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Electrodes and the EQCM Flow Cell.
The AT-cut 10-MHz Carbon quartz crystals were obtained from ICM Technologies (Oklahoma City, OK). For the study of the potential-dependent MT deposition and the subsequent voltammetric studies, QCM crystals covered with a glossy layer of carbon were employed to form the TMFs. The low-volume PEEK EQCM flow cell constructed in-house has a flow-by configuration, similar to that in the cell design by Universal Sensor Inc. (Metairie, LA).
Instruments. The frequency measurements were made using a CHI440 electrochemical quartz crystal microbalance (CH Instruments, Austin, TX). The QCM cell and the oscillator circuit were housed in a Faraday cage (Elchema Inc., Postdam, NY). The carrier solution preloaded in a 10-mL syringe was delivered with a syringe pump (Pump11, Harvard Apparatus, Holliston, MA) through a six-port rotary valve
(Valco Instruments, Houston, TX). A 100-mL sample loop was used for loading the sample solution.
Procedures. The pretreatment of the Au-coated crystal follows our published procedure.[30] To clean the carbon-coated crystals, 1% HNO3 solution was used to soak the crystal to dissolve metal contaminants at the crystal surface, followed by washing with the Micro-90 solution (International Products Inc.,
Burlington, NJ). The carrier solution for the Ag deposition/stripping experiment was 0.1 M KNO3, whereas
that used for the MT adsorption/electrochemistry was a Tris-HCl buffer.
Throughout the various FI-EQCM experiments, a predetermined potential can be applied to the crystal electrode and both the
frequency and the current are monitored as functions of time. The setup can also be operated in the
open-circuit configuration in which no external potential is applied.
EQCM or differential pulse voltammetric measurements can be performed immediately after the cell content has been completely
replaced by the carrier solution, eliminating the necessity of disassembling the cell and avoiding potential
contaminations.
Figure 1a. Schematic of
Low-Volume cell for Flow Injection Quartz
Crystal Microbalance measurements.
Figure 1b.
Electrochemical Workstation where Quartz Crystal
measurements are conducted.
Figure 2a. Quartz
Crystal Flow Cell with oscillator unit and two
representative Au-Quartz Crystals.
Figure 2b.
Metallothionein protein with coordinated metals
bound to alpha and beta domains.
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