M.A.G. Soler

Stability of citrate-coated magnetite and cobalt-ferrite nanoparticles under laser irradiation: a Raman spectroscopy investigation

In this paper, Raman spectroscopy was used to investigate the chemical and structural properties of citrate-coated Fe/sub 3/O/sub 4/ and CoFe/sub 2/O/sub 4/ nanoparticles. The Raman data obtained from the two samples investigated are compared with the Raman data from the literature of bulk maghemite and bulk hematite. The Raman data are used to discuss the higher structural stability of the CoFe/sub 2/O/sub 4/-based sample in comparison to the Fe/sub 3/O/sub 4/-based sample, when submitted to optical illumination at different intensities.

Raman spectroscopy in magnetic fluids.

In this work Raman spectroscopy was used to investigate uncoated magnetic fluids (UMFs) and coated magnetic fluids (CMFs). The coating agents were N-oleoylsarcosine, dodecanoic acid, and ethoxylated polyalcohol. The Raman probe is the hydroxyl (OH) group chemisorbed at the magnetic nanoparticle surface and the measurements were performed in the typical OH bending and OH stretching regions. The room temperature Raman data obtained from the UMFs and CMFs are compared to each other and with the data obtained from liquid water. Suppression of Raman modes from the MFs are discussed in terms of symmetry reduction and in terms of the interaction between the chemisorbed OH-group and the surrounding medium. The relative grafting coefficient associated to different coatings are estimated from the Raman data. The highest grafting coefficient is achieved with a single coating of dodecanoic acid in the hydrocarbon-based MF. The surface-grafting coefficient of the N-oleoylsarcosine-coated MF reduces when the polar liquid carrier replaces the non-polar liquid carrier. In comparison to liquid water, it was found that the hydrogen bonding between the chemisorbed OH-group and the solvent was enhanced in UMFs and reduced in CMFs.

Spectroscopic Study of Maghemite Nanoparticles Surface-Grafted with DMSA

Nanosized maghemite (below 10 nm average diameter), surface-functionalized with meso-2,3-dimercaptosuccinic acid (DMSA), was investigated with respect to the content of DMSA molecules attached onto its surface and the onset of S-S bridges due to oxidation of neighboring S-H groups. To support our investigation, we introduced the use of photoacoustic spectroscopy to monitor thiol groups (S-H) conjugated with Raman spectroscopy to monitor the disulfide bridges (S-S). The normalized intensity (N(R)) of the Raman feature peaking at 500 cm(-1) was used to probe the S-S bridge whereas the normalized intensity (N(P)) of the photoacoustic band-S (0.42-0.65 μm) was used to probe the S-H moiety. The perfect linearity observed in the N(R) versus (1 - N(P)) plot strongly supports the oxidation process involving neighboring S-H groups as the DMSA surface grafting coefficient increases whereas the approach used in this report allows the evaluation of the [S-H]/[S-S] ratio. The observation of the reduction of the hydrodynamic diameter as the nominal DMSA-grafting increases supports the proposed model picture, in which the intraparticle (interparticle) S-S bridging takes place at higher (lower) DMSA-grafting values.

Raman study of ionic water-based copper and zinc ferrite magnetic fluids

Raman spectroscopy is used to investigate the OH-bending and OH-stretching modes of chemisorbed OH-groups in copper-ferrite and zinc-ferrite water-based magnetic fluid samples. Room-temperature Raman spectra were taken from diluted magnetic fluid samples and compared with the spectrum taken from liquid water. The suppression of the symmetric OH-stretching Raman modes from the ionic magnetic fluid sample spectra is discussed in terms of the replacement of a hydrogen atom from the water molecule by the nanoparticle surface. Moreover, changes on the area ratio between hydrogen bonded and nonhydrogen bonded OH-Raman peaks in the ionic magnetic fluid samples, as compared to the OH-Raman peaks from liquid water, are discussed in terms of changes on the hydrogen bond strength.

Thermal and electrical properties of starch–graphene oxide nanocomposites improved by photochemical treatment

Bionanocomposite films have been prepared by casting an aqueous suspension of acetylated starch (ST) and poly(vinyl alcohol) (PVA) loaded with graphene oxide (GO). A photochemical and reagentless method has been successfully performed to convert the GO phase into reduced graphene oxide (RGO). The nanocomposites have displayed improved thermal and electrical properties when the amount of the GO phase is increased and properly converted to RGO. The molecular-level interactions between components are mainly hydrogen-bonding type according to attenuated total reflectance-Fourier transform infrared (ATR-FTIR) and Raman spectroscopies, as well as thermogravimetric analysis (TGA). Scanning electron microscopy (SEM) has confirmed the effective mixing between the GO and the ST-PVA matrix. The thermal diffusivity and electrical resistivity of ST-GO nanocomposites have increased one order and decreased two orders of magnitude, respectively, after the photochemical treatment. These findings have confirmed the effectiveness of the proposed approach to produce starch-based nanocomposites with improved thermal and electrical properties.

Highly efficient photodynamic therapy colloidal system based on chloroaluminum phthalocyanine/pluronic micelles

Phthalocyanine derivatives comprise the second generation of photosensitizer molecules employed in photodynamic therapy (PDT) and have attracted much attention due to their outstanding photosensitizing performance. Most phthalocyanines are hydrophobic compounds that require association to drug delivery systems for clinical use. In this study, formulations of Pluronic F127 micelles incorporated with chloroaluminum phthalocyanine, or else F127/AlClPc, were produced at optimized conditions aiming at efficient and biocompatible PDT colloidal systems. Absorption/emission spectroscopies, as well as dynamic light scattering were performed to evaluate the optimum conditions for the F127 micelle formation and AlClPc incorporation. The micelles formation was attained with F127 concentrations ranging from 50 to 150mgmL(-1). At these conditions, AlClPc photosensitizer molecules were encapsulated into the hydrophobic micelle core and, therefore, readily solubilized in physiological medium (PBS pH 7.2). Encapsulation efficiency of about 90% resulted from different AlClPc concentrations. Identification of singlet oxygen production by irradiated F127/AlClPc formulations indicated good applicability for PDT. In vitro tests conducted with A549 human lung carcinoma cell line incubated with the F127/AlClPc formulations, at different AlClPc loadings, followed by only 18min of light irradiation (660nm LED, fluence of 25.3J/cm(2)), showed a cellular damage as high as 90% for rather low dosages of AlClPc (0.1-5.0μgmL(-1)). Further, no cytotoxicity occurred on non-irradiated cells. These findings suggest those F127/AlClPc formulations are highly promising for PDT applications, since they are easily prepared and the incubation and irradiation times are significantly shortened.

Raman spectroscopy of magnetoliposomes

In this study Raman spectroscopy was used to investigate monolayer and bilayer magnetite-based magnetoliposomes (MLs). The Raman probe is the hydroxyl (OH) group chemisorbed at the magnetite nanoparticle surface. Measurements were performed at room temperature in the typical OH stretching region. The data gathered for both samples are compared to each other and with those obtained for pure water. In comparison to liquid water (2.74 kcal/ mol), it was found that the hydrogen bond strength between the chemisorbed OH-group and the polar headgroup of the inner phospholipid layer was reduced in both the monolayer (2.22 kcal/mol) and the bilayer (1.83 kcal/mol) ML samples.

Carrier kinetics in quantum dots through continuous wave photoluminescence modeling: A systematic study on a sample with surface dot density gradient

A systematic study is presented of continuous wave (cw) photoluminescence (PL) of self-assembled quantum dots (QDs) grown on GaAs (001) by molecular-beam epitaxy as a function of excitation intensity and QD density. The sample used in this work was grown under nonisotropic indium flux that resulted in a QD density gradient across the sample surface ranging from 0 to 1.8×1011 cm−2. The carrier kinetics in the sample is described by a set of coupled rate equations through which the cw PL data from the GaAs barrier, wetting layer (WL), and QDs were simulated as a function of the excitation intensity and QD density. By comparing the PL data with our simulations we infer that carrier capture into the QD occurs directly from GaAs barrier. Auger and phonon-assisted carrier capture from the WL were found to give negligible contribution. With an increase of the QD density we observe an increase of the nonradiative recombination rates of the barrier and at the WL, which we tentatively correlate with the increase of...

Raman spectroscopy in oleoylsarcosine-coated magnetic fluids: A surface grafting investigation

Raman spectroscopy is used to investigate magnetite nanoparticles pre-coated with oleoylsarcosine and dispersed as stable water-based (WE) and hydrocarbon-based (HE) magnetic fluids (MFs). The Raman spectra obtained from the MF samples and from liquid water were compared and the data discussed in terms of the suppression of the symmetrical hydroxyl (OH) vibrational modes. The effective grafting coefficient of the oleoylsarcosine in the WB-MF, with respect to the HB-MF, was estimated through the OH-stretching Raman modes of the OH-group chemisorbed at the nanoparticle surface. It was found that the OH-grafting coefficient in the HB-MF sample is about 3 times lower than the grafting coefficient in the WB-MF sample.

Excitation Transfer through Quantum Dots Measured by Microluminescence: Dependence on the Quantum Dot Density

In this study, spatially resolved cw photoluminescence of self-assembled InAs quantum dots (QDs) on a GaAs matrix has been observed using the microluminescence surface scan technique. A sample containing QD densities from 0 up to 1600 dots/μm 2 was investigated. It was found that the QD density has a strong influence on the diffusion process and there is evidence of two different mechanisms operating at low and high QD concentration ranges that we interpret as photon recycling and interdot carrier tunneling, respectively.