Development Of Some Metal Ions And Anions Optical Sensors And Analytical Applications

The fluorescent probes continue to retain an important position in the development of optical sensor. In the past decades, it has been a rapid development for the research on optical probe. Various fluorescent probes, such as organic dyes, conjugated polymers, semiconductor quantum dots, and noble metal nanoparticles, have been extensively used for various analyzes. They promise advantages of rapidity, sensitivity, high quantum yield, and so on. However, these fluorescent probes still suffers from one or more major deficiencies, such as, poor light stability of organic dyes and conjugated polymers, complex chemical synthesis, high environmental toxicity of semiconductor quantum dots. Recently metal nanoclusters, which provide the missing link between atomic and nanoparticle behavior in metals, have drawn the most attention, because of their molecule-like fluorescence properties due to their sizes compared to the Fermi wavelength of electrons, simple synthesis methods, and good biocompatibility. To date, most of previous work concentrated on the noble mental nanoclusters, especially Au NCs and Ag NCs. Although various synthetic methods have been proposed for the preparation of noble metal NCs, the obtained fluorescent Au NCs and Ag NCs have some drawbacks including low quantum yield and stability. Also, compared to extensive studies on Au NCs and Ag NCs, Cu NCs were much less studied. Hence, it remains a great significance for the development of a simple and facile strategy for the synthesis of water soluble, extremely stable, and highly quantum efficient fluorescent Cu NCs and the application of the resulted Cu NCs in the detection of mental ions and anions. Thus, this thesis focused on the fluorescent probes of copper nanoclusters, and carry out the following work:1) The research of small molecule as fluorescent probes for sensing of Cu2+;2) The research of functional Ag nanoparticles (NPs) as resonance light scattering (RLS) probes for simultaneous sensing of Pb2+and cysteine;3) Facile preparation of fluorescent Cu nanoclusters (NCs) and the research of the suitability of Cu NCs as fluorescent probes.On this basis, the development of some metal ions and anions optical sensors were successfully used for environmental analysis and biochemical analysis. The thesis is divided into six chapters:Chapter1:It introduces literature review and the reasons why to select this subject. In brief,1) The development of the optical sensors based on metal nanomaterials and analytical applications in recent years;2) Synthesis of metal nanoclusters, fluorescence properties, analytical applications and some problems. According to the results of literature analysis, we presented in the reasons why to select this subject on this thesis.Chapter2:The research about small molecule as fluorescent probes for sensing of Cu2+is developed. It was found that Cu2+shows great catalytic effect on p-cresol oxidation by hydrogen peroxide under alkaline condition, leading to an intense fluorescence signal due to fast formation of2,2’-dihydroxy-5,5’-dimethylbiphenyl, an oxidation product of p-cresol. Investigation on the fluorescence spectra of the p-cresol-hydrogen peroxide system demonstrated the catalytic behavior of Cu2+. On this basis, a very simple, sensitive, and selective fluorescent method was established for the determination of trace copper in this study. Under the optimal conditions, the proposed system could respond down to1.0x10-8mol L-1of Cu2+with a linear calibration range from3.0×l0-7mol L-1to5.0×5mol L-1. The relative standard deviation (RSD) is2.1%for7.0x10-6mol L-1Cu2+(n=15). The proposed method was successfully applied to determine trace Cu2+in lake, river and swimming pool water samples with satisfactory results. The results given by the proposed method are in good agreement with those given by atomic absorption spectroscopy method.Chapter3:We investigated the suitability of functional Ag nanoparticles (NPs) as resonance light scattering (RLS) probes for simultaneous sensing of Pb2+and cysteine. This strategy was based on the fact that Pb2+could induce the aggregation of DTC-Ag NPs due to strong metal affinity of DTC along with the enhanced RLS signal. Meanwhile, due to the strong binding preference of cysteine toward Pb2+by forming Pb2+-S bond, Pb2+was removed from the surface of the DTC-Ag NPs, leading to redispersion of DTC-Ag NPs, along with the decreased RLS signal. The DTC capping ligands are generated by a very simple in situ method through reaction of carbon disulfide with diethanolamine as primary precursor molecules under ultrasonic irradation. After optimizing some experimental conditions (including pH value of solution, concentration of DTC-Ag NPs, and ion strength), a very simple and facile sensing system has been developed for detection of Pb2+in water based on RLS technology. The proposed system promises excellent selectivity, wide linear response range and high sensitivity for Pb2+. The linear response ranges for Pb2+was from0.01μM to60μM. The limit of detection (S/N=3?) for Pb2+was as low as4nM. The proposed method was successfully used to detect Pb2+in river and tap water samples, indicating the potential of this new, sensitive and selective method in water quality monitoring. The possibility of the proposed system for sensing of cysteine was also investigated.Chapter4:Facile preparation of water soluble and fluorescent Cu nanoclusters (NCs) stabilized by tartaric acid at room temperature is described and characterized using UV-Vis absorption spectrum, high-resolution transmission electron microscopy, dynamic light scattering and Fourier transform infrared spectroscopy (FT-IR), giving a quantum yield (QY)2.2%against the reference of quinine sulfate. The tartaric acid layer was introduced to prevent the Cu NCs from aggregation or oxidation, increase their water solubility and was found to be highly stable even in1M NaCl. Additionally, this simple surface optimization resulted in surprisingly high efficiency of selective Al3+sensing and other coexistence ions have no obvious effects on the sensing of Al3+. The sensing mechanism to be hypothesized is the interaction between Al3+and carboxyl and hydroxyl groups on the Cu surface along with the enhanced fluorescence signal and blue shift wavelength. Under optical condition, the limit of detection (LOD) for Al3+was as low as12.5nM. Meanwhile, due to the strong binding preference of fluoride toward Al3+, Al3+was removed from the surface of the tartaric acid-Cu NCs, resulting in the disconnection of the interaction between Al3+ions and tartaric acid-Cu NCs, along with the decreased fluorescence signal of tartaric acid-Cu NCs and red shift wavelength. The possibility of the proposed system for sensing of fluoride was also investigated. This result revealed a simple and practical strategy for Al3+and fluoride detection using fluorescent Cu NCs as sensor probe. The method is simple, rapid, sensitive and selective.Chapter5:To obtain Cu nanoclusters (NCs) with high quantum yield, a simple, one-step facile route for preparation of water soluble and fluorescent Cu NCs stabilized by tannic acid (TA) as a model of small molecule is described. The as-prepared TA capped Cu NCs (TA-CuNCs) are characterized by UV-vis spectroscopy, Fourier transform infrared (FT-IR) spectroscopy, luminescence, transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). The Cu NCs show luminescence properties having excitation and emission maxima at360nm and430nm, respectively, with a quantum yield of about14%. The TA-Cu NCs are very stable even in0.3M NaCl, and their luminescent properties show pH independent. The fluorescence (FL) of the TA-Cu NCs is quenched by Fe3+through an electron transfer mechanism, but not by other metal ions. Furthermore, the FL of the TA-Cu NCs shows no changes with the addition of Fe2+or H2O2individually, but it is quenched significantly by their mixture. On this basis, TA-Cu NCs have been demonstrated to build the combination logic gate system to discriminate Fe3+, Fe2+and their mixture. This facile chemosensor can offer a rapid, reliable, sensitive, and selective sensing of Fe3+ions with detection limit as low as10nM and a dynamic range from10nM to10μM. The detection results for ferrous ions in water samples obtained by this method agreed well with that by atomic absorbance spectrometry, suggesting the potential application of this sensing system. Moreover, to demonstrate the potential application of the prepared TA-Cu NCs fluorescent probe with high QY for in cell imaging, the cytotoxicity of TA-Cu NCs was evaluated by CCK-8assays, in which no significant cytotoxic effects have been observed in the presence of TA-Cu NCs, and almost100%of A549cells are alive even in the presence of10μM TA-Cu NCs, indicating it is low toxicity for cell, good biocompatibility and suitable for imaging studies. We demonstrate the feasibility of using TA-Cu NCs for determination of Fe3+in living cells.Chapter6:We have employed tannic acid stabilized copper clusters (TA-Cu NCs) as a novel swithable fluorescence sensor for the detection of the phosphate (Pi) in solution, which was based on the competition between Pi and TA—Cu NCs for the interaction with the Europium ions (Eu+). First, Eu+could induce the aggregation of TA-Cu NCs due to coordination to the oxygen-donor atoms of the carboxylate groups and hydroxyl on the Cu NCs surfaces along with the decrease in the FL intensity of the Cu NCs. Because Eu3+displays a higher affinity for the oxygen-donor atoms in Pi than for the carboxylate groups and hydroxyl on the TA-Cu NCs surface, there is a competition for Eu3+between the oxygen-donor atoms from Pi and those from the carboxylate groups on the Cu NCs surface, which effectively diminishing its quenching efficiency, and the FL intensity of Cu NCs is recovered. Under optical condition, a linear relationship (R2=0.9963) was observed with Pi concentrations from0.07to80μM and the detection limit at an S/N ratio of3for Pi was9.6nM. Because fluorescence quenching of the TA-Cu NCs by Eu3+is inhibited by Pi selectivity, we have obtained a highly sensitive and selective assay for Pi. Herein, a novel switchable phosphate sensing system with highly sensitivity and selectivity is designed using stable and fluorescent Cu NCs that bear surface groups of carboxy groups, combined with Eu3+Moreover, we demonstrate the feasibility of using TA-Cu NCs for determination of Pi in environmental smples.