Sensors for metal ions

In typical work of Yu et al. [29], the arrays were fabricated on ITO glass substrates. The ITO glass layer was patterned by photolithography into perpendicular rows of electrode strips (width 450 pm, spacing 185 pm). The polymer film, a blend of poly(3-octyl thiophene) and fullerene PCBM[6,6] (see Section 6.3), was spin-cast onto the substrate. 

Such microfabricated array devices are suitable for linear or two-dimensional (2D) digital optical cameras. In principle, they may also be actively used as electroluminescent devices. 

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It has been demonstrated that dendrimers can be used also as fluorescent sensors for metal ions. Poly(propylene amine) dendrimers functionalized with dansyl units at the periphery like 34 can coordinate metal ions by the aliphatic amine units contained in the interior of the dendrimer [80]. The advantage of a dendrimer for this kind of application is related to the fact that a single analyte can interact with a great number of fluorescent units, which results in signal amplification. For example, when a Co ion enters dendrimer 34, the fluorescence of all the 32 dansyl units is quenched with a 32-fold increase in sensitivity with respect to a normal dansyl sensor. This concept is illustrated in Fig. 3. 

In the [Zn(2)2]2+ species, a single Zn2+ ion is able to revive the luminescence of all the 32 naphthyl units present in the two dendritic structures. This result shows that dendrimers can be profitably used as supramolecular fluorescent sensors for metal ions, as shown in Fig. 2. In this case, the sensor fluorescence is switched on upon metal ion coordination, and low Zn2+ concentrations (ca. 1 pM) can be easily detected. 

Hall s molecules might be referred to as macrocyclic compounds that are sensors for metal ions. This topic is the subject of the chapter written by Bradshaw and coworkers. The compounds in question are not channels at all but were developed from what might be called the organic-analytical perspective. 

Fig. 5 Schematic representation of a fluorophore F) and quencher (g)-labeled DNAzyme-substrate complex serving as a selective sensor for metal ions...

An optical transduction method that is often used with ultrathin hlms, such as LB hlms, is that of surface plasmon resonance [30, 31]. Surface plasma waves are collective oscillations of the free electrons at the boundary of a metal and a dielectric. These can be excited by means of evanescent electromagnetic waves. This excitation is associated with a minimum in the intensity of the radiation reflected from the thin him system, called surface plasmon resonance (SPR). The sensitivity of SPR is noteworthy, and changes in refractive index of 10 may be monitored thus the technique compares favorably with ellipsometry. The method has been used with LB hlms to provide both gas detectors [29] and sensors for metal ions in solution [32]. 

Twistophanes 10 and 11 represent a new class of cyclophanes that recently emerged as the follow-up compounds to the endobasic host 9 first prepared by Baxter. The cyclic structures comprise substituted 2,2 -bipyridyl groups linked via acetylinic linkers, and they are primarily developed as sensors for metal ions. For both... 

Prodi, L. Montalti, M. Zaccheroni, N. Dallavalle, F. Folesani, G. Lanfranchi, M. Corradini, R. Pagliari, S. Marchelli. R. Dansylated polyamines as fluorescent sensors for metal ions. Photophysical properties and... 

Sensors for metal ions are based on the use of non-fluorescent or weakly fluorescent reagents which form highly fluorescent complexes with the metal ions of interest. For example, the reagent morin (3, 5, 7, 2 4 -pentahydroxyflavone), immobilized on cellulose by covalent bonding, forms intense fluorescent complexes with aluminium (64) and beryllium (65) which are used to sense these ions. The detection limits for these transducers are reported to be 27 ppb for aluminium and 9 ppb for beryllium. 

Prodi L, Montalti M, Zaccheroni N et al (2001) Dansylated polyamines as fluorescent sensors for metal ions photophysical properties and stability of copper(II) complexes in solution. Helv Chim Acta 84 690-706... 

Eq. (13.1). Thus, this system demonstrates the supramolecular strategy to develop luminescent sensors for metal ions. 

Jin J, Zhang X-B, Xie D-X, Gong Y-J, Zhang J, Chen X, Shen G-Li, Yu R-X (2010) Clicking fluoroionophores onto mesoporous silicas a universal strategy towards efficient fluorescent surface sensors for metal ions. Anal Chem 82 6343-6346... 

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