people in the US are at risk of
exposure to Cryptosporidium 5
- Unfortunately, there is no effective
antimicrobial treatment to eradicate this
pathogen - Early detection methods and techniques are
critical for effective control and prevention - Methods are either to labor-intensive,
time-consuming 6, or require sophisticated
specialized equipment 7
6Materials and Methods
BIE 7870
02/07/2008
- Electrochemical Impedance Spectroscopy (EIS)
- CHI 1220 Electrochemical Analyzer (CH
Instruments, Inc. Austin TX) - Three electrode setup
- Working
- Reference
- Counter (Pt wire)
- VMPII Multi-Channel Potentiostat (BioLogic
Instruments, Knoxville, TN) - Same electrode setup as the CHI system
http//chinstruments.com/Products.html http//www.
bio-logic.info/potentiostat/products.htmlVMP3
7Materials and Methods contdTechnical Advantages
BIE 7870
02/07/2008
- Specifications
- Impedance 10 µHz to 1 MHz
- Low current 100 fA min. current
- High current 4 A and 8 A modules
- Ethernet 10/100 and USB2 communication
- Complex or independent impedance measurements
from 10µHz to 500kHz
- Specifications
- Max. potential range 2.4 V
- Compliance voltage 7.5 V
- Current range 2 mA
- Contains an onboard
- digital function generator
- data acquisition system
- potentiostat/bipotentiostat
- Design
- small size
- light weight
- low cost
http//www.bio-logic.info/potentiostat/products.ht
mlVMP3 http//www.ijcambria.com/model_1200A_serie
s_hand.htm
8BIE 7870
02/07/2008
Materials and Methods contd What happens at the
electrode surface?
- Figure 1. The sequential modification of the
gold working electrode beginning with the bare
gold substrate (1), addition of single strand-DNA
(ss-DNA) (2), immersion in 6-mercapto-1-hexanol
(MCH) (3), hybridization with target-DNA (t-DNA)
(4), and addition of Hoechst 33258 (5).
9CV ResultsBare Gold Electrode
BIE 7870
02/07/2008
- Peak Current vs. Scan Rate0.5
Figure 3. Dependence of ipa and ipc on n1/2, for
scan rates 0.005, 0.01, 0.02, 0.03, 0.04, 0.05,
0.06, 0.08, 0.1, 0.15, 0.2, 0.3, and 0.4 Vs-1 of
0.5 mM K3Fe(CN)6 0.01 M PBS. Same experimental
conditions as in Figure 2.
Figure 2. Current versus potential, for
increasing scan rates 0.005, 0.01, 0.02, 0.03,
0.04, 0.05, 0.06, 0.08, 0.1, 0.15, 0.2, 0.3, and
0.4 Vs-1 of 0.5 mM K3Fe(CN)6 0.01 M PBS.
10CV Results and DiscussionModified Gold Electrode
BIE 7870
02/07/2008
- Current vs. Potential
- Modified Gold Electrode
- Cyclic Voltammetry
- Calculated Parameters
- ip (2.69 x 105)n2/3AD01/2Cn1/2
- ip peak current
- n electrons transferred,
- A electrode area, 0.0314 cm2,
- C redox species concentration, 0.5 mM
Table 1. Diffusion coefficients for each step of
the modified gold electrode.
Figure 4. Cyclic voltammograms (in 0.5 mM
K3Fe(CN)6 0.01 M PBS, pH 7.4 scan rate 60 mV
s-1) showing the effect of immobilization of DNA
SAM on Au. The figure shows how the cyclic
voltammogram of bare gold (1) changes after
modification with ss-DNA soaked for twenty-four
hours (2), MCH soaked for 1 hour (3), tDNA soaked
for 1.5 hours (4), and Hoechst 33258 for 5
minutes (5).
Bard, A.J., Faulkner, L.R., 2001. Electrochemical
Methods, Fundamentals and Applications, 2nd ed.
Wiley Sons, New York. Chapter 10. McEwen, et
al. 2008, Manuscript in preparation
11EIS ResultsModified Gold Electrode
BIE 7870
02/07/2008
- Impedance Plot
- Modified Gold Electrode
- Electrochemical Impedance Spectroscopy Parameters
- Rct (RT/n2F2AKa0)(1/C0(1-a)CRa)
- a assumed 0.5
- C0(1- a) CR a C0, C0 0.5 mM
- T 298K
- A electrode area, 0.0314 cm2
- n 1
- F 96485 C mol-1
Figure 5. Electrochemical impedance spectroscopy
(in 0.5 mM K3Fe(CN)63-/4- 0.5 mM K4Fe(CN)63-/4-
in 0.01 M PBS, pH 7.4) showing the effect of
immobilization of DNA SAM on Au. The figure shows
how the Nyquist plot of bare gold (1) changes
after modification with ssDNA soaked for
twenty-four hours (2), MCH soaked for 1 hour (3),
tDNA soaked for 1.5 hours (4), and Hoechst 33258
for 5 minutes (5).
Figure 6. A modified equivalent Randles circuit
used to model impedance data RW, electrolyte
resistance ZW, Warburg impedance Rct,
charge-transfer resistance Cd, double-layer
capacitance.
Bard, A.J., Faulkner, L.R., 1980. Electrochemical
Methods Fundamentals and Applications, 1st ed.
Wiley Sons, New York. Bard, A.J., Faulkner,
L.R., 2001. Electrochemical Methods, Fundamentals
and Applications, 2nd ed. Wiley Sons, New York.
Chapter 10.
12EIS Results contd Modified Gold Electrode
BIE 7870
02/07/2008
Monolayer Thickness
Surface Coverage
- di (e0eiA/Cd)
- di thickness of the ith layer
- Cd double layer capacitance
- e0 the permittivity of free space
- ei is the dielectric constant of the layer
- A electrode area, 0.0314 cm2
- qR 1 - (RctAu/RctSAM)
- RctAu charge-transfer resistance for bare gold
electrode - RctSAM charge-transfer resistance for bare and
DNA-modified gold electrode
Table 2. Measured EIS parameters for each
modification step of the gold electrode.
Horowitz, P., Hill, W., 1989. The Art of
Electronics, 2nd ed., Cambridge University Press,
Cambridge. R.P. Janek, W.R. Fawcett, Langmuir 14
(1998) 3011. McEwen, et al. 2008, Manuscript in
preparation
13Summary
BIE 7870
02/07/2008
- Electrochemical analysis can detect the
modifications of the gold electrode - Specific EC parameters where detected or
calculated - A lab-on-a-chip senor could be possible
- Combining EC-STM imaging may provide a technique
for real-time/ in-situ detection - Utilized different species DNA for comparison
studies
14Reference
BIE 7870
02/07/2008
- J. Watkins, P. Kemp and K. Shepard, in W.B.
Betts, et al, (Eds.), Protozoan Parasites and
Water, The Royal Society of Chemistry, Oxford,
UK. 115 (1995). - WHO Reports Decry Neglect of World Health
Problems, ASM News, 1990, 56, 358. - .J. Hoxie, J.P. Davis, J.M. Vergeront, R.D.
Nashold, and K.A. Blair, Cryptosporidiosis-associa
ted mortality following a massive waterborne
outbreak in Milwaukee, Wisconsin. American
Journal of Public Health, 1997, 87, 2032-2035. - R. Boone. Health News. KSL.com. Online
September 21, 2007. Cited 09 26, 2007.
http//www.ksl.com/index.php?nid201sid1845957.
- A. Newman, Anal. Chem., 1995, 67, 731A.
- (a) EPA 1622, Cryptosporidium in Water by
Filtration/IMS/FA http//www.epa.gov/nerlcwww/1622
ap01.pdf (b) U.S. EPA (2001) Method 1623
Cryptosporidium and Giardia in water by
filtration/IMS/FA. EPA 821-R-01-025, Office of
Water, Office of Science and Technology,
Engineering and Analysis Division, U.S.
Environmental Protection Agency, Washington, DC. - W.L. Current, L.S. Garcia, Cryptosporidiosis,
Clin. Microbiol. Rev., 1991, 4, 325-358.
15Acknowledgments
BIE 7870
02/07/2008
- Presidential Graduate Fellowship
- We appreciate the support from Utah Water
Research Laboratory (UWRL), - Department of Biological Irrigation Engineering
Research Experience for Undergraduates (REU)
Undergraduate Summer Internship - Utah State New Faculty Start-up and Vice
President for Research New Faculty Research
Initiative - Undergraduate Creative Opportunity Grant (URCO)
- Dr. Yu Wang
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