Upconversion Nanoparticles For Anthrax Biomarker Detection And Antibacterial Applications

The luminescence of rare earth doped upconverting nanomaterials(hereinafter referred to as UCNPs)is based on the anti-Stokes principle,that is,emitting of ultraviolet light or visible light by NIR light exciting,which has good light stability,small biological background and good biocompatibility.It has deep penetration depth and is widely used in biological detection.In addition,since the emission spectra of UCNPs coincides with the absorption spectra of most photosensitizers,they are also widely used in the field of photodynamic antibacterial chemotherapy(PACT).In the first chapter,the paper outlines the composition,luminescence mechanism,preparation methods,common surface modification methods and biological applications of UCNPs.Chapter 2:Bacillus anthracis has strong lethality and infectivity,and has a long incubation period.To minimize their potential detrimental effects and for disease control,thus,a sensitive and selective assay of biomarkers is most desirable.In this work,a nanoprobe is constructed by conjugating rare earth doped upconversion nanoparticles(UCNPs)with sodium tripolyphosphate(TPP)and eriochrome black T(EBT).The nanoprobe,UCNPs-TPP/EBT,serves as a platform for the detection of the anthrax biomarker,dipicolinic acid(DPA).In principle,free EBT is blue in alkaline solutions and magenta when combined with UCNPs.With the presence of DP A,DPA displaces EBT from the UCNPs-TPP/EBT nanoconjugate,resulting in a color change from magenta to blue because of the release of free EBT into the aqueous solution.The binding sites on UCNPs are partly preblocked with TPP as the placeholder molecule,leaving a desired number of binding sites for EBT conjugation.On the basis of this dye displacement reaction,a novel colorimetric assay protocol for DPA is developed,deriving a linear calibration range from 2 to 200 μmol·L-1 with a detection limit of 0.9 μmol·L-1,which is well below the infectious dose of the spores(60 μmol·L-1).The assay platform exhibits excellent anti-interference capability when treating a real biological sample matrix.The present method is validated by the analysis of DPA in human serum,and its practical application is further demonstrated by monitoring the DPA release upon spore germination.Chapter 3:Due to the abuse of antibiotics,the antibiotic-risistant bacteria and even super bacteria appeared which poses a huge challenge to the killing of bacteria.Photodynamic antibacterial chemotherapy(PACT)and Ag NPs can effectively kill bacteria and prevent the generation of bacterial resistance.Therefore,this work constructs Ag NPs modified UCNPs nanocomposites for dual-mode antibacterial therapy.The process consists of coating the red-emitting NaYF4:Yb,Mn,Er with SiO2 shell and loading methylene blue(MB),and in-situ growing Ag NPs with a size of 5 nm on the shell to construct UCNPs@SiO2/MB-Ag NPs for a double-mode antibacterial.25 μg·mL-1 UCNPs@SiO2/MB-Ag NPs can kill all the E.coli and S.aureus(106 cfu·mL-1)under irradiated with a 980 nm laser at a power density of 1 W·cm-2 for 10 min.