Electrochemical impedance spectrometry

The advent of ever smaller electrochemically cells (microcells, capillary cells) which can be placed on selected areas of an electrode surface allows spatially resolved measurements of local properties. Spectroscopic methods modified in such a way like e.g. locally resolved electrochemical mass spectrometry have been treated in previous sections. Optical methods incorporating scanning probes wiU be treated below. Classical electrochemical methods like e.g. impedance measurements employing these miniaturized cells [1] thus providing localized information will not be treated in this book. The same applies to scanning electrodes employed in localized electrochemical impedance measurements (LEIS). 

The combination of spectrometry with a microscopy enables spatially (locally) resolved measurements, depending on the scale of resolution the method is termed spectromicroscopy. The in situ combination of spectrometry with electrochemistry is called spectro-electrochemistry. Note that while most forms of spectroscopy involve the interaction of electromagnetic radiation with a system, the term is also used at times in a more general sense as in electrochemical impedance spectroscopy. 

SAMs of allgrlphosphonic acids (butylphosphonic acid, octylphosphonic acid, undecylphosphonic acid and octadecylphosphonic acid) on native niekel oxide allow substrates to be functionalized easily. Monolayer formation has been investigated by diffuse reflectance Fourier transform infrared spectroscopy, non-contact mode atomic force microscopy, contact angle measurements and matrix-assisted laser desorption ionization mass spectrometry. Cyclic voltammetry and electrochemical impedance spectroscopy studies showed that the monolayer increased surface resistance to oxidation. 

Biomolecule detectors incorporate a biorecognition device capable of selectively recognizing the analyte of interest in connection with a signal transducer and a suitable output device. Transduction methods include a variety of optical (surface plasmon resonance [SPR], fluorescence), electrochemical (voltammetry, impedance, field effect), mechanical (cantilever, surface probe microscopy), and mass-based systems (quartz crystal microgravimetry [QCM], mass spectrometry). Selection of the appropriate transduction system is partially determined by the nature of information sought (quantitative or qualitative), the analyte (concentration, molecular weight), the sample size, and assay timeline. 

---