Glucose 6-phosphate sensor

One of the most important sensors needed is one that reliably monitors cell density. An IR fiber-optic cell density probe has been used for this because it can directly monitor cell growth (without dilution) in high-cell-density bacterial fermentations. The ability to do an online sample filtration through the use of hollow fibers or rotating filters has made possible continuous, online measurement of glucose, lactate, and other metabolites. However, glucose, nitrogen substrate, and phosphate sensors that can withstand repeated system sterilization are still needed. 

The observed stability constants ( Tobs) for sensor 57 were 290 with D-fructose and 91 with o-glucose, for sensor 58 they were 1000 with D-fructose and 23 M with o-glucose, for sensor 59 they were 400 with o-fructose and 10 M with o-glucose and for sensor 60 they were 1500 with o-fructose and 55 M with o-glucose in 2 1 (v/v) methanol/water at pH 8.0 (phosphate buffer). 

CL emission. The system allows a simple determination of phosphate in 3 min with a linear range of 4.8-160 pM. Owing to its sensitivity, this method could be satisfactorily applied to the analysis of maximum permissible phosphate concentrations in natural waters [42-44], Also, the maltose-phosphorylase, mutar-ose, and glucose oxidase (MP-MUT-GOD) reaction system combined with an ARP-luminol reaction system has been used in a highly sensitive CL-FIA sensor [45], In this system, MP-MUT-GOD is immobilized on A-hydroxysuccinimide beads and packed in a column. A linear range of 10 nM-30 pM and a measuring time of 3 min were provided, yielding a limit of detection of 1.0 pM as well as a satisfactory application in the analysis of river water. 

The design of fluorescent sensors is of major importance because of the high demand in analytical chemistry, clinical biochemistry, medicine, the environment, etc. Numerous chemical and biochemical analytes can be detected by fluorescence methods cations (H+, Li+, Na+, K+, Ca2+, Mg2+, Zn2+, Pb2+, Al3+, Cd2+, etc.), anions (halide ions, citrates, carboxylates, phosphates, ATP, etc.), neutral molecules (sugars, e.g. glucose, etc.) and gases (O2, CO2, NO, etc.). There is already a wide choice of fluorescent molecular sensors for particular applications and many of them are commercially available. However, there is still a need for sensors with improved selectivity and minimum perturbation of the microenvironment to be probed. Moreover, there is the potential for progress in the development of fluorescent sensors for biochemical analytes (amino acids, coenzymes, carbohydrates, nucleosides, nucleotides, etc.). 

The calibration graphs obtained showed linear relationships between the current decrease and the concentration of acetic acid up to 72 mg l-. The minimum concentration for determination was 5 mg of acetic acid 1". The current difference was reproducible within 6 % for an acetic acid sample contaning 54 mg l 1. The standard deviation was 1.6 mg 1 in 20 experiments. The sensor did not respond to volatile compounds such as formic acid and methanol or to nonvolatile nutrients such as glucose and phosphate ions. 

Measurement. The measurement apparatus for the in vitro test of this sensor is shown in Figure 4. The sensor was dipped into the flask containing 100 ml of phosphate buffered saline solution, pH 7.4, and the output was measured with respect to stepwise changed glucose concentrations of 0 to 2000 mg/dl under the oxygen tensions of 5 to 21%, which prepared by mixing air and N2 gas. 

Binyamin, Chen and Heller reported that wired enzyme electrodes constituted of glassy carbon electrodes coated with poly(4-vinylpyridine) complexed with [Os(bpy)2Cl] and quarternized with 2-bromoethylamine or poly[(iV-vinylimidazole) complexed with [Os(4,4 -dimethyl-2,2 -bypyridine)2Cl] or poly(vinylpyridine) complexed with [Os(4,4 -dimethoxy-2,2 -bypyridine)2Cl] quaternized with methyl groups lost their electrocatalytic activity more rapidly in serum or saline phosphate buffer (pH 7.2) in the presence of urate and transitional metal ions such as Zn and Fe " " than in plain saline phosphate buffer (pH 7.2). It was reported that as much as two-thirds of the current is lost in 2 h in some anodes. However, when a composite membrane of cellulose acetate, Nafion, and the polyaziridine-cross-linked co-polymer of poly(4-vinyl pyridine) quaternized with bromoacetic acid was applied, the glucose sensor stability in serum was improved and maintained for at least 3 days [27,50]. 

Pig. 83. Principle of a sensor containing hexokinase (HK) and glucose-6-phosphate dehydrogenase (G6P-DH) for determination of NADP+, ATP, glucose-6-phosphate, and fructose. 

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