| The exploration of systems capable of sensing and recognizing based on quantum dots (QDs) is a topic of considerable interest. Subtle change of the surface property of QDs can result in a dramatic change in their optical properties. This feature of QDs offers many opportunities for detecting various specific analytes. While most research works focus on the development of QDs based fluorescence sensors, much less attentions are paid to the room-temperature phosphorescence (RTP) properties of QDs and their potential for phosphorescence detection. When the nanohybrids formed between quantum dots and other molecules, the nanohybrids offer unique optical, electrical or magnetic properties that are not found in the individual components. The controlled nanohybrids based on QDs are high of interest for their fundamental importance as well as the application of sensors. The purpose of this dissertation is to explore the RTP properties of Mn-doped ZnS QDs and their nanohybrids for bio/chemosensing. The main contents are summarized as follows:(1) The RTP property of Mn-doped ZnS QDs was explored to develop a novel method for facile, rapid, cost-effective, sensitive and selective detection of enoxacin in biological fluids. The Mn-doped ZnS QDs based RTP method did not need the use of deoxidants and other inducers, and allowed detecting enoxacin in biological fluids without interference from autofluorescence and scattering light of matrix. The Mn-doped ZnS QDs offered excellent selectivity for detecting enoxacin in the presence of main relevant metal ions in biological fluids, biomolecules and other kinds of antibiotics. The precision for eleven replicate detections of 0.4μM enoxacin was 1.8% (RSD). The detection limit (3σ) for enoxacin was 58.6nM. The recovery of spiked enoxacin in human urine and serum samples ranged from 94% to 104%. The developed Mn-doped ZnS QDs based RTP method was employed to monitor the time-dependent concentration of enoxacin in the urine from a healthy volunteer after oral medication of enoxacin. The investigation provides evidences that doped QDs are promising for RTP detection for further applications.(2) A sensing system based on the photoinduced electron transfer (PIET) between Mn-doped ZnS QDs and methyl viologen (MV) was established for quantitative detection of DNA in biological fluids. The RTP intensity of Mn-doped ZnS QDs was quenched by MV adsorbed onto the surface of the QDs due to the photoinduced electron-transfer process. Addition of DNA restored the RTP signal of Mn-doped ZnS QDs due to the competitive binding of DNA with MV from the surface of Mn-doped ZnS QDs. Sensitive detection of DNA with the detection limit (3σ) of 33.6μg L-1 and a linear detection range of 0.08-12 mg L-1 was achieved. The precision for eleven replicate detections of 0.5μM hsDNA was 3.7% (RSD). The interference from autofluorescence and scattering light was avoided due to the phosphorescence nature of the Mn-doped ZnS QDs. The sensitive and rapid detection of DNA as well as the avoidance of modification or immobilization process makes this system suitable and promising for DNA detection.(3) We present a simple method to build nanohybrids from the 3-mercaptopropionic acid-capped Mn-doped ZnS QDs (MPA-capped Mn-doped ZnS QDs) and octa(3-aminopropyl)octasilsequioxane octahydrochloride (OA-POSS) via electrostatic self-assembly and to provide a convenient strategy to develop a novel RTP sensor for detecting DNA in biological fluids. OA-POSS with eight amine groups on each comer acting as cubic linkers organized MPA-capped Mn-doped ZnS QDs into well-defined aggregates, which gave the RTP intensity 7.5 times higher than that of the MPA-capped Mn-doped ZnS QDs. High density of negatively charged phosphate groups of the double helix provided the ability of DNA to compete with negatively charged MPA-capped Mn-doped ZnS QDs and to form rather stable complexes with OA-POSS, leading to the decrease of the RTP of the Mn-doped ZnS QDs/OA-POSS nanohybrids with increase of the concentration of DNA. The precision for eleven replicate detections of 0.5μM hsDNA was 4.8% (RSD). The detection limit (3σ) of the present sensor for DNA was 54.9 nM, comparable to or lower than those of some nanocrystal based non-sequence specific methods for quantitative determination of DNA, but much higher than those of some sequence-specific methods. This methodology can be in principle applied to other biological molecules by modifying Mn-doped ZnS QDs and POSS with suitable functional groups that selectively bind target analytes.
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