Potentiometry biosensors

Potentiometry biosensors, 664 fitness for purpose, 663 hydrogen peroxide determination, 650-1 iodine-iodide buffer, 699 measurement uncertainties, 663 peroxide value, 663-4 transition metal peroxides, 1069 POV see Peroxide value POZ see Primary ozonides Precipitation waters, hydrogen peroxide determination, 637... 

Enzyme sensors are based primarily on the immobilization of an enzyme onto an electrode, either a metallic electrode used in amperometry (e.g., detection of the enzyme-catalyzed oxidation of glucose) or an ISE employed in potentiometry (e.g., detection of the enzyme-catalyzed liberation of hydronium or ammonium ions). The first potentiometric enzyme electrode, which appeared in 1969 due to Guilbault and Montalvo [140], was a probe for urea with immobilized urease on a glass electrode. Hill and co-workers [141] described in 1986 the second-generation biosensor using ferrocene as a mediator. This device was later marketed as the glucose pen . The development of enzyme-based sensors for the detection of glucose in blood represents a major area of biosensor research. 

Biocatalytic membrane electrodes significantly expand the scope of direct potentiometry by enabling biosensors that respond to a whole host of organic substrates to be made. The selectivity of these sensors is a combination of the selectivity of the biocatalyst for the substrate and the ISE for other constituents in the sample that might reach the ISE surface membrane. Thus, the selectivity with respect to other organic constituents in the sample is determined by biocatalyst... 

In this chapter, the fundamental electrochemical principles of potentiometry, voltammetry and/or amperometry, conductance, and coulometry will be summarized and clinical apphcations presented. Next, optodes and biosensors will be discussed. The chapter concludes with a discussion of in vivo and minimally invasive sensors. 

Potentiometry is widely used clmicaUy for the measurement of pH, PCO2 and electrolytes (Nah K, CL, Ca h LP) in whole blood, serum, plasma and urine, and as the basis for some biosensors for metabolites of clinical interest. 

Enzyme biosensors have been described using a range of transduction elements (amper-ometry, potentiometry, optical and photo-thermal). The first biosensor was described in the literature by Clarck and Lyons (1962a) and was based on the use of glucose oxidase combined with electrochemical detection. Since then, this principle has been widely applied in biosensor development, and the enzyme systems used have been mainly oxido-reductases (e.g. tyrosinase, peroxidase and lactase) (Cass etal., 1984 Kulis and Vidziunaite, 2003), and hydrolases (choline esterases) (Andreescu etal., 2002 Nunes etal., 1998). 

In general, electroanalytical detection principles can be divided into three potentiometry, amperometry, and conductometry (or impedometry). Potentiostats used for electrochemical biosensors are mostly equipped with amperometric and... 

At present, several research groups are engaged in preparing suitable layers or membranes for this purpose. Compared to biosensors, these layers are far more stable and they can be prepared for a large variety of compounds. Compared to standard chemosen-sors they are far more selective, so that there is a good chance of a broad application. It is still necessary to develop extremely sensitive methods for detecting substances bound to the imprinted membrane. At present, conductometry [57, 70, 71, 106, 153, 154], capacitance [155], pH-potentiometry [41], voltammetry [69], optical detection [87, 156],... 

Potentiometry is a rarely used detection method employed in biosensors, with enzymes immobilised in an electrodeposited polymer layer, although certain advantages over... 

Different analytes are determined by using electrochemical techniques such as differential pulse voltammetry (e.g., metal ions and chlorhexidine in oral care products, glycolic acid in creams, dyes in lipsticks) or potentiometry (e.g., inorganic compounds and anionic and cationic surfactants in personal care products). Modified carbon electrodes and biosensors have been developed to determine some cosmetic ingredients by techniques such as voltammetry or potentiometry. 

The detection methods used include spectrophotometry, chemiluminescence, fluorescence, amperometry, conductometry, thermometry and potentiometry with ion-selective electrodes or gas sensors. We have focused our attention only on the electrochemical detectors. Some examples of applications of reactor biosensors with the specification of enzyme used, reactor type and detection system are summarized in Table 5. 

Ion-selective electrodes (ISEs) are commercially available for many anions and cations, as indicated in Tables 4-7. Other analytes can be determined using ISEs in an indirect way. Chapter 28.3 deals with various types of jx>tentio-metiic biosensors. A special advantage of ion-selective potentiometry is the possibility of carrying out measurements even in microliter volumes without any loss of analyte. 

Potentiometric MEMS biosensors (potentiometry) are based on potential measurement of an electrode in a solution. This potential is measured in an equilibrium state. In other words, current flow should not exist during the measurement. According to the Nemst equation, the potential is proportional to the logarithm of the concentration of the electroactive species. 

Voltammetric MEMS Biosensors Voltammetric MEMS biosensors measure the current flow at an electrode which is a function of the potential applied to the electrode. Voltammetric measurement gives the current-potential curve or voltammogram. These curves can be used for qualitative, quantitative, thermodynamic and kinetic studies. In contrast to potentiometry, voltammetry gives a linear current response as a function of the concentration, which is a notable advantage [6]. 

Electroanalytical methods have been extensively applied in sensing and biosensing. Potentiometry, amperometry, cyclic voltammetry, linear voltammetry, differential pulse voltammetry, square-wave voltammetry, and electrochemical impedance spectroscopy (EIS) represent the most-used electrochemical techniques used for biosensor fabrication and detection. 

Note BA biamperometric titration CE-CCD capillary electrophoresis with contactless conductivity detection CL chemiluminescence EB electrochemical biosensor FAAS flame atomic absorption spectrometry FIA flow injection analysis HPLC-UV high-performance liquid chromatography with UV detection MC multicommutation P potentiometry SIA sequential injection analysis SP spectrophotometry TB turbidimetry. 

Keywords Amperometry Artificial neural networks Biosensor arrays Electronic tongues Enzyme biosensors Potentiometry Voltammetry... 

For the case of potentiometry, one has to remind that biosensors rely on an enzyme converting substrate into a measurable ion, next detected by the appropriate ISE. The disappearing of a particular ion involved in a catalytic enzyme process might be useful also as the measure principle, only there is not any case to consider here. 

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