Fluorescent Chemosensing Technology For Determination Of Heavy Metal Ions Based On Organic Carriers

In recent years, the research on chemical probes and sensors based on organic dyes remains very active and searching for new fluorophores to improve sensitivity and selectivity of chemical probes and sensors is still a challenge for the analytical research efforts. In this dissertation, a series of novel fluorescent probes and sensors were designed and synthesized to recognize heavy metal ions. The details are summarized as follows:1. In chapter 2, N-methyl-5, 10, 15, 20-tetraphenylporphine(NMTPPH) as an organic carrier has been used to detect trace amount of zinc ions in ethanol-water solution by fluorescence spectroscopy. The fluorescent probe undergoes a fluorescent emission intensity enhancement upon binding to zinc ions in EtOH/H2O (1:1, v/v) solution. The fluorescence enhancement of NMTPPH is attributed to the 1:1 complex formation between NMTPPH and Zn²⁺ which has been utilized as the basis for the selective detection of Zn²⁺. The linear response range covers a concentration range of Zn²⁺ from 5.0×10-7 to 1.0×10-5 mol/L and the detection limit is 1.5×10-7 mol/L. The fluorescent probe exhibits high selectivity over other common metal ions except Cu²⁺. And the probe has been used for determination of Zn²⁺ in water samples with satisfactory results.2. In chapter 3, a ratiometric fluorescent zinc probe of carboxamidoquinoline with a carboxylic acid group was designed and synthesized. Probe exhibits high selectivity for sensing Zn²⁺; increase in fluorescence emission intensity and red-shift of fluorescence emission are observed upon binding Zn²⁺ in EtOH/H2O (1:1, v/v) solution at pH 7.24. The ratiometric fluorescence response is attributed to the 1:1 complex formation between probe and Zn²⁺ which has been utilized as the basis for the selective detection of Zn²⁺. The analytical performance characteristics of the proposed Zn²⁺-sensitive probe were investigated. The probe can be applied to the quantification of Zn²⁺ with a linear range covering from 2.0×10?6 to 5.0×10?5 mol/L and a detection limit of 2.7×10?7 mol/L. The determination of Zn²⁺ in both tap and river water samples shows satisfactory results.3. In chapter 4, we describe the fabrication and analytical characteristics of fluorescence-based zinc ion-sensing glass slides. To construct the sensor, a benzoxazole derivative with a terminal double bond was synthesized and copolymerized with 2-hydroxyethyl methacrylate (HEMA) on the activated surface of glass slides by UV irradiation. In the absence of Zn²⁺ at pH 7.24, the resulting optical sensor emitted fluorescence at 450 nm via excited-state intramolecular proton transfer (ESIPT). Upon binding with Zn²⁺, the ESIPT process was inhibited resulting in blue-shift of fluorescence emission. Thus, the proposed sensor can behave as a ratiometric fluorescent sensor for the selective detection of Zn²⁺. In addition, the sensor shows nice selectivity, good reproducibility and fast response time. The sensing membrane demonstrates a good stability with a lifetime of at least 3 months. The sensor exhibits a linear response toward Zn²⁺ in the concentration range 8.0×10-5-4.0×10-3 mol/L and the detection limit is 4.0×10-5 mol/L. The proposed chemosensor has been successfully implemented for the identification of Zn²⁺ in both tap and river water samples.4. In chapter 5, we describe the fabrication and analytical characteristics of fluorescence-based copper ion-sensing glass slides. To prepare the sensor, a naphthalimide derivative with a terminal double bond was synthesized as a fluorescent carrier. To prevent the leakage of the dye, the carrier is immobilized on a quartz glass plate surface treated with a silanizing agent by UV irradiation. The proposed sensor with visible excitation can be utilized for a copper assay based on fluorescence quenching. The sensor exhibits satisfactory selectivity, reproducibility and response time. The sensing membrane possesses a relatively long lifetime of at least 2 months. Copper ion can be determined in the range between 4.0×10-7- 6.0×10-4 mol/L with a detection limit of 2.0×10-7 mol/L at pH 7.24. The present approach has been demonstrated with the identification of Cu²⁺ in river water sample.5. In chapter 6, a new fluorescent probe for Hg²⁺ based on a rhodamine-thiophene conjugate was synthesized and its fluorescence could be enhanced by the addition of Hg²⁺. The probe shows a high selectivity and sensitivity to Hg²⁺ by forming a 2:1 complex between probe and Hg²⁺ in 50% CH3CN/H2O buffered at pH 6.00. Besides, probe displays a reversible dual chromo- and fluorogenic response toward Hg²⁺ likely due to the chelation-induced ring-openging of rhodamine spirolactam. Hg²⁺ can be determined in the range 5.0×10-8 to 1.0×10-5 mol/L with a detection limit of 2.0×10-8 mol/L. Determination of Hg²⁺ in both tap and river water samples was successfully carried out with the proposed probe.6. In chapter 7, a fluorescent probe for Hg²⁺ based on a rhodamine-coumarin conjugate was designed and synthesized. Probe exhibits high sensitivity and selectivity for sensing Hg²⁺, and increase in fluorescence emission intensity is observed upon binding Hg²⁺ in 50% water/ethanol buffered at pH 7.24. The fluorescence response to Hg²⁺ is attributed to the 1:1 complex formation between probe and Hg²⁺, which has been utilized as the basis for the selective detection of Hg²⁺. Besides, probe was also found to show a reversible dual chromo- and fluorogenic response toward Hg²⁺ likely due to the chelation-induced ring-openging of rhodamine spirolactam. The analytical performance characteristics of the proposed Hg²⁺-sensitive probe were investigated. A wide linear dynamic range of Hg²⁺ from 8.0×10-8 to 2.0×10-5 mol/L was reached with a detection limit of 4.0×10-8 mol/L. The determination of Hg²⁺ in both tap and river water samples was successful.