Nano Research 漂浮的拉曼增强基底

Floating silver film: A flexible surface-enhanced Raman spectroscopy substrate for direct liquid phase detection at gas–liquid interfaces

Zongyuan Wang, Minyue Li, Wei Wang, Min Fang, Qidi Sun, and Changjun Liu ( )

Collaborative Innovation Center of Chemical Science and Engineering, School of Chemical Engineering and Technology, Tianjin University, Tianjin 300072, China

Received: 15 November 2015 Revised: 4 January 2016 Accepted: 5 January 2016

? Tsinghua University Press and Springer-Verlag Berlin Heidelberg 2016

KEYWORDS

liquid phase detection, surface-enhanced Raman,

gas/liquid,

silver film,

poly(vinylpyrrolidone), electron reduction ABSTRACT

In recent years, surface-enhanced Raman spectroscopy (SERS) has developed rapidly and is used for the detection of molecules and biomolecules in liquids.

However, few studies have focused on SERS using a water surface as the substrate.

A floating metal film on water is desirable for an enhanced SERS performance.

In this work, silver nanoparticles (Ag NPs) encased in poly(vinylpyrrolidone) films (Ag-PVP films) were synthesized on the surface of an aqueous solution by room temperature electron reduction. A floating silver film on a water surface was thereby achieved and is reported for the first time. The synthesized Ag-PVP film is an excellent flexible substrate for SERS and has other potential appli-cations. Using the floating silver film as a flexible SERS substrate, 10–11 M of 4-aminothiophenol, 10–6 M of riboflavin, 10–9 M of 4-mercaptobenzoic acid, 10–7 M of 4-mercaptophenol, and 10–7 M of 4-aminobenzoic acid are identified, demonstrating potential use for the floating substrate in the liquid-phase detection of molecules.

1Introduction

Surface-enhanced Raman spectroscopy (SERS) is a powerful technique used for the detection of molecules and biomolecules and it has several outstanding advantages, including single-molecule sensitivity, molecular specificity, and insensitivity to quenching [1–7]. Coinage metals (Ag, Au, and Cu) are the most commonly used SERS substrates [8]. Numerous strategies have been developed to synthesize flexible and efficient substrates, including self-assembly, atomic layer deposition, spin-coating, electron beam lithography, and electrochemical methods [9–14]. Most substrates consist of metal nanoparticle (NP) arrays, where the metal NPs are fixed on a support, such as a glass slide, silicon wafer, sheet of mica, or a smooth metal surface (including both Au and Pt) [15]. The greatest enhancement occurs at a so-called “hot-spot” at the nanogaps between the NPs [15, 16]. The size of the metal NPs and the interparticle distances both

Nano Research 2016, 9(4): 1148–1158 DOI 10.1007/s12274-016-1009-x Address correspondence to ughg_cjl@https://www.wendangku.net/doc/9c14472773.html,

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have significant effects on SERS enhancement [17, 18]. In recent years, SERS has been used as a reliable tool for the study of mechanisms and for the detection of molecules in liquids [16, 19–21]. For the SERS detection of molecules in liquids, the solution containing the target molecules is placed on an SERS substrate or added to a Ag or Au colloid. Subsequently, information about both the concentration and composition can be obtained. Commonly, SERS substrates are inelastic and contain nanogaps with a uniform average size. Small target molecules are easily adsorbed on the surfaces of the metal NPs and the molecules can enter the nanogaps. However, some biomolecules are too large to squeeze into these “hot-spots”, leading to a low SERS signal intensity. In the case of colloid detection, it is difficult to form an aggregated system within analyte-containing liquid because the metal NPs are highly dispersed in the colloids [8, 15]. This also leads to low sensitivity.

Herein, a facile fabrication method for a flexible substrate for the direct SERS detection of target molecules in a liquid phase has been developed. Ag particles encased in poly(vinylpyrrolidone) films (Ag-PVP films) were synthesized at the gas-liquid interface by a one-step electronic reduction procedure. The synthesized Ag-PVP films are able to float on top of water. We controlled the size and interparticle distance of the Ag NPs to form an aggregated system. The Ag-PVP film proved to be a flexible substrate. The flexible SERS substrate was applied to five kinds of target molecules to demonstrate its efficiency as a substrate for achieving direct SERS detection of molecules in a liquid phase.

2 Experimental

2.1 Fabrication of floating Ag-PVP Films

The Ag-PVP films were synthesized via direct reduction on the surface of a pre-prepared solution consisting of AgNO 3 and poly(vinylpyrrolidone) (PVP) (Sigma- Aldrich, M W of approximately 1,300,000). First, AgNO 3 and PVP were added to water to prepare the AgNO 3/ PVP solution. Subsequently , 1.2 mL of the pre-prepared AgNO 3/PVP solution was placed in a glass bowl. The glass bowl was subsequently placed in a quartz tube

for room temperature electron reduction, as shown

in Fig. S1 (in the Electronic Supplementary Material (ESM)). The electron reduction was conducted at room temperature under vacuum conditions (approximately 200 Pa) using glow discharge plasma as the electron source [22–24]. Argon was used as the plasma generating gas. A voltage of 500 V was applied to the electrode; subsequently, the argon was ionized, and argon glow discharge plasma formed. The plasma contained many electrons and under this environment; the Ag + reduced to Ag 0. Unless otherwise specified, the reduction time was 3 min. A rapid reduction was established. A series of Ag ion concentrations (2.5, 5, 10, 20, and 50 mM) were investigated. The PVP concentration was 6.67 mg/mL. The synthesized films were denoted as Ag-PVP-2.5, Ag-PVP-5, Ag-PVP-10, Ag-PVP-20, and Ag-PVP-50, respectively. 2.2 Characterization

The X-ray diffraction (XRD) patterns of the samples were recorded on a Rigaku D/Max-2500 diffractometer at a scanning speed of 6°/min over the 2θ range of 10°–90°. The diffractometer was equipped with a Ni- filtered Cu K α radiation source (λ = 1.54056 ?). The phase was identified via comparison to the Joint Committee on Powder Diffraction Standards (JCPDSs). The X-ray photoelectron spectroscopy (XPS) analyses were performed with a Perkin Elmer PHI-1600 spectrometer using Mg K α (h ν = 1,486.6 eV) radiation. The binding energies were calibrated using the C1s peak (284.6 eV) as a reference. Transmission electron microscopy (TEM) measurements were performed on a Philips Tecnai G2F20 system. The Ag-PVP films were deposited on a copper grid and observed following air drying. The UV–vis absorption spectra of the samples were recorded with a UV-2600 UV–vis spectrophotometer (Shimadzu Corporation). Fourier transform infrared spectra (FTIR) spectra were obtained using a Thermo Nicolet’s Nexus 870 system at room temperature in air. The FTIR spectra were recorded over 32 scans at a resolution of 4 cm –1. 2.3 SERS measurements

Normal Raman and SERS spectra were acquired using an inVia reflex Renishaw Raman Spectroscopy System,

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with a 532 nm laser line as the excitation light. The laser power was 0.35 or 0.07 mW. Typically, the Ag-PVP films were exposed to the laser light three times (for 3 s each time) to obtain the cumulative Raman spectra. The Ag-PVP-50 films were used as SERS substrates to detect 4-aminothiophenol (4-ATP), riboflavin, 4-mercaptobenzoic acid (4-MBA), 4- mercaptophenol (4-MPh), and 4-aminobenzoic acid (4-ABA). After the Ag-PVP-50 film was prepared, an ethanol–water solution containing the target molecules was injected into the solution under the Ag-PVP-50 film. The surface of the Ag-PVP-50 film was irradiated with the laser to obtain the SERS spectra. All the spectra were baseline corrected. The analytical enhancement factor (AEF) is defined and calculated by Eq. (1)

AEF = (I SERS /C SERS )/(I RS /C RS ) (1)

where C SERS and C RS are the target molecule con-centrations, and I SERS and I RS are the Raman intensities of a certain vibration band obtained on the Ag-PVP film and non-SERS substrates, respectively. I SERS and I RS were obtained under identical experimental conditions (such as laser wavelength, laser power, microscope objective, lenses, and spectrometer).

3 Results and discussion

3.1 Morphology and structure

The macroscopic morphologies of the Ag-PVP films prepared from the various Ag ion concentrations were observed using a digital camera, as shown in Fig. 1(a). The original AgNO 3/PVP solution was colorless and transparent. Following the reduction reaction, uniform Ag-PVP films were observed at the Ar and water interface. As the concentration of Ag ions increased, the color of the solution changed from light yellow to brown. The Ag-PVP films were continuous and covered the entire surface of the solution. The cross-sectional views of the films demonstrate that the solutions under the Ag-PVP films are clear and colorless, suggesting that the film formed only at the surface of the solution. This synthesis strategy is reported for the first time. These observations indicate a novel and promising strategy for the preparation of noble-metal film materials. This method has many advantages; it is simple (one step), fast (a few min), economic, and green (a reduction agent is not required and mild operational conditions exist). This method is versatile,

and can be used for other noble-metal polymer films

Figure 1 (a) Digital photographs of Ag-PVP films synthesized from solutions with various Ag ion concentrations. (b) XRD for Ag-PVP-50, under reduction times of 1, 3, and 6 min; (c) XPS result for Ag-PVP-50. (d) FTIR spectra of PVP, plasma-treated PVP, AgNO 3mixture, and plasma-treated PVP; the Ag-PVP-x (x = 1, 2, and 3) samples consist of a mixture of 1 mL of AgNO 3 solution and 0.1 mL of PVP solution (20 mg/mL), and the Ag ion concentrations for Ag-PVP-1, Ag-PVP-2, and Ag-PVP-3 are 10, 50, and 100 mM, respectively.

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by varying the types of metal ions or polymer used. For example, photographs of Ag-poly(ethylene glycol) (Ag-PEG) and Au-PVP films are shown in Fig. S2 (in the ESM). Typical characterization procedures were performed to investigate the composition and structure of the films. The XRD and XPS results for the Ag- PVP-50 films are shown in Figs. 1(b) and 1(c), and the results demonstrate that the Ag ions were reduced to Ag 0. The FTIR of the PVP , and the PVP mixed with various amounts of AgNO 3, before and after the plasma reaction, are shown in Fig. 1(d) and Fig. S3 (in the ESM). Before and after the reaction, the spectra of the PVP show bands at 1,658, 1,290, and 1,019 cm –1, which can be attributed to C=O, C–O, and C–N stretching, respectively . The Ag-PVP-x (x = 1, 2, 3) samples consist of a mixture of 1 mL of AgNO 3 solution and 0.1 mL of PVP solution (20 mg/mL). The Ag ion concentrations for the Ag-PVP-1, Ag-PVP-2, and Ag-PVP-3 samples were 10, 50, and 100 mM, respectively. For the Ag- PVP-1, Ag-PVP-2, and Ag-PVP-3 spectra, an extra peak can be observed at 1,034 cm –1. This is due to the coordination and conjugation of the Ag NPs with the N atoms of the C–N bonds. The FTIR results indicate that the PVP polymer forms a film and hybridizes with the Ag NPs. The peaks at 1,385 and 825 cm –1 are

attributed to excess NO 3–

(Fig. S3 in the ESM).

The formed noble-metal PVP films exhibit excellent stability against surface oxidation. In the case of the Ag-PVP films, the Ag NPs are entrapped within the PVP polymers. This enhances the surface oxidation resistance of the Ag NPs. XPS measurements were

also performed to investigate the surface oxidation

resistance of the of the Ag-PVP samples. The results are shown in Fig. S4 (in the ESM). Following drying, and storage under room temperature conditions for 3 months, the Ag on the surface of the Ag-PVP-50 sample still has a valance state of Ag 0, indicating excellent surface oxidation resistance.

The microscopic morphologies of the Ag-PVP films were observed by TEM, as shown in Fig. 2 and Fig. S5 (in the ESM). All of the Ag-PVP samples showed similar microscopic morphologies, and the Ag NPs were encased in the continuous PVP membrane. Figure 2(a) shows the edge of PVP membrane and it can be observed that the edge of the membrane is torn. Based on this observation, we speculated that the Ag-PVP films are flexible. This speculation was verified by further characterization, which will be discussed further in the document.

The high-resolution transmission electron microscopy (HRTEM) images of the Ag-PVP-10 and Ag-PVP-50 samples are shown in the insets of Figs. 2(a) and 2(b). Most of the Ag NPs in the Ag-PVP-10 sample are monocrystalline, and the (111) and (200) facets of the metallic Ag can be clearly observed, indicating good crystallinity. However, most of the Ag NPs in the Ag- PVP-50 consist of twin crystals. A Fourier transform analysis of the HRTEM image of the twin crystal showed the existence of five crystallographic axes. The fivefold-twinned crystals were formed by defects that developed during the crystal growth throughout

the rapid reduction process [25]. As the Ag ion

Figure 2 TEM images of (a) Ag-PVP-10 and (b) Ag-PVP-50; the insets in (a) and (b) show HRTEM images and Fourier transform analyses of Ag-PVP-10 and Ag-PVP-50. (c) Average particle size and interparticle distance of Ag-PVP films synthesized from solutions with different Ag ion concentrations.

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concentration increased, the distributions of the Ag NPs changed significantly. The size of the Ag NPs increased as the initial concentration of Ag ions increased, i.e., the Ag particle sizes were 8.2, 8.3, 11.2, 14.2, and 30.4 nm for the Ag-PVP-2.5, Ag-PVP-5, Ag-PVP-10, Ag-PVP-20, and Ag-PVP-50 samples, res-pectively. Simultaneously, the interparticle distances decreased as the size of the Ag NPs increased. For example, in the case of the Ag-PVP-20 sample, only slight aggregation of the Ag NPs exists, whereas in the case of the Ag-PVP-50 sample, the aggregation is extensive. The interparticle distances between the Ag NPs were 30, 19, 11, 9.5, and 4.5 nm for the Ag-PVP-2.5, Ag-PVP-5, Ag-PVP-10, Ag-PVP-20, and Ag- PVP-50 samples, respectively. The particle sizes and interparticle distances are shown in Fig. 2(c), as a function of the Ag ion concentration. The particle size and interparticle distance have

significant impacts on the surface plasmon resonance

(SPR) absorption. Figure 3 shows the UV–vis spectra

of the Ag-PVP films. The spectra were obtained by

placing the Ag-PVP films on a glass substrate and

immediately measuring the spectrum in a wet state.

In the case of the Ag-PVP-2.5, Ag-PVP-5, and Ag-

PVP-10 samples, the UV–vis spectra contain one single

SPR band, which is due to the spherical Ag NPs [18].

As the Ag ion concentration increased from 2.5 to 5 to

10 mM, the absorption intensity of the band gradually

increased and the band slightly red-shifted from 420.0

to 425.0 to 430.5 nm. The SPR band of the spherical

Figure 3 UV–vis spectra of Ag-PVP films synthesized from

solutions with different Ag ion concentrations. Ag corresponds to the dipole resonance of the Ag NPs [18]. As the particle size increases, the dipole moment also increases, which provides an explanation for the slight red shift of the SPR peak. The enhanced absorption intensity is due to the increased quantity of the Ag NPs.

In the case of the UV–vis spectra of the Ag-PVP-20 and Ag-PVP-50 samples, shoulder peaks can be observed at about 560 and 650 nm, respectively, in addition to the Ag NP SPR bands (415.5 and 420.0 nm, respectively). The appearance of the shoulder peaks confirms that the Ag NPs have aggregated, and this corresponds with the TEM results [16]. The UV–vis spectra prove that an aggregated system of Ag NPs exists within the PVP organic thin film of the Ag- PVP-50 sample, which should be beneficial for Raman signal enhancement. 3.2 Flexible optical properties To confirm the flexibility of the Ag-PVP films, further

UV–vis measurements were performed. The Ag-PVP-

50 film was placed on a glass substrate and its UV–vis

spectra were recorded as the sample was allowed to

air dry. The results are shown in Fig. 4(a). During the

air drying process, the Ag NP SPR band slightly red-

shifted from 420.0 to 438.0 nm and the aggregated

Ag NP peak increased in intensity and red-shifted to

720 nm. When the interparticle distance is sufficiently

small, the induced electric fields of the metal particles

overlap with each other and the resonance of the localized surface plasmon exhibits a redshift [17]. Coupling of the induced electric fields occurs when the distance between two metal NPs is approximately the diameter of a single particle or less [17]. The red shifts of the two peaks in the Ag NPs/PVP films indicate that the films gradually further aggregated. As the film changed from the wet state to the dry state, the PVP membrane shrunk and the interparticle distance decreased. Therefore, it can be confirmed that the Ag- PVP films are flexible. Similar phenomena were also observed for the Ag-PVP-20 sample (Fig. S6 in the ESM).

A flexible interparticle distance provides a flexible space for the adsorption of molecules of various sizes. We further proved that the insertion of target molecules

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will also change the UV–vis absorption of a film. Figures 4(b) and 4(c) show the UV–vis spectra of a drying Ag-PVP-50 film following the addition of 4-ATP and riboflavin molecules.

The addition of 4-ATP and riboflavin molecules resulted in a similar red-shift in the absorption bands as the sample changed from a wet state to a dry state. A comparison of the UV–vis spectra of the Ag-PVP-50 sample prior to, and following the addition of 4-ATP and riboflavin, shows that the addition of 4-ATP and riboflavin caused a blue-shift in the absorption band (Fig. 5) for both the wet and dry films. Larger target molecules resulted in larger blue shifts. This blue shift suggests that some of the 4-ATP and riboflavin molecules became embedded into the gaps between the NPs, which reduced the aggregation of the Ag NPs, as shown in Fig. 5. The results show that the Ag-PVP films demonstrate flexible optical properties. This further proves that the Ag-PVP films are flexible, and more importantly, that the interparticle distance can spontaneously adjust to accommodate the size of the added molecules. This insertion of the target molecules within the gaps between the NPs suggests that these films would function as good SERS substrates, since electromagnetic field enhancements most strongly occur at the “hot spots” in the NP gaps [15, 16].

Figure 5 Comparison of the UV–vis spectra of the wet and dry Ag-PVP-50 films, prior to, and following the addition of 4-ATP and riboflavin. The concentration of both the 4-A TP and riboflavin in the solution under the Ag-PVP film was 10–5 M.

3.3 SERS performance at gas/liquid interface It is well known that SERS is enhanced by the aggregation of Ag NPs [8, 15]. The Ag-PVP-50 film was selected as an SERS substrate to detect molecules of various sizes because the Ag NPs were significantly aggregated within it. The liquid phase SERS detection process is illustrated in Fig.

6(a). Following the

Figure 4 UV–vis spectra of (a) Ag-PVP-50, (b) Ag-PVP-50 with added 4-ATP, and (c) Ag-PVP-50 with added riboflavin during the

air drying process. The concentration of 4-ATP and riboflavin in the solution under the Ag-PVP film are both 10–5 M.

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preparation of the Ag-PVP-50 film, a certain amount of ethanol-water solution containing the target molecule was injected into the solution under the Ag-PVP-50 film.

The surface of the Ag-PVP-50 film was subsequently irradiated with a laser. The SERS spectra of the target molecules, 4-ATP, riboflavin, 4-MBA, 4-MPh, and 4-ABA were subsequently measured.

Figure 6(b) shows the SERS spectra and normal Raman spectra of 4-ATP . The concentration of the 4-ATP in the different solutions was 10–5, 10–7, 10–9, and 10–11 M. The bands at 1,036, 924, and 625 cm –1 can be assigned to the C=O stretching, pyridine ring breathing, and deformation bands of the Ag-PVP com-plexes, respectively. The slight change in the intensity and peak position of these peaks is due to the insertion of the 4-ATP molecules between the Ag NPs and the PVP chains [19, 26].

At all concentrations, the SERS peaks for the 4-ATP are clearly visible, as shown in Fig. 6(b). The peaks at 1,573, 1,439, 1,392, and 1,142 cm –1 can be assigned to the 4-ATP aromatic ring modes 8b, 19b, 3, and 9b, respectively, which possess b 2-type bands, whereas the peaks at 1,176, 1,072, and 1,006 cm –1 can be assigned to ring modes 9a, 7a, and 18a, respectively, which possess a 1-type bands [27, 28]. As the concentration of 4-ATP decreased, the intensity of the peaks also decreased. However, even at an extremely low con-centration (10–11 M), both the a 1 and b 2-type vibrations are can still be clearly observed, indicating that this method is very sensitive.

The normal Raman spectra for a 10–2 M 4-ATP ethanol solution are shown in Fig. 6(b). Although the concentration of 4-ATP is quite high, there are no peaks observed for 4-ATP; the peaks attributed to the ethanol solvent (1,487, 1,456, 1,278, 1,095, 1,054, and 883 cm –1) are the only peaks that can be observed. This comparison indicates that the use of the Ag-PVP-50 film greatly enhances the Raman signal.

The normal Raman spectra of solid 4-ATP is shown in Fig. 6(b). The spectral features are similar to those in the SERS spectra. However, the peak positions are shifted to higher wavenumbers; a similar phenomenon has been reported in previously published SERS results [29]. A notable observation is that the b 2-type bands are more pronounced than the a 1

-type bands

Figure 6 (a) Schematic diagram of liquid phase SERS detection. (b) The SERS and normal Raman spectra of 4-A TP; the laser power was 0.35 mW; the intensity of the normal Raman spectra of solid 4-A TP has been amplified to provide a clearer view. (c) The SERS and normal Raman spectra of riboflavin; the laser power was 0.07 mW.

in the SERS spectra, which contrasts with the normal Raman spectra of solid 4-ATP . The enhanced b 2-type bands are due to a chemical enhancement mechanism [30, 31], and it can be inferred that a charge-transfer occurs between the 4-ATP and Ag-PVP film substrate. Charge-transfer and electromagnetic enhancements should function as collaborative effects in SERS

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detection.

The enhancement factor (EF) is a general parameter applied to evaluate the performance of the SERS substrate. However, many factors, such as the laser scattering volume and the scale of adsorbed molecules, render the intrinsic SERS enhancement factor difficult to estimate. Thus, we used the AEF to evaluate the SERS performance of the Ag-PVP films [32]. The details regarding the calculation are described in the method section. The AEF is particularly suitable in the case of SERS active liquids [32]. For the band of 4-ATP at 1,072 cm –1, the AEF values are calculated to be 1.0 × 105, 5.4 × 106, 2.3 × 108, and 3.8 × 109, corresponding to the concentrations of 10–5, 10–7, 10–9, and 10–11 M, respectively. According to reported studies [33–36], the EF value of 4-ATP on a variety of SERS substrates has reached 109 ({331}-faceted trisoctahedral Au nanocrystals), 2 × 108 (Au NPs on paper), 107 (Ag films), and 3.63 × 105 (Ag NPs decorated nanometric apertures). Using our method of phase detection, the AEF value could be greater than 109 when the con-centration of 4-ATP is 10–11 M, which is equivalent to, or greater than, the values obtained in most of the above reported works. In terms of the detection limit, this method could detect 4-ATP concentrations as low as 10–11 M. The aforementioned previous works reported 4-ATP detection limits of 3 × 10–7, 1 × 10–9, 1 × 10–10, and 1 × 10–10 M, respectively [33–36]. Therefore, the detection limits measured for the 4-ATP molecules on the floating Ag-PVP films are comparable with the highest reported detection limit values for various SERS substrates. This result indicates that the Ag-PVP films demonstrate an outstanding SERS enhancement performance, including sensitivity and Raman signal enhancement.

Figure 6(c) shows the SERS spectra and normal Raman spectra of riboflavin. The riboflavin concen-trations in the different solutions were 10–4, 10–5, and 10–6 M. Prominent vibrational bands could be observed at 552, 621, 630, 743, 802, 812, 840, 1,084, 1,138, 1,159, 1,226, 1,284, 1,312, 1,349, 1,404, 1,458, 1,501, 1,523, 1,570, and 1,627 cm –1, corresponding to the reported articles [37]. In the case of riboflavin, the enhancement of the vibrational bands is sensitive to its concentration. The intensity of the Raman signal decreases sharply when the riboflavin concentration is diluted to 10–6 M.

However, the major bands at 552, 1,084, 1,159, 1,226,

1,284, 1,349, 1,458, and 1,627 cm –1 are still observable. The normal Raman spectra for a 10–3 M riboflavin aqueous solution show no peaks.

In the case of the riboflavin band at 1,349 cm –1, the AEF values are calculated to be 1.3 × 103, 3.7 × 103, and 6.5 × 103 for the concentrations of 10–4, 10–5, and 10–6 M, respectively. The results indicate that the Ag- PVP film, as an SERS substrate, can not only be applied for the detection of small molecules (4-ATP), but is also suitable the detection of molecules with a larger size (riboflavin).

The SERS and normal Raman spectra of 4-MBA, 4-MPh, and 4-ABA are shown in Fig. S7 (in the ESM). In the case of the SERS spectra of 4-MBA, the bands at 1,583, 1,073, and 1,182 cm –1 can be assigned to the 12 and 8a stretching modes, and the C–H bending of the aromatic ring, respectively, whereas the bands at 1,363 and 1,143 cm –1 are due to the symmetric stretching vibrations and bending modes of dissociated carboxyl groups (COO –), respectively (Fig. S7(a) in the ESM) [38, 39]. In the case of the SERS spectra of 4-MPh, the band at 1,074 cm –1 is due to the ring breathing mode, whereas the bands at 1,594, 1,579, 1,490, 1,170, 1,003, 828, and 633 cm –1 correspond to the ring vibrations of 8a, 8b, 19a, 9a, 18a, 6a, and 12a, respectively (Fig. S7(b) in the ESM) [40]. In the case of the SERS spectra of 4-ABA, the ring modes of 8a and 8b at 1,602 cm –1, 19a at 1,514 cm –1, 19b at 1,496 cm –1, 7a ′ at 1,182 cm –1, 9a at 1,149 cm –1, 7a at 1,133 cm –1, and 1 at 855 cm –1 can be observed (Fig. S7(c) in the ESM) [41]. The band at 1,454 cm –1 and the board band at 1,350–1,400 cm –1 are due to the symmetric and asymmetric stretching vibrations of COO –, respectively [42]. The normal Raman spectra of solid 4-MBA, 4-MPh, and 4-ABA all correspond with previously reported results [38, 43, 44]. Compared with the normal Raman spectra, the frequencies of the SERS peaks have shifted for the three target molecules; however, the spectra are com-parable with previously published results, even at low concentrations (10–9 or 10–7 M) [38–44]. The normal Raman spectra of the high concentration liquid solutions (10–3 or 10–2 M) do not show any peaks attributed to the target molecules, again indicating that a significant enhancement occurs when the Ag-PVP-50 films are used as SERS substrates. The AEF values of 4-MBA,

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4-MPh, and 4-ABA were also calculated. For the band of 4-MBA at 1,583 cm –1, the AEF values are calculated to be 1.2 × 105, 4.6 × 106, and 1.9 × 108 for the con-centrations of 10–5, 10–7 and 10–9 M, respectively. In the case of the band of 4-MPh at 1,074 cm –1, the AEF values are calculated to be 1.9 × 103, 7.1 × 104, and 3.7 × 105 for the concentrations of 10–3, 10–5, and 10–7 M, respectively . In the case of the band of 4-MBA at 1,602 cm –1, the AEF values are calculated to be 3.2 × 103, 1.7 × 105, and 5.0 × 106 for the concentrations of 10–3, 10–5, and 10–7 M, respectively.

4 Conclusions

A fabrication method for Ag-PVP films at the gas- liquid interface of an aqueous solution has been demonstrated. Based on the analysis of UV–vis spectra, it can be concluded that these Ag-PVP films are flexible. At high Ag ion concentrations, the Ag NPs form an aggregated system on top of water. Since PVP is a flexible support, the interparticle distances in the films spontaneously adjust to accommodate molecules of different sizes and target molecules of various sizes can easily embed into the “hot spots” at the gaps between the NPs. The SERS enhancement effect of the Ag-PVP films was investigated using five kinds of target molecules. All the SERS spectra displayed distinctive fingerprint features, even at low target molecule concentrations. The SERS results prove that this strategy can be used to directly detect target molecules in liquids, with excellent SERS perfor-mance. In addition, the electron reduction method can be used for the preparation of other floating noble metal-PVP films. Beyond SERS, the developed floating noble metal-PVP film is promising for use in other applications, such as catalysts [45, 46]. Further progress will be reported in our future works.

Acknowledgements

This work was supported by the National Natural Science Foundation of China (No. 91334206). The authors thank Dr. Jeanne Wynn for her help in the use of English and Dr. Tao Xue for Raman mea-surement. The authors declare no competing financial interests.

Electronic Supplementary Material : Supplementary material (a schematic representative of the glow- discharge plasma generator; the digital photos of Ag-PEG and Au-PVP films; FTIR spectra of PVP , PVP treated by plasma, mixture of AgNO 3 and PVP treated by plasma; XPS result of Ag-PVP-50 after drying and saving under atmosphere at room temperature for 3 months; TEM images of Ag-PVP-2.5, Ag-PVP-5 and Ag-PVP-20; UV–vis spectra of Ag-PVP-20; SERS spectra and normal Raman spectra of 4-MBA, 4-MPh and 4-ABA) is available in the online version of this article at https://www.wendangku.net/doc/9c14472773.html,/10.1007/s12274-016-1009-x.

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Ram_拉曼光谱

拉曼光谱 拉曼光谱学是用来研究晶格及分子的振动模式、旋转模式和在一系统里的其他低频模式的 一种分光技术。[1]拉曼散射为一非弹性散射，通常用来做激发的激光范围为可见光、近红 外光或者在近紫外光范围附近。激光与系统声子做相互作用，导致最后光子能量增加或减少，而由这些能量的变化可得知声子模式。这和红外光吸收光谱的基本原理相似，但两者 所得到的数据结果是互补的。 通常，一个样品被一束激光照射，照射光点被透镜所聚焦且通过分光仪分光。波长靠近激 光的波长时为弹性瑞利散射。 自发性的拉曼散射是非常微弱的，并且很难去分开强度相对于拉曼散射高的瑞利散射，使 得得到的结果是光谱微弱，导致测定困难。历史上，拉曼分光仪利用多个光栅去达到高度的分光，去除激光，而可得到能量的微小差异。过去，光电倍增管被选择为拉曼散射讯号 的侦测计，其需要很久的时间才能得到结果。而现今的技术，带阻滤波器 (notch filters) 可有效地去除激光且光谱仪或傅里叶变换光谱仪和电荷耦合元件 (CCD) 侦测计 的进步，在科学研究中，利用拉曼光谱研究材料特性越来越广泛。 有很多种的拉曼光谱分析，例如表面增强拉曼效应、针尖增强拉曼效应、偏极拉曼光谱……等。 拉曼光谱的特点： 提供快速、简单、可重复、且更重要的是无损伤的定性定量分析，它无需样品准备，样品可直接通过光纤探头或者通过玻璃、石英、和光纤测量。此外 1 由于水的拉曼散射很微弱，拉曼光谱是研究水溶液中的生物样品和化学化合物的理想工具。 2 拉曼一次可以同时覆盖50-4000波数的区间，可对有机物及无机物进行分析。 相反，若让红外光谱覆盖相同的区间则必须改变光栅、光束分离器、滤波器和检测器

SERS(表面增强拉曼散射)理论

SERS 的物理类模型 物理类模型致力于阐释金属表面局域场的增强，它的主要代表包括表面电磁增强模型和镜像场模型。 1、表面电磁增强模型（Electromagnetic Enhancemant Model ，简记为EM ） 表面电磁增强模型[5~7]又可称为表面等离子体共振模型，它认为一个吸附在金属表面的分子的诱发偶极矩是通过金属椭球由入射场和散射场共同产生的。对于椭球比光波波长小的情况，在频率与偶极表面等离子体共振时，散射场比入射场大，这可以看作是椭球外部空间的场密度的影响。因此拉曼散射场会与金属颗粒的强散射场引起的金属颗粒表面的等离子体振荡发生共振，这种共振的结果使振荡分子产生了非常大的能量。 如图2－1所示，把一个可以看成经典电偶极子的分子放在球形金属颗粒外的r 'ρ处，以频率为ω0的平面波照射，分子偶极子会产生频率为ω的拉曼散射，其偶极矩为： ),(),(00ωαωr E r P P ρρρρ?'=' (2-1) 这里的α'是分子的拉曼极化率而P E ρ包括两部分： ),(),(),(000ωωωr E r E r E LM i P '+'='ρρρρρρ (2-2) 其中i E ?是入射场的场强，LM E ρ是用Lorenz-Mie 理论计算获得的散射场场强。在 观察点r ρ处与拉曼散射相关的电场由下式给出 ),(),(),(ωωωr E r E r E sc dip R ρρρρρρ+= (2-3) 图2－1 纳米颗粒表面增强散射示意图

其中，dip E ρ是球形颗粒不存在时振荡偶极子P ρ发射的场，sc E ρ是由球形颗粒产生的必须满足频率ω的边值问题的散射场。 拉曼散射的强度R I 是远场振幅R E ρ的平方：2/)ex p(),(lim r ikr r E I R kr R ω??∞ →=，增强因子G 定义为0R R I I G =，其中0R I 是在金属球形颗粒不存在时的拉曼强度。 那么在小颗粒的限制下，增强因子可由下式给出： [] 230333033303)(3)1/()1/()(3i n n r g a r i r g a g a r i i n n g a i G ρρρρρρρρρ?+'+'-'+'-?+= (2-4) 这里的i ρ指入射场在r '处的偏振态，也就是()i E r E i ρρ00,='ω，r r n ''=/ρρ，g 和g 0是表达式()()21+-εε在ω和ω0处的值，其中ε是胶体颗粒与周围物质的复合介电函数的比值。 当分子在金属球表面上()a r ='即且入射和散射光场的偏振方向与散射平面垂直时，增强因子将由下式给出： 2 0042215gg g g G +++= (2-5) 当Re(ε)等于-2时，g(或g 0)的值将会变大。这也恰好是激发球形颗粒表面等离子体的条件。此时，G 主要决定于gg 0项，方程(2-5)将变成 2 080gg G = (2-6) 于是根据这一模型，当入射光和散射光的频率满足表面等离体子共振条件时， 就可以得到强的SERS 信号，在这种情况下，G 的值将与()[]41ε''-'成正比式中的ε' 和ε'' 分别为()εRe 和()εIm 。 当球体完全被吸附分子覆盖时，可以对每个分子的拉曼散射光求平均，将每一个吸附分子都认为成一个垂直于表面振动的偶极子，则 2 0)21)(21(g g G ++= (2-7) 于是，对于从吸附在球形金属颗粒上的分子观察到SERS 效应的电磁理论，当下列条件满足时，将能够观察到强的增强：（1）颗粒的尺寸必须小于光的波长λ（2）激发频率或散射频率必须满足表面等离体子共振条件（3）分子不能距表面太远。

拉曼光谱的原理及应用.doc

拉曼光谱的原理及应用 拉曼光谱由于近几年来以下几项技术的集中发展而有了更广泛的应用。这些技术是：CCD检测系统在近红外区域的高灵敏性,体积小而功率大的二极管激光器,与激发激光及信号过滤整合的光纤探头。这些产品连同高口径短焦距的分光光度计,提供了低荧光本底而高质量的拉曼光谱以及体积小、容易使用的拉曼光谱仪。 （一）含义 光照射到物质上发生弹性散射和非弹性散射. 弹性散射的散射光是与激发光波长相同的成分.非弹性散射的散射光有比激发光波长长的和短的成分, 统称为拉曼效应 当用波长比试样粒径小得多的单色光照射气体、液体或透明试样时,大部分的光会按原来的方向透射,而一小部分则按不同的角度散射开来,产生散射光。在垂直方向观察时,除了与原入射光有相同频率的瑞利散射外,还有一系列对称分布着若干条很弱的与入射光频率发生位移的拉曼谱线,这种现象称为拉曼效应。由于拉曼谱线的数目,位移的大小,谱线的长度直接与试样分子振动或转动能级有关。因此,与红外吸收光谱类似,对拉曼光谱的研究,也可以得到有关分子振动或转动的信息。目前拉曼光谱分析技术已广泛应用于物质的鉴定,分子结构的研究谱线特征 （二）拉曼散射光谱具有以下明显的特征： a.拉曼散射谱线的波数虽然随入射光的波数而不同,但对同一样品,同一拉曼谱线的位移与入射光的波长无关,只和样品的振动转动能级有关； b. 在以波数为变量的拉曼光谱图上,斯托克斯线和反斯托克斯线对称地分布在瑞利散射线两侧, 这是由于在上述两种情况下分别相应于得到或失去了一个振动量子的能量。 c. 一般情况下,斯托克斯线比反斯托克斯线的强度大。这是由于Boltzmann分布,处于振动基态上的粒子数远大于处于振动激发态上的粒子数。 （三）拉曼光谱技术的优越性 提供快速、简单、可重复、且更重要的是无损伤的定性定量分析,它无需样品准备,样品可直接通过光纤探头或者通过玻璃、石英、和光纤测量。此外 1 由于水的拉曼散射很微弱,拉曼光谱是研究水溶液中的生物样品和化学化合物的理想工具。 2 拉曼一次可以同时覆盖50-4000波数的区间,可对有机物及无机物进行分析。相反,若让红外光谱覆盖相同的区间则必须改变光栅、光束分离器、滤波器和检测器 3 拉曼光谱谱峰清晰尖锐,更适合定量研究、数据库搜索、以及运用差异分析进行定性研究。在化学结构分析中,独立的拉曼区间的强度可以和功能集团的数量相关。 4 因为激光束的直径在它的聚焦部位通常只有0.2-2毫米,常规拉曼光谱只需要少量的样品就可以得到。这是拉曼光谱相对常规红外光谱一个很大的优势。而且,拉曼显微镜物镜可将激光束进一步聚焦至20微米甚至更小,可分析更小面积的样品。 5 共振拉曼效应可以用来有选择性地增强大生物分子特个发色基团的振动,这些发色基团的拉曼光强能被选择性地增强1000到10000倍。（四）几种重要的拉曼光谱分析技术 1、单道检测的拉曼光谱分析技术 2、以CCD为代表的多通道探测器用于拉曼光谱的检测仪的分析技术 3、采用傅立叶变换技术的FT-Raman光谱分析技术 4、共振拉曼光谱分析技术 5、表面增强拉曼效应分析技术 (五) 拉曼频移,拉曼光谱与分子极化率的关系 1、拉曼频移：散射光频与激发光频之差,取决于分子振动能级的改变,所以它是特征的,与入射光的波长无关,适应于分子结构的分析 2、拉曼光谱与分子极化率的关系 分子在静电场E中,极化感应偶极矩P为静电场E与极化率的乘积 诱导偶极矩与外电场的强度之比为分子的极化率 分子中两原子距离最大时,极化率也最大 拉曼散射强度与极化率成正比例 （六）应用激光光源的拉曼光谱法 应用激光具有单色性好、方向性强、亮度高、相干性好等特性,与表面增强拉曼效应相结合,便产生了表面增强拉曼光谱。其灵敏度比常规拉曼光谱可提高104~107倍,加之活性载体表面选择吸附分子对荧光发射的抑制,使分析的信噪比大大提高。已应用于生物、药物及环境分析中痕量物质的检测。共振拉曼光谱是建立在共振拉曼效应基础上的另一种激光拉曼光谱法。共振拉曼效应产生于激发光频率与待测分子的某个电子吸收峰接近或重合时,这一分子的某个或几个特征拉曼谱带强度可达到正常拉曼谱带的104~106倍,有利于低浓度和微量样品的检测。已用于无机、有

表面拉曼增强效应

表面拉曼增强效应 Fleischmann 等人于1974 年对光滑银电极表面进行粗糙化处理后,首次获得吸附在银电极表面上单分子层吡啶分子的高质量的拉曼光谱。但Fleishmann认为这是由于电极表面的粗糙化，电极真实表面积增加而使吸附的吡啶分子的量增加引起的，而没有意识到粗糙表面对吸附分子的拉曼光谱信号的增强作用。一直到1977年，Van Duyne 和Creighton两个研究组各自独立地发现，吸附在粗糙银电极表面的每个吡啶分子的拉曼信号要比溶液中单个吡啶分子的拉曼信号大约强106倍，指出这是一种与粗糙表面相关的表面增强效应,被称为SERS 效应。 表面增强拉曼散射(SERS)效应是指在特殊制备的一些金属良导体表面或溶胶中,在激发区域内,由于样品表面或近表面的电磁场的增强导致吸附分子的拉曼散射信号比普通拉曼散射(NRS) 信号大大增强的现象。 表面增强拉曼克服了拉曼光谱灵敏度低的缺点, 可以获得常规拉曼光谱所不易得到的结构信息, 被广泛用于表面研究、吸附界面表面状态研究、生物大小分子的界面取向及构型、构象研究、结构分析等, 可以有效分析化合物在界面的吸附取向、吸附态的变化、界面信息等。 近来，研究者主要使用在低维纳米结构基底上附载贵金属纳米颗粒的方法来提高 SERS 的增强性能。尤以 Rajh小组[27]将贵金属纳米颗粒附于 TiO2纳米线上得到强的 SERS 增强效应后，陆续有报道[28-31]

贵金属/低维半导体材料如 Ag/ZnO、Au/TiO2及 Ag/Ga2O3被用作SERS 衬底。这些基底的优良 SERS 增强性能均涉及了金属与半导体之间的协同作用，如 Lee[32]、Fan[33]等小组使用高度阵列化的 ZnO纳米针或纳米棒作为模板，制得 Au/ZnO 或 Ag/ZnO 复合纳米结构，具有较好的SERS 增强性能及重现性。而我们所做的螺旋状纳米氧化锌上负载银单质鲜有报道，其表面拉曼增强在光催化反应，污染物降解等方面存在较大价值，前景广阔。 参考文献： [27] Musumeci A, Gosztola D, Schiller T et al. SERS of Semiconducting Nanoparticles (TiO2 Hybrid Composites) [J]. J. Am. Chem. Soc., 2009, 131: 6040-6041 [28] Sirbuly D?J, Tao A, Law M et al. Multifunctional nanowire evanescent wave optical sensors [J]. Adv. Mater., 2007, 19: 61-66 [29] Yang L, Jiang X, Ruan W et al. Charge-transfer-induced surface-enhanced Raman scattering on Ag?TiO2 nanocomposites [J]. J. Phys. Chem. C, 2009, 113: 16226-16231 [30] Prokes S M, Glembocki O J, Rendell R W et al. Enhanced plasmon coupling in crossed dielectric/metal nanowire composite geometries and applications to surface-enhanced Raman spectroscopy [J]. Appl. Phys. Lett.,

拉曼光谱原理及应用简介

拉曼光谱由于近几年来以下几项技术的集中发展而有了更广泛的应用。这些技术是：CCD检测系统在近红外区域的高灵敏性，体积小而功率大的二极管激光器，与激发激光及信号过滤整合的光纤探头。这些产品连同高口径短焦距的分光光度计，提供了低荧光本底而高质量的拉曼光谱以及体积小、容易使用的拉曼光谱仪。（一）含义 光照射到物质上发生弹性散射和非弹性散射.弹性散射的散射光是与激发光波长相 同的成分.非弹性散射的散射光有比激发光波长长的和短的成分,统称为拉曼效应 当用波长比试样粒径小得多的单色光照射气体、液体或透明试样时，大部分的光会按原来的方向透射，而一小部分则按不同的角度散射开来，产生散射光。在垂直方向观察时，除了与原入射光有相同频率的瑞利散射外，还有一系列对称分布着若干条很弱的与入射光频率发生位移的拉曼谱线，这种现象称为拉曼效应。由于拉曼谱线的数目，位移的大小，谱线的长度直接与试样分子振动或转动能级有关。因此，与红外吸收光谱类似，对拉曼光谱的研究，也可以得到有关分子振动或转动的信息。目前拉曼光谱分析技术已广泛应用于物质的鉴定，分子结构的研究谱线特征 （二）拉曼散射光谱具有以下明显的特征： a.拉曼散射谱线的波数虽然随入射光的波数而不同，但对同一样品，同一拉曼谱线的位移与入射光的波长无关,只和样品的振动转动能级有关； b.在以波数为变量的拉曼光谱图上，斯托克斯线和反斯托克斯线对称地分布在瑞利散射线两侧,这是由于在上述两种情况下分别相应于得到或失去了一个振动量子的 能量。

c.一般情况下，斯托克斯线比反斯托克斯线的强度大。这是由于Boltzmann分布，处于振动基态上的粒子数远大于处于振动激发态上的粒子数。 （三）拉曼光谱技术的优越性 提供快速、简单、可重复、且更重要的是无损伤的定性定量分析，它无需样品准备，样品可直接通过光纤探头或者通过玻璃、石英、和光纤测量。此外 1由于水的拉曼散射很微弱，拉曼光谱是研究水溶液中的生物样品和化学化合物的理想工具。 2拉曼一次可以同时覆盖50-4000波数的区间，可对有机物及无机物进行分析。相反，若让红外光谱覆盖相同的区间则必须改变光栅、光束分离器、滤波器和检测器3拉曼光谱谱峰清晰尖锐，更适合定量研究、数据库搜索、以及运用差异分析进行定性研究。在化学结构分析中，独立的拉曼区间的强度可以和功能集团的数量相关。4因为激光束的直径在它的聚焦部位通常只有0.2-2毫米，常规拉曼光谱只需要少量的样品就可以得到。这是拉曼光谱相对常规红外光谱一个很大的优势。而且，拉曼显微镜物镜可将激光束进一步聚焦至20微米甚至更小，可分析更小面积的样品。5共振拉曼效应可以用来有选择性地增强大生物分子特个发色基团的振动，这些发色基团的拉曼光强能被选择性地增强1000到10000倍。 （四）几种重要的拉曼光谱分析技术 1、单道检测的拉曼光谱分析技术

基于聚苯乙烯微球的拉曼增强效应及其应用于金单晶表面单层分子的检测

[Communication] https://www.wendangku.net/doc/9c14472773.html, 物理化学学报(Wuli Huaxue Xuebao ) Acta Phys.-Chim.Sin .,2008,24(11)：1941-1944 November Received:August 6,2008;Revised:September 12,2008;Published on Web:September 30,2008.English edition available online at https://www.wendangku.net/doc/9c14472773.html, * Corresponding author.Email:bren@https://www.wendangku.net/doc/9c14472773.html,;Tel:+86592-2186532. 国家自然科学基金(20673086,20825313)、教育部新世纪优秀人才计划(NCET -05-0564)和国家重点基础研究发展规划(973)项目(2007CB935603)资助 鬁Editorial office of Acta Physico -Chimica Sinica 基于聚苯乙烯微球的拉曼增强效应及其应用于金单晶表面单层分子的检测 林秀梅 王 翔 刘郑 任斌* (厦门大学化学化工学院化学系,固体表面物理化学国家重点实验室,福建厦门361005) 摘要：利用在样品表面上组装聚苯乙烯微球,可以使得表面拉曼信号得到增强.系统考察了增强效应与微球粒子尺寸的依赖关系,发现当微球直径为3.00μm 时,拉曼信号的增强效应最强,可以达到约5倍的增强.进一步利用聚苯乙烯微球的增强效应,获得了单层吸附在Au(111)表面上具有共振增强效应的异氰基孔雀石绿分子的拉曼信号,得到约20倍的信号净增强,相当于约3个数量级的拉曼增强效应,表明利用这种方法可以显著提高单晶表面吸附分子的检测灵敏度.这种增强效应主要是由于激光在透明微球的作用下,在微球底部产生纳米光束流,从而形成高度局域化的电磁场,使拉曼散射过程得到极大的增强.初步探讨了两种类型样品表面获得不同的增强效应的原因. 关键词：聚苯乙烯微球;纳米光束流;金单晶表面;孔雀石绿分子;表面增强拉曼光谱中图分类号：O647 Enhanced Raman Scattering by Polystyrene Microspheres and Application for Detecting Molecules Adsorbed on Au Single Crystal Surface LIN Xiu -Mei WANG Xiang LIU Zheng REN Bin * (State Key Laboratory of Physical Chemistry of Solid Surfaces,Department of Chemistry,College of Chemistry and Chemical Engineering,Xiamen University,Xiamen 361005,Fujian Province,P.R.China )Abstract ：By assembling polystyrene microsphores on a sample surface,the surface Raman signal could be enhanced.The dependence of the enhancement effect on the size of microparticles was systematically investigated and it was found that microparticles with a diameter of 3.00μm showed the highest enhancement of ca 5folds.By utilizing the enhancement effect of the microspheres,the surface Raman intensity of malachite green isothiocyanate (MGITC)adsorbed on Au(111)surface could be enhanced by 20folds,indicating that this method could effectively improve the detection sensitivity of surface Raman spectroscopy for the adsorbed species on single crystal surface.The later signal increment corresponds to the Raman enhancement effect of nearly 3orders of magnitude.The enhancement effect is mainly owing to the formation of nanojets when a laser is focused on the microspheres of appropriate diameter.The formation of nanojets will lead to the highly localized electromagnetic field,which will then significantly enhance the Raman process in the nanojets.The main reason for obtaining different enhancements on two types of samples was analyzed. Key Words ：Polystyrene microsphere;Nanojet;Au single crystal surface;Malachite green isothiocyanate; Enhanced Raman spectroscopy 拉曼光谱作为一种振动光谱技术,可以覆盖分子振动的所有频率区间,在研究各种固/液、固/气和 固/固界面体系中有其独特的优势,更可以用来从分子水平上深入表征各种表面(界面)的结构和过程[1]. 1941

表面增强拉曼散射(SERS)光谱简介

表面增强拉曼散射(SERS)光谱简介 1.拉曼光谱简介： 光与物质分子的碰撞可以分为两类，即弹性碰撞和非弹性碰撞。光的散射可以看作是光子与物质碰撞后运动方向的改变。如果发生的是弹性碰撞，即光子仅改变运动方向而在碰撞过程中没有发生能量交换，这种散射为瑞利散射(Rayleigh scattering)；如果发生的是非弹性碰撞，即光子不仅发生了运动方向的改变，而且在碰撞过程中有能量交换，这种散射就是拉曼散射(Raman scattering)。结合图1我们可以更加清楚地了解光的散射过程。 图1 瑞利散射与拉曼散射的基本原理 在激发光的激发下，分子从它的某一振动态(基态或激发态)跃迁到一个激发虚态，在皮秒时间尺度内跃迁回基态，同时伴随着光子的释放。这时，大部分跃迁回基态时所释放的光子的波长与激发光相同，就是瑞利散射线。另有少数光子的波长与激发光不同，即拉曼散射线，该散射又可以分为两类(见图1)：Stokes 散射和反Stokes散射。由于常温下处于振动基态的分子数远多于处于振动激发态的分子数，所以Stokes谱线要比反Stokes线强得多。拉曼光谱所关心的是拉曼散射光与入射光频率的差值，即拉曼频移。不同的激发光所产生的拉曼散射光频率也不相同，但是拉曼频移是相同的。拉曼频移表征的是化合物的振动—转动能级，在这一点上拉曼光谱与红外光谱是十分相似的[1,2]。 拉曼光谱是一项重要的现代光谱技术，它的应用早已超出化学、物理的范畴，渗透到生物学、矿物学、材料学、考古学和工业产品质量控制等各个领域，成为研究分子结构和组态、确定晶体结构的对称性、研究固体中的缺陷和杂质、环境污染物、生物分子和工业材料微观结构的有力工具。

拉曼光谱在纳米材料方面的应用

拉曼光谱在纳米材料方面的应用 摘要：纳米材料自发现以来，由于其尺寸效应带来的特殊性能使之成为研究热点，应用于各种领域。拉曼 光谱在材料表征中应用广泛，能为纳米材料提供一些特殊的信息，如氧化石墨烯的拉曼增强效应，碳量子 点结构的表征，碳纳米管的表征等。 关键词：拉曼光谱纳米材料表征 Application of Raman Spectroscopy in Nano-Materials Abstract：Nano-materials, due to their unique properties and versatile functions,are the hot topics in various research.Raman spectroscopy is widely used in the characterization of materials,providing composition and structure information at molecular level.For example,the enhanced-raman effect of graphene oxide,the characterization of the structure of the carbon quantum dot,the characterization of carbon nanotubes. Keyword: Raman spectroscopy Nano-materials characterization 1引言 1928年印度实验物理学家拉曼发现了光的一种类似于康普顿效应的光散射效应, 称为拉曼效应。简单地说就是光通过介质时由于入射光与分子运动之间相互作用而引起的光频率改变。拉曼因此获得1930年的诺贝尔物理学奖,成为第一个获得这一奖项并且没有接受过西方教育的亚洲人[1]。 拉曼光谱是研究分子振动的一种光谱方法。它的原理和机制都与红外光谱不同，但它提供的结构信息却是类似的，都是关于分子内部各种简正振动频率及有关振动能级的情况。从而可以用来鉴定分子中存在的官能团。分子偶极矩变化是红外光谱产生的原因，而拉曼光谱是分子极化率变化诱导的,它的谱线强度取决于相应的简正振动过程中极化率的变化的大小。在分子结构分析中，拉曼光谱与红外光谱是相互补充的。例如：电荷分布中心对称的键，如C-C、N=N、S-S等红外吸收很弱，而拉曼散射却很强[2]。因此，一些在红外光谱仪无法检测的信息在拉曼光谱能很好地表现出来[3]。 拉曼光谱作为表征分子振动能级的指纹光谱,已在物理、化学、生物学与材料学科等领域得到广泛应用。拉曼光谱是物质的非弹性散射光谱，能够提供材料在振动和电子性质方面的独特信息。在纳米材料的研究方面，拉曼光谱可以帮助考查纳米粒子本身因尺寸减小而产生的对拉曼光谱的影响以及纳米粒子的引入对玻璃相结构的影响。特别是对于研究低维纳米

SERS表面增强拉曼

Surface-enhanced Raman spectroscopy From Wikipedia, the free encyclopedia (Redirected from Surface-enhanced Raman scattering) Raman spectrum of liquid 2-mercaptoethanol (below) and SERS spectrum of 2-mercaptoethanol monolayer formed on roughened silver (above). Spectra are scaled and shifted for clarity. A difference in selection rules is visible: Some bands appear only in the bulk-phase Raman spectrum or only in the SERS spectrum. Surface-enhanced Raman spectroscopy or surface-enhanced Raman scattering (SERS) is a surface-sensitive technique that enhances Raman scattering by molecules adsorbed on rough metal surfaces or by nanostructures such as plasmonic-magnetic silica nanotubes.[1] The enhancement factor can be as much as 1010 to 1011,[2][3] which means the technique may detect single molecules.[4][5] Contents [hide] ?1History ?2Mechanisms o 2.1Electromagnetic theory o 2.2Chemical theory ?3Surfaces ?4Applications o 4.1Oligonucleotide targeting ?5Selection rules ?6References

2011年拉曼相关基金项目

1、小分子与蛋白质相互作用的表面增强拉曼散射检测方法研究清华大学 2、基于表面等离子体结构的WGM/SERS生物传感特性研究杭州电子科技大学 3、基于光子晶体编码微球的蛋白质SERS检测及其应用东南大学 4、级联放大纳米棒表面的激发电场来提高表面增强拉曼散射西南大学 5、基于金属纳米颗粒-氧化石墨烯符合体系的表面增强拉曼基底的构筑及其用于细胞与药物相互作用研究中国科学院苏州纳米技术与纳米仿生研究所 6、天然气水合物沉积区孔隙水拉曼光谱原位定量分析新方法中国科学院海洋研究所 7、相干拉曼光谱分子测量用光源的研究河北师范大学 8、痕量多溴联苯醚的表面增强拉曼光谱检测山东大学 9、离子液体/金属界面过程的现场电化学表面增强拉曼光谱研究苏州大学 10、基于原子系综集体自旋激发增强的拉曼散射光谱华东师范大学 11、电子声子相互作用及相关问题在若干纳米系统中的拉曼光谱学测量中科院物理所 12、基于金纳米材料自组装“适配体”分子的SERS检测重金属离子的研究北航 13、高活性UV-ERS金属纳米结构的制备及其增强活性研究厦门大学 14、仿自然贵金属纳米结构：设计，组装及在SERS和TERS上的应用中科院上海硅酸盐所 15、植酸类环境友好金属缓蚀试剂自组装单层构效广西研究上海师范大学 16、农林生物质纤维细胞壁超微结构研究北京林业大学 17、基于表面等离子共振效应的自组装体系的分析方法吉林大学 18、基于干涉结构下的表面增强拉曼散射吉林大学 19、金属纳米线纳米间隙电极的可控制备及其应用北京大学 20、拉曼光谱表征可控自组装分子体系中弱相互作用及理论分析厦门大学 21、基于DNA纳米技术的新型SERS开关的设计和基底构建中科院化学所 22、基于SERS技术的环境中PAHs快速分析方法的研究吉林大学

半导体材料表面增强拉曼散射的分析应用

半导体材料的表面增强拉曼散射的分析应用 纪伟，赵兵，尾崎幸 得益于表面增强拉曼散射（SERS）活性衬底的显著发展，SERS技术日益成为在各个领域的一项重 要的分析技术。半导体材料所固有的理化特性提供了基于SERS的分析技术的发展和改进的可能，因此基 于半导体的SERS技术特别有趣。根据半导体材料的SERS的效应，基于半导体的SERS技术可分为两 个区域：（1）半导体增强拉曼散射，其中半导体材料直接用作底物用于增强吸附分子的拉曼信号；（2）半导体介导的增强拉曼散射，其中半导体被用作一个“天线”或“陷阱”，用以调制由金属基板造成的拉曼增强。然而基于半导体的SERS理论仍然不完整，正在不断发展，基于半导体的SERS技术为生物分析，光 催化，太阳能电池，传感和光电器件等领域带来了实质性的进展。这次回顾的目的是概述这一新兴研究领域的最新进展，并特别强调了其分析性能和应用领域。版权所有@015年约翰·威利父子有限公司 关键词：半导体增强拉曼散射;半导体介导增强拉曼散射;基于半导体的SERS技术;半导体材料;金属/半导 体混合动力 介绍 弗莱希曼在1974年对增强拉曼散射效应的开拓性发现有了大量后续进展。【1】由Jeanmaire，Van Duyne，阿尔布雷希特和克赖顿在1977年以后的活动最终开拓了拉曼光谱的一个令人振兴的领域——表面增强拉曼散射（SERS）。【2,3】SERS现在已成为一个非常活跃的研究领域，诸如光学，光子学，表面科学，以及固态物理学领域。【4-6】】]经过40年的发展，由于高灵敏度和特异性分析以及用于非破坏性的实时分析选项原位，SERS已经成为一种广泛使用的强大技术。【7-10】作为一种表面光谱技术，SERS需要使用具有纳米级粗糙度的合适底物来实现拉曼强度的提高。在基于SERS应用程序的开发中，新的SERS活性基底的发展起着关键作用。通常情况下，因为金属纳米颗粒或纳米结构能通过表面等离子体导致共振强电磁增强，它们被广泛地用于实现大幅度的SERS效应。【11-13】迄今为止，我们已经在金属基板上的控制，以及合成金属基片的组装和变形中取得巨大成就。【14-19】然而，这些进步在传感应用不断增加的需求面前仍然不够。半导体材料为传统SERS注入新的活力，由于其独特的光学，化学，电气和催化性能，更多具有发展前景的功能可能会被发现。【20-27】 至今，各种关于在半导体基板上的增强拉曼散射效果的研究一直在进行。这些新的SERS技术可分为两个区域：（1）半导体增强拉曼散射，其中半导体材料直接用作底物用于增强吸附分子的拉曼信号；（2）半导体介导的增强拉曼散射，其中半导体被用作一个“天线”或“陷阱”，用以调制由金属基板（例如金属/半导体异质结构）造成的拉曼增强。与传统的SERS相比，基于半导体的SERS拉曼增强被认为是各种共振（包括表面等离子体，电荷转移，分子和激子共振）的组合。【28】]虽然理论仍然不完整，在不断发展中，但基于半导体的表面增强拉曼光谱技术已被用于开发一些依赖半导体材料不同理化性质的具有前景的应用程序（图1）。这些令人瞩目的成就使人们对SERS的内在本质有了新的认识，并为推进基于SERS的分析应

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