Magnesium sensor

The same design principles apply to the magnesium sensors PET-15 and PET-16, in which the recognition moiety has a smaller cavity . 

The current model for Mg + transport is illustrated in Figure 8 and is believed to be controlled by a magnesium sensor consisting of two specific Mg + binding sites located on the outside of the funnel in the a a sandwich domain that spans the wiUow helices and /3-sheets ° . Studies of similar binding sites in other proteins indicates that these sites will probably have an affinity for Mg + that is slightly less than the average free concentration of Mg + in cells . When the concentration of Mg in the cell drops below... 

The development of a sensor for ionized magnesium turned out to be one of the most difficult challenges of recent years. Several carriers have been designed for this purpose but none have been satisfactory. The first report of a successful measurement of ionized magnesium in an automated clinical analyzer (Thermo, prev. KONE) was published only in 1990 [30]. The ionophore ETH 5520 was used as the active compound. Two other carriers have been used since then ETH 7025 (Roche, former AVL), and a derivative of 1,10-phenenthroline (Nova). All of the magnesium sensors are based on a plastic membrane. Numerical compensations of the influence of calcium ion and the ionic strength are used due to insufficient selectivity of the magnesium sensors. 

More recently, a PVC ISE based on the [4-(l,l,3,3-tetramethylbutyl) phenyl] phosphate/decan-l-ol system in conjunction with a chemometric technique has facilitated magnesium measurements (35). Attempts to make magnesium sensors with magnesium adducts of poly(propylene glycol) in conjunction with tributyl phosphate, di-octylphenyl phosphonate, its 3-nitrophenyl derivative, 2-nitroethyl benzene and 2-nitrophenyl phenyl ether solvents produced instead calcium sensors with = 0.06-0.08. 

Farruggia G, Iotti S, Prodi L et al (2005) 8-hydroxyquinoline derivatives as fluorescent sensors for magnesium in living cells. J Am chem soc 128 344—350... 

Calcium sensors are merely representative of a much wider class of ion sensors, albeit probably the best understood. Fluorescent probes have now been developed for a wide range of metal ions of biological interest, particularly sodium, potassium, magnesium, and zinc. 

Zhujun Z., Seitz W.R., A fluorescent sensor for aluminum(III), magnesium(II), zinc(II) and cadmium(II) based on electrostatically immobilized quinolin-8-ol sulfonate. Anal. 

Shukla S.K., Parashar G.K., Mishra A.P., Misra P., Yadav B.C., Shukla R.K., Bali L.M., Dubey G.C., Nano-like magnesium oxide films and its significance in optical fiber humidity sensor, Sens. Actuat B 2004 98 5-11. 

Clinical chemistry, particularly the determination of the biologically relevant electrolytes in physiological fluids, remains the key area of ISEs application [15], as billions of routine measurements with ISEs are performed each year all over the world [16], The concentration ranges for the most important physiological ions detectable in blood fluids with polymeric ISEs are shown in Table 4.1. Sensors for pH and for ionized calcium, potassium and sodium are approved by the International Federation of Clinical Chemistry (IFCC) and implemented into commercially available clinical analyzers [17], Moreover, magnesium, lithium, and chloride ions are also widely detected by corresponding ISEs in blood liquids, urine, hemodialysis solutions, and elsewhere. Sensors for the determination of physiologically relevant polyions (heparin and protamine), dissolved carbon dioxide, phosphates, and other blood analytes, intensively studied over the years, are on their way to replace less reliable and/or awkward analytical procedures for blood analysis (see below). 

Fig. 10.22. Chelating PCT sensors for calcium and magnesium ions (PCT-11 and PCT-12 Grynkiewicz G. et al. (1985) J. Biol. Chem. 260, 3440. PCT-13 and PCT-14 Haugland R. P., Handbook of Fluorescent Probes and Research Chemicals, 6th edn, Molecular Probes, Inc., Eugene, OR).

The sensor reported by Shirai(69) used a natural carboxylic polyether antibiotic (Aem = 481 nm) for the detection of magnesium and calcium. Detection limits of I0 5 and KT4 M, respectively, were reported but, interference from other metals was difficult to overcome. Ishibashi(69) used a bulkier hexadecyl-acridine orange dye (Xem = 525 nm) plasticized in a PVC membrane for the fluorescent detection of ammonium ions. Signal interference due to superfluous ions and poor detection limits of KT5 M restricted the use of the probe. 

K. Suziki, K. Tohda, Y. Tanda, H. Ohzora, S. Nishihama, H. Inoue, and T. Shirai, Fiber-optic magnesium and calcium ion sensor based on a neutral carboxylic polyether antibiotic, Anal. Chem. 61, 382-384 (1989). 

This two-point measurement technique is used in the system reported by Wicker-sheim and Sun,(27) where a lamp phosphor, tetravalent manganese-activated magnesium fluorogermanate, mentioned above, is used as fluorescent sensor. The excitation... 

Another example is the balanced integration method described by Sun.(29) This technique is designed to achieve 0.01°C resolution using tetravalent manganese-activated magnesium fluorogermanate, the same sensor material that has been used... 

FIGURE 8. Current model for the gating mechanism in the CorA transporter. Left closed conformation with the magnesium binding sites in the sensor occupied. Right postulated open conformation allowing ion transport into the ceU. Adapted by permission of MacmiUan Publishers Ltd. from Reference 71... 

There are a number of possible sensor options for a y-ray spectrometer. These include a germanium sensor or scintillators made of various synthetic materials. Elements that are routinely analyzed with y-rays include silicon, iron, titanium, magnesium, calcium, and aluminum, plus the radioactive elements potassium and thorium (uranium concentrations are usually too low). 

A. Seki, K. Motoya, S. Watanabe and I. Kubo, Novel sensors for potassium calcium and magnesium ions based on a silicon transducer as a light-addressable potentiometric sensor, Anal. Chim. Acta, 382(1-2) (1999) 131-136. 

The book explores various examples of these important materials, including perovskites, zeolites, mesoporous molecular sieves, silica, alumina, active carbons, carbon nanotubes, titanium dioxide, magnesium oxide, clays, pillared clays, hydrotalcites, alkali metal titanates, titanium silicates, polymers, and coordination polymers. It shows how the materials are used in adsorption, ion conduction, ion exchange, gas separation, membrane reactors, catalysts, catalysts supports, sensors, pollution abatement, detergency, animal nourishment, agriculture, and sustainable energy applications. 

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