Glucose solutions interfaces

In biosensor systems employing this type of mediator, the natural substrate for GOD (molecular oxygen) is replaced by a compound which is carefully chosen to be capable of carrying out the same role. The mediator serves to re-oxidise the reduced form of GOD (Eq. (23.2)), following its interaction with glucose (Eq. (23.1)). Consequently, these systems can be operated at the potential of the mediator couple (Eq. (23.3)) and 02 concentration at the electrode/solution interface does not become a limiting factor in the analysis this is particularly important in samples where 02 concentrations are low, such as neonatal blood or microbial fermentations. 

Sun X, Li Y (2005) Hollow carbonaceous capsules from glucose solution. J CoUoid Interface Sci 291 7-12... 

As expected, sensor sensitivity in vitro, measured in aqueous buffered glucose solutions, and in vivo, measured in ISF, may differ significantly from each other. While an effect of the nature of the sensor coating interface to tissue onto the coefficient of in vitro and in vivo sensitivities is expected, it is currently less clear, how large a variation of in vivo sensitivity should be expected when applying sensors of the same architecture material composition and manufacturing a batch to a large population of diabetes patients. 

Similar work was performed by Shaw et al.3 in 1999 when they used FT-Raman, equipped with a charge coupled device (CCD) detector (for rapid measurements) as an on-line monitor for the yeast biotransformation of glucose to ethanol. An ATR (attenuated total reflectance) cell was used to interface the instrument to the fermentation tank. An Nd YAG laser (1064 nm) was used to lower fluorescence interference and a holographic notch filter was employed to reduce Rayleigh scatter interference. Various chemometric approaches were explored and are explained in detail in their paper. The solution was pumped continuously through a bypass, used as a window in which measurements were taken. 

Figure 3.12 — Interfacing of a fermenter to an FI system. The fermenter medium is continuously recycled by a pump to the filter unit, from which the filtrate is guided to a small reservoir (500 /xL). The sample solution is aspirated through a dialyser, the acceptor stream of which is fed to the injector of the FIA system. The analyte content is assayed amperometrically by using the glucose sensor incorporating the enzyme-containing chemically modified electrode. (Reproduced from [86] with permission of Elsevier Science Publishers).

This study on the immobilization of glucose oxidase and the characterization of its activity has demonstrated that a bioactive interface material may be prepared from derivatized plasma polymerized films. UV/Visible spectrophotometric analysis indicated that washed GOx-PPNVP/PEUU (2.4 cm2) had activity approximately equivalent to that of 13.4 nM GOx in 50 mM sodium acetate with a specific activity of 32.0 U/mg at pH 5.1 and room temperature. A sandwich-type thin-layer electrochemical cell was also used to qualitatively demonstrate the activity of 13.4 nM glucose oxidase under the same conditions. A quantitatively low specific activity value of 4.34 U/mg was obtained for the same enzyme solution by monitoring the hydrogen peroxide oxidation current using cyclic voltammetry. Incorporation of GOx-PPNVP/PEUU into the thin-layer allowed for the detection of immobilized enzyme activity in 0.2 M sodium phosphate (pH 5.2) at room temperature. 

GC mode experiments have been applied to the study of immobilized oxi-doreductases such as diaphorase and the glucose oxidase/glucose system (15,21), which has also been investigated by feedback with ferrocenyl mediators (10). In the feedback experiment, the catalytic cycle of the enzyme is dependent on ferrocenium species generated at the tip, as described in Sec. I.C. A generation-collection experiment utilizes a bulk solution concentration of the oxidized mediator, and the tip is poised at a potential sufficiently positive to detect ferrocene, or another reaction product such as H202, present near the interface (Fig. 6). The enzymatic reaction therefore occurs over the whole specimen, wherever there is active enzyme and a supply of substrate. In the feedback experiment, the tip current includes the flux of mediator from bulk solution as well as the flux of reduced mediator due to... 

A problem that arises in the consideration of an extravascular device is that synthetic materials placed in the body tissues rapidly become covered with cells (polymorphonuclear leukocytes and macrophages) and surrounded with relatively impervious fibrous tissue. This could decrease the diffusion rates of glucose and insulin, eventually rendering a chamber useless. One possible solution to this problem is the attachment of proteolytic enzymes to the surface of the chamber to prevent formation and attachment of fibrous tissue at the interface. 

Test for cellulose esters. Cellulose esters respond to the Molisch test for carbohydrates. The sample is dissolved in acetone and treated with 2-3 drops of 2% ethanolic solution of a-naphthol a volume of 2-2.5 ml of concentrated H2SO4 is so added as to form a lower layer. A red to red-brown ring at the interface of the liquids indicates cellulose (glucose). A green ring at the interface indicates nitrocellulose and differentiates it from other cellulose esters. 

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