<title>Potential use of IR dyes for metal ion sensors</title>

Abstract

The fluorescence quenching of molecules by analytes of interest, is a widely employed phenomenon in fluorescence sensing technology. Färster type dipole -dipole energy transfer from dye molecules to transition metal ions, provides a method of monitoring the concentration of these ions with some degree of selectivity. Each metal ion has a different absorption spectrum, hence, in principle it is possible to choose different fluorophores for each metal ion. In the present work, quenching studies of the carbocyanine dye DTDCI by transition metal ions in a viscous solvent and in Naflon polymer matrices are reported. The potential for fabricating near-infrared (NW) energy transfer sensors is assessed, particularly with regard to detecting copper ions in solution.Keywords:-infrared dyes, metal ion sensor, fluorescence quenching, Naflon polymer. INTRODUCTIONNW dyes are the subject of growing interest in the area of time-resolved fluorescence sensors. A main advantage in using them as sensors is the improvement in detection efficiency resulting from low background emission from fluorescent impurities when using NIR excitation. The application of MR dyes as sensors is especially advantageous when laser diodes are used as excitation sources, because of their small size, low cost, high intensity and high repetition rate. Optical fiber coupling can be utilized to allow remote analysis of potentially harmful chemicals.Typical NW dyes are the di-and tricarbocyanines which have aromatic or heteroaromatic ring structures linked by a polymethine chain possessing conjugated carbon/carbon double bonds. In this paper the fluorescence of the carbocyanine dye 3,3'-diethylthiadicarbocyanine iodide DTDCI is reported.The difficulties associated with the use of these N dyes are the small quantum yield when compared to many visible fluorescent dyes 1,2, and the photochemical changes observed in the spectroscopic properties when placed in aqueous solvents or other high polarity solvents. These changes include the appearance of additional bands in the absorption spectra which are attributed to dye molecule aggregation. It has been shown that the internal conversion and the cis/trans photoisomerization within the polymethine chain are the major nonradiative pathways in polymethine dyes.These processes can be an obstacle to using the carbocyanine dyes as sensors.The aim of this study is to use the carbocyanine dye as the sensor molecule for transition metal ions in different environments. The quenching of DTDCI fluorescence was employed to determine the ion concentration using Färster type quenching. We have already successfully demonstrated a metal ion sensor based on Förster energy transfer in the UV/VIS5, but extension to the MR would bring to bear the low cost spin-off technology associated with the optical communications industry. 290/SPIE Vol. 2388 O-8194-1735-1/95/$6.QO Downloaded From: http://proceedings.spiedigitallibrary.org/ on 10/06/2015 Terms of Use: http://spiedigitallibrary.org/ss/TermsOfUse.aspx

A fluorescence lifetime sensor for Cu(I) ions

“…According to equation ( 3) the decay should be exponential for the unquenched sample and then γ should increase linearly with the analyte concentration with τ 0 remaining constant. However, in many real systems [6][7][8][9][10][11][12] the extrapolation of the γ value to zero quencher concentration gives a γ value higher than zero and the τ 0 parameter is not constant with the increase in quencher concentration. The first effect may be explained in terms of the additional donor-donor energy transfer occurring between closely positioned donor molecules and was theoretically treated by Huber [17] and recently studied in our laboratory for perylene fluorescence quenched by cobalt ions in liposomes [18].…”

“…Unfortunately Stern-Volmer quenching offers little opportunity for specificity in metal ion assay because most metal ions and many other analytes quench fluorescence to some extent. Recent research [2,3,[6][7][8][9][10][11][12] has sought to address this fundamental limitation by using the quantum-mechanical spectral overlap criterion required for Förster dipole-dipole non-radiative transfer from a sensor matrix doped with a fluorophore donor to a metal ion acceptor. This condition gives the potential for fabricating intelligent sensors which react only to the metal analyte of interest.…”

“…Sensors based on fluorescence resonance energy transfer (FRET), as it is more widely called, have successfully been applied in our laboratory to the detection of the trace amounts of several metal ions in water solutions [6][7][8][9][10][11][12] with a detection limit down to about 2 ppb [11]. In our approach the metal ion concentration is determined by analysing the time dependence of the non-linear part of the fluorescence decay of the sensing fluorophore in the presence of FRET to the metal analyte.…”

“…In the present paper we report the development of FRET-based lifetime sensing by including a chelating agent specific to a particular ion rather than using direct excitation of the d-d transition in the metal ion hydrated complex as was done previously [6][7][8][9]12]. It is expected that this should lead to higher selectivity and sensitivity of the sensor and this hypothesis is investigated for copper(I) ions selected by the ligand 2,9-dimethyl-4,7-diphenyl-1,10phenanthroline (BCP).…”

“…The crucial point in developing FRET-based sensors is to investigate the kinetics of donor-acceptor energy transfer within the matrix. Our previous studies with transition metal ions in Nafion films have revealed important deviations in the donor fluorescence decay from the corresponding behaviour in bulk solutions [6][7][8][9]12]. The main features of FRET sensors made with ion exchangers are diffusional penetration of analytes through the matrix and inhomogeneous distribution of the analytes around the donor molecules within the matrix.…”