Rapid fabrication of the Au hexagonal cone arrays for SERS applications.

This study performed trace detection using surface-enhanced Raman scattering (SERS) on Au hexagonal cone arrays (Au-HCAs). Uniform porous anodized aluminum oxide (AAO) templates were used, and an Ag film with a cone cavity was prepared using a thermal deposition technique. Next, a series of homogeneous Au-HCAs were prepared controllably via electrodeposition growth technology. The prepared Au-HCAs were used as SERS substrates, and according to the experimental results, the optimal electrodeposition time is 600 s. At this time, Au-HCAs had the highest SERS activity. The detection limit of R6G was 10-9 M, exhibiting high reproducibility and high uniformity at 10-6 M, indicating that Au-HCAs had good stability. Moreover, a good linear correlation between the Raman intensity and the molecular concentration endowed Au-HCAs with good quantitative analysis ability. Therefore, the Au-HCAs exhibited great potential for qualitative and quantitative detection.

Fabrication of triangular Au/Ag nanoparticle arrays with sub-10 nm nanogap controlled by flexible substrate for surface-enhanced Raman scattering.

Large-area ordered nanoparticle arrays have shown great potential as surface-enhanced Raman scattering (SERS) substrates. The preparation methods of metal nanogap with width greater than 10 nm are relatively mature. In contrast, nanomanufacturing methods for sub-10 nm still face challenges in realizing controllable and reproducible features. Herein, a series of triangular Au/Ag nanoparticle arrays (noted as Au/Ag NPAs) with sub-10 nm gap were prepared by utilizing stress-induced local cracking and high expansion coefficient of flexible polydimethylsiloxane (PDMS). The triangular tip-connected Au/Ag NPAs were firstly prepared by depositing Au and Ag films on home-made polystyrene (PS) templates, then gaps with precise size (3 nm, 5 nm, 7 nm, 9 nm and 11 nm) were achieved by controlling the temperature of flexible PDMS, and finally transferred to the silicon wafers using as SERS substrates. The results showed that when the prepared triangular Au/Ag NPAs with 3 nm nanogap were used as reliable SERS substrates, the relative standard deviation of Raman intensity at 621 cm-1mode of Rhodamine 6G (R6G) with concentration of 10-6M was 2.3%, indicating excellent uniformity. The approach showed good controllability and repeatability for SERS analysis, exhibiting good application prospect in surface trace detection.

Facile construction of large-area periodic Ag-Au composite nanostructure and its reliable SERS performance.

With the maturity of nano-manufacturing technology, nano-materials with excellent surface-enhanced Raman scattering (SERS) activities have evolved from homogeneous materials to composite ones, but the structural uniformity of composite materials has not been effectively improved. We successfully obtained a series of Ag-Au composite nanostructures with high SERS activity by using a two-step deposition and confined spheroidization process and one-step in-situ substitution method. Anodized alumina templates with uniform size distribution were employed as the initial confined template for spheroidizing Ag film into periodic Ag nanoparticles (Ag NPs). The composite nanostructure was simply obtained after a one-step in-situ galvanic reaction based on the Ag NPs arrays. The results showed that the prepared Ag-Au composite nanostructure could be used as reliable SERS substrates with low relative standard deviation value of ∼6.25% for crystal violet molecules. Compared with previous reports, this one-step route greatly simplifies the process of preparing periodic composite nanomaterials and provides a new idea for constructing multi-component metal nanostructures.

Quenching of Spin Polarization Switching in Organic Multiferroic Tunnel Junctions by Ferroelectric "Ailing-Channel" in Organic Barrier.

The ferroelectric control of spin-polarization at ferromagnet (FM)/ferroelectric organic (FE-Org) interface by electrically switching the ferroelectric polarization of the FE-Org has been recently realized in the organic multiferroic tunnel junctions (OMFTJs) and gained intensive interests for future multifunctional organic spintronic applications. Here, we report the evidence of ferroelectric "ailing-channel" in the organic barrier, which can effectively pin the ferroelectric domain, resulting in nonswitchable spin polarization at the FM/FE-Org interface. In particular, OMFTJs based on La0.6Sr0.4MnO3/P(VDF-TrFE) ( t)/Co/Au structures with different P(VDF-TrFE) thickness ( t) were fabricated. The combined advanced electron microscopy and spectroscopy studies clearly reveal that very limited Co diffusion exists in the P(VDF-TrFE) organic barrier when the Au/Co electrode is deposited around 80K. Pot-hole structures at the boundary between the P(VDF-TrFE) needle-like grains are evidenced to induce "ailing-channels" that hinder efficient ferroelectric polarization of the organic barrier and result in the quenching of the spin polarization switching at Co/P(VDF-TrFE) interface. Furthermore, the spin diffusion length in the negatively polarized P(VDF-TrFE) is measured to be about 7.2 nm at 20K. The evidence of the mechanism of ferroelectric "ailing-channels" is of essential importance to improve the performance of OMFTJ and master the key condition for an efficient ferroelectric control of the spin polarization of "spinterface".

Large-scale flexible metal-covered polymer nanopillar arrays as highly uniform and reproducible SERS substrates for trace analysis.

While surface-enhanced Raman scattering (SERS) spectroscopy has been studied extensively due to its sensitivity to molecular vibration states, the fabrication of SERS substrates with homogeneous activity over a large area still remains difficult. Here, a facial fabrication of large-scale metal-covered polymer nanopillar arrays used as reliable SERS substrates was developed by nano-pouring process using porous alumina membranes. Our strategy integrates the advantages of low-cost production, high reproducibility and good biocompatibility because the flexible transparent polymer nanopillars are nondestructive to biomaterial surfaces. The as-prepared SERS substrates exhibit highly uniform Raman signals with low relative standard deviation values of 4% at 1169 cm-1 of CV and 8.1% at 1355 cm-1 of R6G, both with the concentration of 10-5 M. The results also show that more than 95% intensity within the limits of the ±10% deviation of the average intensity of signals, indicating excellent stability of SERS signals. In addition, the mechanically flexible substrates can be attached to surfaces with complex morphologies and the good transparency makes the excitation and collection of signals from the backside of the substrates possible, showing great potential in analytical chemistry, food safety, medical diagnostics and other practical SERS detections.

Refractive index modulating Raman spectroscopy based on perovskite PMN-PT ceramics.

A three-layer planar waveguide structure comprising a perovskite (1-x)Pb(Mg1/3Nb2/3Nb2/3)O3-xPbTiO3 (PMN-PT) ceramic sandwiched by two silver films is designed and called PMPW. Using the high sensitivity of ultrahigh-order modes, theoretical analysis is performed to calculate the effective refractive index (ERI) of the PMPW. A detailed analysis of the Raman spectrum of PMN-PT at 795 cm-1 is performed. A comparison of the numerical analysis and experimental results reveals that the nonlinear change in ERI plays a primary role in the Raman signal variation. Analysis of the Raman spectrum of a sample deposited on PMPW confirms that it is effective for modulating Raman signals.

Multifunctional Nanocomposite with Magnetism, Thermosensitivity and Surface Enhanced Raman Scattering Effect.

Multifunctional Fe3O4 @poly(N-isopropylacrylamide-co-acrylamide), Au (Fe3O4 @PNIPAM-AAM, Au) composite with magnetism, themosensitivity, surface enhanced Raman scattering (SERS) effect and drug delivery ability was successfully prepared. Transmittance measurements at 350 nm confirm the composite has a lower critical solution temperature (LCST) about 41 degrees C. Due to the network structure of PNIPAM-AAM, the composite is also an ideal drug carrier. An encapsulation efficiency of 90 wt% was demonstrated by using Ampicillin as a model drug. The drug release process was closely related with the environmental temperature, which was dramatically accelerated at temperature above LCST, and a much greater release amount was achieved. The Raman enhancement effect of such versatile composite was evaluated by using crystal violet (CV) as a probe molecule, which verified the composite is an effective SERS substrate.

SERS activity studies of Ag/Au bimetallic films prepared by galvanic replacement.

Ag films on Si substrates were fabricated by immersion plating, which served as sacrificial materials for preparation of Ag/Au bimetallic films by galvanic replacement method. SEM images displayed that the sacrificial Ag films presenting island morphology experienced interesting structural evolution process during galvanic replacement reaction, and nano-scaled holes were formed in the resultant bimetallic films. SERS measurements using crystal violet as an analyte showed that SERS intensities of bimetallic films were enhanced significantly compared with that of pure Ag films and related mechanisms were discussed. Immersion plating experiment carried out on Ag films on PEN substrates fabricated by photoinduced reduction method further confirmed that galvanic replacement is an easy method to fabricate Ag/Au bimetallic and a potential approach to improve the SERS performance of Ag films.

Synthesis and antitumor activity of novel aroylthiourea derivatives of podophyllotoxin.

A novel series of 4ß-[(4-substituted) aroylthiourea] derivatives of podophyllotoxin were synthesized and their abilities to inhibit the growth of cancer cells were investigated by MTT assay. Compound 4a possessed the highest cytotoxicity on HepG2, A549 and HCT-116 cancer cell lines with the IC(50) values of 0.1 µM. Apoptosis in HCT-116 cells induced by compound 4a was observed by Hoechst33342-Propidium iodide (PI) and acridine orange (AO)-ethidium bromide (EB) double staining assays. DNA flow cytometric analysis revealed that 4a induced cell cycle arrest at G2/M phase and kDNA decatenation assay indicated that 4a inhibited topoisomerase IIα-mediated kDNA decatenation. Our results indicated that compound 4a possessed promising antitumor activity, which need to be studied further.

Surface-enhanced Raman scattering dendritic substrates fabricated by deposition of gold and silver on silicon.

This paper reports a study on the preparation of gold nanoparticles and silver dendrites on silicon substrates by immersion plating. Firstly, gold was deposited onto silicon wafer from HF aqueous solution containing HAuCl4. Then, the silicon wafer deposited gold was dipped into HF aqueous solution of AgNO3 to form silver coating gold film. Scanning electron microscopy reveals a uniform gold film consisted of gold nanoparticles and rough silver coating gold film containing uniform dendritic structures on silicon surface. By SERS (surface-enhanced Raman scattering) measurements, the fabricated gold and silver coating gold substrates activity toward SERS is assessed. The SERS spectra of crystal violet on the fabricated substrates reflect the different SERS activities on gold nanoparticles film and silver coating gold dendrites film. Compared with pure gold film on silicon, the film of silver coating gold dendrites film significantly increased the SERS intensity. As the fabrication process is very simple, cost-effective and reproducible, and the fabricated silver coating gold substrate is of excellent enhancement ability, spatial uniformity and good stability.

Synthesis, cytotoxicity and pro-apoptosis of novel benzoisoindolin hydrazones as anticancer agents.

A series of benzoisoindolin hydrazones as analogues of natural lignan diphyllin were synthesized and the structures of these compounds were established by (1)H-NMR, (13)C-NMR, Mass and high resolution (HR)-MS. The compounds were evaluated for in vitro cytotoxicity against KB, A549 and HCT-116 cancer cell lines by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. Compound 4 possessed the highest growth inhibitory effect. Significant apoptosis of HCT-116 cells treated with compound 4 was observed by Hoechst33342-propidium iodide (PI) and acridine orange (AO)-ethidium bromide (EB) staining assay. Western blot analysis disclosed that compound 4 induced apoptosis via the mitochondrial pathway accompanied by an increased expression of Bax and a decreased expression of Bcl-2.

[A holographic plate silver film-preparation, morphology and SERS activity].

A new method for preparing SERS-active substrate was reported. After being exposed, developed and fixed, the commercially available holographic plate can be used to generate attractive SERS-active silver surface. The obtained silver film was characterized by UV-Vis spectroscopy and scanning electron microscope (SEM) observation. The absorption spectrum locates at around 420 nm with a narrow half-width due to the surface plasmon resonance, which implies that there are silver particles on the prepared substrate with uniform sizes. And the silver particles distribute uniformly anywhere on the holographic plate with a diameter of about 100 nm by SEM observation. Furthermore, the measurements of the SERS spectrum of crystal violet indicate that such substrate has the features of satisfactory reproducibility, long term stability and high SERS activity. The prepared silver film keeps high SERS activity even if it was stored for several months in the air at room temperature.