Silver Nanoparticle Thin Films with Nanocavities for Surface‐Enhanced Raman Scattering

The formation of nanometer‐sized gaps between silver nanoparticles is critically important for optimal enhancement in surface‐enhanced Raman scattering (SERS). A simple approach is developed to generate nanometer‐sized cavities in a silver nanoparticle thin film for use as a SERS substrate with extremely high enhancement. In this method, a submicroliter volume of concentrated silver colloidal suspension stabilized with cetyltrimethylammonium bromide (CTAB) is spotted on hydrophobic glass surfaces prepared by the exposure of the glass to dichloromethysilane vapors. The use of a hydrophobic surface helps the formation of a more uniform silver nanoparticle thin film, and CTAB acts as a molecular spacer to keep the silver nanoparticles at a distance. A series of CTAB concentrations is investigated to optimize the interparticle distance and aggregation status. The silver nanoparticle thin films prepared on regular and hydrophobic surfaces are compared. Rhodamine 6G is used as a probe to characterize the thin films as SERS substrates. SERS enhancement without the contribution of the resonance of the thin film prepared on the hydrophobic surface is calculated as 2×10⁷ for rhodamine 6G, which is about one order of magnitude greater than that of the silver nanoparticle aggregates prepared with CTAB on regular glass surfaces and two orders of magnitude greater than that of the silver nanoparticle aggregates prepared without CTAB on regular glass surfaces. A hydrophobic surface and the presence of CTAB have an increased effect on the charge‐transfer component of the SERS enhancement mechanism. The limit of detection for rhodamine 6G is estimated as 1.0×10^?8 M . Scanning electron microscopy and atomic force microscopy are used for the characterization of the prepared substrate.     

Cetylpyridinium Chloride Activated Trinitrotoluene Explosive Lights Up Robust and Ultrahigh Surface‐Enhanced Resonance Raman Scattering in a Silver Sol

Surface‐enhanced resonance Raman scattering (SERRS) is not realized for most molecules of interest. Here, we developed a new SERRS platform for the fast and sensitive detection of 2,4,6‐trinitrotoluene (TNT), a molecule with low Raman cross section. A cationic surfactant, cetylpyridinium chloride (CPC) was modified on the surface of silver sols (CP‐capped Ag). CPC not only acts as the surface‐seeking species to trap sulfite‐sulfonated TNT, but also undergoes complexation with it, resulting in the presence of two charge‐transfer bands at 467 and 530 nm, respectively. This chromophore absorbs the visible light that matches with the incident laser and plasmon resonance of Ag sols by the use of a 532.06 nm laser, and offered large resonance Raman enhancement. This SERRS platform evidenced a fast and accurate detection of TNT with a detection limit of 5×10^?11 M under a low laser power (200 μW) and a short integration time (3 s). The CP‐capped Ag also provides remarkable sensitivity and reliable repeatability. This study provides a facile and reliable method for TNT detection and a viable idea for the SERS detection of various non‐resonant molecules.     

Gold‐Loaded Carbon Nanoparticles from Poly(vinyl alcohol)‐b‐poly(acrylonitrile) Non‐Shell‐Cross‐Linked Micelles

Herein we show that a new amphiphilic poly(vinyl alcohol)‐b‐poly(acrylonitrile) block copolymer dispersed in water can be easily loaded with gold nanoparticles by addition of chlorauric acid followed by reduction by sodium borohydride. After deposition of the so‐loaded micelles onto a silicon wafer, followed by an appropriate thermal treatment, the poly(acrylonitrile) core of the micelles is carbonized, while the poly(vinyl alcohol) shell is completely decomposed and volatilized, leading to gold encapsulated in carbon nanoparticles. The morphology of the micelles is maintained during thermal treatment without requiring shell‐cross‐linking of the micelles prior to pyrolysis.     

Simultaneous Capture,Detection, and Inactivation of Bacteria as Enabled by a Surface‐Enhanced Raman Scattering Multifunctional Chip

Herein, we present a multifunctional chip based on surface‐enhanced Raman scattering (SERS) that effectively captures, discriminates, and inactivates pathogenic bacteria. The developed SERS chip is made of a silicon wafer decorated with silver nanoparticles and modified with 4‐mercaptophenylboronic acid (4‐MPBA). It was prepared in a straightforward manner by chemical reduction assisted by hydrogen fluoride etching, followed by the conjugation of 4‐MPBA through Ag? S bonds. The dominant merits of the fabricated SERS chip include excellent reproducibility with a relative standard deviation (RSD) value smaller than 11.0 %, adaptable bacterial‐capture efficiency (ca. 60 %) at low concentrations (500–2000 CFU mL^?1), a low detection limit (down to a concentration of 1.0×10² cells mL^?1), and high antibacterial activity (an antibacterial rate of ca. 97 %). The SERS chip enabled sensitive and specific discrimination of Escherichia coli and Staphylococcus aureus from human blood.     

Microwave‐Assisted Synthesis of Crosslinked Poly(vinyl alcohol) Nanocomposites Comprising Single‐Walled Carbon Nanotubes,Multi‐Walled Carbon Nanotubes,and Buckminsterfullerene

We report a facile method to accomplish the crosslinking reaction of PVA with SWNTs, MWNTs, and C‐60 using MW irradiation. Nanocomposites of PVA crosslinked with SWNT, MWNT and C‐60 were prepared expeditiously by reacting the respective carbon nanotubes with 3 wt.‐% PVA under MW irradiation, maintaining a temperature of 100 °C, representing a radical improvement over literature methods to prepare such crosslinked PVA composites. This general preparative procedure is versatile and provides a simple route to manufacture useful SWNT, MWNT and C‐60 nanocomposites.

     

Preparation of antimicrobial poly(vinyl alcohol) nanofibers containing silver nanoparticles

Polyvinyl alcohol (PVA) nanofibers containing Ag nanoparticles were prepared by electrospinning PVA/silver nitrate (AgNO₃) aqueous solutions, followed by short heat treatment, and their antimicrobial activity was investigated for wound dressing applications. Since PVA is a water soluble and biocompatible polymer, it is one of the best materials for the preparation of wound dressing nanofibers. After heat treatment at 155 °C for 3 min, the PVA/AgNO₃ nanofibers became insoluble, while the Ag⁺ ions therein were reduced so as to produce a large number of Ag nanoparticles situated preferentially on their surface. The residual Ag⁺ ions were reduced by subsequent UV irradiation for 3 h. The average diameter of the Ag nanoparticles after the heat treatment was 5.9 nm and this value increased slightly to 6.3 nm after UV irradiation. It was found that most of the Ag⁺ ions were reduced by the simple heat treatment. The PVA nanofibers containing Ag nanoparticles showed very strong antimicrobial activity. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 2468–2474, 2006     

Boron Nitride Nanosheets Improve Sensitivity and Reusability of Surface‐Enhanced Raman Spectroscopy

Surface enhanced Raman spectroscopy (SERS) is a useful multidisciplinary analytic technique. However, it is still a challenge to produce SERS substrates that are highly sensitive, reproducible, stable, reusable, and scalable. Herein, we demonstrate that atomically thin boron nitride (BN) nanosheets have many unique and desirable properties to help solve this challenge. The synergic effect of the atomic thickness, high flexibility, stronger surface adsorption capability, electrical insulation, impermeability, high thermal and chemical stability of BN nanosheets can increase the Raman sensitivity by up to two orders, and in the meantime attain long‐term stability and extraordinary reusability not achievable by other materials. These advances will greatly facilitate the wider use of SERS in many fields.     

Preparation of Polymer Nanofibers Containing Silver Nanoparticles by Using Poly(N‐vinylpyrrolidone)

Summary: Poly(N‐vinylpyrrolidone) (PVP) was used in two methods to prepare polymer nanofibers containing Ag nanoparticles. The first method involved electrospinning the PVP nanofibers containing Ag nanoparticles directly from the PVP solutions containing the Ag nanoparticles. N,N‐Dimethylformamide was used as a solvent for the PVP as well as a reducing agent for the Ag⁺ ions in the PVP solutions. In the second method, poly(vinyl alcohol) (PVA) aqueous solutions were electrospun with 5 wt.‐% of the PVP containing Ag nanoparticles. The Ag nanoparticles were evenly distributed in the PVA nanofibers. PVP containing Ag nanoparticles could be used to introduce Ag nanoparticles to other polymer nanofibers that are miscible with PVP.

TEM image of a PVA nanofiber electrospun with 5 wt.‐% of the PVP containing Ag nanoparticles.     

Surprisingly Long‐Range Surface‐Enhanced Raman Scattering (SERS) on Au–Ni Multisegmented Nanowires

Very long range surface‐enhanced Raman scattering is observed from a nickel nanowire that is separated by 120 nm from a pair of gold nanodisks. The excitation of the surface‐plasmon resonance (SPR) from the gold nanodisk pair generates an enhanced electromagnetic field near the nickel segment (SEM, left), leading to Raman intensity greater than the nickel alone (right).

     

Poly(vinyl alcohol) Chains Grafted onto the Surface of Copper Oxide Nanoparticles: Application in Synthesis and Characterization of Novel Optically Active and Thermally Stable Nanocomposites Based on Poly(amide-imide) Containing N-trimellitylimido-L-valine Linkage

Green polymer nanocomposites (NCs) show unique properties of combining the advantages of nanofillers and organic polymers. In this study, in order to control the dispersion of nanoparticles (NPs) in a polymer matrix, first, poly(vinyl alcohol) (PVA) as a green modifier was grafted on the surface of the CuO NPs to obtain CuO-PVA nanohybrid. Then poly(amide-imide) (PAI) was synthesized by the direct step growth polymerization of N-trimellitylimido-L-valine and 4,4′-methylenebis(3-chloro-2,6-diethylaniline) in ionic liquid medium. Finally, CuO-PVA hybrids were incorporated into the PAI matrix using ultrasonic technique for the preparation of PAI/CuO-PVA NCs. The obtained PAI/CuO-PVA NCs were characterized by different methods. The results of thermogravimetric analysis showed that thermal stability of the NCs was enhanced by incorporation of CuO-PVA nanohybrid compared to the pure PAI.     

Raman spectral study of solid and dissolved poly(vinyl alcohol) and ethylene-vinyl alcohol copolymer

We have measured the Raman spectra of ethylene-vinyl alcohol copolymer (EVOH) and poly(vinyl alcohol) (PVOH). Spectra of 88% hydrolyzed PVOH were examined from the partially crystalline solid, from PVOH dissolved in both H₂O and D₂O, and from films precipitated from these solutions. The spectrum in H₂O differs from that of the starting material by disappearance of sharp bands having Raman shift values of 1146 and 1093 cm^?1, strengthening of a band near 915 cm^?1, decrease in frequency of bands at 480, 1356, and 1441 cm^?1, and increase in frequency of bands at 369, 413, 1023, 1371, and 2910 cm^?1. The spectrum of the film shows partial reversal of these trends. With D₂O as the solvent, the band shifts are slightly different from those listed above and new bands appear. These changes are indicative of loss of crystallinity, change in stereochemistry, and partial deuteration of hydroxyl during dissolution of this PVOH sample at room temperature. © 1994 John Wiley & Sons, Inc.