Exploring copper nanostructures as highly uniform and reproducible substrates for plasmon-enhanced fluorescence.

The unique properties of metallic nanostructures of coinage metals that can sustain localized surface plasmon resonances (LSPR) put them at the centre of plasmon-enhanced phenomena. The theory of plasmonic phenomena based on LSPR is well-established. However, the fabrication of plasmonic substrates, reproducibly, is still challenging for applications in surface-enhanced Raman scattering (SERS) and surface-enhanced fluorescence (SEF). In this work we describe well-ordered copper nanostructures (CuNSs), produced by electrodeposition and nanosphere lithography, as active substrates for SEF. After a detailed spectroscopic and microscopic characterization, CuNSs are successfully applied as SEF-active substrates using a well-known perylene derivative as a target molecule. The signal reproducibility from CuNS substrates was established by comparing the results against those obtained from a simply roughened Cu substrate. Under optimal conditions, signal variability is around 4%.

Characterization of bacteria using its O-antigen with surface-enhanced Raman scattering.

The O-antigen determines the specificity of bacterial serotype, a sort of bacterial fingerprinting. In this work we report the extraction, purification and characterization of the O-antigen of two pathogenic bacteria, Escherichia coli O16 and Salmonella typhimurium. Molecular fingerprints found in the vibrational spectra represent a powerful analytical technique for identification (or differentiation) of molecular moieties in complex systems such as pathogens. In addition, advantages of vibrational Raman scattering are unique thanks to the high sensitivity and specificity achieved via surface-enhanced Raman scattering (SERS). SERS is used here to take advantage of characteristic vibrational frequency differences of O-antigens, thus allowing bacterial differentiation. Characteristic fundamental vibrational modes associated with the monosaccharide N-acetylglucosamine and deformations of the O-antigen chains provide the main spectroscopic differences between the O-antigens of E. coli O16 and S.typhimurium.

Two-photon polymerization for fabricating structures containing the biopolymer chitosan.

Two-photon polymerization is a powerful tool for fabricating three-dimensional micro/nano structures for applications ranging from nanophotonics to biology. To tailor such structure for specific purposes it is often important to dope them. In this paper we report on the fabrication of structures, with nanometric surface features (resolution of approximately 700 nm), using two-photon polymerization of an acrylic resin doped with the biocompatible polymer chitosan using a guest-host scheme. The fluorescence background in the Raman spectrum indicates the presence of chitosan throughout the structure. Mechanical characterization reveals that chitosan does not affect the mechanical properties of the host acrylic resin and, consequently, the structures exhibit excellent integrity. The approach presented in this work can be used in the fabrication of micro- and nanostructures containing biopolymers for biomedical applications.

SERRS for single-molecule detection of dye-labeled phospholipids in Langmuir-Blodgett monolayers.

The coupling of molecular excitations to localized surface plasmon resonances (LSPR) in silver or gold nanostructures is at the center of single-molecule detection (SMD) using surface-enhanced Raman scattering (SERS). The effect is attributed to the enhanced scattering power caused by coupling with the surface plasmons of the metal. The most efficient coupling is attained when the excitation is in resonance with the molecule and the nanostructure, the case of surface-enhanced resonance Raman scattering (SERRS). This incredible effect has the potential to be a powerful optical tool when used in conjunction with vibrationally differentiable chromophores. Here we present a unique study where the targeted system is a phospholipid that is tagged with a xanthene dye (the SERRS probe), a chromophore that dominates the Raman signal when the laser is in resonance with its absorption. The labeled phospholipid was incorporated into a single fatty acid Langmuir monolayer at varying concentrations and transferred onto a silver nanoparticle film to form Langmuir-Blodgett (LB) monolayers. Because the xanthene dye is tagged to a much larger molecule, the chances of dye aggregation (formation of dimers or higher aggregates) is negligible. Single-molecule detection of the dye tag (SERRS probe monomer) is readily achieved and demonstrated through the use of doped LB monolayers, Raman microscopy, spectral mapping, and efficient coupling of the laser line into the dye absorption band and plasmon resonances.

Molecular and morphological characterization of bis benzimidazo perylene films and surface-enhanced phenomena.

Thin solid films of bis benzimidazo perylene (AzoPTCD) were fabricated using physical vapor deposition (PVD) technique. Thermal stability and integrity of the AzoPTCD PVD films during the fabrication ( approximately 400 degrees C at 10(-6) Torr) were monitored by Raman scattering. Complementary thermogravimetric results showed that thermal degradation of AzoPTCD occurs at 675 degrees C. The growth of the PVD films was established through UV-vis absorption spectroscopy, and the surface morphology was surveyed by atomic force microscopy (AFM) as a function of the mass thickness. The AzoPTCD molecular organization in these PVD films was determined using the selection rules of infrared absorption spectroscopy (transmission and reflection-absorption modes). Despite the molecular packing, X-ray diffraction revealed that the PVD films are amorphous. Theoretical calculations (density functional theory, B3LYP) were used to assign the vibrational modes in the infrared and Raman spectra. Metallic nanostructures, able to sustain localized surface plasmons (LSP) were used to achieve surface-enhanced resonance Raman scattering (SERRS) and surface-enhanced fluorescence (SEF).

Nanostructured films employed as sensing units in an "electronic tongue" system.

Nanostructured films of lignin (macromolecule extracted from sugar cane bagasse), polypyrrole (conducting polymer) and bis butylimido perylene (organic dye) were used in the detection of trace levels of fluorine (from H2SiF6), chlorine (from NaClO), Pb(+2), Cu(+2), and Cd(+2) in aqueous solutions. Langmuir monolayers on ultrapure water were characterised by surface pressure-mean molecular area (II-A) isotherms. Langmuir-Blodgett (LB) films were transferred onto gold interdigitated electrodes and used as individual sensing units of an electronic tongue system. Impedance spectroscopy measurements were taken with the sensor immersed into aqueous solutions containing the ions described above in different molar concentrations. Fourier transform infrared absorption (FTIR) was employed to identify possible interactions between the LB films and the analytes in solution, and no significant changes could be observed in the FTIR spectra of BuPTCD and Ppy. Therefore, the results for lignin point to an interaction involving the electronic cloud of the phenyl groups with the metallic ions.

Retention of cobalt on a humin derived from brown coal.

In this work, the retention of cobalt on a humin (HU) derived from a brown coal is studied. Through a systematic and coordinated investigation of the behavior of the metal ions in solution (speciation diagrams as a function of pH) and their adsorption and precipitation processes with reactive functional groups of the solid (sorption isotherms), the interactions of different Co(II) species with HU are probed. To further confirm the nature of these interactions, the complementary spectroscopic techniques of FTIR, Raman microspectroscopy, UV-visible absorption and XRD are employed. Molecular modeling techniques are used to gain information about the stability of different Co(II) species as a function of pH, as well as the stability of Co(II) species complexed with benzoic acid, a common surface component of humic substances. It is found that the selectivity that humin has for different Co(II) species, as well as the amount of Co(II) that it can retain, are both highly dependent on pH. Through Raman microspectroscopy measurements, the presence and location of Co(OH)(2) precipitates on the surface of HU is confirmed.

Surface-enhanced Raman scattering on colloidal nanostructures.

Surface-enhanced Raman scattering combines extremely high sensitivity, due to enhanced Raman cross-sections comparable or even better than fluorescence, with the observation of vibrational spectra of adsorbed species, providing one of the most incisive analytical methods for chemical and biochemical detection and analysis. SERS spectra are observed from a molecule-nanostructure enhancing system. This symbiosis molecule-nanostructure is a fertile ground for theoretical developments and a realm of applications from single molecule detection to biomedical diagnostic and techniques for nanostructure characterization.

Molecularly organized Langmuir-Blodgett films from a ruthenium biphosphine complex.

Langmuir-Blodgett (LB) films from a ruthenium complex mer-[RuCl3 (dppb)(4-Mepy)] (dppb = PPh2 (CH2)4PPh2; 4-Mepy = 4-methylpyridine), termed Ru-Pic, display a distinct color, which is different from the coloration exhibited by cast films or chloroform solutions. The solution and cast films are red, while the LB films are green-bluish. The manifestation of the blue color in the LB film finds its explanation in a unique absorption band at 690 nm, which is associated with the oxidation of the phosphine moieties. Fluorescence emission and absorption-reflection infrared spectroscopy measurements revealed the molecular organization in the LB films. In contrast, cast films showed a random distribution of complexes. Surface-enhanced Raman scattering was also used in an attempt to identify the main interactions in Ru-Pic.

Vibrational and surface-enhanced vibrational spectra of 6-nitrochrysene.

The infrared and Raman spectra of solids and thin solid films of 6-nitrochrysene, its electronic spectra, and resonance Raman scattering (RRS) obtained with UV-laser excitation at 325 nm are reported. The vibrational assignment is supported by ab initio computations at the B3LYP/6-311G(d, p) level of theory. The molecular organization in nanometric films evaporated onto smooth metal surfaces of silver and copper was probed using reflection-absorption infrared spectroscopy (RAIRS). The results of the surface-enhanced Raman scattering (SERS) and surface-enhanced infrared absorption (SEIRA) obtained from nanometric films evaporated onto silver island films are also discussed. It was found that the molecule efficiently interacts with silver island film surfaces, and that the interaction leads to extensive photochemical reaction at the metal surface under laser illumination.

Surface-enhanced Raman scattering for ultrasensitive chemical analysis of 1 and 2-naphthalenethiols.

The results of the search for the optimal experimental conditions for ultrasentitive chemical analysis of 1-naphthalenethiol (1-NAT) and 2-naphthalenethiol (2-NAT) using surface-enhanced Raman scattering (SERS) are discussed. The report begins with a review of the vibrational spectra, including infrared and Raman spectra of the target molecules, and the interpretation of the observed frequencies aided by local density functional theory (DFT) calculations at the B3LYP/6-311G(d,p) level of theory. Several metal nanostructures were tested for SERS activity, including island films and colloids of silver, gold and copper. Correspondingly, the most effective laser line for excitation in the visible and near infrared region was sought. The achieved detection limit for 1-naphthalenethiol, and for 2-naphthalenethiol, on silver nanostructures is in the zeptomole regime.

Vibrational spectra and surface-enhanced vibrational spectra of 1-nitropyrene.

The present report on the vibrational spectra of 1-nitropyrene (1NP) describes the infrared and Raman spectra; their interpretation is aided by local density functional theory (DFT) calculations at the B3LYP/6-311G(d, p) level of theory and by the surface-enhanced vibrational spectra (SEVS) with the final objective of trace organic analytical applications. The surface-enhanced Raman scattering (SERS) on silver island films and mixed silver/gold island films was investigated with several laser lines in the visible region. Surface-enhanced infrared absorption (SEIRA) was attempted on silver and gold island films. The interface of the organic 1-NP with smooth metal surfaces of silver and copper was also probed using reflection-absorption infrared (RAIRS) spectra that, in conjunction with the transmission spectra, allow one to extract the molecular orientation in vacuum evaporated thin solid films. Chemical adsorption of 1-NP on silver and further photochemical decomposition of the 1-NP-metal adsorbates was detected with all visible laser lines. Resonance Raman scattering (RRS) using UV-laser excitation at 325 nm was also recorded.

Surface-enhanced Raman scattering and micro-Raman imaging of Langmuir-Blodgett films of rhodium phthalocyanine.

Rhodium phthalocyanine (RhPc) was synthesized and ultra thin Langmuir-Blodgett (LB) films of RhPc were successfully fabricated. The LB film characterization was carried out using both UV-vis absorption spectra and Raman scattering. The Raman spectroscopy was carried out using 633 and 780 nm laser lines. LB films were deposited onto Ag nanoparticles to achieve the surface-enhanced pre-resonance Raman scattering (pre-SERRS) and surface-enhanced Raman scattering (SERS) for both laser lines, respectively, which allowed the characterization of the RhPc ultra thin films. The morphology of the LB RhPc neat film is extracted from micro-Raman imaging.

Surface enhanced fluorescence and Raman imaging of Langmuir-Blodgett azopolymer films.

The spectroscopic properties and surface-enhanced spectra of Langmuir-Blodgett (LB) films of methacrylic homopolymer (HPDR13) are presented. It is shown that LB film displays strong fluorescence attributed to the spatial restrictions imposed by its structure. The emission is observed in conjunction with photoisomerization, a process clearly demonstrated by the formation of surface-relief gratings in the LB film [C.R. Mendonça et al., Macromolecules 32 (1999) 1493]. Surface-enhanced Raman scattering (SERS), Surface-enhanced resonance Raman scattering (SERRS) and surface-enhanced fluorescence (SEF) were observed for LB films of HPDR13 deposited onto silver island films. SERS measurements were also carried out on a sample fabricated with one monolayer LB film deposited onto silver islands followed by one overlayer of silver (LB sandwiched between two layers of silver islands). The polymer interacts very weakly with the metal surface (physisorption), and the enhancement effect is determined by the local electric field enhancement. The strong SERS and SERRS signals were suitable for micro-Raman imaging. Line, area mapping and global images of the LB monolayer on silver island are reported. The transfer ratio in the fabrication of the LB suggests a homogeneous coating of the silver islands, thereby the chemical images show the variation of the SERS intensity due to surface enhancement.