Electrochemical Performance of Lithographically-Defined Micro-Electrodes for Integration and Device Applications

Abstract

Small; lithographically-defined and closely-spaced metallic features of dimensions and separation in the micrometer range are of strong interest as working and counter electrodes in compact electrochemical sensing devices. Such micro-electrode systems can be integrated with microfluidics and optical biosensors, such as surface plasmon waveguide biosensors, to enable multi-modal sensing strategies. We investigate lithographically-defined gold and platinum micro-electrodes experimentally, via cyclic voltammetry (CV) measurements obtained at various scan rates and concentrations of potassium ferricyanide as the redox species, in potassium nitrate as the supporting electrolyte. The magnitude of the double-layer capacitance is estimated using the voltammograms. Concentration curves for potassium ferricyanide are extracted from our CV measurements as a function of scan rate, and could be used as calibration curves from which an unknown concentration of potassium ferricyanide in the range of 0.5–5 mM can be determined. A blind test was done to confirm the validity of the calibration curve. The diffusion coefficient of potassium ferricyanide is also extracted from our CV measurements by fitting to the Randles–Sevcik equation (D = 4.18 × 10−10 m2/s). Our CV measurements were compared with measurements obtained using macroscopic commercial electrodes, yielding good agreement and verifying that the shape of our CV curves do not depend on micro-electrode geometry (only on area). We also compare our CV measurements with theoretical curves computed using the Butler–Volmer equation, achieving essentially perfect agreement while extracting the rate constant at zero potential for our redox species (ko = 10−6 m/s). Finally, we demonstrate the importance of burn-in to stabilize electrodes from the effects of electromigration and grain reorganization before use in CV measurements, by comparing with results obtained with as-deposited electrodes. Burn-in (or equivalently, annealing) of lithographic microelectrodes before use is of general importance to electrochemical sensing devices

Real-Time Convolutional Voltammetry Enhanced by Energetic (Hot) Electrons and Holes on a Surface Plasmon Waveguide Electrode

“…The diffusion coefficient of potassium ferricyanide ( D 0 ) in our electrolyte was reported as 4.18 × 10 –10 m 2 /s . The diffusion coefficient of potassium ferrocyanide ( D R ) in our electrolyte was obtained by fitting CV measurements to the Randles–Sevcik equation, yielding 3.56 × 10 –10 m 2 /s.…”

“…The concentration distribution of the oxidized species, C O ( z , t ), satisfying the first of eqs , is written as where μ is defined as with b = RT / F (where R is the gas constant (J/(mol K))), T is the temperature (K), and F is the Faraday constant (C/mol). η is the overpotential (V), η = E – E 0 , where E is the potential of the WE through which the current flows, and E 0 is the equilibrium potential established when no current flows.…”

“…The diffusion coefficient of potassium ferricyanide (D 0 ) in our electrolyte was reported as 4.18 × 10 −10 m 2 /s. 31 The diffusion coefficient of potassium ferrocyanide (D R ) in our electrolyte was obtained by fitting CV measurements to the Randles−Sevcik equation, 31 The change in refractive index per unit concentration of potassium ferricyanide (K 3 [Fe(CN) 6 ]), α O , is needed to connect the experimental results with theory. The refractive index of our four concentrations of potassium ferricyanide, C O = 0.5, 1, 3, 5 mM (0.35, 0.69, 2.07, and 3.45 mol/m 3 ), dissolved in our electrolyte, were measured using a prism coupler (Metricon) at λ 0 = 1312 nm and plotted in Figure S-2 in the Supporting Information.…”

Infrared surface plasmons on a Au waveguide electrode open new redox channels associated with the transfer of energetic carriers

“…WE and CE were then selected and electrically burned in before use by injecting a current (ramp function) along an electrode structure until its resistance stabilized. Burn-in induces grain reorganization through annealing, which stabilizes the electrodes before use in an electrochemical experiment ( 34 ). The chip was affixed to the bottom of a petri dish, and electrochemical, optical, or resistance measurements were carried out as required.…”

Low-Grade Thermal Energy Harvesting and Self-Powered Sensing Based on Thermogalvanic Hydrogels

“…The potential can be increased by developing and optimizing the basic thermodynamic principle, i.e., applying a redox couple and electrolyte combination with a high Se. In addition to increasing the potential of individual thermogalvanic cells, another hot research area focuses on device integration and applications [ 80 , 81 ]. The output voltage of thermogalvanic-integrated devices can be increased by optimizing the polymer network or using different bridging methods.…”