Upconversion Luminescent Nanoparticles Based Novel Method For Fluorescence Biosensing

Upconversion luminescent nanomaterials(UCNP)is a kind of material which emits high-energy light after being excited by low-energy light.In recent years,upconversion nanomaterials have developed rapidly,their properties,such as low autofluorescence,high quantum yield,long fluorescence lifetime,photobleaching resistance,low biological toxicity,narrow emission bands,and deep tissue penetration make them widely used in biomedicine domain,such as: disease diagnosis,cell imaging,and photocontrolled release drugs.The combination of upconversion nanomaterials and biosensing and imaging technology can achieve high-contrast imaging and high-sensitivity detection,and can also be used as a nanocarrier and optical switch.In this thesis,based on the excellent luminescence properties of upconversion nanoparticles,a simple functionalized nanosystem was constructed and applied them for intracellular p H imaging and light-controlled sustained-release nucleic acid drugs.The main contents are as follows:1.p H sensing and imaging in living cells are of great significance for understanding cell behavior and disease diagnosis.We designed a label-free nanoprobe(Lipo-UCNP@phenol red)based on the fluorescence internal filtration effect,which was used for ratiometric fluorescence sensing and imaging of intracellular p H values.The nanoprobe consists of three parts: upconversion nanoparticles(UCNP),the phenol red that acting as p H responsive group and UCNP quencher,and polyethylene glycolated(PEG)phospholipids.The nanoprobe is assembled by van der Waals force interaction between PEGylated phospholipids hydrophobic tail and the oleic acid ligands on UCNP surface.Because the ultraviolet absorption spectrum of phenol red at 557 nm at physiological p H and the emission spectrum of upconversion nanoparticles at 540 nm have a good overlap,so the upconversion emission at 540 nm is quenched by the fluorescence internal filtration effect.In addition,the absorption intensity of phenol red at 557 nm varies with the change of p H value,which makes the upconversion emission spectrum at 540 nm change.While the upconversion emission at 655 nm is not affected because there is no ultraviolet absorption of phenol red molecule here.Therefore,the ratio of the upconversion emission intensity at 540 nm and 655 nm is used as the output signal to detect the p H fluctuation in living cells.Fluorescence confocal imaging was used to characterize the cell localization of the nanoprobe during endocytosis and the minimal changes in intracellular p H.These experimental results indicated that the nanoprobe could sensitively and reliably monitor the temporal and spatial p H changes in the process of cell endocytosis and the p H fluctuations of living cells under external stimulation.2?The stimulus-responsive drug release system is quite important in the accurate diagnosis and treatment of cancer cells.In this paper,a sustained-release hydrogel system with nucleic acid aptamers loaded with upconversion nanoparticles was constructed,and the upconversion nanoparticles were used to emit 365 nm ultraviolet light for light-controlled release of DNA.Two partially complementary acrydite and photo-cleavable pc-linker modified DNA strands were designed.Hydrogels were prepared by the base complementary pairing between DNA and free radical polymerization of acrydite and acrylamide and polyethylenimine modified upconversion nanoparticles(PEI-UCNP)were loaded into the hydrogels.The experimental results display that under the irradiation of 980 nm laser,the 365 nm ultraviolet light emitted by PEI-UCNP in the hydrogel can effectively cut off the pc-linker bond in the DNA chain,so as to continuously release the nucleic acid drugs with biological activity.