Molecular sensors based

The methods of anion detection based on fluorescence involve quenching, complex formation, redox reactions and substitution reactions (Fernandez-Gutierrez and Munoz de la Pena, 1985). This chapter will be restricted to anion molecular sensors based on collisional quenching (in general, they exhibit a poor selectivity) and on recognition by an anion receptor linked to a fluorophore (fluoroionophore). 

Rogers CW, Wolf MO. Luminescent molecular sensors based on analyte coordination to transition-metal complexes. Coord Chem Rev 2002 233-234 341-50. 

Figure 16.4 Principle of the PCT (photoinduced charge transfer), chemically driven, luminescent molecular sensor based on the donor-spacer-acceptor architecture, (a) Binding of analyte trigger to the donor (green) moiety results in hypsochromic shift of absorption (emission) band (b) binding of the same analyte to the acceptor moiety (red) results in bathochro-mic shift of corresponding transition...

Hong, F.T., Molecular sensors based on the photovoltaic effect of bacteriorhodopsin origin of differential responsivity. Mater. Sci. Eng. C, 4, 267, 1997. Reprinted with corrections. Mater. Sci. 

SENSORS BASED ON FREE-STANDING MOLECULARLY IMPRINTED POLYMER MEMBRANES. COMPUTATIONAL MODELLING OF SYNTHETIC MIMICKS OF BIORECEPTORS... 

Particularly attractive for numerous bioanalytical applications are colloidal metal (e.g., gold) and semiconductor quantum dot nanoparticles. The conductivity and catalytic properties of such systems have been employed for developing electrochemical gas sensors, electrochemical sensors based on molecular- or polymer-functionalized nanoparticle sensing interfaces, and for the construction of different biosensors including enzyme-based electrodes, immunosensors, and DNA sensors. Advances in the application of molecular and biomolecular functionalized metal, semiconductor, and magnetic particles for electroanalytical and bio-electroanalytical applications have been reviewed by Katz et al. [142]. 

Thomas, R.C. and Hughes, R.C., Sensors for Detecting Molecular Hydrogen Based on Pd Metal Alloys, Journal of Electrochemical Society, 144(9), 3245,1997. 

S. Marx, A. Zaltsman, I. Turyan and D. Mandler, Parathion sensor based on molecularly imprinted sol-gel films, Anal. Chem., 2004, 76, 120. 

Abstract Silver clusters, composed of only a few silver atoms, have remarkable optical properties based on electronic transitions between quantized energy levels. They have large absorption coefficients and fluorescence quantum yields, in common with conventional fluorescent markers. But importantly, silver clusters have an attractive set of features, including subnanometer size, nontoxicity and photostability, which makes them competitive as fluorescent markers compared with organic dye molecules and semiconductor quantum dots. In this chapter, we review the synthesis and properties of fluorescent silver clusters, and their application as bio-labels and molecular sensors. Silver clusters may have a bright future as luminescent probes for labeling and sensing applications. 

Class 3 fluorophores linked, via a spacer or not, to a receptor. The design of such sensors, which are based on molecule or ion recognition by a receptor, requires special care in order to fulfil the criteria of affinity and selectivity. These aspects are relevant to the field of supramolecular chemistry. The changes in photophysical properties of the fluorophore upon interaction with the bound analyte are due to the perturbation by the latter of photoinduced processes such as electron transfer, charge transfer, energy transfer, excimer or exciplex formation or disappearance, etc. These aspects are relevant to the field of photophysics. In the case of ion recognition, the receptor is called an ionophore, and the whole molecular sensor is... 

Box 10.2 Calixarene-based fluorescent molecular sensors for sodium ions... 

Anions play key roles in chemical and biological processes. Many anions act as nucleophiles, bases, redox agents or phase transfer catalysts. Most enzymes bind anions as either substrates or cofactors. The chloride ion is of special interest because it is crucial in several phases of human biology and in disease regulation. Moreover, it is of great interest to detect anionic pollutants such as nitrates and phosphates in ground water. Design of selective anion molecular sensors with optical or electrochemical detection is thus of major interest, however it has received much less attention than molecular sensors for cations. 

Many fluorescent molecular sensors for halide ions (except F ) are based on collisional quenching of a dye. In particular, the determination of chloride anions in living cells is done according to this principle. Examples of halide ion sensors are given in Figure 10.29. 

None of the involved species are fluorescent. Therefore, for fluorescence signaling of citrate recognition, carboxyfluorescein is first added to the medium because binding to the receptor in the absence of citrate is possible and causes deprotonation of carboxyfluorescein, which results in high fluorescence. Citrate is then added, and because it has a better affinity for the receptor than carboxyfluorescein, it replaces the latter, which emits less fluorescence in the bulk solvent as a result of protonation. Note that this molecular sensor operates in a similar fashion to antibody-based biosensors in immunoassays. It was succes-fully tested on a variety of soft drinks. 

Figure 5.19. Molecular structure of pH sensors based on Di(2,2 -bipyridyl)(5,5 -diaminomethyl-2,2 -bipyridyl)-ruthenium II complexes.

Notwithstanding the excellent analytical features inherent in molecular phosphorimetric measurements, their use has been impeded by the need for cumbersome cryogenic temperature techniques. The ability to stabilize the "triplet state" at room temperature by immobilization of the phosphor on a solid support [69,70] or in a liquid solution using an "ordered medium" [71] has opened new avenues for phosphorescence studies and analytical phosphorimetry. Room-temperature phosphorescence (RTF) has so far been used for the determination of trace amounts of many organic compounds of biochemical interest [69,72]. Retention of the phosphorescent species on a solid support housed in a flow-cell is an excellent way of "anchoring" it in order to avoid radiationless deactivation. A configuration such as that shown in Fig. 2.13.4 was used to implement a sensor based on this principle in order to determine aluminium in clinical samples (dialysis fluids and concen-... 

This chapter will introduce the field of sensors based on molecular imprinted polymers (MIPs). MIPs are highly cross-finked polymers that are formed with the presence of a template molecule (Haupt and Mosbach 2000 Wulff 2002). The removal of the template molecule from the polymer matrix creates a binding cavity that is complementary in size and shape to the template molecule and is fined with appropriately positioned recognition groups (Scheme 15.1). 

Blanco-Lopez MC, Lobo-Castanon MJ, Miranda-Ordieres AJ, Tunon-Blanco P. Electrochemical sensors based on molecularly imprinted polymers. Trends Anal Chem 2004 23 36-48. 

Kriz D, Ramstrom O, Svensson A, Mosbach K. Introducing biomimetic sensors based on molecularly imprinted polymers as recognition elements. Anal Chem 1995 67 2142-2144. 

Li CY, Wang CF, Wang CH, Hu SS. Development of a parathion sensor based on molecularly imprinted nano-Ti02 self-assembled film electrode. Sens Actual B 2006 117 166-171. 

Tabushi I, Kurihara K, Naka K, Yamamura K, Hatakeyama H. Supramolecular sensor based on SN02 electrode modified with octadecylsilyl monolayer having molecular-binding sites. Tetrahedron Lett 1987 28 4299-4302. 

Sukeerthi, S. and Contractor, A. Q. (1999). Molecular sensors and sensor arrays based on polyaniltne microtubules. Anal. Chem. 71(11), 2231-2236. 

Another fluorescence-based method for assaying activity and enantioselectivity of synthetic catalysts, specifically in the acylation of chiral alcohols, was recently reported [27]. The idea is to use a molecular sensor that fluoresces upon formation of an acidic product (acetic acid). Adaptation to high-throughput evaluation of enantioselective lipases or esterases needs to be demonstrated. 

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