Monolayer Assembly Of Pyrene On Glass Surfaces And Studies On Their Selective Sensing To Organic Copper(Ⅱ) Salts

Copper is on one side essential for life but on the other hand, depending on the dose, may be highly toxic to organisms. So its determination in water samples is warranted by the narrow window of concentration between essentiality and toxicity. Thus, due to. the urgent need for selective copper determination in many biological, geological, environmental and industrial samples, in recent years, various methods have been developed and reported, such as flame or graphite furnace atomic absorption spectroscopy (FAAS, GFAAS), inductively coupled plasma emission or mass spectrometry (ICP-ES, ICP-MS), total reflection X-ray fluorimetry (TXRF) and anodic stripping voltammetry (ASV), spectrophotometric methods and electrochemistry methods. Among them, spectrofluorimetry with fluorescent probe has now attracted the attention of many researchers with the advantages of emission signals being non-destructive, quick, sensitive and multiple choices in signals or parameters including emission intensity, anisotropy, lifetime and even excimer or exciplex formation. As everyone knows, copper(Ⅱ) ion is a paramagnetic ion with an empty d shell and can strongly quench the fluorescence of a fluorophore near it via electron or energy transfer. Based upon the quenching properties, a number of fluorescent homogeneous sensors and fluorescent film sensors for copper(Ⅱ) have been designed and prepared. Most of sensors are designed by combining fluorescent elements with copper(Ⅱ) ionphores. Although the homogeneous sensors are rapid, simple and show promise for near real-time evaluation of copper(Ⅱ) ions in environmental samples, from the viewpoint of practical use, film sensors have a number of advantages like being re-usable, no consumption of reagents and ease to be made into devices. Therefore, design and preparation of fluorescent film sensors for copper(Ⅱ) have become the focus of the research.Generally speaking, a fluorescent film sensor is composed of three parts: fluorescent sensing element, substrate and linker. Its sensing performance is determined by the sensitivity of sensing element to environment or the interaction between functional group and the analyst, such as hydrogen bond, van der Waals force, chelating effect etc.. The films can be prepared by either physical or chemical method. Compared with physical method, the film sensor, where sensing element is immobilized on substrate surface via chemical bond, can avoid, at least in theory, the leaking of the chemicals and the contamination to the analytical system. In addition, the films prepared via chemical ways are re-usable, and are not easy to be damaged.On the basis of the considerations mentioned above and the reviews on fluorescent sensors of copper(Ⅱ) ions, several film sensors for organic copper(Ⅱ) salts were designed and prepared by immobilizing a typical fluorophore, pyrene, on glass slide surfaces via different spacers. All the sensing films show high sensitivity and selectivity to organic copper(Ⅱ) salts. Furthermore, their sensing ability, high sensitivity, ideal reversibility and long lifetime make them worthwhile to be exploited further.Two pyrene-modified fluorescent film sensors with different spacer structures have been designed and prepared in this dissertation. These film sensors have been successfully used to detect organic copper(Ⅱ) salts in aqueous solution.In the first experimental part of this dissertation, pyrene was immobilized onto glass slide surface through surface reaction with the epoxide-terminated SAM via methylene group and diethyltriamine which turn out to be a new kind of fluorescent film sensor for effectively detecting organic copper(Ⅱ) salts in aqueous solution. It has been demonstrated that the sensing performance of the film to copper(Ⅱ) was dependent strongly on the nature of its counter ions. The special "counter ions effect" during the process of sensing copper(Ⅱ) may be understood by considering the physical behavior of the fluorophore moieties in the immobilized state. It should be appropriate to use the "two-dimensional solution model" (also termed as "spacer layer screening effect"), which was proposed by our group, to explain the quenching behaviors of various copper(Ⅱ) salts to the emission of the present film. Compared with the results reported earlier, the response of this film to Cu(Ac)₂ was at least 60 times sensitive than that of the previous film, and the LOD is as low as 6.2×10^-7 M. It is believed that presence of the diethylenetriamine subunits enhances the enrichment of the quencher ion in the nearby of the fluorophore, and results in increase in the sensitivity of the film to the copper(Ⅱ) salts. That is to say that the higher sensitivity of the present film towards organic copper(Ⅱ) salts was a combined result of "counter ion effect" and chelating effect. Furthermore the presence of other divalent metal ions and inorganic copper(Ⅱ) salts show little interference. The nature of the quenching is static and the sensing process is reversible.In the second part of the research, pyrene was immobilized on glass slide surface through surface reaction with the epoxide-terminated SAM via a longer spacer with more chelating point, triethyltetramine. As expected, the sensitivity of the film to Cu(Ac)₂ is higher, but the interference of inorganic copper salts to the measurement is increased, which can be attributed to the increase in the chelating ability of the spacer to copper ions. It is to be noted that all the results can be explained by the same model as mentioned in the first part of this dissertatio. n. Again, the quenching is static in nature and the sensing process is reversible.