Small organic molecule-functionalized upconversion nanoparticles for detection and bioimaging

In recent years the bio-detection and bio-imaging are hot research areas, more and more probes have been reported to monitor intracellular and intercellular substances, which are highly sensitive, high-resolution and low-cost. Though they have many advantages, these probes have some main limitations such as short lifetime, small penetration depth, damage to the samples and autofluorescence.Therefore new probes should be developed to overcome these shortcomings.On the other hand, upconversion nanoparticles (UCNPs) have got considerable interest and have many potential applications in this field. Compared with conventional fluorescent probes, UCNPs have many advantages: chemical stability, non-autofluorescence from bio-samples, large light penetration depth, long lifetime (millisecond scale) and less damage to samples. To better understand the development of UCNPs, this thesis introduces basic principles and applications of the UCNPs,followed by some experimental methodologies such as synthetic methods, purification methods, basic characterization techniques, spectroscopy and electrochemical techniques and bio-applications. This thesis focused on developing new UCNP-based probes,using Luminescence Resonance Energy Transfer(LRET) processfor bio-detection and bio-imaging, and this thesis contains two parts. In the first part, a Hg2+ UCNP-based probe is elaborated. Hg2+ is an extremely toxic ion, which will accumulate in human bodies and cause severe nervous system damage. Therefore, the sensitive and efficient monitoring of Hg2+ is of great importance. In this part, a thiazole-derivative-functionalized NaYF4 probe is demonstrated, and upconversion emission intensity ratio of 540 nm to 803 nm (I540/I803) is employed as a ratiometric signal to detect Hg2+ in living cells and showed excellent photostability and high selectivity, with detection limit to be 0.21 μM. The structure of nano-probe was characterized by transmission electron microscopy (TEM), Powder X-ray diffraction (Powder XRD) and the low cytotoxicity was confirmed by an MTT assay. The UCL (upconversion luminescence) test in Hela cells was carried out by confocal microscopy. The results demonstrated that organic-dye-functionalized UCNPs should be a good strategy to detect toxic metal ions when studying cellular bio-systems. In the second part, an improved Cu2+-NaYF4-based probe is demonstrated. Cu2+ plays a key role in metabolism. Its disequilibrium in human body will cause several severe diseases. Therefore, sensitively and efficiently monitoring Cu2+ in both environment and human body is of great importance. In addition, developing an inorganic-organic hybrid probe with multi-channel responses to more accurately detect ions in living systems is very challenging but highly desirable. In this part, for the first time, electrically-active ferrocene group was attached onto the framework of optically-active Rhodamine to form a new dye (RB-FC), which could be further loaded onto the surface of silica-coated UCNPs to construct a novel nano probe (RB-FC-UCNPs) to detect Cu2+ through both electrochemical method and optical ways. Upon the interaction with Cu2+, this as-prepared nano-probe showed obvious changes in absorption, emission and electrochemical parameters. The detection employed absorption intensity at 558 nm (A558), emission intensity ratio of 540 nm to 654 nm (I540/I654) as spectral signals, and oxidation peak of cyclic voltammetry curve as electrochemical signal, demonstrating high stability and low detection limit of this novel probe. In addition, bio-imaging test revealed that this probe could be applied in detecting and visualizing Cu2+ in A549 cells with low cytotoxicity. Doctor of Philosophy (MSE)