Upconversion Fluorescent Nanoprobes With Physical Modulation For Bio-imaging And Detection

Upconversion nanomaterials with these merits such as strong upconversion luminescence were widely studied and used in many fields of applications. At present,upconversion nanoparticles（UCNPs） with high efficiency and multi-color emission can be synthesized by adjusting the lanthanides dopant and proration, which can improve the basic physic and chemical properties. Moreover, due to the high penetration of near-infrared laser, no cell and tissue damage, high signal to noise and good compatibility. Therefore, upconversion nanoparticles have great value in these fields of biological fluorescent imaging, bio-detection and drug therapy, which is also a popular topic in the world. In the paper, these topics are discussed such as physicochemical properties adjusting of UCNPs, animal and plants imaging in vivo,accurate detection of chemical regents and qualitative detection of biological irritation, and these results are included as following:（1） Multicolor upconversion luminescence was tuned successfully. By varying the type and the concentration of the lanthanide dopants, the relative ratio of blue emission, green emission and red emission was varied, so that the emission color can be finely controlled in the all visible light.（2） NaLuF₄:18%Yb³⁺/2%Er³⁺ UCNPs exhibited obviously stronger luminescence after doping with 5% Zn²⁺. By doping 5% Zn²⁺ in NaLuF₄:18%Yb³⁺/2%Er³⁺ UCNPs,the upconversion luminescence intensity was improved to a extent. It is ascribed to the lowered crystal field symmetry of Er³⁺ sites. Er³⁺ ions at the sites with lower crystal field symmetry can generate electronic clouds with lager asymmetry and thus leads to the perturbation of energy levels for improving the electronic transfer probability, and the UCL intensity was enhanced.（3） Reversible energy transfer between Er³⁺ and Tm³⁺ ions was confirmed. The excitation power density dependence of upconversion emission intensity indicates clearly the energy transfer from Tm³⁺ to Er³⁺ ions under the excitation of low power density（5×102⁹×102W/cm2）. Meanwhile, it also reveals the inverse energy transfer from Er³⁺to Tm³⁺ions under the excitation of relatively higher power density（4.1×104⁴.9×104W/cm2）. Moreover, under the high power density excitation（4.1×104⁴.9×104 W/cm2）, it was found that high irradiation motivated the unlock dark sensitizers, breaking the bottleneck effect of high concentration Yb³⁺ doping so that intense upconversion emission was achieved.（4） The cell fluorescent imaging was completed. Compared with the conventional optical imaging, the upconversion fluorescent imaging can be conducted directly without slicing process and trauma, which provide a navigation for the disease diagnose and therapy.（5） Upconversion fluorescent nanoprobes for detection of sodium fluorescein.The UC fluorescent nanoprobes with an acidic ligand can quickly capture the basic sodium fluorescein in plant cells and forms a close UCNPs@SF system based on a LRET. The integrated intensity ratio of the blue emission of NaLuF₄:18%Yb³⁺/0.5%Tm³⁺ nanoprobes and green emission of sodium fluorescein.The concentration of SF can be easily addressed according to IIRGB signal. In the manuscript, employing a 980 nm-diode infrared power source of 0.2 W/mm2, the detection limitation of SF can reach to 0.14 ug/cm3 in living onion cells if the concentration of upconversion nanoprobes is properly controlled.（6） Upconversion fluorescent nanoprobes for irritation assessment of basic organic dyes. The excretion process of Rh B and SF can be clearly presented by in vivo upconversion luminescence imaging, and the results indicated that these organic dyes can be excreted absolutely and be safe for the beings. At the same time, the irritation of Rh B and SF are assessed in jellyfish cells. It is obviously determined that Rh B has recoverable physical injury to the cells while SF presents unrecoverable biochemical injury to the cells.