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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: Gpol 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