Controllable Preparation And Applications In Sensing Analysis Of Noble Metal Core@shell Nanocrystals

Controllable preparation of gold nanoparticles（Au NPs）has attracted much attention in the field of materials research,because its unique catalytic and optical properties vary greatly with their different morphology.Among all kinds of morphology of the Au NPs,gold nanorods（Au NRs）with the different optical properties unlike the spherical particle are much interested.Au NRs show the unique Surface Plasmon Resonance（Surface Plasmon Resonance,SPR）adjustable features with the different length to diameter ratio.Moreover,through regulating length to diameter ratio of the Au NRs,the SPR absorption peaks can be realized adjustable optical properties in the visible light area.Additionally,combined with several other merits of Au NRs,such as the simple synthetic method,stable chemical properties,the advantage of high production yield,Au NRs are more and more widely applied in material science,optoelectronics,food and environmental analysis,biomedical detection and disease diagnosis and treatment and so on.The core-shell structure of the nanocrystal,in which Au NRs are as core and other noble metals as shell,can make full use of its abundant SPR performance.Furthermore,on the basis of combining with the catalysis and optical properties of the two different noble metals,the core-shell noble metal nanocrystals showed excellent physical and chemical properties in various areas,such as catalysis,optics,electricity and sensing analysis.Because physical and chemical characteristics of the core-shell noble metal nanocrystals have close relations with their morphology and size,how to control the growth of these core-shell noble metal nanocrystals and how to realize the controllable preparation of their morphologies,size,crystal structures and adjustable optical properties or in addition how to realize the further complex and heterogeneous interface controllable recombination with other functional materials,such as TiO₂ nanometer sheet（NSs）and graphene,are more and more important to develop photoelectric devices and electrochemical devices.Besides,the application of sensory analysis technology has especially important scientific value and exploring significance.In this thesis,based on Au NRs with different aspect ratio as core and other noble metals as shell,controllable preparation of core@shell nanocrystals is used as the breakthrough point.We further exploring the catalytic properties and optical properties with the different morphology,size and composition of core@shell nanocrystalline.Finally and more importantly,based on the prepared noble metal core@shell nanocrystallines and their different properties,we developed several chemical sensors to realize heavy metal,H₂O₂and biomarkers detection.1.The green and controllable preparation and optical properties of Au nanocrystals with different aspect ratios are studiedBecause the Au NRs has different optical characteristics from that of spherical Au NPs,the material preparation,properties and sensing applications of the noble metal nanocrystals with core-shell structure based on Au NRs as the core are carried out in this study.Therefore,Au NRs are first synthesized using the method of seed growth in water phase.The green preparation methods of Au NRs implement different length to diameter ratio of the Au NRs.Moreover,further study on optical properties of Au NRs with different length to diameter ratio of the Au NRs is explored.The good morphologies and uniform dispersion of the prepared Au NRs can be as a good foundation for the following preparation of core-shell noble metals nanocrystals.2.The controllable preparation and photoelectrochemical（PEC）properties of Au@Ag core@shell NRs and their application in sensor fabrication are studiedAg NPs have excellent properties,such as catalytic and sterilizing,etc.,and so have been applied to the catalysis,biological analysis,medicine and other fields.However,the problem,which is the difficult regulation of morphology and instability of storage in the aqueous phase,is one of the major application problems of Ag NPs.We adopt the"bottom-up"chemical methods to explore the green preparation methods of the core@shell structure nanocrystals which are Au NRs as core and Ag as shell.Through the simple and controllable preparation,Au@Ag core@shell NRs with different Ag layer thickness in water phase are prepared.And then,making use of the Local Surface Plasmon Resonance（LSPR）effect,photo-sensitive materials TiO2 nanosheets（NSs）can get enhanced photoelectric responses.We explored the composite condition of Au@Ag NRs and TiO₂NSs,as well as mechanism,and more importantly,we fabricated a PEC sensor for heavy metal,mercury ion(Hg²⁺).After optimizing the test conditions,the prepared PEC sensor was applied for fast and sensitive detection of of Hg²⁺in serum.3.The controllable preparation and electrochemical catalytic properties of Au@Pd core@shell NRs and their application in electrochemiluminescence（ECL）biosensor fabrication are studiedPd NPs are widely used in electrochemical catalytic fields such as catalysis and photocatalysis,etc.,because of their excellent catalytic properties.For the purpose of reducing the cost and improving the catalytic activity,solving the dispersion problem as they are loaded in catalytic system is the high-profile to the researchers.Furthermore,considering the influence of morphology on the catalytic activity,preparing Pd NPs with different morphologies is one of research hot topic in the nanomaterials field.We adopt the"bottom-up"chemical methods via Au NRs as core and Pd as shell to explore a green and simple preparation method of Au@Pd core@shell NRs in water phase,and study its mechanism.We further discuss the influence of their electrochemical catalytic properties for H2O2 reduction.Based on the excellent electrochemical catalytic properties of Au@Pd NRs,we designed a novel and robust ECL biosensing strategy which using Au@Pd NRs as electrochemical catalytic materials and 96-well microtiter plate as transfer device.The developed ECL biosensor was applied in detecting tumor markers with high specificity and sensitivity,and getting satisfied results.4.The controllable preparation and catalytic properties of Au@Pt core@shell NRs and their application as mimic enzyme in detection of H₂O₂ are studied.The same as Pd,Pt also have excellent catalytic properties and is widely used in various fields.However,how to effectively improve the catalytic efficiency of Pt and reduce its cost has always been one of research hot topic in the field of noble metal nanomaterials preparation.In this part,we study the controllable preparation of Au@Pt core@shell NRs via the"bottom-up"chemical methods and explore a green and simple preparation method of Au@Pt NRs in water phase.Furthermore,their catalytic properties in water phase are explored.Through this method,the prepared Au@Pt NRs can effective catalytic oxidation of the reaction between H₂O₂ and tetramethyl benzidine（TMB）.In this reaction,Au@Pt NRs are showing excellent catalytic property and can be as mimic enzyme to replace the horseradish peroxidase to some extent.Based on this discovery,we developed a H₂O₂ sensing strategy using as Au@Pt NRs horseradish peroxidase mimic enzyme and won the wide detection range and low detection limit.Furthermore,in order to reduce the use of the precious metal cost,we try to use a kind of magnetic nanomaterials,CoFe₂O₃-rGO as Au@Pt NRs adsorption carrier.By means of CoFe₂O₃-rGO,after the catalytic reaction,the catalyst loaded on CoFe2O3-rGO can be separated from the test solution after a magnetism process with the aid of a magnet.All of the efforts are to achieve the goal of catalyst recycling and cost reducing.