Sensors colorimetric

Colorimetric sensors for saccharides are of particular interest in a practical sense. If a system with a large color change can be developed it could be incorporated into a diagnostic test paper for D-glucose, similar to universal indicator paper for pH. Such a system would make it possible to measure D-glucose concentrations without the need of specialist instrumentation. This would be of particular benefit to diabetics in developing countries. 

Shinmori et al. have synthesized a diboronic acid saccharide receptor bearing a photoresponsive azobenzene group, 51 that was used as a light-gated saccharide sensor [119]. When the azobenzene unit is switched by photoirradiation, from the more stable trans-conformation to the thermodynamically unfavorable cis-isomer, it shows high D-glucose and D-allose selectivity. The formation of cyclic 1 1 complexes between saccharide and the dye in its cis-geometry explains the selectivity order. 

Koumoto and Shinkai demonstrated that azobenzene derivatives bearing one or two aminomethylphenylboronic add groups 52 and 53 can be used for practical colorimetric saccharide sensing in neutral aqueous media [120]. Observed K,pp for 53 were 433 for D-fructose and 13.0 for D-glucose in 1 1 (v/v) methanol-water at pH 7.5 (phosphate buffer). 

James and co-workers recently prepared diazo dye system 55a, which shows a large visible change from purple to red on saccharide binding [122,123]. With azo dye 55a the wavelength maximum shifts by ca. 55 nm to a shorter wavelength upon saccharide complexation. f pp for 55a were 2550 for D-fructose and 123 D-glucose in 52.1 wt% methanol-water at pH 11.32 (carbonate buffer). 

With dye molecule 50 it was proposed that at intermediate pH a boron-nitrogen interaction exists, whereas at high and low pH this bond is broken. What makes the equilibria of dye molecule 55a more interesting is the presence of the anilinic hydrogen, which can give rise to different species at high pH. 

Takeuchi has prepared a boronic acid dye 159, which undergoes an absorption spectral change on addition of nucleosides The boronic acid binds with the ribose and the dimethylaminophenylazo moiety can stack with the adenine of the nucleoside. 

Shinmori has synthesised a diboronic acid-saccharide receptor bearing a photoresponsive azobenzene group 161, which was used as a light-gated saccharide sensor. When the azobenzene unit is switched by photoirradiation 

So far, there are only few reports about fluorescent oligomers that change their constitution upon addihon of an analyte. In contrast, there are many examples of fluorescent molecules that undergo a conformational change upon addition of certain analytes (e.g., molecular beacons [7]). Although conformationally dynamic receptors are sometimes discussed in the context of DCC [8], these systems will not be described in more detail in the present chapter. 

Artificial receptors can be converted into sensors by covalent attachment of a signaling unit such as a fluorescent dye. An interesting alternative are so alled indicator displacement assays (IDAs) [9]. These assays are based on receptors that are bound to dyes (or fluorescent ligands) via noncovalent interactions. Upon addition of an analyte, the dyes are displaced, which results in a change of their optical properties. These changes can be used to identify and/or quantify the analyte. 

When a solution containing variable amounts of malate and tartrate was added to the multicomponent sensor, a characteristic UV-Vis spectrum response was obtained. Since the different receptor-dye complexes and the free dyes all have different colors, the information about the analytes was dispersed over the entire spectrum. To analyze the spectral changes, a multilayer preceptron (MLP) artificial neural network (ANN) was employed (see Glossary in Box 7.1). To train the ANN, the UV-Vis absorption data of 45 calibration samples containing different amounts of malate and tartrate (0-1.2 mM) were used. For each sample, the absorbances at 

27 wavelengths between 375 and 675 nm were taken as the data input. The training consisted of correlating the input (UV-Vis data) with the output (concentration of the analytes malate and tartrate). The predictive power of the trained network was then evaluated with four vaUdation samples. The absolute errors of the predictions were found to be between 1 and 6%. After further training with new calibration samples, the error was consistently lower than 2%. These results show that a dynamic rruxture of receptor-dye complexes can be used as a powerful sensor. 

Principal A PCA is a statistical tool that allows us to reduce a multidimensional 

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Javaid M., Keay P., A generic technique for coating doped sol-gel films onto the inside of tubes for use as colorimetric sensors,/. Sol-Gel Sci. Technol. 2000 17 55-59. 

Chatteijee, A., Balaji, T., Matsunaga, H., and Mizukami, F. 2006. A reactivity index study to monitor the role of solvation on the interaction of the chromophores with amino-functional silanol surface for colorimetric sensors. J. Mol. Graphics Model. 25 208-218. 

Song J, Cisar JS, Bertozzi CR. Functional self-assembling bolaamphiphilic polydiacetylenes as colorimetric sensor scaffolds. J Am Chem Soc 2004 126 8459-8465. 

Yoon J, Chae SK, Kim J-M. Colorimetric sensors for volatile organic compounds (VOCs) based on conjugated polymer-embedded electrospun fibers. J Am Chem Soc 2007 129 3038-3039. 

N. A. Rakow and K. S. Suslick. 2000. A Colorimetric Sensor Array for Odour Visualization. Nature 406 710. 

This strong plasmon absorption and its sensitivity to the local environment have made Au NPs and nanomaterials attractive candidates as colorimetric sensors. Colorimetric response can be due to the metal particle aggregation, which affects the SPR band of the isolated particles due to plasmon coupling and induced dipoles. 

Figure 3.18 Colorimetric sensor based on Au NPs for the detection of K+ ions.

As mentioned before, the changes in the properties of Au NPs upon their aggregation provides a way to identify the association process and design optical nanobiosensors through the detection of S P R absorption changes [ 198]. For example, Au NPs have been used as colorimetric sensors that show color changes with different aggregation states of DNA [199, 200]. 

Abstract A novel colorimetric method, digital color analysis (DCA), was proposed using a digital color analyzer and was applied to various quantitative analyses using chromatic-ity coordinates and suitable sensors for visual colorimetry based on the characteristics of human visual perception by virtual simulations based on digital color information. On the basis of DCA, we developed a visual colorimetric sensor for Li+, NH4+ and protein determination by the mixing of two kinds of lipophilic dyes, whose optimum mixing ratio... 

The simple compound shown in Fig. 12a is used as a colorimetric sensor for fluoride on addition of fluoride ions to a solution in dichloromethane or DMSO, a visible change from a yellow to purple solution becomes evident [134]. This is quenched, however, by addition of water. 

Fig. 12 Colorimetric sensor receptors, a For fluoride, b Amide macrocycle which can detect fluoride, acetate or H2PO4 the moiety in bold lies above the plane of the rest of the molecule...

Cryptate 72, in which the aryl spacer of 71 is replaced with a furanyl unit, acts a colorimetric sensor for anions. UV-vis titrations in aqueous solution gave log K values for the 1 1 halide/receptor adducts of 3.98 for chloride, 3.01 for bromide and 2.39 for iodide. X-ray diffraction studies confirm that bromide is held between the two copper atoms. Under the same conditions 72 also interacts strongly with azide (log K=4.7) and thiocyanate (log X=4.28) anions. This receptor is interesting because of its lack of selectivity compared to 71. The complex appears to be able to expand and contract its bite length in order to accommodate anions of various sizes. 

James and coworkers [38] have synthesized an azo dye molecule with boronic acid, receptor 40, which can act as a colorimetric sensor for detection... 

The detection of anions such as HPO - in water is a challenging task due to the competing solvation effect between water and anions. Han and Kim [63] have recently reported a colorimetric sensor that can detect HPO4" in aqueous solution at neutral pH. The dinuclear Zn(II) complex of 2,6-bis [bis(2-pyridylmethyl)amino]methyl -4-methylphenol (H-bpmp) 80 was synthesized. 

Fig. 1. Complete experimental setup for monitoring and control system for fermentor. T, feed tank V, control valve v, valves F, fermentor t, thermocouple c, coils A, dilutions tanks Bm, multichannel pump C, controller Tt, temperature transmitter Tb, biomass transmitter Sb, biomass optical sensor D, equipment to remove air bubbles R, rotammeter Ft, tangential filter Co, computer So, ethanol colorimetric sensor Vi, injection valve d, waste E+R, reagents-enzymes tanks B, pumps.

Rakow NA, Sushck KS. A colorimetric sensor array for odour visualization. Nature 2000 406 710-12. 

Suslick KS, Rakow NA, Sen A. Colorimetric sensor arrays for molecular recognition. Tetrahedron 2004 60 11133-8. 

Zhang C, Suslick KS. A colorimetric sensor arrays for organics in water. J Am Chem Soc 2005 127 11548-9. 

Zhang C, Suslick KS. Colorimetric sensor array for soft drink analysis. J Agric Food Chem 2007 55 237-42. 

Janzen MC, Ponder JB, Bailey DP, Ingison CK, Suslick KS. Colorimetric sensor arrays for volatile organic compounds. Anal Chem 2006 78 3591-600. 

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