Transcript Electrochemical Quartz Crystal Microbalance

Electrochemical Quartz Crystal
Microbalance
By:
Jay Leitch
Outline
•
What Is E-QCM?
•
History & Background Theory of this technique
–
•
Literature Review
–
•
Introduction of Basic QCM theory
Detection of Antimicrobial drugs
Proposal
–
Combining SERS with EQCM for protein characterization
•
Summary
•
References
What is EQCM?
EQCM is an acronym for Electrochemical Quartz Crystal Microbalance
EQCM was first introduced by Kanazawa et. al. in 1990
It is a extremely sensitive label-free technique that is capable of measuring
the mass in the nanogram to sub-monolayer range while simultaneously
probing the electrical properties of the system
This technique makes use of the piezoelectric effect of quartz to induce
an oscillation at the fundamental frequency (4-10 MHz) of the quartz crystal
What is EQCM
Piezoelectric effect: a mechanical deformation (on the order of 10-100nm) is produced
when an electric field is applied [or vice versa].
~
Eac
This oscillation creates an acoustic shear wave that penetrations into the media above the
crystal. This wave is sensitive to changes in the viscosity of the media or physical
adsorption of materials onto the crystal, which is typically shown by a decrease in
frequency
Q. Xie. et. al. J. Chem. Ed. 2007, 84, 681-4
W.H. King. Anal. Chem. 1964, 36, 1735-39
-7.50
150
-6.25
125
-5.00
100
-3.75
75
-2.50
50
-1.25
25
0.00
m / ng
f / Hz
What is EQCM?
Sauerbrey Equation:
(used for perfectly elastic film)
f  
2 f o2
A  q q
m
f   C  m
0
0
100
200
300
400
500
Time / s
where  f is the change in frequency, f o is the fundamental frequency of
quartz crystal, A ,  q ,  q are the area, density and shear modulus of the
quartz crystal, respectively, and m is the change in mass on the crystal
surface
What is EQCM?
Problems with QCM:
• The surface charge can affect adsorption of molecules (i.e.
SiO2 layer carriers negative charge inhibiting adsorption of
anionic species)
• It can be difficult to model since we lack control outside of the
sample preparation (solutions cannot be to complicated)
Solution – Couple with electrochemistry:
• Thus, by adding electrochemical techniques, we can alter the
charge on the surface to adsorb/desorb a wide range of
molecules and we can two independent data sets (i.e.
frequency shifts with EC data) to allow for modeling of more
complex reactions
f / Hz
What is EQCM?
0
100
200
300
Time / s
400
500
What is EQCM?
Counter electrode
Adapted from
http://w3.bgu.ac.il/ziwr/prizes/WangYing.htm
Adapted from ALS
http://www.als-japan.com/1194.html
Adapted from CH instruments
http://www.chinstruments.com/chi400.html
Uses in Literature
• Slippage at adsorbate–electrolyte interface (L. Daikhin et. al.)
• Response of the Electrochemical Quartz Crystal Microbalance for
Gold Electrodes in the Double-Layer Region using different
electrolytes (V. Tsionsky et. al)
• Underpotential deposition of metals (Buttry et. al.)
• Oxide Growth on Ti and Zn (Lemon et. al.)
• Influence of potential on Immobilized Films (Bott)
• Swelling and Contraction of Ferrocyanide-Containing Polyelectrolyte
Multilayer (Grieshaber et. al.)
• Monitoring the gold-thiosulfate leaching reaction (Breuer et. Al)
• Sensor for DNA hybridization (Hwang et. al.)
Literature Review
A. Ferancova,J. Labuda and W. Kutner. Electroanalysis. (2001), 13, 1417-23.
Electrochemical Quartz Crystal Microbalance Study of Accumulating Properties of the bCyclodextrin and carboxymethylated b-Cyclodextrin Polymer Films with Respect to the
Azepine and Phenothiazine Type Antidepressive Drugs
Goal of the study:
Characterize the accumulation properties of
antidepressent drugs (shown to the right) in the
two polymer films by EQCM.
This determining drug accumulation is important
in controlled drug release.
A. Ferancova, et. al. Electroanalysis. (2001), 13, 1417-23
Literature Review
  CDP
  CDPA
•
Cyclic voltammograms (1’&1) show a larger
anodic peak current for CDPA than CDP
•
The positive shift in frequency (2’&2), which
suggests a loss in mass, is smaller for CDPA
than CDP.
•
Combining these CV with QCM data suggests
the formation stabilized complex between
drug and polymer
Experimental Conditions:
- Pt/quartz (5MHz) electrode
- Phosphate buffer (pH 7.4, 0.1M)
- levomepromazine (44 μM in cationic state)
- accumulation: 120 s at -0.15V
-scan rate: 10 mV/s
A. Ferancova, et. al. Electroanalysis. (2001), 13, 1417-23
Literature Review
  CDPA
  CDP
•
Anodic peak current at 0.8V suggests that the
ion exchange is pH dependent (particularly for
CDPA)
•
pH 2.5 used to normalize thickness is
carboxylates are protonated in CDPA
•
At pH > 3: CDPA becomes deprotonated, which
allows for ion exchange of the cationic drug
•
At pH > 7: Deprotonation of drug making it less
water-soluble
ipaCDPA 
A. Ferancova, et. al. Electroanalysis. (2001), 13, 1417-23
i CDP
pa
i CDPA
pa
Literature Review
  CDP
  CDPA
Conditions:
- Conc. of all drugs are 20μM
- accumulation -0.15 V
- pH 7.4
•
•
•
A plateau is obtained for all drugs tested after 120s
Current is generally higher for CDPA than CDP
Prochlorperazine (III) shows the frequency shift for both polymers, however,
trimipramine (V) and chloropromazine (IV) have the highest peak current for CDP &
CDPA respectively
A. Ferancova, et. al. Electroanalysis. (2001), 13, 1417-23
Literature Review
  CDP
  CDPA
•
All signal show an increase with
concentration
•
The signals from CDPA are
significantly higher than CPD
•
From the concentration data the
sorption constant and Gibb free
energy sorption can be
determined for the various drugs
using Langmuir isotherm
 pol 

 C pol
a
Csol
(1   )
where   f / f 
or
 = i pa / i pa
From the stability constants, the
sorption free energy can be
determined from:
Gpol  RT ln  pol
A. Ferancova, et. al. Electroanalysis. (2001), 13, 1417-23
Conclusions
•  -CDP and  -CDPA films are useful for a reversible accumulation of the
azepine and phenothiazine type anti-depressive drugs
•
Accumulation is pH dependent with a maximum at pH 7
•
Drug accumulation is much higher in the anionic form of the  -CDPA film
than in the non-ionic  -CDP film, which makes it more ideal for sensors and
drug accumulation and release.
•
The free energy of sorption, Go , have been determined from the Langmuir
sorption isotherms for both polymers.
Proposal
To couple Surface Enhanced Raman with EQCM to
monitor the kinetic adsorption of peripheral proteins
to a model bilayer and monitor the changes in
structure and orientation under the influence of an
applied electric field
a)
Monitor changes in the adsorbed bilayer as a
function of electrode potential
b)
Flow water soluble proteins into the EQCM cell
and characterize as a function of potential
Proposal
•
Assemble a model cell membrane consisting
of DMPC, cholesterol and GM1
•
Apply a positive potential adsorption
potential (0.4V vs. SCE)
•
Sweep the potential in the negative direction
and monitor the change in frequency as the
adsorbed layer lifts from the electrode
surface
•
Cycle in the anodic direction and record the
change in frequency upon re-adsorption of
the film
24
22
20
18
-2
This data will confirm whether the desorption
-adsorption cycle results in a change in
structure of the film or if the bilayer is
destroyed upon desorption
C / F cm
•
16
14
12
10
8
6
4
2
0
-1.2
-1.0
-0.8
-0.6
-0.4
-0.2
E / V vs SCE
0.0
0.2
0.4
Proposal
•
Monitor the change in frequency while
simultaneously collecting SERS
spectra at a constant potential
•
Once the change in frequency reaches
a plateau, the maximum coverage is
obtained
•
Rinse with electrolyte to remove any
unbound proteins
•
Determine the structure and
orientation of the adsorbed protein
(using SERS) and monitor the change
in frequency (QCM) with respect to
electrode potential
785 nm
Summary
• EQCM is a highly sensitive technique (probe ng –pg)
quantities
• Can simultaneously measure both the physical
adsorption processes and electronic properties at the
interface
• Can be used for a wide range of applications such as
monitoring mass transport of redox reactions,
adsorption/desorption, etc.
• Can be easily coupled to other spectroscopic techniques
References
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
W.H. King. Anal. Chem. (1964), 36, 1735-39
Q. Xie. et. al. J. Chem. Ed. (2007), 84, 681-4
H. D. Abruna. Electrochemical Interfaces: Modern Techniques for
In-situ Interface Characterization. (1991), p.531-63.
A. Ferancova, et. al. Electroanalysis. (2001), 13, 1417-23
L. Daikhin, et. al. Electrochimica Acta 45 (2000) 3615–21
V. Tsionsky, et. al. J. Electrochem. Soc., (1996), 143, 2240-4
D. Buttry and M. Ward. Chem. Rev. (1992), 92, 1355-79
B. Lemon and J. T. Hupp. J. Phys. Chem. B (1997), 101, 2426-29
D. Griershaber, et. al. Langmuir. (2008), 24, 13668-76
D. Gimenez-Romero. J. Electrochem. Soc., (2006), 153, J32-9
P. L. Breuer. J. Appl. Electr. (2002), 32, 1167–74
Y. Su, et. al. Biotechnol. Prog. (2008), 24, 262-72
Langmuir Isotherm