Carbon Dots-based Nanocomposits:SERS Properties,and Application In Catalytic And Biological Detection

In recent years,carbon dots?CDs?have attracted dramatic attention and extensive research interest owing to their unparalleled physical and chemical properties,including unique quantum size and edge effects,tunable photoluminescence,large optical absorptivity,applicable photoelectric conversion capability,favorable biocompatibility,good chemical stability,and low toxicity,ease of decoration and functional integration.These features offer the potential for exciting applications in photovoltaic devices,bioimaging and sensing,catalysis,medical diagnosis,and analytical detection.CDs based nanocomposites have also drawn increasing attention because the combination of different characteristics could offer additional brilliant properties.To improve and extend their functions,CDs are usually combined with other functional nanomaterials to form nanocomposites,such as noble metal/CDs and semiconductor/CDs.The research on CDs is mainly focused on fluorescence,great progress has been made both experimentally and theoretically,showing great prospects.However,the research on the structure of CDs mainly used traditional methods such as infrared,NML and XPS,and they are only as auxiliary research.While,it is difficult to obtain the inherent information of carbon materials,especially electronic structure information.Raman spectroscopy is the most commonly used,non-destructive and high resolution technology for characterizing of carbon material family?graphene,carbon nanotubes,graphite,diamond?,which can not only obtain its structure information,but also its electronic structure information.As a new star in carbon materials family,CDs are rarely studied by Raman spectroscopy.The Main reasons come from the fluorescence of CDs.Therefore,in order to facilitate the study,we combine CDs with metal to quench fluorescence and endow it have SERS properities.Surface-enhance Raman scattering?SERS?spectroscopy has single-molecule sensitivity and offers rich chemical and structural information.It has developed into a remarkable analysis technique,especially in the field of surface and interface.Considering the unique advantages of SERS,in this paper,we combined SERS technology with CDs/metal or semiconductor nanocomposites to study the SERS properties and expand applications in the fields of catalysis,energy,biology and the environment.It mainly includes the following four aspects:?1?We developed a rapid,simple and controllable method for the preparation of three different kinds of core-shell CDs/Ag nanocomposites based on the CDs with different luminescent?blue,green,red?to directly reduce Ag⁺to Ag NPs.It was found that different luminescent CDs/Ag nanocomposites have excellent SERS properties and selectivity.Raman spectra of different CDs under different excitation wavelengths were studied for the first time,and the charge transfer?CT?mechanism of CDs/Ag nanocomposite were studied by SERS technology.Raman spectroscopy can be used to not only better analyze the structure and electric characteristics of CDs,but also study the internal charge transfer information of CDs/Ag nanocomposites.?2?Investigated the SERS and catalytic properties of the core-shell structured Ag@blue CDs nanocomposite and Ag@blue CDs modified TiO₂ nanofiber hybrid.It was found that both of them have higher SERS property and catalytic activity,the Ag@blue CDs NPs used as the SERS substrate also exhibited excellent peroxidase-like catalytic activity for in situ super-sensitive monitoring of the oxidation of TMB by H₂O₂,a plasmon-enhanced driven photocatalytic reaction of PNTP dimerizing into DMAB,and catalytic driven reduction of PNTP to PATP in the presence of NaBH₄ in real time.This revealed that the Ag@blue CDs nanocomposite had higher catalytic activity than the Ag individual NPs and CDs.Ag@blue CDs combined with TiO₂ offered it more efficient catalytic performance of degradating pollutant MB,and SERS was used to monitor its catalytic degradation process.Using SERS technology to study the CDs based composite nanomaterials catalytic process and reaction mechanism,which expanded the application of SERS and CDs in the field of catalysis and environment.?3?In order to further explore the essential characteristics of graphene carbon dots hybridized with sp² and sp³,a kind of small-sized core-shell structure Ag/graphene quantum dots?GQDs?nanocomposites were constructed.Raman spectrum was used to study the structure and optical properties of GQDs,and the charge transfer?CT?process of Ag and GQDs.Since GQDs have better photoelectric properties,especially high efficient charge transfer capacity,they are suitable for the photoelectric field.In this regard,we have designed two kinds of different Ag/GQDs,Ag NPs SPR properties could enhance the light absorption and GQDs could improve charge transfer ability.Then,we first put forward and design small size core-shell structured Ag/o-GQDs and Ag/r-GQDs NPs systems to research CT ability of the DSSCs well-known dye N719 by SERS technique,and probe into the two GQDs factor influence in CT ability respectively.We found that the presence of GQDs contribute to facilitating superior conversion efficiency performance,and achieving higher CT degree compared to individual Ag NPs.Therefore,Ag/GQDs/N719 is a very promising DSSC system,which provided guidance for SERS technology studying the CT in DSSC and broadened the application of CDs in devices.?4?Based on the advantages of small size,good biocompatibility,strong enzymatic catalytic capacity and highly SERS sensitivity of Ag/GQDs nanocomposites,etc.,it make possiable that the Ag/GQDs applied in living cell.Then,we used Ag/GQDs as catalysts to study the catalytic activity through in situ super-sensitive monitoring of the oxidation of TMB in present of H₂O₂ in living cell in real time by SERS,and then detected the H₂O₂ in the cell.In addition,the combination of enzyme-catalyzed reaction and enzyme-linked immunoassay?ELISA?have achieved the detection of AFP.Taking this as an example,it has provided a theoretical basis for further detection of various antigens,peptides and DNA.It has laid a foundation for the construction of SERS highly sensitive and fast detection technology for enzyme-catalyzed reactions at the cell level and extended its application in biology and medicine.