Abstract

Abstract

Abstract

Abstract

Abstract
The complexes of ruthenium(II) with phenanthroline (Phen), diphenylphenanthroline (Ph(2)Phen) and with 4,4'-dicarboxy-2,2'-bipyridine acid (Dcbpy) ([Ru(Phen)(2)Dcbpy]Cl(2) and [Ru(Ph(2)Phen)(2)Dcbpy]Cl(2)) were synthesized and the variation of the correspondent fluorescence intensity and lifetime with the pH characterized, Luminescence Intensity, emission wavelength and excited state lifetime all show a typical sigmoid variation with pH in the range 3-9, demonstrating the suitability of this complex for luminescence sensing applications. In aqueous solutions (28% ethanol) the complexes [Ru(Phen)(2)Dcbpy]Cl(2) and [Ru(Ph2Phen)2Dcbpy]Cl2 show, respectively, the following properties: apparent pK(a) of 3.6 +/- 0.4 and 3.7 +/- 0.4; lifetimes of the protonated species 0.46 +/- 0.01 mu s and 0.38 +/- 0.02 mu s and ionised species 0.598 +/- 0.001 mu s and 0.61 +/- 0.08 mu s. The [Ru(Phen)(2)Dcbpy]Cl(2) complex was immobilised in the tip of optical fibers using a hybrid sol-gel procedure based on tetraethoxysilan and phenyltriethoxysilan enabling pH sensitive fiber probes. The immobilised complex shows the following lifetimes: protonated species 1.05 +/- 0.04 mu s and ionised species 1.16 +/- 0.04 mu s. These characteristics show that these ruthenium(II) complexes are good indicators for pH sensing, either in aqueous solution or immobilised in sol-gel, and are well suited for intensity and/or frequency domain interrogation.

Abstract
Cyanobacteria deteriorate the water quality and are responsible for emerging outbreaks and epidemics causing harmful diseases in Humans and animals because of their toxins. Microcystin-LR (MCT) is one of the most relevant cyanotoxin, being the most widely studied hepatotoxin. For safety purposes, the World Health Organization recommends a maximum value of 1 mu g L(-1) of MCT in drinking water. Therefore, there is a great demand for remote and real-time sensing techniques to detect and quantify MCT. In this work a Fabry-Perot sensing probe based on an optical fibre tip coated with a MCT selective thin film is presented. The membranes were developed by imprinting MCT in a sol-gel matrix that was applied over the tip of the fibre by dip coating. The imprinting effect was obtained by curing the sol-gel membrane, prepared with (3-aminopropyl) trimethoxysilane (APTMS), diphenyl-dimethoxysilane (DPDMS), tetraethoxysilane (TEOS), in the presence of MCT. The imprinting effect was tested by preparing a similar membrane without template. In general, the fibre Fabry-Perot with a Molecular Imprinted Polymer (MIP) sensor showed low thermal effect, thus avoiding the need of temperature control in field applications. It presented a linear response to MCT concentration within 0.3-1.4 mu g L(-1) with a sensitivity of -12.4 +/- 0.7 nm L mu g(-1). The corresponding Non-Imprinted Polymer (NIP) displayed linear behaviour for the same MCT concentration range, but with much less sensitivity, of -5.9 +/- 0.2 nm L mu g(-1). The method shows excellent selectivity for MCT against other species co-existing with the analyte in environmental waters. It was successfully applied to the determination of MCT in contaminated samples. The main advantages of the proposed optical sensor include high sensitivity and specificity, low-cost, robustness, easy preparation and preservation.