Electrochemical sensing techniques

Table 15.1 Overview of multi-gas instruments that incorporate electrochemical sensors for in situ detection of volcanic gases as portable backpack and fixed-installation instruments, as well as commercial instruments based on electrochemical sensing techniques...

Topics discussed above are some basic principles and techniques in voltammetry. Voltammetry in the frequency domain where i-E response is obtained at different frequencies from a single experiment known as AC voltammetry or impedance spectroscopy is well established. The use of ultramicroelectrodes in scanning electrochemical microscopy to scan surface redox sites is becoming useful in nanoresearch. There have been extensive efforts made to modify electrodes with enzymes for biosensor development. Wherever an analyte undergoes a redox reaction, voltammetry can be used as the primary sensing technique. Microsensor design and development has recently received... 

Cyclic voltammetry provides a very convenient method for determining the redox potentials of couples as the peak potentials for the cathodic, E, and anodic, pa, processes of a reversible couple are related, at 25 °C, to the redox potential by pa = E /2 = E° + 0.285/n volts and E. = pa/2 = E° — 0.285/n volts. pc/2 and EpJ2 are the potentials at a point half-way up the wave at these points the current is half the maximum value, i.e. ipc for the cathodic wave or ipa for the anodic wave. Again, this technique will yield redox potentials only if the couple is reversible in the electrochemical sense, but this is now very readily established through the above relationship that pa — -Epc = A p = 57/n mV and by the requirement that ipjip3 = 1. In addition it should be established that Ep is independent of the scan rate, v, and that the process is diffusion controlled by showing ip/v h to be constant. 

The present section is devoted to MIP-aided electrochemical sensors. Here, versatility in using electroanalytical techniques for determination of the analytes and their advantage over other detection techniques have been emphasized. A range of recognition MIP materials has been described. Several review papers, related to the electrochemical sensing based on MIPs, have already been available [16, 22-24]. The present chapter focuses on recent achievements in this research area. 

We recently incorporated the ruthenium(II) bipyridyl moiety into acyclic, macrocyclic, and lower rim caUx[4Jarene structural frameworks to produce a new class of anion receptor capable of optical and electrochemical sensing (226, 253. 254). Stability constant determinations in DMSO using H NMR titration techniques demonstrated that these acyclic receptors (131 and 132) form strong complexes with chloride and dihydrogen phosphate anions (stronger than with analogous monopositive cobaltocenium based receptors). The ruthenium ion is dipositive and hence the electrostatic interactions are particularly favorable. The 4,4 -substituted ruthenium bipyridyls were observed to bind anions more... 

Liu, C. C., and F. W. Klink. Electrochemical sensing and monitoring techniques and devices. Tutorial Lectures in Electrochemical... 

Electrochemical analytical techniques are some of the oldest in chemistry and can be divided into potentiometry, voltammetry and conductimetry. They are most important as detectors after chromatographic separations and as chemical and biological sensors. They generally involve the use of electrodes that are housed in electrochemical cells. All electrochemical cells contain two electrodes but some have three. The first electrode is the actual working electrode (also called a sensing or indicator electrode) and the second is a combined reference electrode and auxiliary (counter) electrode. If there are three electrodes, the reference and counter electrodes are separate. 

All sensing techniques demonstrate specific strengths, yet sometimes overlapping, areas of application. In this case, both electrochemical and optical techniques, can allow analysis in real-time, in situ, non-destructive, label-free, thin films and interfaces analysis [33-35],... 

A number of methods for sensing or analyzing charged or neutral species in solution using voltaimnetric techniques have been identified. However, in the electrochemical sensing of noiu edox-active species, supramolecular chemistry can play a particularly important role in this area with... 

Sensing layer Transduction approach Electrochemical Analyte technique Sample Comment Reference... 

In this chapter, we have reported some examples related to DNA sensors, especially used in food applications, by employing electrochemical detection techniques. A variety of sensing systems based on label-free techniques utilizing electrochemical and/or surface activity as well as direct methods that rely on the intrinsic electrochemical properties of DNA (the oxidation of purine bases, particularly guanine) have been presented in the different sections of this chapter. 

Various physical transducers can be used to detect interaction of the immobilized DNA probe with the analyte. Commonly used detection systems include optical (MarvUc, 1997 Jordan, 1997 Lee, 2001), electrochemical (Wang, 2001 Palecek, 2001) or mass sensitive devices (Storri, 1998 Ebara, 2000). Considering the growing number of potential applications, simphcity and low cost are some of the major design parameters in both microarray and other biosensor apphcations. Therefore, increased attention has been given to relatively simple detection or sensing techniques such as fluorescence measurements. This method offers faster assays without the need for specific substrate properties such as in the mass-sensitive quartz-crystal microbalance (Storri, 1998 Ebara, 2000) or in more complex optical techniques such as surface plasmon resonance (Jordan, 1997 Lee, 2001). 

---