Nanoscintillator Materials For Biodetection And X-ray Imaging Application

Since its discovery in 1895,X-rays have been widely applied in the fields of security inspection,biomedical application,material analysis,national defense and military,and X-ray radiation astronomy.The scintillator,which can convert high-energy particles or radiation into visible light,is the key to X-ray related technology and has been called"jewel crystal".Benefitted from the fast development of nanoscience in recent years,many researchers have turned their attention to nanoscintillator technology.Based on the preparation of novel rare-earth fluoride scintillator nanomaterials,characterization of radioluminescence properties,and exploration of luminescence mechanism,this thesis has developed a series of background-free in vitro detection for cancer markers and flexible X-ray imaging films.This articles consist of five chapters,the main contents are listed as follows:In the first chapter,we briefly introduced the definition,properties,and research background of X-ray and scintillator materials,and described the application of nanoscintillators in imaging and therapy.Then,we introduced several types of fluorescence immunoassay methods and the application of different nanomaterials in fluorescence immunoassay.We then give a brief history of the development of X-ray imaging technology and future trends.Finally,based on the existing technological barriers of fluorescence immunoassay and X-ray imaging,combined with the advantages of nanoscintillators,the topic selection and research content of this paper are briefly introduced.In the second chapter,to solve the nonspecific autofluorescence background,we prepared the Na Gd F₄:Tb（15 mol%）nanoparticles,followed by coating with an inert shell of Na YF₄ via a coprecipitation method.The inert shell can effectively passivate the surface defects of Na Gd F₄:Tb（15 mol%）nanoparticles and isolate them from interacting with polar molecules in the solution environment,thereby enhancing the luminescent properties of the nanoparticles.Through a series of characterization,Na Gd F₄:Tb（15 mol%）@Na YF₄ nanoparticles have the advantages of uniform,easy modification,bright emission,high stability,and so on,and are expected to be used as fluorescence tags for X-ray fluorescence immunoassays.Compared to conventional ultraviolet-visible light,X-rays,which is a widely accessible source in hospitals and laboratories,can effectively avoid the interference of nonspecific autofluorescence background and improve the signal-to-noise ratio.Therefore,by modifying the antibody on the surface of Na Gd F₄:Tb（15 mol%）@Na YF₄ nanoparticles,we applied it to X-ray fluorescence immunoassay.The method showed high accuracy,specificity,reliability,which was comparable to the accuracy of the commercial detection kit.This method provides a new idea for the development of a new generation of fluorescence immunoassay.In the third chapter,we prepared Na Lu/Gd F₄:Tb@Na YF₄ nanoparticles in order to avoid the autofluorescence inhomogeneous detection under ultraviolet-visible light excitation in complex biological samples.By modifying the lysozyme aptamer with specific recognition ability on the surface of nanoparticles,and hybridizing a short strand of DNA with black hole quencher,a lysozyme detection probe was constructed,in which the fluorescence signal was recovered（on）in the presence of the target,and the fluorescence signal was quench（off）in the absence of the target.Unlike the traditional heterogeneous detection,the optical sensor has the advantage of"mix-and read",which greatly improves the detection efficiency.Most importantly,the homogeneous optical detection sensor uses X-rays as the excitation,which can effectively avoid the interference of biological chromophores in complex samples,is beneficial to improve the sensitivity of detection and analysis,and reduce false-positive signals.Due to the narrow emission peak of lanthanide rare-earth ions,which show little interference with each other,the high-throughout detection in complex biological samples can be realized by modifying different recognition molecules on the surface of nanoscintillators doped with different rare-earth ions.In the fourth chapter,we were aiming at the main contradiction between the morphology and optical performance of persistent luminescence materials.Low-temperature coprecipitation was carried out to synthesize a new family of rare-earth lanthanide ions doped persistent luminescence materials.The size and morphology of persistent luminescence materials were controllable and multicolor persistent luminescence modulation from the ultraviolet-visible to the near-infrared（NIR）can be achieved.Among them,Tb³⁺-doped Na Lu F₄ nanoparticles show excellent afterglow performance,which can last for 30 days after the stoppage of X-ray excitation.Combined with the optical characterization of persistent luminescence and the first principle calculation based on density functional theory,Tb³⁺-doped Na Lu F₄nanoparticles were selected as the main research object to study the mechanism of persistent luminescence.Different from traditional inorganic persistent luminescence materials,in which defects in the crystal lattice were generated during the calcination,the distortion occurs inside the lattice after the interaction of X-ray with Tb³⁺-doped Na Lu F₄ nanoparticles,generating Frenkel defects to capture electrons and holes.When the Frenkel defect restored to its original lattice,electrons-holes were released to the luminescent center to generate persistent luminescence.Based on this,we have established a novel persistent luminescence mechanism model based on Frenkel defects,which is expected to guide the synthesis of new types of persistent luminescence materials.In the fifth chapter,inspired by the theoretical guidance of Chapter 4,the persistent luminescence performance of Tb³⁺-doped Na Lu F₄ nanoparticles was characterized under light stimulation and thermal stimulation.Frenkel defects possess the ability to trap electrons and holes.High-temperature is beneficial to release the electrons and holes trapped by Frenkel defects.Electrons and holes recombine in the luminescent center to produce radiation transitions.Current X-ray imaging technologies involving flat-panel detectors（FPD）have difficulty in imaging three-dimensional（3D）objects.Tb³⁺-doped Na Lu F₄ nanoparticles combined with thin-film fabrication were used to prepare a flexible and stretchable X-ray imaging film.The flexible X-ray imaging film was able to conformably attach to the internal surface of the object,thus achieving high-resolution X-ray full-view imaging.Unlike traditional flat plate detector,this technology can customize the imaging film according to the size of the object,and can also combine with an optical microscope to realize X-ray microscopic imaging.Moreover,stretchable X-ray imaging film greatly improves the imaging resolution.X-ray imaging films featuring high-resolution,flexible,stretchable are particularly suitable for mammograms,dental imaging,and industrial detection.