Preparation Of Nanocrystals/Electrospun Composite Fibers And Their Applications In Biochemical Sensing

When the electrospun nanofibers meet some nanocrystals such as the noble nanoparticles,semiconductor nanocrystals,graphene,carbon nanotubes,luminescent carbon dots,and inorganic quantum dots,the as-obtained functionalized composite electrospun nanofibers are widely aroused extensive attention in sensor,catalysis,biomedicine,flexible electronics and so on.Wherein,in environmental and biochemical analysis,the nanocrystals/composite electrospun nanofibers are employed as film-based catalysts or solid sensor to apply in catalytic reduction of environmental pollutants and biochemical sensor due to their large surface ratio area,high porosity,uniform diameter,large length-diameter ratio and three-dimensional networked structures.However,the fabrication of functional nanocrystals/electrospun nanofibers and their applications in catalytic reduction of environmental pollutants and biochemical sensor still exist some challenges.At first,there are seldom reports that diversified nanocrystals-doped electrospun nanofibers are used to catalyze the reduction of environmental pollutants based on the synergistic effect and mechanism between different nanocrystals.Secondly,in terms of fabrication of composites electrospun nanofibers based on high molecular polymers as hosts,aboundant functional groups on their surfaces can be regarded as many“golden keys”,and they will open many novel strategies to decorate and assemble functional nanocrystals,sensing elements and target-binding sites on electrospun nanofibrous surfaces,which are rarely exploited.Thirdly,comparing with directly nanocrystal-doped electrospun nanofibers,assembly of nanocrystals on electrospun nanofibrous surfaces are beneficial to improving the utilization of nanocrystals and solving some problems in biochemical sensing such as low sensitivity,poor selectivity,instability and dissatisfactory reproducibility.Therefore,to address these issues,we have systematically carried out researches on the preparation of nanocrystals/electrospun nanofibers and their applications in synergistic catalysis and biochemical sensing.The major points of this thesis includes the following four main points:1.Synergistic catalytic effect of Cu2-_x Se and rGO co-embedded in electrsopun nanofibers for the reduction of a refractory 4-NP.A new heterogeneous catalytic composite composed of nonstoichiometric Cu2-_xSe nanoparticles?NPs?with high copper deficiency and graphene oxide?GO?is prepared by co-embedded in electrospun nanofibers of polyvinylpyrrolidone?PVP?support.Wherein,the GO in nanofibers are converted into reduced GO?rGO?via heat treatment.In the presence of NaBH₄,the as-prepared composite Cu2-_xSe/rGO/PVP nanofibers were demonstrated a superior catalytic activity toward the reduction of 4-nitrophenol?4-NP?,which resulted from synergistic effect between Cu2-_xSe and rGO in PVP nanofibers including improving the reaction rate,decreasing the activation energy of reaction and providing numbers of reaction sites for reactants.Furthermore,the Cu2-_x Se/rGO/PVP nanofibers exhibit a favorable water-stable property via heat treatment to solid the hydrophilic PVP matrix,which make the composite display a good reusability,stability in aqueous solution and separability from water medium.This work not only presents a direct,convenient and effective approach to dope semiconductor nanomaterials into polymer nanofibers,but also provides fundamental routes and more opportunites for further investigations about the synergetic effect between different materials based on the platform of electrospun nanofibers.2.Electrostatic assemblies of well-dispersed AgNPs on electrospun nanofirbous surfaces as highly active SERS substrates for wide-range pH sensing.Surface enhanced Raman scattering?SERS?has shown highly promising in biochemical analysis,wherein noble metal nanoparticles?NMNPs?such as silver nanoparticles were employed as substrates because of their strong localized surface plasmon resonance?LSPR?properties.However,SERS-based sensor such as pH sensing was restricted because of the aggregation of NMNPs in acid medium or biosamples with high ionic strength.Herein,by using the electrostatic interaction as a driving force,AgNPs are assembled on the surface of ethylene imine polymer?PEI?/polyvinyl alcohol?PVA?electrospun nanofibers,which are then applied as highly sensitive and reproducible SERS substrate with an enhancement factor?EF?of 10⁷¹0⁸.When p-aminothiophenol?p-ATP?as an indicator with its b₂ mode,a good and wide linear response ranging from1.98 to 11.20 of pH could be available,and the as-prepared nanocomposite fibers then could be fabricated an excellent pH sensors in complicate biological samples such as urine considering that the pH of urine could reflect the acid-base status of persons.This work not only emerges a cost-effective,direct and convenient approach to homogeneously decorate AgNPs on the surface of polymer nanofibers,but also supplies a route for preparing other noble metal nanofibrous sensing membranes in more biochemical analysis areas.3.Surface-engineered QDs/electrospun nanofibers as a networked fluorescence aptasensing platform toward biomarkers.Membrane-based fluorescent sensing platform is a facile,point-of-care and promising technique in chemo/bio-analytical fields.However,the existing fluorescent sensing films for cancer biomarkers remain problematic:dissatisfactory sensitivity and selectivity,low utilization of probes encapsulated in films as well as tedious design of membranes structure.In this work,a novel fluorescent sensing platform by bio-grafting quantum dots?QDs?onto the surface of electrospun nanofibers?NFs?is fabricated.The aptamer integrated into the QDs/NFs can result in highly specific for recognizing and capturing biomarkers.A partial complementary DNA-attached gold nanoparticles?AuNPs?are employed to efficiently hybridize with the rest of aptamer to quench the fluorescence of QDs by nanometal surface energy transfer?NSET?between the both,which is constructed for prostate specific antigen?PSA?assay.Taking advantage of networked nanostructure of aptamer-QDs/NFs,the fluorescent film can detect PSA with high sensitivity and a detection limit of 0.46 pg/mL,which was further applied in clinical real serum samples.Coupling the surface grafted techniques to advanced network nanostructure of electrospun NFs,the proposed aptasensing platform can be easily extended to achieve sensitive and selective assay for other biomarkers.4.Quantum dots/carbon dots-based dual-emitted fluorescence electrospun nanofibrous test film for Cu²⁺-mediated biosensing.Increasing demands for sensitively,selectively,visually,portabily quantifying the disease-related biomarkers,electrospun nanofibrous films have been received great upsurge due to their high surface ratio area,networked structure,easy fabrication and functionalization,and low cost.Here,we prepared a dual-emitting quantum dots?QDs?/carbon dots?CDs?fluoresecence electrsopun nanofibers?NFs?by doping CDs inside NFs and electrostatically assembling QDs onto NFs surfaces.Because of the fluorescence resonance energy transfer?FRET?process between QDs and CDs on NFs,and the strongly quenching response to Cu²⁺of QDs,the as-prepared nanofibrous films can sensitively,selectively and visually detect Cu²⁺based on ratiometric fluoresecnt signals.With a sandwich-type immunoreaction,CuO nanoparticels-labelled antibody were captured in each working zones.Under acid condition,numerous Cu²⁺were released from CuO NPs.The varied concentrations of biomarker proteins can be indirectly quatified by using dual-emitting nanofibrous films to react with different concentrations of Cu²⁺.Taking advantages of the ratiometric fluorescence signals of this electrospun NFs and Cu²⁺-mediated signal amplifying strategy,this electrospun NFs are capable of detecting alpha fetoprotein?AFP?with high sensitivity?detection limit of 8.3 pg/mL?and selectivity.This strategy has a promising candidate with point-of-care assay for clinical diagnostics and biomedical researches.In summary,we have prepared four nanocrystals/electrospun NFs by directly doped method and surface assemble strategies.Meanwhile,we systematically investigated the synergistic effect between nanocrystals in electrospun NFs and their synergistically catalytic reduction for 4-nitrophenol as a typically environmental pollutants.In addition,the nanocrystals assembling from inner to surface on electrospun NFs can not only improve the utilization of nanocrystals,but also prepared portable nanocrystals/electrospun nanofibrous films with high sensitivity and selectivity for biochemical sensing.This thesis will provid sufficient experimental evidences and new insights for the fabrication of more functionlized nanocrystals/electrospun NFs.Moreover,it will expand the applications of the nanocrystals/electrospun NFs in environmental and biochemical analysis.