The Application Of Fluorescence Biosensor Based On Quantum Dots@SiO₂ Microspheres

As a kind of novel fluorescent probes, quantum dots had superior optical characteristics than conventional organic fluorescent dyes. So it caught more and more attention of researchers. The preparation of QDs@Si O2 composite microsphere can improve the performance of QDs. It included the great stability, no fluorescence signal intervention due to the transparent and stable structural, the universal platform for surface modification because of the large volume and large specific surface area, the enhancement of the biocompatibility which depended on the low toxicity, and so on.In chapter 1, we described the basic properties and the main prepared methods of QDs. We introduced the synthesis and classification of QDs@Si O2 microspheres, and their application in biomedical analytical field.In chapter 2, QD-Au NP@Si O2 mesoporous microspheres have been fabricated as a novel enzyme-mimic nanosensor. Cd Te quantum dots(QDs) were loaded into the core, and Au nanoparticles(NPs) were encapsulated in the outer mesoporous shell. QDs and Au NPs were separated in the different space of the nanosensor, which prevent the potential energy or electron transfer process between QDs and Au NPs. As biomimetic catalyst, Au NPs in the mesoporous silica shell can catalytically oxidize glucose as glucose oxidase(GOx)-mimicking. The resultant hydrogen peroxide can quench the photoluminescence(PL) signal of QDs in the microsphere core. Therefore the nanosensor based on the decrease of the PL intensity of QDs was established for the glucose detection. The linear range for glucose was in the range of 5–200 μM with a detection limit(3s) of 1.32 μM.In chapter 3, we developed of a ratiometric photoluminescence(PL) sensor comprising dual-emission QDs@Si O2 nanoparticles for the detection of Zn2+ and IO3-. The PL signal of the red-emitting QDs in the Si O2 nanoparticles core worked as a reference, while the PL signal of the green-emitting QDs covalently linked onto the silica surface could be selectively quenched or restored by the analyte. After PL quenching of the green-emitting QDs by phenanthroline(Phen), Zn2+ can recover the PL under alkaline conditions via the formation of a Zn–Phen complex in the solution. Besides, IO3- can interact with the green-emitting QDs through oxidation–reduction reactions under acidic conditions, leading to further PL quenching. Under the optimized conditions, linear relationships between the PL intensity ratio of the ratiometric system and ion concentration were obtained from 5 to 100 μM for Zn2+ and from 5 to 150 μM for IO3-. The limits of detection(LOD) for Zn2+ and IO3- were 1.15 and 1.76 μM, respectively.In chapter 4, multifunctional mesoporous silica nanoparticles(MSNs)-based “gate-like” ensembles were fabricated for drug delivery through passive targeting and H2O2-sensitive drug release. The ensembles constituted QDs core and 3-aminobenzeneboronic acid functionalized Au nanoparticles(APBA-Au NPs) capped mesoporous silica shell. Anti-cancer drug doxorubicin(DOX) was used as the model drug to investigate the release behavior of the MSNs system. After the drug loading, the MSNs carriers retained the drug without leakage owing to the clogging of Au NPs to the pores outlet. And Au NPs could be selectively detached from the surface of mesoporous silica upon exposing to H2O2 and facilitated the release of the encapsulated guests at a controlled manner. Therefore, the Au NPs anchored on MSNs could serve as efficient gatekeepers to modulate the on-off of the pores.