Lecture 1-3pre- master electro_removed PDF

Potentiometric Biosensor Makes use of the selectivity offered by many of the high selective ISEs. Makes use of the very high selectivity of offered by the enzymatic reactions. Either the product or the reactant of the enzymatic reaction is monitored using ISEs. Ca...

Potentiometric Biosensor Makes use of the selectivity offered by many of the high selective ISEs. Makes use of the very high selectivity of offered by the enzymatic reactions. Either the product or the reactant of the enzymatic reaction is monitored using ISEs. Can be applied for the determination of many neutral and organic species (e.g., Urea). The main limitation is the high cost of enzymes. Examples A simple-potentiometric method for determination of acid and alkaline phosphatase enzymes in biological fluids and dairy products using a nitrophenylphosphate plastic membrane sensor  Enzyme electrodes In the case of the enzymatic membranes, stability of the biosensor depends on proper anchor of enzyme molecules to their surface or in membrane bulk. Various methods of the enzyme immobilisation in and/or within the supports with different functional groups were analysed. To obtain functional groups on the support surface,various methods of chemical modifications were applied. The enzyme converts an analyte into a product that is detected at the sensor surface.To obtain the biosensor response, the analyte must penetrate through the membrane to the catalytically active sites of the enzyme and then the products partially diffuse to the sensor surface and away into the bulk solution. The mass transport trough the membrane is mainly driven by the concentration gradients of species then, diffusive  POTENTIOMETRIC TRANSDUCERS BASED MOLECULARLY IMPRINTED POLYMERS (MIP) A molecular imprinted polymer (MIP) is a polymer that was formed in the presence of a molecule that is extracted afterwards, thus leaving complementary cavities behind. These polymers show a certain chemical affinity for the original molecule and can be used to fabricate sensors, catalysis or for separation methods. The functional mechanism is similar to antibodies or enzymes. Potentiometric Sensors of Molecular Imprinted Polymers for Specific Binding of Chlormequat  Imprinted polymer electrode sensor In the recent years, molecular imprinting technology (MIT) has been considered as an attractive method to produce artificial receptors obtained with the memory of size, shape, and functional groups of the template molecules. MIPs have been widely used as mimetic molecular recognition receptors with recognition sites for a given molecule structure. The different strategies used in the preparation of MIP, including precipitation polymerization, emulsion polymerization, core–shell approaches, and bulk processes.  The specific recognition property of MIPs was based on the formation of complexes between the appropriate functional monomers with the templates which mainly could bind covalently or non- covalently. Non-covalent interactions between the functional monomers and the template are probably the most flexible regarding the selection of the possible template molecules and the functional monomers (ex: acrylic acid, methacrylic acid, acrylamide…etc). These complexes were then immobilized by copolymerization with a high concentration of cross- linkers (Ethylene glycol dimethacrylate (EGDMA)) in the presence of iniator (ex: AIBN, potassium per sulphate.  After the polymerization was complete, the templates were removed, providing binding sites in the MIPs that had complementary shapes, sizes, and functionalities toward the target template. With these tailor-made binding sites, MIPs not only recognize the shape and size of a given template but also respond to the functional groups of the molecule. Molecular imprinting technology Self-assembling approach Pre-organized apporach Non-covalent Metal coordination Covalent interactions interactions interactions semi-covalent imprinting polymers Gas Sensors  pCO2 Electrode The measurement of pCO2 is based on its linear relationship with pH over the range of 10 to 90 mm Hg. H2 O  CO2  H2 CO3  H   HCO3  The dissociation constant is given by  H  HCO    k 3 a  pCO2 Taking logarithms pH = log[HCO3-] – log k – log a – log pCO2 Biosensor - an analytical device that exploits a biocatalytic reaction Consists of: biocatalyst (enzyme, cells, tissue) transducer (converts the biological or biochemical signal into a quantifiable electrical or optical signal)  First biosensor - Clark (1962): glucose sensor with glucose oxidase and oxygen electrode Glucose + O2 Gluconic acid + H2O2 Oxygen electrode (1956) working electrode: Pt cathode (-0.6 V) reference electrode: Ag/AgCl electrodes separated from measured solution with a gas permeable mebrane Leland C. Clark, Jr. with the first enzyme electrode Personal glucose meter for diabetics (Medisense Britain, Ltd.)