Experiment 4: Electropolymerized Conducting Polymers.
Introduction:
Conductive polymers (CP) exhibit very useful properties such as flexibility, solubility [1], electrical conductivity, low energy optical transitions, low ionization potential, and high electron affinity.[2] These characterizations make them such effective candidates for many applications such as antistatic and antimagnetic shielding devices[3], microwave attenuation[4], light emitting devices, optical sensors, enzymatic biosensors[5], electronic circuits, and detectors of odors and flavors. The most widely known conducting polymers are polypyrole, polyanaline, and polythiophene. By applying an electrical potential (reversible reaction), these polymers can be reduced. The role of these polymers when they are used as active templates in biosensor applications is the immobilization of dynamic species on the electrode. This will contribute to enhancing the sensitivity and the accuracy of analyte detection. CPs have been used for stabilizing numerous biological species such as enzymes, antibodies, haptens, DNA, and more interestingly the whole cells. [1]
Aim:
The aim of performing this experiment is to create a conducting polypyrrole film which consists of a stabilized enzyme, identify the film and its characteristics, and utilize it as glucose biosensor.
Procedure:
“Refer to Manual for NANO 3101/8302, Electropolymerized Conducting Polymers, Flinders University, p.24-29.”
Results and Discussion:
In the biosensor uses, the deposition of the polymers on the electrode surface can be done by applying an oxidative potential. During this action, the enzymes can be stabilized, and by modifying the deposition time, the amounts of the deposited layer can be recreated. The sensitivity, selectivity, and the accuracy of detection of the biosensors are reliant on the architecture of the polymer, the biological activity of the enzymatic immobilization, and the electropolymerisation circumstances.
In this experiment, the glucose oxidase (enzyme) was immobilized in a conducting polypyrole film on an electrode to find out their appropriateness as a functioning electrode. The performance of the electrode was measured through a Cyclic Voltammogram (CV) of ferricyanide
The geometric area of the electrode was measured by a ruler, and it was found to be 3.14 mm ²which is identical to 0.00314 cm².
The Randles-Sevcik equation is used in the redox reactions
at 25 C °
Where is the peak current, A is the electrode area (cm²), n is the number of electrons involved, C is the concentration of the bulk (mol/ml) for active species, v is the scan rate (V/s), and D is the diffusion coefficient.
n = 1, therefore
, therefore = 0.002756809.
V = 20mV/s = 0.02 V/s, therefore
C = 10 mM = 0.01 mol/L = 0.00001 mol/mL.
can be determined from figure.1
Figure 1: Cyclic Voltammograms (CV) as a function of escalating the scan rate for Platinum Electrode in ferrricyanide solution.
This c ...
1. Experiment 4: Electropolymerized Conducting Polymers.
Introduction:
Conductive polymers (CP) exhibit very useful properties such as
flexibility, solubility [1], electrical conductivity, low energy
optical transitions, low ionization potential, and high electron
affinity.[2] These characterizations make them such effective
candidates for many applications such as antistatic and
antimagnetic shielding devices[3], microwave attenuation[4],
light emitting devices, optical sensors, enzymatic biosensors[5],
electronic circuits, and detectors of odors and flavors. The most
widely known conducting polymers are polypyrole, polyanaline,
and polythiophene. By applying an electrical potential
(reversible reaction), these polymers can be reduced. The role
of these polymers when they are used as active templates in
biosensor applications is the immobilization of dynamic species
on the electrode. This will contribute to enhancing the
sensitivity and the accuracy of analyte detection. CPs have been
used for stabilizing numerous biological species such as
enzymes, antibodies, haptens, DNA, and more interestingly the
whole cells. [1]
Aim:
The aim of performing this experiment is to create a conducting
polypyrrole film which consists of a stabilized enzyme, identify
the film and its characteristics, and utilize it as glucose
biosensor.
Procedure:
“Refer to Manual for NANO 3101/8302, Electropolymerized
Conducting Polymers, Flinders University, p.24-29.”
Results and Discussion:
In the biosensor uses, the deposition of the polymers on the
electrode surface can be done by applying an oxidative
potential. During this action, the enzymes can be stabilized, and
by modifying the deposition time, the amounts of the deposited
layer can be recreated. The sensitivity, selectivity, and the
2. accuracy of detection of the biosensors are reliant on the
architecture of the polymer, the biological activity of the
enzymatic immobilization, and the electropolymerisation
circumstances.
In this experiment, the glucose oxidase (enzyme) was
immobilized in a conducting polypyrole film on an electrode to
find out their appropriateness as a functioning electrode. The
performance of the electrode was measured through a Cyclic
Voltammogram (CV) of ferricyanide
The geometric area of the electrode was measured by a ruler,
and it was found to be 3.14 mm ²which is identical to 0.00314
cm².
The Randles-Sevcik equation is used in the redox reactions
at 25 C °
Where is the peak current, A is the electrode area (cm²), n is the
number of electrons involved, C is the concentration of the bulk
(mol/ml) for active species, v is the scan rate (V/s), and D is the
diffusion coefficient.
n = 1, therefore
, therefore = 0.002756809.
V = 20mV/s = 0.02 V/s, therefore
C = 10 mM = 0.01 mol/L = 0.00001 mol/mL.
can be determined from figure.1
Figure 1: Cyclic Voltammograms (CV) as a function of
escalating the scan rate for Platinum Electrode in ferrricyanide
solution.
This can be done by evaluating the average of the anodic and
cathodic peak current. An example for tabulating the electrode
area experimentally will be shown below. At the scan rate of
20mV/s, the average peak current will be equal to
3. = 0.00001735.
A is the unknown electrode area.
cm²
The calculations above were repeated for the different scan
rates, the table below summarizes those calculations
Scan Rate (V)- mV/S
Peak Current (
Electrode Area (A) - cm²
20
0.00001735
0.0165
50
0.00002595
0.0156
100
0.00003625
0.0154
200
0.0000491
0.0147
Table.1. A summary of the bulk electrode’s calculations
The CV shown in figure 1 for scan rates ranging from 20 to 200
mV/s indicated a formal potential between 210 and 300 mV,
with a difference in peak potential of about 0 mV for some and
40 mV for the others. This means that the system is reversible
4. as the peak potential is reliant on the scan rate and the peak
currents increase continuously with the scan rate; these results
were comparable to the theory, also mathematical confirmation
of these results can be seen in Table1. Additionally, as it can
be seen from Table1, when increasing the scan rate, the
electrode area decreased over time due in large part to the
electrolyte which caused erosion of the electrode.
To explain the mechanism of the CV in more detail, the
ferricyanide solution is electrolyzed by placing it in contact
with the electrode surface. Then, making that surface amply
positive and negative, allows the electron to transfer (. The
surface is started at a particular voltage with respect to the
reference electrode, which is Ag/AgCl. The electrode voltage is
increased and decreased at a linear rate, and finally, the voltage
is changed back to the original value at the same linear rate.
When the surface becomes sufficiently negative and positive, a
solution species exchanges electrons with the surface. This
results in a measurable current in the electrode circuitry. When
the voltage cycle is reversed, which is the case in this
experiment, the electron transfer between electrode and
chemical species will often be reversed. These features are
illustrated in Figure 1 and 2.
Figure 2: CV for Electrode coating with polypyrole
It was observed that the peak current and the potential were
much larger in the electrode coated with polypyrole than those
without polymers. Moreover, in the CV of the electrode coated
with polypyrole, the background current was notably larger due
to the polymers overreacting. It can be implied that their areas
at the different scan rates provided were larger mainly because
of the polypyrole layer thickness protecting the electrode
surface from the corrosion as the polypyrole’s resistivity is
strong.
Figure.2 Shows the CV of the electrode coated with polypyrole.
The electrode surface area coated with polymer appeared as a
5. smooth dark film with brown spots, which indicates that the
electrode is of high quality.
The table below demonstrates , and E° (reversible potential) at
different scan rates:
Scan Rate (V)- mV/S
E°
20
0.00003075
27
50
0.0000579
29
100
0.000097
51
200
0.0001675
53
Table.2. , and E° for the electrode coated with polypyrrole.
Example of calculating E° at 20 mV/s scan rate.
E° = Ep, anodic – Ep, cathodic = 279 – 252 = 27.
The total charge was found to be 6.779 mc.
In the glucose analysis, it was observed that increasing
concentrations of the glucose in the buffer solution leads to an
increase in the peak current (Figure 3). The calibration curve
6. supports this result by indicating the concentration of the
glucose is proportional to the current.
Figure 3. Time Vs current for the glucose addition.
Conclusion:
In closing, the conductive polymer films are fitting in
bioseonsor uses due to their electrochemical sensitivity to the
presence of chosen ions in a solution. Therefore the
development of a glucose biosensor based on conducting
polymers immobilized with enzyme has intrigued many
scientists around the world. This is because of its capability to
detect different biological species in various environments.
Questions:
1- How do the geometric and experimentally determined
electrode’s area compare and what other factors may affect the
apparent electrode surface area?
The geometric electrode area (0.00314 cm²) was slightly bigger
than the experimentally determined electrode’s area, which is
because of the reaction’s effects on the electrode. The factors
that might have an effect on the appearance of the surface area
include the surface roughness of the electrode [6] as well as the
concentration of the electrolyte, polymers and enzymes. Other
factors might be the enzyme stability, the amounts of voltages
applied to the electrode, the purity of the electrode and the
electrolyte, the electrode’s resistivity, reaction time, and any
unknown containments in the film, or the solutions.
2- Which area did you use for the subsequent calculations and
why?
The calculated electrode area at 200 mV/S scan ratewas used for
the subsequent calculations due to its capability to obtain the
desired plot within the given area.
7. 3- Produce a calibration graph of current vs. glucose
concentration.
Figure 4: Calibration Curve of Current Vs.Glucose
Concentration
4- Determine the concentration of glucose in the sports drinks?
Figure5: Time Vs Current for Sport Drinks
By finding the maximum current for each addition of sports
drinks and applying this number to the equation obtained from
the calibration curve, the concentration of glucose in sports
drinks can be determined.
From figure 3: y= 82.212x-0.1419 (1)
Where y is the maximum current of each addition of sports
drinks, x is the concentration of glucose in sports drinks.
Rearranging ( 1),
After adding 1ml,
= 0.001726 mM
The calculations above were repeated for the 10 additions.
The average concentration was found to be 0.001726 mM, which
is the concentration of glucose in sports drinks.
5- If a different amount of enzyme were incorporated into the
polymer electrode, how would the results differ?
The enzyme behaves as an organic catalyst in the reaction. In
one case, when adding higher amounts of enzyme to the
polymer, the reaction will be faster which will cause the
production of a higher current. On the other hand, when a
smaller amount of enzyme is added, the reaction will be slower;
therefore the current will be less.
6- If a lower potential were chosen for the TB analysis, what
effect would it have on the plot? Would a lower potential be
advantageous? Explain why/why not.
If a lower potential was chosen for the Time Based analysis, the
current would be less. This is an advantage because it might
8. lead to increasing the sensitivity of the biosensor which would
therefore increase the analyte detection.
7- What range of glucose concentrations in this electrode useful
over?
From the data found in the experiment, the range of glucose
concentrations would be 0.00115 mM to 0.0107 mM. However,
from the literature, the range is 2-30mM.
8- Calculate Km and Vmax by performing a Michaelis-Menten
analysis.
Where V is the rate of reaction is the concentration of the
glucose, Vmax and Km are constants which can be determined
from the calibration curve. Due to the difficulties in solving this
equation, the values of these constants obtained from this
experiment should be comparable to the literature. Therefore,
these values were taken from that reading material; Km was
tabulated to be 1.5 mM, while Vmax was 1 nm/s. [7]
9- How does this biosensor compare to other you have used or
researched?
Glucose biosensors are extremely capable sensors compared to
the others since they can detect different things easily. They can
be used in clinical diagnostics, environmental monitoring, food
freshness, and biochemical and chemical monitoring. The
techniques of manufacturing this biosensor vary greatly due the
inexpensive, relatively reliable starting materials.
10- If you were able to repeat the experiment several times what
variables would change to optimize the biosensor?
The data that was obtained from the experiment was adequate.
However, in order to improve the performance of the biosensor,
the area of the electrode could be changed, the concentration of
the glucose oxidase might be altered, and the film thickness
could be adjusted. Also, different concentrations of the
9. polypyrole and the electrolyte would optimize the biosensor.
11- Discuss the factors that limit the sensors dynamic range and
relative sensitivity, the concentration range and errors associate
with the biosensor. Also discuss the reproducibility of the
technique?
All of the factors that can be optimized to produce a better
biosensor affect the overall sensitivity of the biosensor.
The factors that limit the sensors dynamic range are dependent
on the scan rate, the polymer’s conductivity, thickness, and
resistivity. Furthermore, enzyme stability, concentration of the
glucose, and electrode surface area can be considered as other
elements that limit the biosensors.
Generally, as glucose concentration increases, so does the
current. Thus, concentration is a limiting factor.
The errors that may be associated with the biosensor included,
but are not limited to: calibration/human error, concentration of
the electrolytic solution, and the thickness of the coated
polymer.
The reproducibility of the technique can be demonstrated in the
calibration curve of the immobilized enzyme, its stability, and
the electrode preparation; illustrating homogenous enzyme
kinetics that can be easily repeated. This technique is
considered to be a very reliable one because the starting
materials such as polypyrole and glucose oxdiaze are readily
accessible. Also, using the electrochemical analyzer to perform
the CV of the electrodes is convenient even with the facilities
with limited resources. Therefore, this analytical method can be
simply modified for the determination of other biological
species.
10. References:
1. Voelcker, N., Nanotechnology 3 GE, Laboratory Manual
2010, Adelaide, South Australia Flinders University
2. Gerard, M., A. Chaubey, and B.D. Malhotra,
Application of conducting polymers to biosensors, in Biosensors
and Bioelectronics. 2002. p. 345-359.
3. Bagotsky, V.S., Fundamentals of Electrochemistry
Second ed. The Electrochemical Society Series 2006, Hoboken:
Wiley & Sons, Inc.
4. Kuhn, H.H., A.D. Child, and W.C. Kimbrell, Toward
real applications of conductive polymers, in Synthetic Metals.
1995. p. 2139-2142.
5. Trojanowicz, M., Application of Conducting Polymers
in Chemical Analysis, in Microchimica Acta. 2003, Springer
Wien. p. 75-91.
6. De Levie, R., The influence of surface roughness of
solid electrodes on electrochemical measurements, in
Electrochimica Acta. 1965. p. 113-130.
7. Sadik, O.A., et al., Electropolymerized Conducting
Polymers as Glucose Sensors, in Journal of Chemical Education.
1999, American Chemical Society. p. 967-null.
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