Vitor M. Zamarion

Ultrasensitive SERS nanoprobes for hazardous metal ions based on trimercaptotriazine-modified gold nanoparticles.

Trimercaptotriazine-modified gold nanoparticles exhibit strong SERS effects, yielding vibrational profiles very sensitive to the presence of heavy metal ions. Because of the contrasting response observed for selected vibrational bands in the SERS profiles, they provide useful nanoprobes for Hg2+ and Cd2+ ions, allowing direct quantitative assays by employing relative peak intensity ratios instead of using internal standards.

The coordination chemistry at gold nanoparticles

In gold nanoparticles the surface metal atoms play a major role, determining their chemical and physical properties by interacting with donor-acceptor species or ligands in a similar way as the related metal complexes. In addition, coherent oscillations of the metal electrons in resonance with the frequency of the exciting light give rise to localized surface plasmons responsible for an enhancement of the local electric field and SERS effect, allowing a wide range of applications in chemistry, biology and nanotechnology. Multifunctional bridging ligands can be employed for simultaneously binding metal ions and surface atoms. The attractive point of this approach is the possibility of exploiting the charge controlled stabilization by the metal complexes, while imparting new characteristics and properties to the modified nanoparticles. As a matter of fact, a new, exciting field of coordination chemistry can be envisaged, combining metal nanoparticles and metal complexes, in the light of supramolecular and surface plasmon resonance effects.

Hybrid Scaffolds Built From PET and Collagen as a Model For Vascular Graft Architecture

A hybrid material with excellent mechanical and biological properties is produced by electrospinning a co-solution of PET and collagen. The fibers are mapped using SEM, confocal Raman microscopy and collagenase digestion assays. Fibers of different compositions and morphologies are intermingled within the same membrane, resulting in a heterogeneous scaffold. The collagen distribution and exposure are found to depend on the PET/collagen ratio. The materials are chemically and mechanically characterized and biologically tested with fibroblasts (3T3-L1) and a HUVEC culture in vitro. All of the hybrid scaffolds show better cell attachment and proliferation than PET. These materials are potential candidates to be used as vascular grafts.

Unraveling the nature of Turkevich gold nanoparticles: the unexpected role of the dicarboxyketone species

By monitoring the synthesis of the Turkevich gold nanoparticles, under appropriate conditions, it was possible to probe the formation of the dicarboxyketone intermediate species, revealing their unexpected strong interaction with the gold nanoparticles. The dicarboxyketone species exhibited a contrasting spectral and kinetics behaviour in relation to citrate stabilized products, explaining several existing controversial points, such as the lack of reproducibility and variable SERS response. In these species, because of the covalent interaction, the chemical mechanisms involved in SERS predominate over the electromagnetic contribution observed for the citrate stabilized gold nanoparticles. New interesting aspects were found, such as a greater stabilization and strong SERS response observed even for the non-aggregated nanoparticles.

How relevant can the SERS effect in isolated nanoparticles be

Gold nanoparticles electrostatically stabilized with negatively charged ruthenium complexes were individually monitored based on their characteristic plasmon bands, by means of hyperspectral dark field microscopy. Very strong SERS enhancements were observed for the isolated gold nanoparticles at exciting wavelengths in resonance with the surface plasmon band, using confocal Raman microscopy, revealing a contrasting behaviour between the agglomerated and non-agglomerated systems. The results highlighted the relevant role played by the surface enhanced resonance Raman mechanisms (SERRS) in isolated nanoparticles, more than compensating for the lack of local hot spots, in relation to the agglomerated systems.

Communication: Chemisorption of muonium on gold nanoparticles: A sensitive new probe of surface magnetism and reactivity

Chemisorption of muonium onto the surface of gold nanoparticles has been observed. Muonium (μ+e-), a light hydrogen-like atom, reacts chemically with uncapped 7 nm gold nanoparticles embedded in mesoporous silica (SBA-15) with a strong temperature-dependent rate. The addition rate is fast enough to allow coherent spin transfer into a diamagnetic muon state on the nanoparticle surface. The muon is well established as a sensitive probe of static or slowly fluctuating magnetic fields in bulk matter. These results represent the first muon spin rotation signal on a nanoparticle surface or any metallic surface. Only weak magnetic effects are seen on the surface of these Au nanoparticles consistent with Pauli paramagnetism.

Gold nanoparticles functionalised with Ru–dicarboxybipyridine–trimercaptotriazine: SERS effect and application in plasmonic dye solar cells

A dicarboxybipyridine–trimercaptotriazine ruthenium complex, primarily designed for dye–sensitised solar cells (DSSC), has been successfully employed in the generation of electrostatically stabilised gold colloids, because of its high negative charge and capability of binding to gold nanoparticles via the sulphur groups. Strong SERS enhancements have been obtained for the isolated gold nanoparticles, as monitored by dark field hyperspectral and confocal Raman microscopy. A preliminary design of TiO2 solar cell incorporating the ruthenium dye in association with the gold nanoparticles, has been tested, in the presence of a cobalt complex mediator. The results were considered rather promising, in spite of the slight decay of efficiency in relation to the original dye cell, owing to lixiviation processes and electron recombination effects at the interface.

Investigation of the Photocatalytic Activity of Titanium Dioxide Films Under Visible Light Measured by Electrospray Mass Spectrometry

We report, for the first time, the photocatalytic activity of pure TiO2 P-25 in the form of thin homogeneous mesoporous films under visible light activation. The study was accomplished by analyzing the photodegradation rate of two water contaminant molecules, 2-naphthol and methyl orange, via an electrospray mass spectrometry technique with the use of ammonium hexafluorophosphate as an internal standard. The employed methodology can also be used to run different semiquantitative assays and study other film mediated photocatalytic processes. It was observed that TiO2 films can easily promote photooxidation of 2-naphthol under the incidence of visible light and in the presence of oxygen gas by showing almost complete photodegradation after about 6 hours of reaction. Photooxidation of methyl orange was also observed, yet the decay rate was slower. This process was also confirmed through identification of by-products of the reaction via mass spectrometry and through the decay of the absorbance peak at 468 nm via UV-vis spectrophotometry. This photoactivity of pure TiO2 P-25 films under visible light is attributed to its narrower band gap that occurs because of the thermal treatment that titania undergoes in the process of synthesis of the films. The use of these films as photocatalysts is an advantage since they work as a heterogenous catalyst in the absence of UV radiation.