Facile SERS screening of melamine in bovine milk with 2D printed AgNPs/glass fabric filter paper as the flexible substrate

Melamine is one of the most frequently detected adulterants in dairy products.The current study proposes a surface-enhanced Raman spectroscopy(SERS)-based analytical tool for fast and reliable screening of melamine in bovine milk.A hand-held Raman spectrometer was used in conjunction with a substrate composed of silver nanoparticles(AgNPs)that was 2D printed onto glass fiber(GF)filter paper.Under optimized conditions,a sensitive and fingerprint-like signal at 674 cm^(-1) was obtained.The AgNPs/GF substrate exhibited high sensitivity to melamine in milk down to 1.9498×10^(-5)mg/mL,which is well below the USA and EU safety limits(2.5×10^(-3)mg/mL).Remarkably,the proposed technology was also highly reproducible,showing spot-to-spot and block-to-block variations below 3.3%and 4.9%at 674 cm^(-1) in Raman intensity,respectively.The characteristic peak intensity and concentration of melamine showed an acceptable linear relationship(R^(2)=0.9909)within the range of 0.0001-1 mg/mL.Overall,the method established in this study can provide an efficient and effective method for the quantitative target screening and detection of melamine in dairy products.

Controllable Synthesis of Au NRs and Its Flexible SERS Optical Fiber Probe with High Sensitivity

The surface-enhanced Raman scattering(SERS) optical fiber probes were successfully prepared by self-assembling on polyelectrolyte multilayers. Gold nanorods(Au NRs) were used as SERS enhancement material to give excellent biological affinity and stability to the SERS optical fiber probes. Au NRs were synthesized by seed growth method. The synergistic effect between AgNO_(3) and surfactant was investigated, and the highest yield was found when AgNO_(3) was 500 uL. Meanwhile, different SERS optical fiber probes were obtained by selecting silane coupling agent, polyelectrolyte multilayer and graphene oxide(GO) to treat quartz fiber. It was found that the SERS optical fiber probes obtained by the self-assembled on polyelectrolyte multilayers method performed better than those by other methods. In addition, Mapping was combined with finite element simulation to analyze the electromagnetic field distribution at the fiber end face.The electromagnetic field distribution of Au NRs was investigated, the difference of electromagnetic field intensity around the Au NRs with different arrangements was compared, the strongest signal was obtained when the Au NRs were head-to-head. Finally, sensitivity of the optimized SERS optical fiber probes could reach 10^(-9)mol/L, with excellent stability and repeatability.

Label-free breast cancer detection and classification by convolutional neural network-based on exosomes surface-enhanced raman scattering

Because the breast cancer is an important factor that threatens women's lives and health,early diagnosis is helpful for disease screening and a good prognosis.Exosomes are nanovesicles,secreted from cells and other body fluids,which can reflect the genetic and phenotypic status of parental cells.Compared with other methods for early diagnosis of cancer(such as circulating tumor cells(CTCs)and circulating tumor DNA),exosomes have a richer number and stronger biological stability,and have great potential in early diagnosis.Thus,it has been proposed as promising biomarkers for diagnosis of early-stage cancer.However,distinguishing different exosomes remain is a major biomedical challenge.In this paper,we used predictive Convolutional Neural model to detect and analyze exosomes of normal and cancer cells with surface-enhanced Raman scattering(SERS).As a result,it can be seen from the SERS spectra that the exosomes of MCF-7,MDA-MB-231 and MCF-10A cells have similar peaks(939,1145 and 1380 cm^(-1)).Based on this dataset,the predictive model can achieve 95%accuracy.Compared with principal component analysis(PCA),the trained CNN can classify exosomes from different breast cancer cells with a superior performance.The results indicate that using the sensitivity of Raman detection and exosomes stable presence in the incubation period of cancer cells,SERS detection combined with CNN screening may be used for the early diagnosis of breast cancer in the future.

SURFACE-ENHANCED RAMAN SPECTRA OF p-AMINOBENZOIC ACID ADSORBED ON Ag2CO3 COLLOIDS

It was observed that the p-aminobenzoic acid(PABA)molecules adsorbed on A92CO3 colloids exhibited strong SERS effect,the enhancement factor is estimated at 10~7—10~8 The mechanism of SERS effect on PABA adsorbed on the colloids was discussed.

Multivariate analysis of serum surface-enhanced Raman spectroscopy of liver cancer patients

Early diagnosis of liver cancer plays a significant role in reducing its high mortality.In this preliminary study,the feasibility of using serum surface-enhanced Raman spectroscopy(SERS)to identify liver cancer was studied.Serum samples were obtained from liver cancer patients and healthy controls.The differences between the SERS spectra of pre-operation and postoperation of liver cancer patients were also analyzed.The general shape and trend of SERS spectra of health control and liver cancer patients were similar.Multivariate analysis,e.g.,PLSSVM,might be useful for the discrimination of serum SERS spectra of pre-operation and post-operation.

Comparison of Surface-enhanced Raman Scattering Spectra of Two Kinds of Silver Nanoplate Films

Surface-enhanced Raman scattering（SERS） spectra of different silver nanoplate selt-assembled tllmS at different excitation wavelengths were fairly compared. Shape conversion from silver nanoprisms to nanodisks on slides was in situ carried out. The SERS spectra of 4-mercaptopyridine（4-MPY） on these anisotropic silver nanopar- ticle self-assembled films present that strong enhancement appeared when the excitation line and the surface plasmon resonance（SPR） band of silver substrate overlapped. In this model, the influence of the crystal planes of silver na- noplates on SERS enhancement could be ignored because the basal planes were nearly unchanged in two kinds of silver nanoplate self-assembled films.

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.

一种新型肽核酸单体的FTIR,FT-Raman光谱及SERS研究

报道了S-胸腺嘧啶-L-半胱氨酸的FTIR光谱,及其固态、饱和液态的FT-Raman光谱。通过红外与拉曼光谱的结合,对其分子结构中各基团的振动情况进行了较为全面的解析;实验发现,该化合物在银胶上的最佳SERS的浓度为10-4mol·L-1,氨基峰在酸性条件下增强,羧基峰在碱性条件下增强,而其他基团峰随pH值的改变变化不大。依据SERS作用机理和规律,推测S-胸腺嘧啶-L-半胱氨酸在银胶表面的吸附是通过硫原子、羧基、氨基、胸腺嘧啶环和其中的氮原子与银原子配位,且胸腺嘧啶环是倾斜着与银纳米颗粒相吸附;该吸附模型的建立为拉曼光谱更深入研究PNA、多肽及其他生物分子提供了十分重要的信息和有益的参考。

Ferroelectrically modulate the Fermi level of graphene oxide to enhance SERS response

Surface-enhanced Raman scattering(SERS)substrates based on chemical mechanism(CM)have received widespread attentions for the stable and repeatable signal output due to their excellent chemical stability,uniform molecular adsorption and controllable molecular orientation.However,it remains huge challenges to achieve the optimal SERS signal for diverse molecules with different band structures on the same substrate.Herein,we demonstrate a graphene oxide(GO)energy band regulation strategy through ferroelectric polarization to facilitate the charge transfer process for improving SERS activity.The Fermi level(Ef)of GO can be flexibly manipulated by adjusting the ferroelectric polarization direction or the temperature of the ferroelectric substrate.Experimentally,kelvin probe force microscopy(KPFM)is employed to quantitatively analyze the Ef of GO.Theoretically,the density functional theory calculations are also performed to verify the proposed modulation mechanism.Consequently,the SERS response of probe molecules with different band structures(R6G,CV,MB,PNTP)can be improved through polarization direction or temperature changes without the necessity to redesign the SERS substrate.This work provides a novel insight into the SERS substrate design based on CM and is expected to be applied to other two-dimensional materials.

Au@Ag Core-shell Nanorods Self-assembled on Polyelectrolyte Multilayers for Ultra-High Sensitivity SERS Fiber Probes

We demonstrated a chemical process in the fabrication of a SERS fiber probe with an ultrahigh sensitivity.The synthesis was carried out by preparing Au@Ag core-shell nanorods (Au@Ag-NRs) selfassembled on polyelectrolyte (PE) multilayers,for which Au@Ag-NRs were controlled by adjusting the silver layer thickness.The effect of silver layer thickness of Au@Ag-NRs on the SERS performance of the fiber probe was investigated.The SERS fiber probe shows the best performance when the silver layer thickness is controlled at 8.57 nm.Under the condition of optimizing silver layer thickness,the fiber probe exhibits ultra-high sensitivity (i e,10^(-10) M crystalline violet,CV),good reproducibility (i e,RSD of 3.5%) and stability.Besides,electromagnetic field distribution of the SERS fiber probe was also investigated.The strongest enhancement is found within the core of fiber,whereas a weakened electromagnetic field exists in the fiber cladding layer.The SERS fiber probe can be a good candidate in ultra-trace detection for biomedical and environmental areas.

Raman and Surface-enhanced Raman Scattering of Chlorophenols

Raman spectrum is a powerful analytical tool for determining the chemical information of compounds. In this study, we obtained analytical results of chlorophenols（CPs） molecules including 4-chlorophenol（4-CP）, 2,6-dich- lorophenol（2,6-DCP） and 2,4,6-trichlorophenol（2,4,6-TCP） on the surface of Ag dendrites by surface-enhanced Raman scattering（SERS） spectra. SEM images indicate that the SERS substrate of Ag dendrites is composed of a large number of polygonal nanocrystallites, which self-assembled into a 3D hierarchical structure. It was found that there were distinct differences for those three molecules from Raman and SERS spectra. This indicates that SERS could be a new tool of detection technique regarding trace amounts of CPs.

Controllable Silver Plating on Silica for Surface-enhanced Raman Scattering

We proposed a facile and rapid method for preparing silica-silver core-shell（SSCS） substrates to use Ag electroless plating on SiO2@Au-seed particles.UV-Vis-NIR absorption spectrometer and SEM were employed to monitor the reaction process of the formation of Ag on the surfaces of silica beads,and the optical resonance of the substrate could shift from visible to NIR region.It has been found that surface-enhanced Raman scattering（SERS） enhancement changes with the electroless plating time and the SSCS substrate with the plating time of 90 s（90SSCS） shows the strongest SERS response under the laser excitation at 514.5 nm.Signals collected over multiple spots and substrate of rhodamine 6G（R6G） resulted in a relative standard deviation（RSD） of 9.75%.The calculated enhancement factor（EF） was approximately 105 ＂106.SSCS substrate exhibits high SERS performance,which is due to electromagnetic SERS enhancement with additional localization field within closely packed Ag nanoparticles decorated on the SiO2 nanoparticles.And this substrate presents tunable and broad localized surface plasmon resonance（LSPR）,so this method may open a new way for SERS studies with other laser excitation.

Molybdenum Nanoscrews:A Novel Non-coinage-Metal Substrate for Surface-Enhanced Raman Scattering

For the first time, Mo nanoscrew was cultivated as a novel non-coinage-metal substrate for surface-enhanced Raman scattering(SERS). It was found that the nanoscrew is composed of many small screw threads stacking along its length direction with small separations. Under external light excitation, strong electromagnetic coupling was initiated within the gaps, and many hot-spots formed on the surface of the nanoscrew, which was confirmed by high-resolution scanning near-field optical microscope measurements and numerical simulations using finite element method. These hotspots are responsible for the observed SERS activity of the nanoscrews. Raman mapping characterizations further revealed the excellent reproducibility of the SERS activity. Our findings may pave the way for design of low-cost and stable SERS substrates.

Self-assembly 2D plasmonic nanorice film for surface-enhanced Raman spectroscopy

As an ultrasensitive sensing technology,the application of surface enhanced Raman spectroscopy(SERS)is one interesting topic of nano-optics,which has huge application prospectives in plenty of research fields.In recent years,the bottleneck in SERS application could be the fabrication of SERS substrate with excellent enhancement.In this work,a two-dimensional(2D)Ag nanorice film is fabricated by self-assembly method as a SERS substrate.The collected SERS spectra of various molecules on this 2D plasmonic film demonstrate quantitative detection could be performed on this SERS substrate.The experiment data also demonstrate this 2D plasmonic film consisted of anisotropic nanostructures has no obvious SERS polarization dependence.The simulated electric field distribution points out the SERS enhancement comes from the surface plasmon coupling between nanorices.And the SERS signals is dominated by molecules adsorbed at different regions of nanorice surface at various wavelengths,which could be a good near IR SERS substrate for bioanalysis.Our work not only enlarges the surface plasmon properties of metal nanostructure,but also exhibits the good application prospect in SERS related fields.

The Fabrication and Detection Performance of High Sensitivity Au-Ag Alloy Nanostar/Paper Flexible Surface Enhanced Raman Spectroscopy Sensors

Au-Ag alloy nanostars based flexible paper surface enhanced Raman spectroscopy sensors were fabricated through simple nanostar coating on regular office paper,and the surface enhanced Raman spectroscopy detection performances were investigated using crystal violet dye analyte.Au-Ag nanostars with sharp tips were synthesized via metal ions reduction method.Transmission electron microscope images,X-Ray diffraction pattern and energy dispersive spectroscopy elemental mapping confirmed the nanostar geometry and Au/Ag components of the nanostructure.UV-Vis-NIR absorption spectrum shows wide local surface plasmon resonance induced optical extinction.In addition,finite-difference time-domain simulation shows much stronger electromagnetic field from nanostars than from sphere nanoparticle.The effect of coating layer on Raman signal intensities was discussed,and optimized 5-layer coating with best Raman signal was obtained.The Au-Ag nanostatrs homogeneously distribute on paper fiber surface.The detection limit is 10-10 M,and the relationship between analyte concentrations and Raman signal intensities shows well linear,for potential quantitative analysis.The calculated enhancement factor is 4.795×10^(6).The flexible paper surface enhanced Raman spectroscopy sensors could be applied for trace chemical and biology molecule detection.

Selective synthesis of three-dimensional ZnO@Ag/SiO2@Ag nanorod arrays as surface-enhanced Raman scattering substrates with tunable interior dielectric layer

We describe the synthesis of three-dimensional(3D) multilayer ZnO@Ag/SiO2@Ag nanorod arrays by the physico–chemical method. The surface-enhanced Raman scattering(SERS) performance of the 3D multilayer Zn O@Ag/SiO2@Ag nanorod arrays is studied by varying the thickness of dielectric layer SiO2 and outer-layer noble Ag. The 3D Zn O@Ag/SiO2@Ag nanorod arrays create a huge number of SERS "hot spots" that mainly contribute to the high SERS sensitivity. The great enhancement of SERS results from the electron transfer between ZnO and Ag and different electromagnetic enhancements of Ag nanoparticles(NPs) with different thicknesses. Through the finite-difference time-domain(FDTD) theoretical simulation, the enhancement of SERS signal can be ascribed to a strong electric field enhancement produced in the 3D framework. The simplicity and generality of our method offer great advantages for further understanding the SERS mechanism induced by the surface plasmon resonance(SPR) effect.

APPLICATION OF SURFACE-ENHANCED RAMAN SPECTORSCOPY FOR CHARACTERIZING HUMIC SUBSTANCES

Surface-enhanced Raman Spectroscopy(SERS)has been used to characterize hurnic substances.By using HNO_3 -roughened silver foils as the enhancing surface,both fluorescence quenching and strong SERS signals have been observed at the same time.The results obtained herein show that SERS is a particularly sensitive and highly selective technique for the characterization of humic substances in the environment. Humic substances axe receiving ever-inereasing attention because of their importance in the environment. Very recently,we have reported the first successful application of Raman spectroscopy for characterizing humic substances.In this present paper,the application of surface-enhanced Raman spectroscopy(SERS)for humic substances has further been investigated.To our knowledge,no such studies have previously been reported.The results obtained herein dearly demonstrate that SERS has a great deal of promise as an analytical method for“In Situ”characterizing humic substances in the environment.

Surface-enhanced Raman scattering sensor based on fused biconical taper zone of optical fiber

In this paper, a novel surface-enhanced Raman scattering （SERS） sensor combined with fused biconical taper fiber （FBTF） and film coated with silver sols is proposed. This structure is designed to significantly increase the SERS active surface when the length of the taper is increased and the radius is reduced, since the penetration depth is inversely proportional to the taper radius and proportional to the taper length according to the fiber-optic evanescent-wave theory. Based on the SERS sensing principle, the feasibility of FBTF sensor is analyzed in this paper. As a result, the Raman spectrum of R6G is obtained from the fused biconical taper zone surface coating with the silver sols in our experiments. The detected concentration is up to 10-7mol/L.

用SERS研究一种新的钌(Ⅱ)联吡啶配合物及其与DNA的作用机理

着重讨论了用ＳＥＲＳ研究Ｒｕ（ｂｐｙ）２ｄｐｐｚ配合物及其与ＤＮＡ作用的机理。当这种钌配合物与ＤＮＡ发生作用时，只是它的ｄｐｐｚ配体插入了ＤＮＡ双链的碱基对中，与碱基对形成了共轭体系，影响了Ｒｕ 配合物的ＭＬＣＴ跃迁，产生了荧光，同时也在拉曼谱图和电子吸收谱图上有所表现。

适配体调控高SERS活性金纳米检测多菌灵

利用柠檬酸三钠还原氯金酸(HAuCl_4)制备具有较高表面增强拉曼散射(surface-enhanced Raman scattering,SERS)活性的金纳米(gold nanoparticles,AuNPs)溶胶作为基底,结合适配体与靶向物质特异性结合的性质,建立一个稳定性和重现性好的检测靶物质多菌灵(carbendazim,CBZ)的SERS定量检测方法。结果表明,在AuNPs浓度为6 mmol/L、NaCl浓度为15 mmol/L、维多利亚蓝B(Victoria blue B,VBB)浓度为0.25 mmol/L以及适配体溶液浓度为27 nmol/L的条件下,该法检出限为4.13 nmol/L,线性范围6.5 nmol/L~520 nmol/L,相关系数为0.998 8。