Electrical Double Layer based devices
SEED signal increases with decreasing electrode dimensions. SEED signal is nominally correlated with electrode current density. Since Electrode current density increases as electrode dimensions decrease during a redox reaction, the total SEED signal due to a redox reaction increases. The corresponding total current decreases.
Multiple Analyte Measurement in SEED. SEED can measure change in oxidation states of ions trapped on an electrode surface. This property can be used to detect analytes through mediation by functionalized spot on monolith electrode. This technique has been used to measure turnover of glucose on glucose oxidase trapped at the surface and surface bound double stranded miRNA
Immersing a metal (electrode) in a salt solution will spontaneously accumulate ions due to image charge to form the well known electrical double layer (EDL). Sign of the charge depends on the Fermi level (i.e., the electrochemical potential) difference between the metal and the solution. For example, gold will accumulate negative ions (i.e., anions). The interfacial structure composed of EDL is typically 2-100 nm thick (depending on the salt concentration). The highly mobile and dynamic nanometer scale thin film controls a range of macroscopic behavior, such as electrochemical reaction rate, energy density storage capacity of electrochemical super-capacitor, immunospecific binding, and cell function, to name a few. A platform technology, called Scanning Electrometer for Electrical Double-layer (SEED) is invented and developed based on the dynamical properties of EDL. By scanning a laser beam, SEED allows measurement of multiple redox reaction over a monolith electrode.
Relevent Publications
- "Multianalyte electrochemical biosensor on a monolith electrode by optically scanning the electrical double layer", Biosensors and Bioelectronics, 2014, 57, 41-47.
- “Direct Mapping of Local Redox Current Density on a Monolith Electrode by Laser Scanning,” Biosensors and Bioelectronics, 2013, 47, 408-414.
- "Fabrication and Properties of Redox Ion Doped Few Monolayer Thick Polyelectrolyte Film for Electrochemical Biosensors at High Sensitivity and Specificity. Electroanalysis, 2013, 25, 1557-1566.
- “Localized Electrochemistry on a 10 μm Spot on a Monolith Large Electrode: An Avenue for Electrochemical Microarray Analysis”, Analytical Chemistry, 2009, 81, 6055-6060.
Principle of SEED signal. The AC potential modulates the ions at a fixed frequency. The ion oscillation is restricted within the EDL of thickness ~10 ζ, where ζ is the Debye length. Due to passivation no oscillation on the polymer resist side will occur. The oscillation causes modulation of the optical path length. SEED measures the amplitude, Δ of the path length oscillation. The optical signal, Δ is measured as a function of potential between the solution and the reference electrode (VDC or V). The redox current, I is measured between counter and working electrode. Similar to redox current (Imax), Δmax is also a linear function of analyte concentration.