Design,preparation,post-modification And Nitric Oxide Sensing Application Of Neodymium Sensitized Rare-earth Upconversion Nanomaterials

Nd³⁺sensitized rare-earth upconversion nanomaterials can absorb near-infrared light located at 808 nm.The excited light at this wavelength has deep tissue penetration depth and low tissue overheating effect in biological applications,so it has unique advantages in bio-sensing,bio-imaging and other fields.However,the outmost sensitized layer in the classic multi-shell structured Nd³⁺sensitized rare-earth upconversion nanomaterials usually contains high level sensitizer Nd³⁺,resulting in upconversion luminescence?UCL?quenching assosiated with energy transfer between high level sensitizer Nd³⁺and surface quenchers.In addition,the luminescence center of the classical Nd³⁺sensitized rare-earth upconversion nanostructure is located in the core zone.The fluorescence resonance energy transfer?FRET?efficiecncy is low when organic small molecule fluorescent probes are loaded onto the surface of Nd³⁺sensitized rare-earth upconversion nanostructure for the construction of FRET based bio-sensing since much too long distance between the luminescence center and the fluorescent probes.In this paper,the inert element Lu³⁺was doped into the sensitized shell of the classical Nd³⁺sensitized sandwiched structure of Na YF₄:Yb/Er@Na YF₄:Yb@Na Nd F₄:Yb to improve the upconversion luminescence efficiency.Surface initiated atom transfer radical polymerization?SI-ATRP?technique was used to convert the hydrophobic upconversion nanomaterials to hydrophilic one by using two monomers with different functional groups.The ratio of the two monomers was adjusted to achieve moderate hydrophobicity for the loading of hydrophobic fluorescent probe?Rh B-OPD?and sensing nitric oxide?NO?according to ratio upconversion fluorescence detection.Furthermore,an energy-concentrating zone nanostructure of Na YF₄:Gd/Nd/Yb@Na YF₄:Yb@Na YF₄:Yb/Er@Na Lu F₄ with a thin optically-inert shell was designed and prepared to improve the efficiency of FRET based bio-sensing system,and used to load Rh B-OPD for the construction of NO sensing probe by using a“tun-on”detection mode.The details are as follows:?1?Design and preparation of Nd³⁺sensitized upconversion nanostructure with high luminescence efficiency for the ratiometric fluorescent detection of NO.Nd³⁺sensitized multi-shell structure UCNPs?Na YF₄:Yb/Er@Na YF₄:Yb@Na Nd F₄:Yb/Lu?was successfully prepared by a binary sodium solvothermal strategy.The fluorescence intensity of such nanostructure reached the highest level at the optimized Lu³⁺doping ratio of 60%in the sensitized shell.Then the hydrophilic modification of UCNPs was realized by using SI-ATRP technology with the two monomers of styrene and polyethylene glycol methacrylate.A rhodamine B?Rh B?derivate of Rh B-OPD was synthesized and loaded onto UCNPs surface through hydrophobic interaction for ratiometric fluorescent NO sensing.Rh B-OPD will react with NO and convert to Rh B.Rh B could absorb the upconversion fluorescence at 540 nm,wheras not at 660 nm.And thus,the ratio of fluorescence intensity at 540 nm and 660 nm(UCL₅₄₀/UCL₆₆₀)varies with the concentration of NO and was used to ratiometric fluorescent NO sensing,providing a detection limit of 8.38?M.?2?Novel Nd³⁺sensitized UCNPs with energy-concentrating zone to construct a NO sensing probe with turn-on mode.Novel Nd³⁺sensitized UCNPs?UCNPs-n??Na YF₄:Gd/Nd/Yb@Na YF₄:Yb@Na YF₄:Yb/Er@Na Lu F₄?with energy-concentrating multi-shell structure were designed and prepared.Doping Er³⁺into the shell shortens the distance between activators and the surface-loaded fluorescence probe,leading to improve the FRET efficiency.Moreover,a thin optically inert Na Lu F₄ shell is epitaxially grown as the outermost shell to increase the upconversion fluorescence intensity while ensuring high FRET efficiency.Amphiphilic phosphatidylcholine molecules were modified onto UCNPs surface by hydrophilic-hydrophobic interaction to realize the hydrophilic functionalization of UCNPs-n.Finally,Rh B-OPD was loaded into the hydrophobic cavity on the phosphatidylcholine modified UCNPs-n,providing a NO detection system.Unlike the NO detection system realized by quenching the upconversion fluorescence at 540 nm in the first part of the work,the NO detection system constructed by UCNPs-n rely on the ratio of fluorescence intensity at 580 nm and 540 nm(Rh B-F₅₈₀/UCL₅₄₀)in view of higher FRET efficiency and the resultant excitation of Rh B at 580 nm(Rh B-F₅₈₀).