Synthesis Of Upconversion Nanoparticles And Its Applications In Biosensing

Upconversion nanoparticles(UCNPs)are usually composed of the oxides,fluorides,halogen oxides or other substrates as matrix and doped with trivalent rare earth ions(Er3+,Eu3+,Yb3+,Tm3+,Ho3+ etc.)as energy transfer system.UCNPs can convert low-energy light(NIR or IR)to higher-energy light(UV or visible)through multiple photon absorptions or energy transfers.Compared with the traditional downconversion fluorescent materials,UCNPs attract much more focus due to their unique optical and chemical properties,such as sharp absorption and emission bands,high quantum yields,long lifetimes,low toxicity,superior photostability,low autofluorescence from biosamples and better penetration depth.Therefore,UCNPs can be used as suitable candidates in biosensing and bioimaging.Based on fluorescence resonance energy transfer(FRET)technique,we designed and constructed two new types of sensors for the detection of lysozyme and sequence-specific DNA.The major contents were described as follows.1.A Simple Strategy Based on Upconversion Nanoparticles for a Fluorescent Resonant Energy Transfer BiosensorA novel aptasensor was fabricated for the detection of lysozyme and DNA based on fluorescence resonance energy transfer(FRET)technique between upconversion nanoparticles(UCNPs)and dye labeled aptamer.NaYF4:Yb,Er nanoparticles as UCNPs were synthesized and attached with dye labeled aptamer through a cationic polymer as an electrostatic linker to quench the upconversion fluorescent intensity.The intensity can be restored after the addition of lysozyme or the complementary DNA(target DNA)because of their strong interaction with the aptamer.The sensor provided a linear concentration range from 30 to 210 nM for lysozyme and 40 to 200 nM for the target DNA,the limits of the detection were 2.5 nM and 2.8 nM,respectively.The sensor was also used to monitor lysozyme level in both human saliva and serum samples,and the results were consistent with the reported values.UCNPs can act as excellent emitters due to their low autofluorescence and high penetration depth of biosamples.The method was simple and convenient without the extra procedure of bioconjugations,which was desired to put in use for various targets determination in the future.2.An upconversion nanocomposite for fluorescence resonance energy transfer based cholesterol-sensing in human serumUCNPs are extremely useful for analytical applications,since they display a high signal-to-noise ratio,and their photobleaching can be ignored.Herein,a novel upconversion nanocomposite composed of ?-cyclodextrin(?-CD)derivative modified UCNPs and rhodamine B(RB)was prepared for the detection of cholesterol(Cho).The upconversion luminescence emission can serve as a Cho-sensing signal by an effective fluorescence resonance energy transfer(FRET)process,using UCNPs as the donor and RB as the quencher.The sensor for Cho detection in human serum shows excellent sensitivity and selectivity,which has the potential for clinical applications in the analysis of other biological and environmental samples.3.An Upconversion Fluorescent Resonant Energy Transfer Biosensor for Hepatitis B virus(HBV)DNA Hybridization DetectionWe fabricated a novel fluorescent resonant energy transfer(FRET)biosensor for the detection of hepatitis B virus(HBV)DNA using poly(ethylenimine)(PEI)modified upconversion nanoparticles(NH2-UCNPs)as donor and gold nanoparticles(Au NPs)as acceptor,respectively.Two single-stranded DNA,which are partially complementary to each other,were first binded with NH2-UCNPs and Au NPs,respectively.The FRET process occured when NH2-UCNPs and Au NPs were mixed and the upconversion luminescence was quenched.However,upon the addition of the target DNA,Au NPs were far away from NH2-UCNPs and the luminescence could be restored because of the formation of the more stable double-stranded DNA.The sensor provided a linear concentration range from 5.0 to 50 nM for the target DNA and the limit(LOD)of the detection was 1.0 nM.Meanwhile,we optimized and discussed the preparation conditions of NH2-UCNPs,to obtain an optional condition for the preparation.The amino-group functionalized upconversion nanoparticles were directly prepared by the hydrothermal method,which was simple and convenient.The sensor we designed for the target DNA detection shows high sensitivity and good selectivity,which has the potential for clinical applications in the analysis of HBV and other biomolecules.