Constructing SERS Hot Spots With Small Gaps And Study On Principle Of Actively Capturing Target Molecules

Surface Enhanced Raman Spectroscopy(SERS)realizes highly sensitive detection by providing molecular fingerprint information.During the past decades,with the development of nano science and technology,especially the rapid development of nano-material synthesis technology,SERS has brought about rapid changes,especially the attention and thinking on the hot spots in SERS substrate.Researchers devoted themselves to the design and construction of SERS substrates with rich hot spots,and a large number of related experiments and theories also emerged.However,the key problem in SERS detection research is how to construct a large number of smaller gap hot spots with a simple method,and let the target molecules enter these hot spots actively,and realize the transformation from hot spots to effective hot spots.Based on the key influencing factors analysis in the research process of SERS detection,aiming at the key problem of how to use simple methods to build a large number of hot spots and let target molecules actively enter these hot spots,this thesis successfully realizes the construction of a variety of small gap SERS hot spots structures and the principle of automatically capturing target molecules.The main contents are summarized as follows:(1)Designing and constructing a long-period and highly stable three-dimensional small gap SERS hot spots matrix.By adding the nonvolatile solvent glycerol aqueous solution to the traditional aqueous Ag NPs sol and adjusting the content of glycerol,optimizing the best proportion to generate three-dimensional hot spots matrix with stably and efficiently for at least 20 minutes.Combining with dark field microscope,in situ UV-vis absorption spectroscopy,and dynamic SERS spectra analysis,the properties of constructed long-period and highly stable three-dimensional small gap SERS hot spots matrix are explored.Realizing the highly sensitive and stable detection of 10-8 mol/L NOD,TBZ and METH.(2)The aggregation process of nanoparticles is analyzed and used for in-situ dynamic monitoring of cupping effect substances.Combined with in-situ TEM and theoretical analysis,the behavior of nanoparticles in the formation of hot spots is further analyzed and the concept of FLERS(Flocculation Enhanced Raman Spectroscopy)was proposed.During the evaporation process of the solution,the nanoparticles come close to each other and gather together to form a flocculation,with the gap between the nanoparticles always maintained at 7-9 nm.When the amount of sol is 5 μL,the flocculation can exist stably for about 7 minutes.FLERS method was specifically applied to in-situ noninvasive monitoring,and combined with mass spectrometry analysis,it was found that effectors such as histamine and disulfide protein might be produced after cupping,which to some extent explained the scientific principle of traditional Chinese medicine cupping method.(3)A general SERS method for actively capturing target molecules in small gaps(hot spots)based on a nanocapillary pumping model is developed.Using the liquid-liquid interface self-assembly method to construct a large area of two-dimensional hot spots,and the gap between the nanoparticles was about 16 nm at the initial stage of evaporation and about 6 nm at the end.In this process,nanoparticles are close to each other,forming a nanocapillary pumping model with ubiquitous hot spots.At the same time,the pressure difference at different gaps is calculated,which shows that the solvent always carries the target molecules to move to the smaller gap between nanoparticles to realize hot spot activation.This method can be used for highly sensitive detection of various types of target molecules.And in situ monitoring of the death process of single A549 cells under photothermal stimulation was also successfully achieved.(4)The MoS2-Ag heterogeneous nanopocket with small gaps was designed and constructed,and a highly stable and ultra-sensitive SERS method was developed.Compared with the nanocapillary pumping model,the SERS signal intensity of the method based on MoS2-Ag heterogeneous nanopocket was generally increased by 3-7 times.At the same time,due to the sealing effect of monolayer MoS2 film,the target molecules can stay in the nanopocket for a period of time with the solvent,and the stability is greatly improved,realizing the efficient and stable detection of 5-6 minutes at the low concentration of 10-11 mol/L.In addition,the highly stable and sensitive detection of different types of molecular such as pesticide residues(PQ),poisons(bromadiolone),food colorants(lemon yellow)and anti-tumor drugs(5-FU)were investigated.