Investigation On The Application Of Cyanine Dyes As Optical Molecular Chemosensors

Better sensitivity and selectivity would be obtained if the measurement is performed by cyanine dyes for the following reasons: first, cyanine dyes themselves bear the merits of large molar absorbability,high fluorescence quantum yield and so on; second, measurement can be carried out in near-IR region by regulating the length of methylene chain and can reduce the interference from background effectively. Therefore, the investigation and exploitation of probe of cyanine dyes have attracted many researchers'attention recently. In this dissertation, I would continue to develop the application of cyanine dyes as optical molecular chemosensors on the base of previous work of predecessor. This dissertation consists of five chapters summarized as follows.In chapter 1, Structure characters, classifications and the correlation between wavelength and structure of cyanine dyes were firstly summarized. Then introduced various qualities and application of them, emphasis was focused on aggregation,the application in the determination of nucleic acids and protein,the application as optical molecular chemosensors of them. Finally, based on the concerning updated developments, the research objective of this dissertation was presented.In chapter 2, two novel hemicyanine dyes HC1 and HC2 were synthesized; the application as optical chemosensors of them was also discussed. This chapter was divided into two parts.In part 1, the spectral character of HC1 and HC2 as ratiometric fluorescent molecular chemosensors for pH was studied. Because of the little difference in the structure, their ratios of fluorescence emissions cover with two different broad range, which are ideal for accurate near- physiological and alkalescent conditions pH measurements respectively. HC1 could also be used for the determination of pH of tap water.In part 2, a colorimetric fluoride ion sensing in aqueous solution was investigated based on competitive-binding mechanism. HC1, which had the p-hydroxy in its stucture, could form steady ternary equilibrium system HC1-Zr-EDTA with [Zr(H2O)2EDTA]. Addition of fluoride caused dissociation of HC1 from HC1-Zr-EDTA system. Besides its high sensitivity and specificity, the semi-quantitative determination by"naked-eye detection"is possible by this method. This system was also used for the determination of fluoride ion in commercial toothpaste and obtained satisfactory result compared with the result obtained by ISE.In chapter 3, the application of anionic heptamethine cyanine (HMC) dyes to the determination of phosphate-containing anions was studied with ternary ion-association equilibrium system. Experiments proved that HMC could interact intensely with oppositely charged Tb3+. The mechanism study showed that the electrostatic interaction resulted in the transformation from monomer to aggregate of HMC and also the formation of HMC- Tb3+ association. Tb3+ was once reported interact intensely with phosphate-containing anions, HMC in the HMC- Tb3+ system was replaced by the phosphate-containing anions when phosphate-containing anions were added to HMC-Tb3+ association system. With the aggregate of HMC destroyed, the monomer increased. Therefore, an absorbance recovery method was developed for the determination of phosphate-containing anions with HMC;In chapter 4, a new di-topic sensing system for the determination of Hg2+ and sulfhydryl-containing amino acids in a highly selective and sensitive manner was developed. Changes of spectral of CyL showed that inter-molecular aggregation of heptamethine cyanine dyes could be formed when the N and S of cyanine molecules chelated with Hg2+ under the sensing conditions. Thus a new method for the determination of Hg2+ in the near-IR region was set up. It was reported that many other chelating species, especially those containing S- or N- donors such as Cys, are of strong thermodynamics preference to bind Hg2+ ions in water, then Cys was added to CyL- Hg2+ and found that the Hg2+-induced H-dimers-dominated optical response was switched OFF. Therefore, according to the recovery of monomer of CyL, another sensing system was set up by the same probe. The method provided significant elicitations for some di-topic sensing system using"OFF"and"ON"of aggregation of heptamethine cyanine dyes.In chapter 5, some unsuccessful examples in my experiments were summarized during my graduate study. I hope that all of us should study from them to avoid the same mistake in the further research in this field.