The Fabrication Of Quantum Dots Composites And Its Application For Biological Small Molecule Detection

In recent years,semiconductor quantum dots?QDs?have been widely investigated as a class of quasi-zero-dimensional nanometer luminescent materials.The three-dimensional dimensions in size of QDs are below 100 nm and are atoms or clusters of atoms consisting of a small number of atoms or molecules.When the size of QDs is comparable to the size of Bohr diameter for excitation,the QDs exhibit special physical and chemical properties which include the quantum size effects,surface effects,dielectric confinement effects,macroscopic quantum tunneling effects and so on.Due to their high fluorescence intensity,good stability,broad excitation spectra,symmetric and narrow emission spectrum,tunable maximum emission wavelength with changeable sizes and compositions,high resistance to photobleaching and good biocompatibility,QDs have superior optical properties over conventional fluorescent dyes,which have been successfully used as fluorescent probe,energy donor in fluorescent resonance energy transfer,fluorescence labeling and fluorescence imaging.In this paper,we have researched the preparation,modification,assembly,and application of CdTe QDs and carbon quantum dots?CDs?and used the synthesis of modified QDs and their materials as a fluorescent probe for exploratory study.This paper mainly constructs the following three methods for the fluorescent detection of biological small molecule:?1?A fluorescence assay is described for the determination of dopamine?DA?.The water-soluble CdTe QDs are synthesized with NaHTe as tellurium source and3-mercaptopropionic acid?MPA?as a stabilizer by one-step aqueous phase method.The nanoparticles of silica-coated QDs are synthesized with necessary modification on the surface of QDs by hydrothermal method.The QD@SiO₂ can be interacted with the target dopamine?DA?by amide reaction,hydrogen bonding or electrostatic interaction.The DA is oxidized to dopamine quinone structure under catalytic action of tyrosinase in the oxygen atmosphere,the fluorescence of QD@SiO₂ decreases significantly due to an electron transfer quenching processes.The assay has a linear calibration plot in the 0.05 to 30?M DA concentration range and a 12.5 nM detection limit under the optimized conditions.The method can be applied to the determination of DA in spiked human serum samples and there coveries rang from 98.0%to 104.0%are obtained.?2?A ratiometric fluorescence assay is described for the determination of epinephrine?EP?and norepinephrine?NE?.CdTe QDs and CDs are prepared by hydrothermal method.The APTES modified on the surface CDs and the CDs@SiO₂nanoparticles are prepared.The amide groups on the surface of the modified CDs and the carboxyl groups on the surface of the CdTe QDs are bound by amide reaction.The obtained CDs@SiO₂@QDs nanocomposites have 460 nm and 610 nm emission peaks at 370 nm excitation spectra.The nanocomposites are reacted with the neurotransmitter of EP and NE,the fluorescence of CDs@SiO₂@QDs decreases slightly at 460 nm and obviously weakens at 610 nm emission peaks.This may be due to that the redox reaction of EP and NE during the reaction and the electron transfer process between CdTe QDs on the surface of CDs@SiO₂@QDs and neurotransmitters.The relative changes in fluorescence quenching at these two wavelengths can be used as a ratio of fluorescent probes for EP and NE analysis applications.Under the optimal conditions,the fluorescence response ratio of CDs@SiO₂@QDs at 460 nm and 610 nm emission speaks shows a good linear range from a certain range with the concentration of EP and NE.The assay has a linear calibration plot in the 0.01 to 20?M EP concentration range with lower detection limit of 6.8 nM and in the 0.005 to10?M NE concentration range with detection limit of 2.1 nM,respectively.The method also has good selectivity and high sensitivity for EP and NE,which provides potential practical application prospect for the detection of real samples.?3?A fluorescence assay is described for the determination of copper ion(Cu²⁺).CdTe QDs are synthesized with NaTe₂O₃ as tellurium source,MPA as a stabilizer and NaBH₄ as reducing agent by hydrothermal method.The CdTe QDs are activated by EDC/NHS and reacted with the 3-aminobenzeneboronic acid?M-APBA?.The B-O bond of 3-aminobenzeneboronic acid on the surface of functionalized QDs can react specifically with Cu²⁺,which makes the fluorescence of QDs decrease obviously.The fluorescence signal ratio of M-APBA-QDs has a linear calibration plot in the 0.01 to 20?M Cu²⁺concentration range and a 7.6 nM detection limit under the optimized conditions.The method has good selectivity and can be used for the detection of Cu²⁺in the real samples,which has good practical application ability for the detection of Cu²⁺.