Microelectrodes, chemically modified

F. Bedioui, S. Trevin, and J. Devynck, Chemically modified microelectrodes designed for the electrochemical determination of nitric oxide in biological systems. Electroanalysis 8, 1085-1091 (1996). 

Natan, Michael J. and Wrighton, Mark S., Chemically Modified Microelectrode... 

Fig. 14.45. Amperometric recordings from a single canine pancreatic (3-cell bathed in Ca2+-free physiological buffer. Bars indicate the application of solution from a micropipette. In the trace on the left, the solution applied was Ca2+-free physiological buffer with 64 mM K+. (Reprinted from Lan Huang and Robert Kennedy, Exploring Single-Cell Dynamics Using Chemically-Modified Microelectrodes, in Trends in Analytical Chemistry, Vol. 14, p. 160, Fig. 3, copyright 1995, with permission from Elsevier Science.)...

O Shea, T.J. and S.M. Lunte (1994). Chemically modified microelectrodes for capillary electrophoresis/electrochemistry. Anal. Chem. 66(2), 307-311. 

Natan MJ, Wrighton MS. Chemically modified microelectrode arrays. Prog Inorg Chem... 

Huang, L., Shen, H., Atkinson, M. A., Kennedy, R. T. 1995. Detection of exocytosis at individual pancreatic beta-ceUs by amperometry at a chemically-modified microelectrode. Proc. Natl. Acad. Sci. U.S.A. 92 9608-9612. 

Zhang S, Sun W-l, Xian Y-z, Zhang W, Jin L, Yamamoto K, Tao S, Jin, J (1999) Multichannel amperometric detection system for liquid chromatography to assay the thiols in human whole blood using the platinum microelectrodes chemically modified by copper tetra aminophthalocyanine. Anal Chim Acta 399(3) 213-221... 

In this chapter, we discuss voltammetric methods and associated electrochemical sensors, including chemically modified electrodes. Voltammetric techniques use a microelectrode for microelectrolysis. Here, the potential is scanned and a dilute solution of the analyte produces, at a given potential, a limiting current (microampere range or less), which is proportional to the analyte concentration. Am-perometry is the application of voltammetry at a fixed potential to follow, via the current, changes in concentration of a given species, for example, during a titration. Amperometric measurements also form the bases of electrochemical sensors. 

See also DNA Sequencing. Enzymes Enzyme-Based Electrodes. Forensic Sciences Blood Analysis. Immunoassays, Techniques Enzyme Immunoassays. Microelectrodes. Polarography Techniques Organic Applications. Purines, Pyrimidines, and Nucleotides. Sensors Chemically Modified Electrodes. Voltammetry Organic Compounds. 

See also Atomic Absorption Spectrometry Principles and Instrumentation. Atomic Emission Spectrometry Inductively Coupled Plasma. Flow Injection Analysis Principles Instrumentation Detection Techniques Environmental and Agricultural Applications Clinical and Pharmaceutical Applications Industrial Applications. Microelectrodes. Sensors Chemically Modified Electrodes. Thin-Layer Chromatography Overview. Water Analysis Freshwater Seawater - Inorganic Compounds. 

Other types of planar NO microsensors include Pt microelectrodes chemically modified by electrodeposition of metaUoporphyrin-like nickel(II) complexes. For example, tetrasul-fonated phthalocyanine tetrasodium (NiTSPc) was electrodeposited on the bare electrode surface by repetitive cychc voltammetry (21). Alternatively, electrode functionalization using nickel(4-iV-tetramethyl)pyridyl porphyrin (NiTmPyP) as an electrocatalyst was also carried out by applying multiple pulses in differential pulse amperometry (22). In this case, the electrocatalyst was entrapped in a NO selective polymer network of a negatively charged acrylic acid resin that prevented access by anionic interfering species. 

Chemically modified electrodes have also been employed as detectors for CEEC [33,34]. Specifically, carbon paste modified with cobalt phthalocyanine was explored in our laboratories for selective detection of thiols [33]. Electrodes were produced by packing a 150 pm i.d. fused silica capillary with modified carbon paste to a depth of approximately 5 mm. This electrode was used for the selective detection of cysteine in urine. Later, ruthenium cyanide-modified electrodes were used for the simultaneous detection of thiols and disulfides at +850 mV (vs. Ag/AgCl) [34]. Modified carbon fiber microelectrodes were prepared by cycling the potential between 500 and 1000 mV at a scan rate of 50 cycles in an acidic deoxygenated plating solution containing RuClj, K RuiCN), and KCl. Detection limits for cystine were 3 pM. The selective detection of cystine in urine of a patient with kidney stones was demonstrated. 

Many of the chapters in this book have been devoted to various aspects of electroanalytical chemistry at diamond electrodes, for example, the preparation and characterization methods for BDD (Chapter 2), the question of the large potential working range (Chapter 3 for aqueous solution, and Chapter 6 for a wide variety of non-aqueous solutions), the influence of the boron doping levels on the kinetics for redox reactions (Chapters 4 and 5), the characterization and influence of the surface termination (Chapter 7 for hydrogen termination and Chapter 10 for oxygen termination), chemically modified surfaces in general (Chapter 9), metal-modified and ultrasmooth surfaces (Chapter 11), and the use of microelectrodes (Chapter 18) and nanostructured diamond electrode surfaces (Chapter 19). 

Various analytical strategies based on the use of chemically modified electrodes are presented. We describe the use of conventionally sized as well as microelectrodes in the determination of mercury and copper ions in solution and point to the potential utility of modMed electrodes in carrying out speciation studies. Also discussed is the use of carbon fiber microelectrodes modified with alkaline phosphatase as amperometric biosensors. Finally, we present some preliminary findings on the development of a mo fied platinum electrode for the determination of nitric oxide. 

It is clear that the use of chemically modified electrodes lends itself to numerous and varied analytical applications. By the judicious choice of electrode modifier the properties of the interface can be exquisitely tuned in a controlled fashion to achieve discrimination based on various chemical interactions including coordination, Donnan exclusion, enzyme activity, size exclusion and others. In addition, the use of microelectrodes has extended the range of applications. We feel confident that as new analytical challenges arise and as our ability to control... 

Figure 5.4 Current response for a 12.5 pm platinum microelectrode modified with a [Os(bpy)2 py(p3p)]2+ monolayer following a potential step where the overpotential rj was —100 mV the supporting electrolyte is 0.1 M TBABF4 in acetonitrile. The inset shows ln[fp(f)] versus f plots for the Faradaic reaction when using a 12.5 pm (top) and 5 pm (bottom) radius platinum microelectrode. Reprinted with permission from R. J. Forster, Inorg. Chem., 35, 3394 (1996). Copyright (1996) American Chemical Society...

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