Glucose immobilized

Glucose Immobilization of glucose oxidase, peroxyoxalate-H202 CL 0.05 pM 42... 

Glucose Immobilized glucose oxidase, luminol-H202 CL 15 xM 103... 

N. PEKEL, B. SALIH, O. GUVEN, Activity studies of glucose immobilized onto ply(N-vinylimidazole and metal ion chelated Poly(N-vinylimidazole) hydrogels , J. Molecular Catalysis B Enzymatic, 21 (2003) 273-282... 

A more robust SERS substrate has been developed by Van Duyne and coworkers that can be modified for biological applications.[21, 22] For many years researchers have attempted to develop SERS based glucose sensors. Theses attempts have fallen short due to the inability to get the glucose immobilized close to the SERS substrate. This technical hurdle was overcome recently by Van Duyne and coworkers who utilizing specially prepared SERS substrates and short chain alkanes have been able to show that SERS can be utilized as a glucose sensor.[23] These platforms are able to detect glucose over a concentration range of 10-400 mg/dL. 

Activity studies of glucose immobilized onto poly(N-vinyl imidazole) and metal ion chelated poly (N-vinyl imidazole) hydrogels. J. Mol. Catalysis B Enzym., 21, 273. 

Sittampalam, G. Wilson, G. S. Amperometric Determination of Glucose at Parts Per Million Levels with Immobilized Glucose Oxidase, /. Chem. Educ. 1982, 59, 70-73. 

Immobilization. The fixing property of PEIs has previously been discussed. Another appHcation of this property is enzyme immobilization (419). Enzymes can be bound by reactive compounds, eg, isothiocyanate (420) to the PEI skeleton, or immobilized on soHd supports, eg, cotton by adhesion with the aid of PEIs. In every case, fixing considerably simplifies the performance of enzyme-catalyzed reactions, thus faciHtating preparative work. This technique has been appHed to glutaraldehyde-sensitive enzymes (421), a-glucose transferase (422), and pectin lyase, pectin esterase, and endopolygalacturonase (423). 

P-amylase, and debranching enzymes. Conversion of D-glucose to D-fmctose is mediated by glucose isomerase, mosdy in its immobilized form in columns. Enzymic degradation of starch to symps has been well reviewed (116—118), and enzymic isomerization, especially by immobilized glucose isomerase, has been fiiUy described (119) (see Syrups). 

Manufacture. HFS containing 42% fmctose is produced commercially by column isomerization of clarified and refined dextrose hydrolyzate using an immobilized glucose isomerase. Enriched symp containing 90% fmctose is prepared by chromatographic separation and blended with 42% HES... 

Two types of immobilization are used for immobilizing glucose isomerase. The intracellular enzyme is either immobilized within the bacterial cells to produce a whole-ceU product, or the enzyme is released from the cells, recovered, and immobilized onto an inert carrier. An example of the whole-ceU process is one in which cells are dismpted by homogenization, cross-linked with glutaraldehyde, flocculated using a cationic flocculent, and extmded (42). 

Multienzyme Electrodes. Coupling the reactions of two or more immobilized enzymes increases the number of analytes that can be measured. An electro-inactive component can be converted by an enzyme to a substrate that is subsequentiy converted by a second enzyme to form a detectable end product (57). For example, a maltose [69-79-4] sensor uses the enzymes glucoamylase and glucose oxidase, which convert... 

The resonant frequency of the crystal is inversely proportional to the mass of the Pmssian blue coating. When the immobilized enzyme acts on its substrate, glucose-6-phosphate [54010-71-8] (4), electrons are transferred to the Pmssian blue. In order to maintain electrical neutraUty, cations... 

Fig. 4. Schematic of a multisequence biosensor in which the target glucose is first converted to glucose-6-phosphate, G6P, in the test solution by hexokinase. G6P then reacts selectively with glucose-6-phosphate dehydrogenase immobilized on the quartz crystal surface. Electrons released in the reaction then chemically reduce the Pmssian blue film (see Fig. 3), forcing an uptake of potassium ions. The resulting mass increase is manifested as a...

The dye is excited by light suppHed through the optical fiber (see Fiber optics), and its fluorescence monitored, also via the optical fiber. Because molecular oxygen, O2, quenches the fluorescence of the dyes employed, the iatensity of the fluorescence is related to the concentration of O2 at the surface of the optical fiber. Any glucose present ia the test solution reduces the local O2 concentration because of the immobilized enzyme resulting ia an iacrease ia fluorescence iatensity. This biosensor has a detection limit for glucose of approximately 100 ]lM , response times are on the order of a miaute. 

Table 2. Typical Operating Parameters for Immobilized Glucose Isomerase and Penicillin V Acylase...

Immobilized enzyme Glucose isomerase Penicillin V acylase... 

The Immobili dEn me System. The glucose isomerases used are immobilized and granulated to a particle size between 0.3 and 1.0 mm. The enzyme granulates must be rigid enough to withstand compaction when they are packed iato the column. Ca " acts as an inhibitor in the system, and therefore calcium salts need to be removed from the feed symp. Conversely, Mg " acts as an activator, and magnesium salts are added to the feed symp. 

During operation, the immobilized enzyme loses activity. Most commercial enzymes show decay as a function of time (Eig. 12). The glucose isomerase ia a reactor is usually replaced after three half-Hves, ie, when the activity has dropped to around 12.5% of the initial value. The most stable commercial glucose isomerases have half-Hves of around 200 days ia practical use. To maintain the same fmctose content ia the finished symp, the feed-flow rate is adjusted according to the actual activity of the enzyme. With only one isomerization reactor ia operation, the result would be excessive variations ia the rate of symp production. To avoid this, several reactors at different stages ia the cycle of enzyme decay are operated ia combiaation. 

A CSP with a smaller (i-cyclodextrin moiety (seven glucose units) immobilized on silica gel (ChiraDex ) is able to separate the dansyl-derivatives [5-(dimethy-lamino)-naphthalin-l-sulfonylchloride] of amino acids [26]. 

FIGURE 4 Activity of glucose-6-phosphate dehydrogenase as a function of time for ( ) the enzyme immobilized on the polyphosphazene/ alumina support and (o) in the presence of free enzyme and non-activated support. (From Ref. 23.)... 

Allcock, H. R., and Kwon, S., Covalent linkage of proteins to surface-modified poly(organophosphazenes) Immobilization of glucose-6-phosphate dehydrogenase and trypsin, Macromolecules. 19, 1502, 1986. 

Later on, such S-layer-based sensing layers were also used in the development of optical biosensors (optodes), where the electrochemical transduction principle was replaced by an optical one [97] (Fig. 10c). In this approach an oxygen-sensitive fluorescent dye (ruthenium(II) complex) was immobilized on the S-layer in close proximity to the glucose oxidase-sensing layer [97]. The fluorescence of the Ru(II) complex is dynamically quenched by molecular oxygen. Thus, a decrease in the local oxygen pressure as a result of... 

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