Self-assembled monolayers fluorescent

Kittredge KW, Fox MA, Whitesell JK (2001) Effect of alkyl chain length on the fluorescence of 9-alkylfluorenyl thiols as self-assembled monolayers on gold. J Phys Chem B 105 10594-10599... 

In this part we will describe recent achievements in the development of biosensors based on DNA/RNA aptamers. These biosensors are usually prepared by immobilization of aptamer onto a solid support by various methods using chemisorption (aptamer is modified by thiol group) or by avidin-biotin technology (aptamer is modified by biotin) or by covalent attachment of amino group-labeled aptamer to a surface of self-assembly monolayer of 11-mercaptoundecanoic acid (11-MUA). Apart from the method of aptamer immobilization, the biosensors differ in the signal generation. To date, most extensively studied were the biosensors based on optical methods (fluorescence, SPR) and acoustic sensors based mostly on thickness shear mode (TSM) method. However, recently several investigators reported electrochemical sensors based on enzyme-labeled aptamers, electrochemical indicators and impedance spectroscopy methods of detection. 

In one such approach we seek to exploit the potential signal transduction properties of the thermochromic Dawson [40] polyoxometalates and combine this with a fluorescent POM-hybrid to produce a device that could respond optically as a function of the local environment, see Figure 2.12. In this example, the clusters would be positioned on a gold surface using SAMs (Self-assembled monolayer) with a cationic tail and local positional control could be aimed using self-assembly, or even by means of an atomic force microscope tip. 

Xie, F., Baker, M. S., and Goldys, E. M. (2008). Enhanced Fluorescence Detection on Homogeneous Gold Colloid Self-Assembled Monolayer Substrates. Chem. Mater. 20 1788-1797. 

Performing the same measurements on samples where the gold surfaces had been passivated with mPEG-thiol (see section 4.1), leaving the subsequently self-assembled monolayers only at the bottom of the nanocavities, average fluorescence enhancement (across multiple samples) of 6.9 0.7 for Cy-5 has been obtained (46). In this case, the fill fraction for fluorescence emission was 3.1%. What the comparison of these measures shows is that the enhancements with and without... 

The examples of small combinatorial libraries presented in this chapter were all fabricated manually, but automation of the process could be implemented using for example the already developed techniques for microarray fabrication, microspotter robots for fabrication, and fluorescence scanner for analysis. We hope that this chapter constitutes a clear explanation of the fabrication of combinatorial libraries of fluorescent self assembled monolayers and their applications. 

Chrisstoffels, L. A. J. Adronov, A. Frechet, J. M. J. Surface-Confined Light Harvesting, Energy Transfer, and Amplification of Fluorescence Emission in Chromophore-Labeled Self-Assembled Monolayers. Angew. Chem. Int. Ed. 2000, 39, 2163-2167... 

Flink, S. Van Veggel, F. C. J. M. Reinhoudt, D. N. A Self-Assembled Monolayer of a Fluorescent Guest for the Screening of Host Molecules. Chem. Commun. 1999, 2229-2230... 

There are various potential applications of photophysical phenomena in analytical chemistry. The relatively short lifetimes of most excited states, however, is a serious drawback to the construction of practical devices but studies which focus on finding ways to extend triplet lifetimes have now been described by Harriman et al. Kneas et al. have examined new types of luminescent sensor on polymer supports, and both Neurauter et al. and Marazuela et al. have designed sensors based on the ruthenium(II) polypyridine complex for the detection of carbon dioxide. A system, based on the formation of twisted intramolecular charge transfer states, has been devised for measuring the molecular weight of polymeric matrices (Al-Hassan et a/.), and the chemical reactivity at the interface of self-assembled monolayers has been assessed using fluorescence spectroscopy (Fox et al). 

FIGURE 8.1 Fluorescence changes of the self-assembled monolayer in the presence of saxitoxin. (From Kele, P. et ah, Chem. Commun., 14, 1494, 2006. With permission.)... 

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