Fluorescent sensors design

The PAH polymeric layer played an important role in our fluorescence sensor design. First, its positive charges enabled the deposition of anionic dextran that was labeled with the pH indicator fluorescein on the surface of the nanoparticles. More importantly, the PAH polymeric layer separated between the fluorescein molecules and the metal particle. In fact, the thickness of the polymeric layer was over 10 nm, which is larger than the Forster distance required for efficient energy transfer between the fluorophore and the metallic gold particles. 

Photoinduced electron transfer (PET) has been widely used as the preferred tool in fluorescent sensor design for atomic and molecular species [52-57], PET sensors generally consist of a fluorophore and a receptor linked by a short spacer. The changes in the oxidation/reduction potential of the receptor upon guest binding can alter the PET process creating changes in fluorescence. 

The above examples demonstrate the need for keeping the design of the receptor moiety central to the overall sensor design strategy all of the above being selective sensors for group 1 ions. Compound 4 is an example of a historical milestone in fluorescence sensor design. On... 

Photoinduced electron transfer (PET) has been wielded as a tool of choice in fluorescent sensor design for protons and metal ions. Design of fluorescent sensors for neutral organic species presents a harsher challenge due to the lack of electronic changes upon inclusion. The design of a fluorescent sensor based on the boronic acid saccharide interaction has been difficult due to the lack of sufficient electronic changes found in either the boronic acid moiety or in the saccharide moiety. Furthermore, facile boronic... 

Klymchenko AS, Demchenko AP (2002) Electrochromic modulation of excited-state intramolecular proton transfer the new principle in design of fluorescence sensors. J Am Chem Soc 124 12372-12379... 

Sharma, V., Wang, Q. and Lawrence, D. S. (2008). Peptide-based fluorescent sensors of protein kinase activity Design and applications. Biochim Biophys. Acta. 1784, 94—99. 

Fabbrizzi L., Licchelli M., Taglietti A., The Design of Fluorescent Sensors for Anions Taking Profit from the Metal-Ligand Interaction and Exploiting Two Distinct Paradigms, J. Chem. Soc., Dalton Trans. 2003 3471-3479. 

The chromophore environment can affect the spectral position of the absorption and emission bands, the absorption and emission intensity (eM, r), and the fluorescence lifetime as well as the emission anisotropy, e.g., in the case of rigid matrices or hydrogen bonding. Changes in temperature typically result only in small spectral shifts, yet in considerable changes in the fluorescence quantum yield and lifetime. This sensitivity can be favorably exploited for the design of fluorescent sensors and probes [24, 51], though it can unfortunately also hamper quantification from simple measurements of fluorescence intensity [116], The latter can be, e.g., circumvented by ratiometric measurements [24, 115],... 

Fig. 23 (a) DNAzyme-based sensor design with two dabcyl quenchers and a FAM fluorophore (top) and mechanism of operation (bottom), (b) Fluorescence response before and after complete cleavage through Pb2+ inset contains the corresponding image of the DNAzyme probe in the absence (left) and presence of Pb2+ (after 2 min of reaction time, right). (Reprinted with permission from [150]. Copyright 2003 American Chemical Society)... 

Thus, there are many possibilities to avoid homo-FRET or to use it efficiently in the design of fluorescence sensors. The excited-state energy can flow to the dyes in particular environments, and by manipulating with a single trigger dye, one can provide efficient collective sensor response by switching on and off the whole ensemble of fluorescence emitters. 

Xu H, Aylott JW, Kopelman R (2002) Fluorescent nano-PEBBLE sensors designed for intracellular glucose imaging. Analyst 127 1471-1477... 

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.). 

E-3 (Figure 10.26) is the first example of an ionophoric calixarene with appended fluorophores, demonstrating the interest in this new class of fluorescent sensors. The lower rim contains two pyrene units that can form excimers in the absence of cation. Addition of alkali metal ions affects the monomer versus excimer emission. According to the same principle, E-4 was designed for the recognition of Na+ the Na+/K+ selectivity, as measured by the ratio of stability constants of the complexes, was indeed found to be 154, while the affinity for Li+ was too low to be determined. 

Saari and Seitz [250] used the tip of an optical fibre as the sensing microzone to immobilize a suitable reagent (fluoresceinamine) in order to construct a fluorescence sensor for pH measurements the design was inspired by previous work of Peterson et al., who used a dye immobilized at the tip of an optical fibre for pH absorptiometric measurements [251]. The... 

Barone PW, Parker RS, Strano MS. In vivo fluorescence detection of glucose using a single-walled carbon nanotube optical sensor design, fluorophore properties, advantages, and disadvantages. Analytical Chemistry 2005, 77, 7556-7562. 

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