Faradaic impedance spectroscopy

E. Katz, L. Alfonta, and I. Willner, Chronopotentiometry and Faradaic impedance spectroscopy as methods for signal transduction in immunosensors. Sens. Actuators B 76, 134-141 (2001). 

Label-free detection of ligand-aptamer interaction was also demonstrated by means of impedance spectroscopy technique [52,53]. Simultaneously, Radi et al. [52] and Rodriguez et al. [53] reported application of Faradaic impedance spectroscopy (FIS) in detection of interaction of proteins with DNA aptamers. The detection method is based on the measurement of resistance in presence of redox mediator Fe(CN)6-In absence of target protein, the negatively charged aptamer repulse the redox mediator molecules from the sensor surface. In a paper by... 

Patolsky, K, Zayats, M., Katz, E., and Willner, I. (1999) Precipitation of an insoluble product on enzyme monolayer electrodes for biosensor applications Characterization by faradaic impedance spectroscopy, cyclic voltammetry, and microgravimetric quartz crystal microbalance analyses. Anal. Chem. 71, 3171-3180... 

The nse of faradaic impedance spectroscopy as a means to identify affinity complexes between the aptamers and small molecules is, however, more difficult... 

Alfonta, L., Bardea, A., Khersonsky, O., Katz, E., Willner, I. (2001). Chronopotentiometry and faradaic impedance spectroscopy as signal transduction methods for the biocatalytic precipitation of an insoluble product on electrode supports routes for enzyme sensors, immunosensors and DNA sensors. Biosens Bioelectron 16, 675-687. 

R. Gabai, N. Sallacan, V. Chegel, T. Bourenko, E. Katz, I. Willner, Characterization of the swelling of acrylamidophenylboronic acid-acrylamide hydrogels upon interaction with glucose by faradaic impedance spectroscopy, chronopotentiometry, quartz crystal microbalance (QCM), and surface plas-mon resonance (SPR) experiments, Journal of Physical Chemistry B 2001, 105, 8196. 

Large differences between the interfacial properties of ds and ssDNAs observed earlier by capacitance measurements [10, 37] suggested that a.c. impedance measurements could be used to detect DNA hybridization on electrodes [433, 434] (Sect. 12.8.). A three-component ODN system on a gold electrode (involving avidin-biotin interactions) was used to detect specific DNA sequences by means of faradaic impedance spectroscopy [435]. Impedance spectroscopy does not seem, however, to be the most convenient method for the DNA biosensor faster and simpler voltam-metric or chronopotentiometric methods will probably be more convenient. Gon-ductivity of the perfect DNA, contrasting with a loss of conductivity in duplexes with mismatched bases, may be of use in... 

Boronic acids have been used in the development of surface plasmon resonance (SPR) [174,175] quartz crystal microbalance (QCM) sensors [174,176,177], Faradaic impedance spectroscopy [177], ion-sensitive field effect transistors (ISFET) [178], and chemical exchange saturation transfer (CEST) contrast agents in magnetic resonance imaging (MRl) [179]. The swelling of phenylboronic add polymers has also been used to control the release of insulin (180,181]. 

Different electronic transduction means were discussed, including faradaic impedance spectroscopy, chronopotentiometry, chronocoulometry, and micro-gravimetric quartz-crystal-microbalance measuranents. The different methods reveal high sensitivities that allow the detection of 5(X>-2(X)0 copies of DNA in 10-50 jL of samples. These rapid advances in electronic DNA detection open the way to construct electrode chips for the parallel or consecutive analyses of a collection of nucleic acids. The technologies to construct such electrode arrays are available, and robotic methods for the site-specific spotting of such arrays are known. This suggests that the different approaches are sufficiently ripe to be harnessed and optimized for practical targets. 

Faradaic and non-Faradaic impedance spectroscopies are effective methods to probe the interfacial electron-transfer resistance at a functionalized electrode. In Faradaic impedance sensors, the interaction between a biological receptor and a target species... 

Impedance spectroscopy has been extensively used to follow changes of the interfacial properties of electrodes upon immobilization of enzymes and to characterize biocatalytic processes at enzyme-modified electrodes. Faradaic impedance spectroscopy can be used to study the kinetics of the electron transfer originating from bioelectrocatalytic reactions. It should be noted, that for characterizing redox-active biomolecules by impedance spectroscopy no additional redox probe is added to the electrolyte solution, and the measured electron-transfer process corresponds to the entire bioelectrocatalytic reaction provided by the biocatalyst. Under the condition that the enzyme is not saturated by the substrate, the electron-transfer resistance of the electrode is also controlled by the substrate concentration. Thus, the substrate concentration can be analyzed by the impedance spectroscopy following values [9]. 

Faradaic impedance spectroscopy investigation of Fe(CN)4 transport in P2VP brush-modified ITO. (a) Equivalent electronic circuit used to model physicochemical processes associated with the faradaic impedance spectra, (b) Typical impedance spectra (Nyquist plot), Im(Z) vs. Re(Z), for decreasing pH values (from a to g) Hne best fit to the equivalent circuitry, (c) Titration curve showing changes of the electron transfer resistance derived from (b) and fitted by (a) upon variation of the pH going in the (i) acidic then (ii) basic and (iii) acidic directions. (Adapted from Motornov, M., et al., ACS Nano, 2,41-52,2008.)... 

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