Impedance spectroscopy devices

Impedance Detection, Fig. 12 Generalized structure of an impedance spectroscopy device using Fourier analysis for the processing of response signals... 

Other sensor platforms have also been explored, such as surface plasmon resonance, field-effect transistors, other optical/spectrophotometric methods, for example, Raman spectroscopy and chemiluminescence, and electrochemical techniques. Very recently, Cai et al. have demonstrated that arrays of carbon-nanotube tips with an imprinted nonconducting polymer coating can recognize proteins below the picograms per liter level, using electrochemical impedance spectroscopy. Devices for the specific recognition of human ferritin and human papillomavirus-derived E7 protein were described (Figure 34). 

The authors of this paper propose for the first time an updated, prospective method for impedance spectroscopy based on an essentially new design of the electrode system. In this case, the electrode system is replaced by an extended electric conductor immersed into the electrolyte. An alternating voltage is applied to the ends of the conductor connected directly to a measuring device. This signal induces two identical and electrochemically conjugated electrodes at the both ends of the conductor. The polarity of these electrodes is variable by fed frequency. They come in contact at the non-polarized centre of the extended conductor. The linear coordinate of the non-polarized centre is estimated on the condition of a conjugation of cathodic and anodic process ... 

For sensitive measurements such as impedance spectroscopy and fast transients, it is not advisable to perform the measurement in the glove box. It is possible to perform the measurements near the measuring equipment, using a transfer system that maintains the inert atmosphere. Such a transfer device may be a hermetically closed metal box which contains the appropriate electrical connections, such as BNC plugs. Thus, the electrochemical cell should be assembled... 

This book is intended to provide a background and training suitable for application of impedance spectroscopy to a broad range of applications, such as corrosion, biomedical devices, semiconductors and solid-state devices, sensors, batteries, fuel cells, electrochemical capacitors, dielectric measurements, coatings, elec-trochromic materials, analytical chemistry, and imaging. The emphasis is on generally applicable fundamentals rather than on detailed treatment of applications. The reader is referred to other sources for discussion of specific applications of impedance. ... 

Combination of impedance spectroscopy with other physical methods (SPR, QCM, FUR spectroscopy) is especially productive in characterization of the interfacial properties of sensing and bioelectronic devices. 

It was hrst reported in 2001 [32] that the evaluation by impedance spectroscopy of a biased zirconia sensor with an attached LaFeOa-SE has shown that only the electrode resistance is a function of NO2 content. Consequently, impedance spectroscopy offers a method for directly probing the electrode reactions that are the basis for mixed-potential-type gas sensors [67]. As a result of further development by using impedance spectroscopy in zirconia-based gas sensors with oxide-SEs, a new type of YSZ-based sensor for detecting total NO and HCs at high temperatures has been proposed recently [2, 14, 21, 62, 74, 96-100]. In this case, the change in the complex impedance of the device attached with a specific oxide-SE was measured as a sensing signal. 

X. Cheng, Y. Liu, D. Irimia, U. Demirci, L. Yang, L. Zamir, W. R. Rodriguez, M. Toner and R. Bashir, Cell detection and counting through cell lysate impedance spectroscopy in microfluidic devices. Lab Chip, 1, 746-755 (2007). 

J. Yang and D.C. Martin, Impedance spectroscopy and nanoindentation of conducting poly(3,4-ethylenediox)4hiophene) coatings on microfabricated neural prosthetic devices, J. Mater. Res., 21(5), 1124-1132 (2006). 

Impedance spectroscopy measures the frequency response of the electric impedance. In an impedimetrie sensor, the molecules to be characterized are adsorbed on the electrodes, or on a surface between a pair of electrodes. This process of absorption changes the electrical performance of the device. By measuring the impedance between the electrodes, some conclusions can be established. " ... 

The underlying principle of impedimetrie techniques is electrical impedance spectroscopy. These techniques are used in biochemical and environmental appUcations because of their sensitivity, however, with varying success. A wide variety of designs of the devices is known for the analysis of hiomaterials. " ... 

FIGURE 46.19 Impedance spectroscopy, (a) Schematic diagram of the impedance measurement device analysis plots (b) Nyquist plot and (c) Bode plot. 

Conductometric sensors measure the change in conductivity of a selective layer in contact with two electrodes upon its interaction with the analyte. Conductometric sensors are often based on field-effect devices. For example, capacitance sensors such as the above-mentioned field-effect capacitor [5] belong to this group. Capacitive detection was also employed in conjunction with imprinted electropolymerized polyphenol layers on gold electrodes [36]. The sensitive layer was prepared by electropolymerization of phenol on the electrode in the presence of the template phenylalanine. The insulating properties of the polymer layer were studied by electrochemical impedance spectroscopy. Electrical leakages through the polymer layer... 

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