Controllable Fabrication Of Large Area GNR Oriented Arrays And Their Specific SERS Enhancement Properties

With the development of society and the improvement of people’s living standards,trace detection has received increasing attention,involving many fields such as food safety,forensic science,bioanalysis,archaeology,anti-terrorism explosion,and drug safety.Surface enhanced Raman scattering（SERS）is a technique that uses a strong local electric field generated by surface plasmon coupling to amplify the Raman signal of target molecules millions of times to achieve trace detection,of which sensitivity and reliability depend on the strength and stability of the plasmon coupling in SERS substrate.Therefore,the key to high-performance and high-reliability trace detection is to fabricate strong coupling plasmon substrate with specific structures.Gold nanorods（GNR）are plasmonic materials with large light scattering cross sections,excellent chemical stability and biocompatibility.Due to the plasmonic coupling between adjacent rods,the array assembled by the rods can generate a strong local electric field excited by visible light.Therefore,GNR array is one of the most concerned SERS substrates.The results demonstrate convincingly that the plasmonic coupling between the rods strengthens remarkably with the rods getting close,and the arrays with the rods assembled vertically have the best SERS performance.Therefore,it is a significant improvement in efficient trace detection to prepare regular small-spacing,vertically-oriented GNR arrays.In addition,recent studies have shown a specifically enhance of chiral assembly structures to the Raman signal of chiral molecules.Therefore,constructing a regular chiral GNR array will effectively enhance the SERS detection ability of chiral molecules.Based on the above assumption,this paper mainly carries out the following two aspects of research:1.Preparation and SERS application of GNR vertical arrays with small spacing.With GNR as the construction unit,the electrostatic repulsion range between compression rods is compressed through the modification of 12-（pyridin-4-yl）-dodecane-1-thiol（PDT）to construct a self-assembly mode controlled by strong van der Waals gravity.Combined with microenvironment regulation,the idea of micro region limited self-assembly is carried out to prepare a macro scale high regular small spacing GNR vertical array for SERS detection.The results of optical photos,scanning electron microscope（SEM）images and atomic force microscope（AFM）images show that the vertical arrays have uniform hexagonal dense stacking structure on the centimeter scale and are highly uniform with the spacing as small as 3.3 nm.In addition,by controlling the concentration of GNR in the solution,the coverage of the arrays can be controlled while maintaining its structure,with a maximum of 70%.Using the arrays as SERS substrates can effectively detect malachite green（MG）probe molecules in the ultra-low concentration range of 10^-9-10^-15 M.And in the mapping test,the relative standard deviation（RSD）of the Raman signal strength for multiple characteristic peaks is only about 10%,and the RSD of the single point signal between different array samples is about 5%,demonstrating excellent SERS sensitivity and signal stability.The arrays can similarly demonstrate excellent performance in multichannel detections of multimolecular mixed samples and detections of biomacromolecules at a low concentration.Furthermore,the number of array layers is also adjusted,and uniform multilayer arrays are prepared.2.Preparation and chiral selective SERS application of GNR chiral arrays.A spatially limited self-assembly scheme is designed by directly adding chiral inducing molecules.It is found that N-acetyl-D-cysteine（D-NAC）have moderate interaction with Au by comparing 7 commonly used chiral inducing molecules,and it can effectively induce GNR chiral assembly under the protection of hexadecyl trimethyl ammonium bromide（CTAB）micelles.Interestingly,the inducing molecules of opposite chirality can induce assembled arrays of enantiochiral structures up to centimeter in size.Through high magnification SEM characterizations of the chiral arrays,it can be seen that the chiral tilt angle of GNRs is about 30°,there is a chiral torsion between the rods,and tilt with an outward rotation at two center points.The corresponding electron diffraction pattern shows that the diffraction points of the arrays have spot tailing,and the spacing of the diffraction crystal planes has changed,with chiral structure characteristics.In orthogonally polarized mode,the arrays show yellow and green spots,and the spots’colour will completely reversed when the position is rotated 90°,providing strong evidence that the arrays are chirally assembled and have the conditions to carry out experiments for Raman applications.The detections of non chiral molecular MG using both ordinary CTAB-GNRs vertical arrays and the chiral arrays show that the SERS signal enhancement of MG by the three chiral arrays is about 150%higher than that of CTAB-GNRs vertical arrays.The RSD of Raman signal peak at 1616 cm^-1 in random 40 region is only 7.4%.The simultaneous detection of MG and methyl orange（MO）can clearly distinguish characteristic peaks of MG and MO.Therefore,the chiral arrays fully inherit all the advantages of vertical arrays.Next,R-GNRs arrays induced by S-type molecules are taken as examples to detect chiral enantiomer.The results show the chiral arrays exhibit stronger SERS enhancement of chiral molecules than the CTAB-GNRs vertical arrays,and the signal enhancement of S-type molecules is more significant than that of R-type molecules,vice versa.Then,chiral proteins such as bovine serum albumin are selected as probe molecules.Raman detection results indicate that the enhancement effect of the chiral arrays is much better than that of ordinary vertical arrays,and the SERS signal detection ability of R-GNRs chiral assemblies is stronger.Finally,the direct Raman detection analysis results of DNA and mi RNA,which are extremely difficult to detect at low concentrations,show that the R-GNRs arrays have the best detection performance,with a minimum detection limit of 5×10^-11 M.This indicates that the chiral arrays have excellent detection ability for the recognition of chiral substances and the potential for the detection of pathological DNA and RNA at low concentrations.