1. Field of Invention
The present invention relates to a transition metal-ligand complex that shows changes in its luminescence lifetime characteristic and/or luminescence intensity as a function of the polarity and/or hydrogen bonding properties of its environment, and a sensor, probe, system and method based on the complex for detecting the presence, amount or concentration of a polar solvent in a medium.
2. Description of Related Art
There is extensive interest in optical chemical sensing in the fields of bio-engineering, environmental science and industry. Fiber Optic Chemical Sensors and Biosensors, ed. Wolfbeis, O. S., CRC Press, Boca Raton, Fla., 1991, vols. I and II; Topics in Fluorescence Spectroscopy. Volume 4: Probe Design and Chemical Sensing, ed. Lakowicz, J. R., Plenum Press, New York, 1994; Seitz, W. R., CRC Crit. Rev. Anal. Chem., 1988, 19, 135; Rao, G., Bambot, S. B., Kwong, C. W., Szmacinski, H., Sipior, J., Holavanahali, R., and Carter, G., in Topics in Fluorescence Spectroscopy. Volume 4: Probe Design and Chemical Sensing, ed. Lakowicz, J. R., Plenum Press, New York, 1994, pp. 417-448. Among a number of sensing schemes, luminescence lifetime-based sensing is one of the preferred methods, because of its unique advantages of being insensitive to signal drift resulting from leaching and photobleaching of indicator dye, variations of light source intensity, and stability of the photodetector.
Although sensors based on the principle of phase-modulation fluorometry have been reported for sensing pH (Szmacinski, H. S., and Lakowicz, J. R., Anal. Chem., 1993, 65, 1668), CO2 (Sipior, J., Bambot, S., M., Romauld, Carter, G. M., Lakowicz, J. R., and Rao, G., Anal. Biochem., 1995, 227, 309), NH3 (Chang, Q., Sipior, J., Lakowicz, J. R., and Rao, G., Anal. Biochem., 1995, 232, 92) and glucose (Lakowicz, J. R, and Maliwal, B. P., Anal. Chim. Acta, 1993, 271, 155), none has heretofore been developed for sensing polar solvents, such as methanol, ethanol and water.
A methanol or ethanol sensor is of great interest for various applications, particularly in the chemical and biochemical processing industries. For example, such a sensor would be useful in the petroleum industry for measuring and controlling the concentration of methanol and ethanol, which have replaced tetraethyl lead as the anti-knocking agent in most gasoline products. In the biochemical engineering industry, methanol and ethanol bio-sensors have been used to monitor and control methanol concentration in polysaccharide fermentation (Austin, G. D., Sankhe, S. K., and Tsao, G. T., Bioprocess Eng., 1992, 7, 241), and ethanol concentration in yeast fermentation (Paul, C. D., and Maerz, U., Biotechnol. Educ., 1991, 2, 59). Additionally, a methanol sensor would be useful in chromatographic and other separations where methanol is widely used.
Because methanol is a very polar molecule, a sensor for detecting methanol in non-polar media can be constructed using a solvatochromic indicator dye. Although solvatochromic dyes have been used for decades as polarity indicators in solutions (Reichardt, C., Solvent and Solvent Effects in Organic Chemistry, VCH Publishers, New York, 2nd edn., 1988; Reichardt, C., Chem. Rev., 1994, 94, 2319; Kumoi, S., Oyama, K., Yano, T., Kobayashi, H., and Ueno, K., Talanta, 1970, 17, 319; Kumoi, S., Kobayashi, H., and Ueno, K., Talanta, 1972, 19, 505; Reichardt, C., Asharin-Fard, S., Blum, A., Eschner, M., Mehranpour, A. M., Milart, P., Niem, T., Schafer, G., and Wilk, M., Pure and Appl. Chem., 1993, 65, 2593; Kolling, O. W., Anal. Chem., 1981, 53, 54; Kolling, O. W., and Goodnight, J. L., Anal. Chem., 1973, 45, 160; Figueras, J., J. Am. Chem. Soc., 1971, 93, 3255; Gaines, G. L., Jr., Anal. Chem., 1976, 48, 450; Gordon, J. E., J. Phys. Chem., 1966, 70, 2413; and Brooker, L. G. S., Craig, A. C., Heseltine, D. W., Jenkins, P. W., and Lincoln, L. L., J. Am. Chem. Soc., 1965, 87, 2443), they did not become a part of any practically useful methanol sensor until Hubert and coworkers reported using them in a polymer film sensor for detecting polar additives in hydrocarbon blends. Hubert, C., Fichou, D., Valat, P., Garnier, F., and Villeret, B., Polymer, 1995, 36, 2663. Specifically, Hubert et al. created a polymer film for sensing small polar molecules, such as methanol and ethanol, by doping Reichardt""s dye in a poly(methyl methacrylate) (PMMA) polymer matrix, and spin-coating the mixture on a piece of glass slide. The film displayed an absorption maximum at 654 nm in methanol-free naphtha, which moved to 542 nm in a mixture of 2% methanol in naphtha. By monitoring the absorbance change at 654 nm, the sensor could detect methanol at a level down to 0.1% concentration. A drawback to Hubert et al.""s sensor is that it requires careful pre-treatment before measuring because it is subject to interference from atmospheric humidity. Additionally, the present inventors have found in a preliminary experiment that Reichardt""s dye is not photostable. Such instability will limit the use of the sensor in practice.
Besides methanol and ethanol, another solvent that can be detected by a polar sensor is water. Water is the most common impurity or contaminant in many organic solvents, particularly solvents that are miscible with water. As such, a sensor capable of detecting the presence and amount of water would be useful in numerous applications, including, for instance, detecting gasoline leakage from tanks, measuring the organic (or water) content in waste industrial liquid, and monitoring the alcohol content in processes for fermenting liquor. As discussed later in this application, such a water sensor can be constructed based on the principle of luminescence lifetime, using a transition metal-ligand complex as an indicating molecule immobilized in a hybrid solid support of organic polymer, carboxymethyl cellulose, and inorganic polymer (sol-gel). An advantage of using luminescent metal-ligand complexes is their long decay times over 100 ns, which allow simple and low cost instrumentation for lifetime based sensing.
Based on the foregoing background, a need exists for a new and improved sensor to detect the presence, amount and/or concentration of polar solvents, such as methanol, ethanol and water.
The inventors have discovered a novel transition metal-ligand complex that is useful as a sensor for detecting and measuring a physical and/or chemical characteristic of a sample, such as monovalent or divalent cation concentration, anion concentration, oxygen concentration, pH, viscosity and polarity.
Specifically, their invention relates to a transition metal-ligand complex, which comprises:
(i) a transition metal; and
(ii) at least one bi- or tri-dentate imine ligand.
In a preferred embodiment, the complex has a luminescence lifetime characteristic that changes as a function of the polarity or hydrogen bonding properties of its environment.
In another preferred embodiment, the intensity of luminescence emitted by the complex changes as a function of the polarity or hydrogen bonding properties of its environment.
The invention further relates to a sensor for use in determining the presence, amount or concentration of a polar solvent in a medium, which comprises a transition metal-ligand complex containing a transition metal and at least one bi- or tri-dentate imine ligand.
Additionally, the invention relates to a method for determining the presence, amount or concentration of a polar solvent in a medium, which comprises:
(ii) determining, in the absence of the polar solvent, a luminescence lifetime characteristic of a sensor, wherein the sensor comprises a transition metal-ligand complex containing a transition metal and at least one bi- or tri-dentate imine ligand;
(iii) contacting the medium with said sensor;
(iii) determining a change in the luminescence lifetime characteristic of said sensor; and
(iv) determining the presence, amount or concentration of the polar solvent in the medium based on the change in the luminescence lifetime characteristic of said sensor.
The invention also relates to a method for determining the presence, amount or concentration of a polar solvent in a medium, which comprises:
(i) determining, in the absence of the polar solvent, the intensity of luminescence emitted by a sensor, wherein the sensor comprises a transition metal-ligand complex containing a transition metal and at least one bi- or tri-dentate imine ligand;
(iii) contacting the medium with said sensor;
(iii) determining a change in the luminescence intensity of said sensor; and
(iv) determining the presence, amount or concentration of the polar solvent in the medium based on the change in the luminescence intensity of said sensor.
Furthermore, the invention relates to a probe for determining the presence, amount or concentration of a polar solvent in a medium, which comprises:
(i) a sensor comprising a transition metal-ligand complex containing a transition metal and at least one bi- or tri-dentate imine ligand; and
(ii) connected to the sensor, optical transmission means for transmitting luminescence excitation radiation to the sensor and transmitting luminescence emitted by the sensor to a detector.
Finally, the invention relates to a system for determining the presence, amount or concentration of a polar solvent in a medium, which comprises:
(i) a sensor comprising a transition metal-ligand complex containing a transition metal and at least one bi- or tri-dentate imine ligand;
(ii) an excitation light source for irradiating said sensor; and
(iii) means for measuring a lifetime characteristic and/or intensity of luminescence emitted by said sensor.