Phosphorescence Probe Research And Analytical Application Based On Manganese Doped Zinc Sulfide Quantum Dots

Quantum dots (QDs) have received great interest in many research areas due to their characteristic physical and chemical qualities with size-tunable light emission, high tolerance and manifold fluorescence tincts. Doped QDs potentially maintain nearly all of the above advantages, meanwhile avert the self-quenching phenomenon. In Recent years, doped quantum dots have become an active subject in chemo/biosensing and bioimaging areas. In this work, doped QDs and doped coer/shell QDs were synthesized, the as-synthesized doped QDs were characterized by several methods. Taking advantage of their room-temperature phosphorescence quality, we construct optical probes of ions and small molecules and exploit application research.Chapter 1, we described the species and optical properties of QDs, synthesis and research progress of doped QDs. Finally, we provided the significance and contents of this dissertation.Chapter 2, N-acetyl-L-cysteine (NAC) capped Mn doped ZnS quantum dots (QDs) were synthesized through hydrothermal process. The phosphorescence emission of doped QDs located at 583 nrn with the excitation wavelength at 315 nm. The phosphorescence intensity of QDs could be quenched dramatically with the growth of the concentration of Co2+ ion. The novel phosphorescence probe based on NAC capped QDs was developed for detecting cobalt ion with linear dynamic range of 1.25×10-6 M-3.25×10-5 M. The limit of detection and RSD were 6.00×10-8 M and 2.3%, respectively. Interferences experiments showed excellent selectivity superior to multitudinous cations, for instance, alkali, alkalineearth and transitional metal ions. The probable quenching mechanism was studied through phosphorescence decays, too. The proposed phosphorescence probe was ulteriorly applied to detect trace cobalt ion in real water samples with recoveries 97.79%-103.32%.Chapter 3, based on the phosphorescence quenching of the synthesized NAC-Mn:ZnS QDs by catechin, a simple, rapid and specific quantitative method for catechin was proposed. Under the optimal experimental conditions, the quenched intensity of the phosphorescence versus catechin concentration from 0.75 μM to 30.00 μM gave a linear response with an excellent correlation coefficient of 0.9996, and the limit of detection 1.15 ×10-8 M. Some metal ions, amino acids and some sugar molecules do not impact on the determination of catechin. Since the present QDs-based RTP method does not need deoxidants or other inducers as conventional RTP detection methods, and avoids interference from autofluorescence and the scattering light of the matrix that are encountered in spectrofluorometry, this method can be used to detect the content of catechin in body fluid. The possible quenching mechanisms were mainly static quenching.Chapter 4, N-Acetyl-L-cysteine (NAC) and L-cysteine (Cys) capped Mn doped ZnS quantum dots (NAC-Mn/ZnS QDs and Cys-Mn/ZnS QDs) are firstly prepared by hydrothermal methods. These QDs display strong phosphorescence emission peaks at 583 nm and 580 nm upon excitation at 315 nm and 306 nm, respectively. Since their room-temperature phosphorescence is efficiently quenched by L-ascorbic acid (AA), they have been employed as phosphorescence probes for detecting AA. The linear working ranges are 2.50 μM-37.50 μM and 2.50 μM-47.50 μM and the limits of detection are 0.72 μM and 1.38 μM for NAC-Mn/ZnS QDs and Cys-Mn/ZnS QDs, respectively. The possible quenching mechanisms have been discussed in detail. The QDs probes are highly selective to AA over other common ions, amino acids, glucose and bovine serum. Finally, they have been applied successfully for detection of AA in human urine samples with satisfactory results. Our work provides a simple and convenient phosphorescence method to determine AA in real samples.Chapter 5, we report a turn-on phosphorescence probe for detection of histidine based on Co2+-adsorbed N-acetyl-L-cysteine (NAC) capped Mn: ZnS quantum dots (QDs) which is directly synthesized by the hydrothermal method. The phosphorescence of NAC-Mn:ZnS QDs is effectively quenched by Co2+ attributing to the adsorption of Co2+ onto the surface of QDs with a concomitant in suppressing the recombination process of hole and electron of QDs. The phosphorescence of Co2+-adsorbed NAC-Mn:ZnS QDs can be recovered by binding of Co2+with histidine. The quenching and regeneration of the phosphorescence of NAC-Mn:ZnS QDs have been studied in detail. The as-prepared QDs-based probe is applied to determine histidine with a linear range of 1.25 μM-30.00 μM and a detection limit of 0.74 μM. Co2+-adsorbed NAC-Mn:ZnS QDs show high sensitivity and good selectivity to histidine over other amino acids, metal ions and co-existing substances. The proposed QDs probe has been successfully applied to determination of histidine in human urine samples with good recoveries of 98.50%-103.00%.Chapter 6, NAC capped Mn doped ZnS/ZnS quantum dots (QDs) have been synthesized and characterized as a phosphorescence ion probe for detecting ultrasensitive Cu (Ⅱ). The phosphorescence of NAC-Mn:ZnS/ZnS QDs is strongly quenched with the increasing of the concentration of Cu2+ion, the phosphorescence probe of detecting Cu2+ is structured based on NAC-Mn: ZnS/ZnS QDs. Under the optimum conditions, the linear working range is 0.00 M-10.00×10-6 M and the limits of detection is 8.97 x 10"9 nM with a RSD of 2.8%. Meanwhile, the effect of foreign ions displays a low interference response in the detection of Cu2+ ion. Moreover, based on phosphorescence decays of NAC-Mn:ZnS/ZnS QDs, the quenching mechanism between NAC-Mn:ZnS/ZnS QDs and Cu2+ ion is preliminarily discussed. The phosphorescence probe has been successfully applied to detecting Cu2+ in human urine samples with good recoveries of 98.60%-102.00%.