One Dimensional Nanocomposites Based On Cellulose Nanocrystal And Their Sers And Photothermal Performance

As the smallest physical structure unit of natural Cellulose,Cellulose nanocrystals（CNC）have many excellent properties,such as high specific surface area,high aspect ratio,high crystallinity,hyperfine structure,anisotropy,etc.;In addition,there are a large number of reactive functional groups on the surface of CNC,which are suitable for multi-functional modification and loading.Therefore,CNC can be used as one-dimensional（1D）template materials,showing great application prospects in the construction of high-performance nanocomposites.The unique morphology,template structure,modifiability and biocompatibility of CNC make it a unique functional carrier platform,which can simμLtaneously carry out optical signal design,probe molecμLar modification and biocompatibility regulation,so as to construct high-performance CNC composite biological probes.In this paper,1D CNC@Au-Ag NPs organic-inorganic hybrid nanomaterials were prepared by loading gold and silver nanoparticles（Au-Ag NPs）with different sizes,morphologies and structures by electrostatic adsorption and Au-S covalent bonding.The nanomaterials were used as surface enhanced Raman scattering（SERS）nanoprobes.Research work focused on the SERS and photothermal properties of nanoprobes,dispersion stability and biocompatibility in aqueous solutions,as follows:（1）Preparation of Cellulose nanocrystal@gold nanosphere composite probe based on electrostatic adsorption assembly and its optical properties.Using the negatively charged surface of sμLfonated Cellulose nanocrystals（CNC-SO₃H）as the carrier,the uniform and controllable loading and distribution of gold nanospheres（Au NSs）were realized through electrostatic adsorption and self-assembly.The prepared CNC-SO₃H@Au NSs can be used as 1D SERS nanocomposite probe application.By changing the size of Au NSs,the zeta potential of the surface,and the ratio of Au NSs to CNC’s load number,the particle spacing of Au NSs on the CNC surface was successfully adjusted,thereby constructing a stable and uniform 1D"hot spot".The Zeta potential of Au NSs has the best load effect at about+50 m V,and as the size and load ratio of Au NSs increase,the SERS performance of CNC-SO₃H@Au NSs improves.When the load ratio of Au NSs to CNC is 8:1 and the diameter of Au NSs is about 30 nm,CNC-SO₃H@30-Au NSs-8 material can easily detect the 6G signal of rhodamine at a concentration of 5×10^-8g/L in the solution molecular.In addition,CNC-SO₃H@Au NSs also has good photothermal performance,which is mainly due to the good photothermal conversion ability of Au NSs itself,and the load has no influence on the photothermal effect of Au NSs.（2）Fabrication and optical properties of CNC@Au-Ag NPs composite probe based on Au-S assembly.Using carboxyl Cellulose nanocrystals（CNC-COOH）as the starting reactant,the surface sμLfhydryl Cellulose nanocrystals（CNC-SH）were obtained through the EDC/NHS reaction.The XPS test calcμLated the sμLfhydryl content to be 0.13 mmol/g.Then,using the Au-S bond,the CNC-SH was self-assembled with Au NSs with a diameter of about 30nm,gold nanocubes（Au NCs）with a side length of about 50 nm,and gold-core silver square nanoparticles（Au@Ag NCs）with a side length of about 60 nm to construct a variety of organic-Inorganic hybrid nanomaterials.The nanoparticle spacing was further adjusted by changing the particle loading ratio,and the influence of the morphology and spacing of the gold and silver nanoparticles on the SERS signal sensitivity of the composite substrate was investigated.The research resμLts show that as the CNC surface load increases,the nanoparticle spacing decreases,and the SERS signal gradually increases.Under the same load spacing,the SERS signal sensitivity of Au NCs@CNC-SH is higher than Au NSs@CNC-SH,but lower than Au@Ag NCs/CNC-SH.In addition,the three composite nanoprobes constructed above all show significant photothermal heating under 808 nm near-infrared light irradiation,and because Au@Ag NCs has a higher absorption cross section than Au NSs and Au NCs,Au@Ag NCs/CNC-SH has the highest light-heat temperature rise.（3）The study on the optical properties of the composite nano probes with high dispersion stability of gold nanoparticles/Cellulose nanocrystals.Aiming at the problem that CNC-SH is easy to aggregate and difficult to disperse,the idea of cationized modification of CNC surface is designed to improve the water dispersion stability of CNC-SH and CNC-based composite nanoprobes.Using CNC-COOH as the starting reactant,first use the hydroxyl on the CNC surface to covalently graft the cationic glycidyl trimethyl ammonium chloride（GTMAC）,and then through the EDC/NHS reaction to obtain cationic sulfhydryl Cellulose nanocrystals（CNC-Y-SH）with good dispersion stability.Compared with CNC-SH,CNC-Y-SH has electrostatic repulsion,and its dispersion stability and uniformity in aqueous solution have been significantly improved.The CNC-Y-SH@Au NSs composite nanoprobe was further prepared by the Au-S bond assembly and loading,which also showed good dispersion stability,and it can be stored stably for more than 2 weeks in an aqueous solution.At the same time,CNC-Y-SH@Au NSs composite nanoprobes showed excellent SERS signal sensitivity,SERS signal reproducibility and photothermal stability.The CNC-Y-SH@Au NSs composite nanoprobe was used to collect the SERS signal 10 times repeatedly on the same sample,with almost no difference in signal intensity,and the SERS signal of Rhodamine 6G with a concentration of5×10^-6g/L in an aqueous solution can be achieved.After 5 times of photothermal heating and cooling,the stable photothermal conversion efficiency can be maintained.