Construction Of Lanthanide-doped NIR-Ⅱ Fluorescent Nanoprobes For Bacterial Infection Imaging And Anti-Counterfeiting Applications

Bacterial infections are a serious ongoing threat to human health.Early and accurate diagnosis of diseases associated with bacterial infections in vivo is critical to reducing morbidity and mortality.Traditional and currently used clinical methods for bacterial detection are time-consuming and difficult to achieve non-invasive,real-time monitoring.Therefore,within the context of modern technology,there is an urgent need to develop analytical techniques for efficient diagnosis of bacterial infections in vivo.And with the development of science and technology,counterfeiting technology is also progressing,making it difficult to distinguish authenticity,so it is very necessary to develop efficient and difficult to imitate anti-counterfeiting technology.The excitation and emission of lanthanide-doped nanomaterials can range from the UV-visible（UV-Vis）to the near-infrared region,especially their luminescence in the second near-infrared region（NIR-Ⅱ）,where the penetration depth in biological tissue is significantly increased due to less light scattering and absorption,while the autofluorescence of tissue can be neglected.Lanthanide-doped nanomaterials also have the advantages of narrow emission,long luminescence lifetime,resistance to photobleaching and good biocompatibility,so lanthanide-doped NIR-Ⅱ luminescent nanoprobes are suitable for non-invasive,real-time and precise monitoring of bacterial infections in vivo.In addition,lanthanide-doped nanomaterials are well suited for high-level anti-counterfeiting applications due to their abundant 4f energy levels and near-infrared excitation properties.Therefore,in this thesis,based on lanthanide-doped NIR-Ⅱ luminescent nanomaterials,a series of novel fluorescent probes are designed for imaging and identification of bacterial infections in vivo by doping with different lanthanide ions and surface functionalization;three nanomaterials exhibiting visible and NIR-Ⅱ dual luminescence under multi-modal excitation are also prepared by constructing core@multishell structures for advanced anti-counterfeiting and latent fingerprint imaging.The main research contents are as follows:（1）Vancomycin（Van）,which can specifically bind to Gram-positive bacteria such as S.aureus,is covalently coupled to the surface of Na Gd F₄:Nd@Na Gd F₄ down-conversion nanoparticles（DCNPs）,which exhibit strong luminescence in the NIR-Ⅱ window,for use as fluorescent probes to enable in vivo imaging of bacterial infections.Both in vitro detection and in vivo imaging results show that the Van-modified NIR-Ⅱ fluorescent probe can distinguish Gram-positive from Gram-negative bacteria with a high degree of selectivity.The biocompatibility of the fluorescent probe is verified by methyl thiazolyl tetrazolium（MTT）assay and histological analysis.（2）A Gram-positive bacteria-specific responsive NIR-Ⅱ fluorescent probe is synthesized based on electrostatic binding of Cu_2-xSe nanoparticles and Van-modified DCNPs（Na Gd F₄:Nd,Yb@Na Gd F₄）,for in vivo imaging of positive bacterial infections with high signal-to-noise ratio.The NIR fluorescence of the nanoprobe is obviously weakened owing to the spectral overlap of Cu_2-xSe nanoparticles absorption with the DCNPs emission.Because Van-modified DCNPs preferentially bind to Gram-positive bacteria,the presence of Gram-positive bacteria precisely disconnects the bond between Van-modified DCNPs and Cu_2-xSe nanoparticles,by which a strong fluorescent signal is enabled.In vivo studies show that the NIR-Ⅱ luminescence of this probe is significantly increased at the site of Gram-positive bacterial infection,while no significant luminescence is observed in the area of Gram-negative bacterial infection.（3）Two lanthanide-doped nanoparticles with non-overlapping NIR-Ⅱ emission are surface modified with Van and polymyxin B（PMB）,which can respectively target Gram-positive and Gram-negative bacteria,as multiplexed fluorescent probes for specific imaging and bacteria differentiation.The two core-shell（cs）nanoparticles are Na YF₄:Nd,Yb@Na YF₄（cs Nd,Yb）with 980 and 1060 nm emission under 808 nm excitation,and Na YF₄:Yb,Er,Ce@Na YF₄（cs Yb,Er,Ce）with 1525 nm emission under980 nm excitation.In vitro experiments confirm that cs Nd,Yb-PMB and cs Yb,Er,Ce-Van can be used to detect different types of bacteria.In vivo simultaneous multiplexed NIR-Ⅱ imaging of Gram-positive/negative bacterial infection is demonstrated.The good biocompatibility of the nanoprobes is demonstrated by MTT assay,monitoring the distribution in major organs at different times,and histological analysis.（4）Threelanthanide-dopedcore@multishellnanoparticles Na YF₄:Yb,Er/Ho/Tm@Na YF₄@Na YF₄:Nd@Na YF₄ are prepared by doping with different luminescent ions.These nanoparticles can achieve dual upconversion visible and downconversion NIR-Ⅱ emission of Er/Ho/Tm under near-infrared laser（980 nm）excitation,and non-overlapping NIR-Ⅱ emission under 980 or 808 nm excitation.The luminescence interference of nanomaterials under different laser excitation wavelengths can be avoided by precisely controlling the distribution of lanthanide ions in the core-shell layer.Experimental results show that multi-color anti-counterfeiting and information encryption under near-infrared laser excitation can be achieved using water-based inks containing the designed core@multishell nanostructures,which are highly covert and difficult to forge.The designed core@multishell nanopowders can also be used for efficient identification of latent fingerprints on complex surfaces.