3D金纳米胶囊SERS基底对食品污染物的快速检测

首先采用种子生长法合成金纳米双锥体,再通过水和正丁醇的乳化体系液液组装而形成3D纳米胶囊。这些金胶体具有六边形密排多层壳,由于强粒子间等离子体耦合,显示出低反射率和强宽带吸收。结晶紫(CV)作为探针分子具有较高的灵敏性和重复性,同时,对孔雀石绿(MG)、福美双(THR)、噻苯咪唑(TBZ)的检测极限均达到了10-9mol/L。

Triangular Au-Ag framework nanostructures prepared by multi-stage replacement and their spectral properties

Triangular Au-Ag framework nanostructures （TFN） were synthesized via a multi-step galvanic replacement reaction （MGRR） of single-crystalline triangular silver nanoplates in a chlorauric acid （HAuCl4） solution at room temperature. The morphological, compositional, and crystal structural changes involved with reaction steps were analyzed by using transmission electron microscopy（TEM）, energy-dispersive X-ray spectrometry （EDX）, and X-ray diffraction. TEM combined with EDX and selected area electron diffraction confirmed the replacement of Ag with Au. The in-plane dipolar surface plasmon resonance （SPR） absorption band of the Ag nanoplates locating initially at around 700 nm gradually redshifted to 1 100 nm via a multi-stage replacement manner after 7 stages. The adding amount of HAuCl4 per stage influenced the average redshift value per stage, thus enabled a fine tuning of the in-plane dipolar band. A proposed formation mechanism of the original Ag nanoplates developing pores while growing Au nanoparticles covering this underlying structure at more reaction steps was confirmed by exploiting surface-enhanced Raman scattering （SERS）.

吸附色素蛋白与纳米银粒子间的光诱导电子传递

采用表面增强拉曼光谱研究了吸附态微过氧化物酶和细胞色素 c的光诱导还原 .结果表明 ,吸附于粗糙银电极表面的过氧化物酶和细胞色素 c在 4 1 3 nm激光连续照射下被部分还原 .光诱导还原可归因于电极表面纳米银粒子的定域表面等离子体吸收使得自由电子受激 ,受激电子进而转移进入吸附分子空轨道 。

Surface-enhanced Raman Scattering of Aflatoxin B1 on Silver by DFT Method

The structure, electrostatic properties, and Raman spectra of aflatoxin B1 （AFB1） and AFB1-Ag complex are studied by density functional theory with B3LYP/6- 311G（d,p）/Lan12dz basis set. The results show that the surface-enhanced Raman scattering （SERS） and pre-resonance Raman spectra of AFB1-Ag complex strongly depend on the adsorption site and the excitation wavelength found to enhance 102-103 order compared to of the incident light. The SERS factors are normal Raman spectrum of AFB1 molecule due to the larger static polarizabilities of the AFB1-Ag complex, which directly results in the stronger chemical enhancement in SERS spectra. The pre-resonance Raman spectra of AFB1-Ag complex are explored at 266, 482, 785, and 1064 nm incident light wavelength, in which the enhancement factors are about 10^2-10^4, mainly caused by the charge-transfer excitation resonance. The vibrational modes are analyzed to explain the relationship between the vibrational direction and the enhanced Raman intensities.

Nonlinear Stark effect observed for carbon monoxide chemisorbed on gold core/palladium shell nanoparticle film electrodes, using in situ surface-enhanced Raman spectroscopy

The potential （E）-dependent vibrational behavior of a saturated CO adlayer on Au-core Pd-shell nanoparticle film electrodes was investigated over a wide potential range, in acidic, neutral, and basic solutions, using in situ surface-enhanced Raman spectroscopy （SERS）. Over the whole of the examined potential region （-1.5 to 0.55 V vs. NHE）, the peak frequencies of both the C-OM and the Pd-COM band （here, M denotes the multiply-bonded configuration） displayed three distinct linear regions： dvc oM/dE decreased from -185-207 （from -1.5 to -1.2 V） to -83-84 cm-1/V （-1.2 to -0.15 V）, and then to 43 cm-1/V （-0.2 to 0.55 V）; on the other hand, dvpd coM/dE changed from -10 to -8 cm I/V （from -1.5 to -1.2 V） to ^-31 to -30 cm-1/V （-1.2 to -0.15 V）, and then to -15 cm-1/V （-0.2 to 0.55 V）. The simultaneously recorded cyclic voltammograms revealed that at E 〈 -1.2 V, a hydro- gen evolution reaction （HER） occurred. With the help of periodic density functional theory calcula- tions using two different （2 × 2）-3CO slab models with Pd（111）, the unusually high dvc-oM/dE and the small dVPd-CoM/dE in the HER region were explained as being due to the conversion of COad from bridge to hollow sites, which was induced by the co-adsorbed hydrogen atoms formed from dissociated water at negative potentials.

In-situ electrochemical surface-enhanced Raman spectroscopy in metal/polyelectrolyte interfaces

Polyelectrolyte becomes more and more popular in electrocatalysis.The understanding of electrode/polyelectrolyte interfaces at the molecular level is important for guiding further the polyelectrolyte-based electrocatalysis.Herein,we demonstrate an in-situ surface-enhanced Raman spectroscopic method by using a three-electrode spectroelectrochemical cell towards characterizing the electrode/polyelectrolyte interfaces.The Ag/AgCl and Ag/Ag_(2)O electrodes are used as the reference electrode in the acidic and the alkaline systems,respectively.The working electrode is made of a transparent carbon thin film which loads the electrocatalysts.The applications of this method are demonstrated through the in-situ characterizations of the p-methylthiophenol adsorbed on the Au and Pt and the electrochemical oxidation of Au on polyelectrolyte membranes.The potential-dependent spectral features of these two systems show that this method is a powerful tool for investigating the electrode/polyelectrolyte interfaces in electrocatalysis.

Fabrication of SERS-Active Au@Au@Ag Double Shell Nanoparticles for Low-Abundance Pigment Detection

Au@Au@Ag double shell nanoparticles were fabricated and characterized using TEM,STEM-mapping and UV-Vis methods.Using crystal violet as Raman probe,the surface-enhanced Raman scattering(SERS)activity of the as-prepared Au@Au@Ag nanoparticles was studied by comparing to Au,Au@Ag and Au@Au core-shell nanoparticles which were prepared by the same methods.Moreover,it can be found that the SERS activity was enhanced obviously by introduction of NaCl and the concentrations of NaCl played a key role in SERS detection.With an appropriate concentration of NaCl,the limit of detection as low as 10^(-10)mol/L crystal violet can be achieved.The possible enhanced mechanism was also discussed.Furthermore,with simple sample pretreatment,the detection limit of 5μg/g Rhodamine B(RhB)in chili powders can be achieved.The results highlight the potential utility of Au@Au@Ag for detection of illegal food additives with low concentrations.

Highly Sensitive Silver Nanorod Arrays for Rapid Surface Enhanced Raman Scattering Detection of Acetamiprid Pesticides

The determination of pesticide residue on agricultural products is increasingly important. Exposure to pesticides can cause severe acute reactions in humans, including aplastic anemia and leukemia. In this work, we developed a rapid and sensitive method to detect acetamiprid pesticide residue based on surface-enhanced Raman scattering. Silver nanorod （AgNR） arrays were fabricated by oblique angle deposition technology and were used as SERS substrates. Prior to detection, the AgNR arrays were cleaned with nitric acid solution or a mixture of methanol and acetone. Compared to the unwashed AgNR arrays, the AgNR arrays washed with methanol and acetone shows a signal enhancement 1000 times greater than the unwashed AgNR array due to the effective removal of the impurities on its surface. The limit of detection of acetamiprid was determined to be 0.05 mg/L. In addition, the molecular structure of acetamiprid was simulated and the corresponding vibration modes of the characteristic bands of acetamiprid were calculated by density function theory. To demonstrate its practical application, the AgNRs array substrates were applied successfully to the rapid identification of acetamiprid residue on a cucumber＇s surface. These results confirmed possibility of utilizing the AgNRs SERS substrates as a new method for highly sensitive pesticide residue detection.

Probing the role of surface speciation of tin oxide and tin catalysts on CO_(2) electroreduction combining in situ Raman spectroscopy and reactivity investigations

Electrochemical CO_(2)reduction to formate is a promising approach to store renewable electricity and utilize CO_(2).Tin oxide catalysts are efficient catalysts for this process,while the mechanisms underneath,especially the existence and role of oxidized tin species under CO2 electroreduction conditions remain unclear.In this work,we provide strong evidence on the presence of oxidized tin species on both SnO_(2)and Sn during CO_(2)reduction via in situ surface‐enhanced Raman spectroscopy,while in different nature.Reactivity measurements show similar activity and selectivity to formate production on SnO_(2)and Sn catalysts.Combined analysis of Raman spectra and reactivity results suggests that Sn(IV)and Sn(II)oxide species are unlikely the catalytic species in CO_(2)electroreduction to formate.

Highly Effective Detection of Amitraz in Honey by Using Surface-Enhanced Raman Scattering Spectroscopy Coupled with Chemometric Methods

As an effective and universal acaricide, amitraz is widely used on beehives against varroasis caused by the mite Varroa jacobsoni. Its residues in honey pose a great danger to human health. In this study, a sensitive, rapid, and environmentally friendly surface-enhanced Raman spectroscopy method (SERS) was developed for the determination of trace amount of amitraz in honey with the use of silver nanorod (AgNR) array substrate. The AgNR array substrate fabricated by an oblique angle deposition technique exhibited an excellent SERS activity with an enhancement factor of -10^7. Density function theory was employed to assign the characteristic peak of amitraz. The detection of amitraz was further explored and amitraz in honey at concentrations as low as 0.08 mg/kg can be identified. Specifically, partial least square regression analysis was employed to correlate the SERS spectra in full-wavelength with Camitraz to afford a multiple-quantitative amitraz predicting model. Preliminary results show that the predicted concentrations of amitraz in honey samples are in good agreement with their real concentrations. Compared with the conventional univariate quantitative model based on single peak’s intensity, the proposed multiple-quantitative predicting model integrates all the characteristic peaks of amitraz, thus offering an improved detecting accuracy and anti-interference ability.

Surface-enhanced vibrational spectroscopies in electrocatalysis:Fundamentals,challenges,and perspectives

Electrocatalysis offers a promising approach towards chemical synthesis driven by renewable energy.Molecular level understanding of the electrochemical interface remains challenging due to its compositional and structural complexity.In situ interfacial specific characterization techniques could help uncover structure-function relationships and reaction mechanism.To this end,electrochemical surface-enhanced Raman spectroscopy(SERS)and surface-enhanced infrared absorption spectroscopy(SEIRAS)thrive as powerful techniques to provide fingerprint information of interfacial species at reaction conditions.In this review,we first introduce the fundamentals of SERS and SEIRAS,followed by discussion regarding the technical challenges and potential solutions.Finally,we highlight future directions for further development of surface-enhanced spectroscopic techniques for electrocatalytic studies.

Density Functional Theory Study on Raman Spectra of Rhodamine Molecules in Different Forms

Rhodamine molecules are one of the most used dyes for applications related to Raman spectroscopy. We have systematically studied Raman spectra of Rhodamine 6G, Rhodamine 123, and Rhodamine B （RhB） molecules using density functional theory. It is found that with BP86 functional the calculated Raman spectra of cationic Rhodamine molecules are in good agreement with corresponding experimental spectra in aqueous solution. It is shown that the involvement of the counter ion, chlorine, and the specific hydrogen bonds has noticeable effects on the Raman spectra of RhB that can partially explain the observed difference between Raman spectra of RhB in solution and on gold surfaces. It also indicates that an accurate description of surface enhanced Raman scattering for Rhodamine molecules on metal surface still requires to take into account the changes induced by the interracial interactions.

Direct identification of the carbonate intermediate during water-gas shift reaction at Pt-NiO interfaces using surface-enhanced Raman spectroscopy

Noble metal-reducible oxide interfaces have been regarded as one of the most active sites for water-gas shift reaction.However,the molecular reaction mechanism of water-gas shift reaction at these interfaces still remains unclear.Herein,water-gas shift reaction at Pt-NiO interfaces has been in-situ explored using surface-enhanced Raman spectroscopy by construction of Au@Pt@NiO nanostructures.Direct Raman spectroscopic evidence demonstrates that water-gas shift reaction at Pt-NiO interfaces proceeds via an associative mechanism with the carbonate species as a key intermediate.The carbonate species is generated through the reaction of adsorbed CO with gaseous water,and its decomposition is a slow step in water-gas shift reaction.Moreover,the Pt-NiO interfaces would promote the formation of this carbonate intermediate,thus leading to a higher activity compared with pure Pt.This spectral information deepens the fundamental understanding of the reaction mechanism of water-gas shift reaction,which would promote the design of more efficient catalysts.

Detection of DNA Mutations Using Novel SERS （Surface-Enhanced Raman Spectroscopy） Diagnostic Platform

This article describes the detection of DNA mutations using novel Au-Ag coated GaN substrate as SERS （surface-enhanced Raman spectroscopy） diagnostic platform. Oligonucleotide sequences corresponding to the BCR-ABL （breakpoint cluster region-Abelson） gene responsible for development of chronic myelogenous leukemia were used as a model system to demonstrate the discrimination between the wild type and Met244Val mutations. The thiolated ssDNA （single-strand DNA） was immobilized on the SERS-active surface and then hybridized to a labeled target sequence from solution. An intense SERS signal of the reporter molecule MGITC was detected from the complementary target due to formation of double helix. The SERS signal was either not observed, or decreased dramatically for a negative control sample consisting of labeled DNA that was not complementary to the DNA probe. The results indicate that our SERS substrate offers an opportunity for the development of novel diagnostic assays.

Facile Synthesis of Micro/Nano Binary Dendritic Gold Structures for SERS and Superhydrophobic Applications

Via a galvanic displacement reaction, well-defined micro/nano binary dendritic gold structures were prepared on silicon wafers in fluoride acid solution containing HAuCI4 at 50 ℃. The gold deposits were characterized with scanning electron microscopy （SEM）, energy-dispersive X-ray （EDX） spectrum and X-ray diffraction （XRD）. The investigation of the surface-enhanced Raman scattering （SERS） reveals that the film of gold dendrites was an excellent substrate with significant enhancement effect. Also, the gold dendritic structured surface exhibited a remarkable superhydrophobic property with a contact angle of approximately 165° and low contact angle hysteresis after further simple surface modification with n-dodecanethiol.

Land use and forested landscape changes at Sakaerat Environmental Research Station in Nakhorn Ratchasima province, Thailand

The Sakaerat Environmental Research Station （SERS） was established to promote long-term ecological research （LTER） and to demonstrate sustainable forest management and biodiversity conservation. In the past decade, the government has put a lot of effort into rehabilitating degraded forest both inside and surrounding the SERS landscape in order to link fragmented forest patches. However, there is a lack of appropriate methods that allow the measurement of the effectiveness of reforestation. The objective of this paper is to quantify land use and landscape structure changes between 1990 and 2002. The study area encompasses the SERS and its buffer zone. Land use/land cover maps were visually interpreted into 9 classes using temporal Landsat-TM images. These classes were dry evergreen forest, mixed deciduous forest, dry dipterocarp forest, secondary growth, plantation, grassland, old clearing, agriculture ＆ settlement, and water body. In addition, a Geographic Information System （GIS） and FRAGSTATS package were used to assess fragmentation indices. The results revealed that the annual increment rate of dry evergreen forest and dry dipterocarp forest were 0.51% and 0.97%, respectively. In addition, the total area of forest plantation expanded to roughly three times or increased 193.23% during this period. Agricultural and settlement area decreased 7.56% per year. Most of this area was replaced by plantation and natural regeneration. The fragmentation indices indicated that the remaining dry evergreen forest was highly aggregated or had low fragmentation. The number of patches decreased from 7 to 5, and mean patch size increased significantly. However, mixed deciduous forest and dry dipterocarp forest were relatively fragmented. Mixed deciduous forest showed higher fragmentation. Mean patch size area was substantially decreased from 293 ha in 1990 to 123 ha in 2002 and the mean nearest neighbor distance increased by approximately 400 m during this period.

Polyacrylic acid sodium salt film entrapped Ag-nanocubes as molecule traps for SERS detection

Surface-enhanced Raman spectroscopy （SERS） is a fast analytical technique for trace chemicals; however, it requires the active SERS-substrates to adsorb analytes, thus limiting target species to those with the desired affinity for substrates. Here we present networked polyacrylic acid sodium salt （PAAS） film entrapped Ag-nanocubes （denoted as Ag-nanocubes@PAAS） as an effective SERS-substrate for analytes with and without high affinity. Once the analyte aqueous solution is cast on the dry Ag-nanocubes@PAAS substrate, the bibulous PAAS becomes swollen forcing the Ag-nanocubes loose, while the analytes diffuse in the interstices among the Ag-nanocubes. When dried, the PAAS shrinks and pulls the Ag-nanocubes back to their previous aggregated state, while the PAAS network ＂detains＂ the analytes in the small gaps between the Ag-nanocubes for SERS detection. The strategy has been proven effective for not only single- analytes but also multi-analytes without strong affinity for Ag, showing its potential in SERS-based simultaneous multi-analyte detection of both adsorbable and non-adsorbable pollutants in the environment.

Alumina-coated Ag nanocrystal monolayers as surfaceenhanced Raman spectroscopy platforms for the direct spectroscopic detection of water splitting reaction intermediates

A novel Ag-alumina hybrid surface-enhanced Raman spectroscopy （SERS） platform has been designed for the spectroscopic detection of surface reactions in the steady state. Single crystalline and faceted silver （Ag） nanoparticles with strong light scattering were prepared in large quantity, which enables their reproducible self-assembly into large scale monolayers of Raman sensor arrays by the Langrnuir-Blodgett technique. The close packed sensor film contains high density of sub-nm gaps between sharp edges of Ag nanoparticles, which created large local electromagnetic fields that serve as ＂hot spots＂ for SERS enhancement. The SERS substrate was then coated with a thin layer of alumina by atomic layer deposition to prevent charge transfer between Ag and the reaction system. The photocatalytic water splitting reaction on a monolayer of anatase TiO2 nanoplates decorated with Pt co-catalyst nanoparticles was employed as a model reaction system. Reaction intermediates of water photooxidation were observed at the TiO2/solution interface under UV irradiation. The surface-enhanced Raman vibrations corresponding to peroxo, hydroperoxo and hydroxo surface intermediate species were observed on the TiO2 surface, suggesting that the photo-oxidation of water on these anatase TiO2 nanosheets may be initiated by a nucleophilic attack mechanism.

Surface plasmon-enhanced photochemical reactions on noble metal nanostructures

Nanoscale noble metals can exhibit excellent photochemical and photophysical properties, due to surface plasmon resonance(SPR) from specifically collective electronic excitations on these metal surfaces. The SPR effect triggers many new surface processes, including radiation and radiationless relaxations. As for the radiation process, the SPR effect causes the significant focus of light and enormous enhancement of the local surface optical electric field, as observed in surface-enhanced Raman spectroscopy(SERS) with very high detection sensitivity(to the single-molecule level). SERS is used to identify surface species and characterize molecular structures and chemical reactions. For the radiationless process, the SPR effect can generate hot carriers, such as hot electrons and hot holes, which can induce and enhance surface chemical reactions. Here, we review our recent work and related literature on surface catalytic-coupling reactions of aromatic amines and aromatic nitro compounds on nanostructured noble metal surfaces. Such reactions are a type of novel surface plasmon-enhanced chemical reaction. They could be simultaneously characterized by SERS when the SERS signals are assigned. By combining the density functional theory(DFT) calculations and SERS experimental spectra, our results indicate the possible pathways of the surface plasmonenhanced photochemical reactions on nanostructures of noble metals. To construct a stable and sustainable system in the conversion process of the light energy to the chemical energy on nanoscale metal surfaces, it is necessary to simultaneously consider the hot electrons and the hot holes as a whole chemical reaction system.

Reproducibility in Surface-Enhanced Raman Spectroscopy

Surface-enhanced Raman spectroscopy（SERS） is an intense ongoing hot topic because it is an attractive tool for sensing or detecting molecules in trace amounts. Despite its high specificity and sensitivity, the SERS technique has not been established as a routine analytic method most likely due to the low reproducibility of the SERS signal. This review considers the influence factors to produce the poor reproducibility during the SERS measurement. This review starts with the discussion of calculation of surface-enhanced Raman intensity in order to explain the reason why it is so difficult to achieve a high reproducibility of SERS measurement from the origin of enhancement mechanism. Then we focus on the fabrication of SERS substrates generally including two types：① single particles and ② arrays on substrate that are directly used to detect molecules or other components.In addition, we discuss the molecule factors and optical system for the reproducibility for sample-to-sample or spot-to-spot on a substrate. In the final part of this review, some effects resulting in the irreproducibility of Raman bands＇ position from recent literatures are discussed.