Thiol-ene Click Reaction As A Facile And General Approach For Surface Functionalization Of Colloidal Nanocrystals

Oleic acid(OA)and/or oleylamine(OAm)are generally used as the surface ligands for stabilization of inorganic nanocrystals(NCs).The hydrophobic and inert surface of the NCs limits their applications such as in biomedical areas.Hence the surface modifications are essential in many physical and chemical processes.In this study,we report a facile and versatile strategy for modification of NCs by ultraviolet-induced thiol-ene chemistry,in which thiol-terminated polyethylene glycol(HS-PEG)and its derivatives can react directly with double bonds in OA/OAm ligands to form covalent linking within one-step.Through this strategy,various hydrophobic NCs with different compositions and morphologies were able to convert into water combining with functionalization of active groups.As a proof-of-concept,this strategy was used to construct a sensor for detecting avidin based on upconverting luminescence analysis.Therefore,this strategy provides a new tool for designing and tuning the surface properties of NCs.The main results are as following:Synthesize the oleic acid(OA)and/or oleylamine(OAm)capped nanocrystals(NCs)included the upconversion nanoparticles(UCNPs),Fe3O4 nanoparticles,Cu9S5 nanoparticles,WS2:Gd nanoflakes with the high temperature hydrothermal method;then the derivatives of HS-PEG are modificated on the surfaces of nanomaterials using the thiol-ene click reaction between the thiol groups and the carbon-carbon double bonds in OA/OAm ligands.After that,the characteristics of the nanomaterials before and after modification are tested,it is found that the nanomaterials change to be water-soluble and have founctional surfaces,the shape and size are not changed.The process of reaction is simple,fast,convenient,efficient and with large-scale.The UCNPs modificated with HS-OEG-NH2 using the thiol-ene click reaction between the thiol groups and the carbon-carbon double bonds in OA/OAm ligands are further reacted with the NHS-biotin to get the UCNPs-biotin nanoparticles;the Ag nanoparticles modificated with GSH are further reacted with the NHS-biotin to get the Ag-biotin nanoparticles.In the mixture of UCNPs-biotin nanoparticles and Ag-biotin nanoparticles,the UCNPs modificated with biotin are used as the energy donors,while the Ag nanoparticles modificated with biotin are used as the energy acceptors.After adding the avidin,the Ag nanoparticles can be connected to the surfaces of the UCNPs because of the strong interaction between the biotin and avidin,leading to the UCNPs’ fluorescence quenching due to the process of fluorescence resonance energy transfer(FRET)between the UCNPs and the Ag nanoparticles.The quenching degree of UCNPs will be increased with the concentration of Ag nanoparticles on the surface of UCNPs increased,thus the concentration of the avidin can be detected.