Design And Construct Of Multifunctional Polymeric Composites Based On Cadmium Selenide Quantum Dots

Since the discovery of quantum dots and gold nanorods,we have a certain understanding of their structure and properties.Quantum dots with different morphologies or gold nanorods with different size could be synthesized.The combination of synthetic nanoparticles with polymer materials to prepare nanocomposites that can be used in biomedical research still faces many challenges.The preparation of aqueous monodisperse nanocomposite particles with cadmium selenide quantum dots(Cd Se QDs)is of beneficial to improve the sensitivity and detection effect for quantum dot biological probes.In order to obtain the scientific rules and methods for regulating the structure of amphiphilic triblock copolymer and monodispersed cadmium selenide quantum dot nanocomposite particles,we combined computer simulation and experimental to explore the relationship between the monodisperse cadmium selenide quantum dot nanocomposite particles and molecular structure of amphiphilic triblock copolymers.Using dissipative particle dynamics(DPD)method,we simulated the assemble behavior of amphiphilic fluorine copolymers,methoxypolyethylene glycols-block-poly(2-(diethylamino)ethyl methacrylate)-block-poly(2,2,3,4,4,4-hexafluorobutyl methacrylate)(O_mA_nF_p)and cadmium selenide quantum dots(Cd Se QDs)to construct of cadmium selenide quantum dot nanocomposite particles(O_mA_nF_p@QDs).The formation mechanism of monodisperse polymer nanocomposite particles was successfully revealed on the mesoscopic scale.At the same time,the effects of different polymerization degrees of blocks F,A and O in the amphiphilic triblock copolymer and different O_mA_nF_p and Cd Se concentrations in the system on the structural properties of monodispersed O_mA_nF_p@QDs were also studied.The results show that with the increase of the polymerization degree of the hydrophilic block O,the dispersibility and stability of O_mA_nF_p@QDs increase,and the particle size decreases.As the polymerization degree of the hydrophobic blocks A and F increases,the number of Cd Se QDs encapsulated in the O_mA_nF_p@QDs becomes uniform,and the particle size of the nanocomposite particles increases.When the initial volume fraction of Cd Se in the system remains unchanged,as the concentration of the block copolymer O_mA_nF_p increases,the number of empty micelles in the system increases,and the particle size of the aggregates formed in the system becomes uneven.Based on the above results,we conclude that the degree of polymerization of the blocks O to prepare monodisperse O_mA_nF_p@QDs with good stability and uniform particle size are 90 and 120,the required polymerization degree of block A and F are 10 and 15,respectively.The optimal volume fractions of O_mA_nF_p,Cd Se QDs and water in this simulated system are 6%,0.25%and 93.75%,respectively.Based on the simulated results,firstly,a series of amphiphilic fluorine copolymers,methoxypolyethylene glycols-block-poly(2-(diethylamino)ethyl methacrylate)-block-poly(2,2,3,4,4,4-hexafluorobutyl methacrylate)(O_mA_nF_p)were successfully synthesized.The monodisperse nanocomposite O_mA_nF_p@QDs was prepared after O_mA_nF_p and Cd Se QDs assembling in aqueous solution.The obtained O_mA_nF_p@QDs is colloidally stable in aqueous solution.The hydrodynamic diameters(D_h,DLS)of these O_mA_nF_p@QDs can be tuned between40 nm to 61 nm by choosing amphiphilic fluorine copolymers with different hydrophobic portions.The obtained O_mA_nF_p@QDs solution are found stable over a wide p H range(4.0-12.0)with no sign of aggregation.The PL intensity of O_mA_nF_p@QDs in 400 m M Na Cl solution changes only slightly.Block O and F in the copolymer offer O_mA_nF_p@QDs with good biocompatibility and low levels of nonspecific binding to bovine serum albumin proteins(BSA).These advantages render O_mA_nF_p@QDs an attractive candidate as ideal fluorescent probes in advanced biomedical imaging studies.The fluorescence intensity enhancement of CdSe QDs by plasmonic gold nanorod(Au NR)is crucial for development of new generation quantum dot bio-probes that have low quantum dots dosage but high fluorescence resolution.Au NR with longitudinal surface plasmon resonance absorption(L-LSPR)at 638 nm is used as plasmonic antenna.Cd Se QDs with maximum absorbance/emission at 625/636 nm is used as quantum emitter.First,the surface of Au NR is coated with different thickness silica shells and then positively charged Cd Se QDs are attached to the surface of silica-coated gold nanorod(Si O₂@Au NR)via electrostatic interaction to preliminarily construct the plasmonic fluorescence enhancement nanostructure QDs@Si O₂@Au NR.After self-assembly of QDs@Si O₂@Au NR and O₁₁₃A₁₁F₁₉,the colloidally stable plasmonic fluorescence enhancement nanocomposite O₁₁₃A₁₁F₁₉@QDs@Si O₂@Au NR is successfully prepared.The overlap of plasmonic Au NR L-LSPR with the absorption and fluorescence emission spectra of Cd Se QDs and the appropriate distance between Au NR and surrounded Cd Se QDs is crucial for constructing this plasmonic fluorescence enhancement nanocomposite.The thickness of silica shells is finely controlled to regulate the distance between the plasmonic Au NR and surrounded Cd Se QDs in O₁₁₃A₁₁F₁₉@QDs@Si O₂@Au NR.A maximum of more than 3.3 times florescence enhancement could achieve for O₁₁₃A₁₁F₁₉@QDs@Si O₂@Au NR with 22±1.2 nm silica thickness in comparation to fluorescent intensity of bare Cd Se QDs solution with the same concentration.Using the finite difference time domain(FDTD)method,we investigate the interaction between Cd Se QDs and Au NR.The simulated results demonstrate the fluorescence enhancement of Cd Se QDs arise from their enhanced excitation rate and the emission decay rates when quantum emitters coupled to the electromagnetic field generated from plasmonic Au NR due to its highly confined electromagnetic resonances effect.These reported findings provide valuable guidance to rationally design more biocompatible and super-resolution bio-probes for bioimaging and sensing.