A Direct Immunoassay Based on Surface-Enhanced Spectroscopy Using AuNP/PS-b-P2VP Nanocomposites.

A biosensor was developed for directly detecting human immunoglobulin G (IgG) and adenosine triphosphate (ATP) based on stable and reproducible gold nanoparticles/polystyrene-b-poly(2-vinylpyridine) (AuNP/PS-b-P2VP) nanocomposites. The substrates were functionalized with carboxylic acid groups for the covalent binding of anti-IgG and anti-ATP and the detection of IgG and ATP (1 to 150 µg/mL). SEM images of the nanocomposite show 17 ± 2 nm AuNP clusters adsorbed over a continuous porous PS-b-P2VP thin film. UV-VIS and SERS were used to characterize each step of the substrate functionalization and the specific interaction between anti-IgG and the targeted IgG analyte. The UV-VIS results show a redshift of the LSPR band as the AuNP surface was functionalized and SERS measurements showed consistent changes in the spectral features. Principal component analysis (PCA) was used to discriminate between samples before and after the affinity tests. Moreover, the designed biosensor proved to be sensitive to different concentrations of IgG with a limit-of-detection (LOD) down to 1 µg/mL. Moreover, the selectivity to IgG was confirmed using standard solutions of IgM as a control. Finally, ATP direct immunoassay (LOD = 1 µg/mL) has demonstrated that this nanocomposite platform can be used to detect different types of biomolecules after proper functionalization.

Simultaneous determination of aspartame, cyclamate, saccharin and acesulfame-K in powder tabletop sweeteners by FT-Raman spectroscopy associated with the multivariate calibration: PLS, iPLS and siPLS models were compared.

For the first time, a procedure for simultaneous determination of the main artificial sweeteners, aspartame (ASP), cyclamate (CYC), saccharin (SAC), and acesulfame-K (ACSK) by a spectroscopic method associated with the multivariate calibration is proposed. These analytes were quantified in tabletop sweeteners samples using FT-Raman spectroscopy. Liquid chromatography-tandem mass spectrometry (LC-MS/MS) was used as reference method. Partial least squares (PLS), interval PLS (iPLS), and synergism PLS (siPLS) methods were evaluated in a comparative study where the selected interval models presented better results. Multivariate regression models, such as PLS, iPLS and siPLS were built and the lower root mean square errors for prediction (RMSEP) found were 0.027-0.031% w/w, 0.316-0.363% w/w, 0.082-0.184% w/w, and 0.040-0.049% w/w to ASP, CYC, SAC, and ACSK, respectively. The coefficient of determination for prediction (R2p) varied between 0.978 and 0.979, 0.969-0.977, 0.952-0.994, and 0.959-0.965 for ASP, CYC, SAC and ACSK, respectively. The analysis of model's residues was made by bias and permutation tests to evaluate systematic and trend errors. The selected intervals by iPLS and siPLS were evaluated and the bands related to the vibrational modes of the analytes were assigned with the aid of density functional theory calculations (DFT).

Fake turquoises investigated by Raman microscopy.

Turquoise is frequently adulterated by unscrupulous dealers and, not rarely, simulants are commercialized as true stones. On the other hand, turquoise is a cryptocrystalline mineral and its use in adornments commonly demands some kind of treatment to facilitate its manipulation, such as impregnation using oil or fats, consolidation with resin and stabilization or reconstitution made with resins. In this work, Raman microscopy was employed in the investigation of turquoise adornments aiming to differentiate processed turquoise from fakes or simulants. Only one out of the five adornment objects analyzed was truly stabilized turquoise (powdered turquoise aggregated with a resin). Another one was constituted of turquoise, calcium carbonate, phthalocyanine blue and resin; the other objects were dyed minerals.

Mefenamic acid anti-inflammatory drug: probing its polymorphs by vibrational (IR and Raman) and solid-state NMR spectroscopies.

This work deals with the spectroscopic (supported by quantum chemistry calculations), structural, and morphological characterization of mefenamic acid (2-[(2,3-(dimethylphenyl)amino] benzoic acid) polymorphs, known as forms I and II. Polymorph I was obtained by recrystallization in ethanol, while form II was reached by heating form I up to 175 °C, to promote the solid phase transition. Experimental and theoretical vibrational band assignments were performed considering the presence of centrosymmetric dimers. Besides band shifts in the 3345-3310 cm(-1) range, important vibrational modes to distinguish the polymorphs are related to out-of-phase and in-phase N-H bending at 1582 (Raman)/1577 (IR) cm(-1) and 1575 (Raman)/1568 (IR) cm(-1) for forms I and II, respectively. In IR spectra, bands assigned to N-H bending out of plane are observed at 626 and 575 cm(-1) for polymorphs I and II, respectively. Solid-state (13)C NMR spectra pointed out distinct chemical shifts for the dimethylphenyl group: 135.8 to 127.6 ppm (carbon bonded to N) and 139.4 to 143.3 ppm (carbon bonded to methyl group) for forms I and II, respectively.

Probing the local environment of hybrid materials designed from ionic liquids and synthetic clay by Raman spectroscopy.

Hybrid organic-inorganic material containing Laponite clay and ionic liquids forming cations have been prepared and characterized by FT-Raman spectroscopy, X-ray diffraction, and thermal analysis. The effect of varying the length of the alkyl side chain and conformations of cations has been investigated by using different ionic liquids based on piperidinium and imidazolium cations. The structure of the N,N-butyl-methyl-piperidinium cation and the assignment of its vibrational spectrum have been further elucidated by quantum chemistry calculations. The X-ray data indicate that the organic cations are intercalated parallel to the layers of the clay. Comparison of Raman spectra of pure ionic liquids with different anions and the resulting solid hybrid materials in which the organic cations have been intercalated into the clay characterizes the local environment experienced by the cations in the hybrid materials. The Raman spectra of hybrid materials suggest that the local environment of all confined cations, in spite of this diversity in properties, resembles the liquid state of ionic liquids with a relatively disordered structure.

Block copolymer mimetic self-assembly of inorganic nanoparticles.

Emerging strategies for assembling inorganic nanoparticles into ensembles with multiscale organization are establishing a new paradigm for the synthesis of devices and functional materials with applications ranging from drug delivery to photonics. In this work, the solution self-assembly of amphiphilic ionic block copolymers into morphologically tunable aggregates provides the inspiration and design strategy for nanoparticle building blocks with the essential chemical and conformational features of ionic block copolymer chains in aqueous media. We produce inorganic nanoparticles with surface-tethered mixed brushes of hydrophobic and chargeable hydrophilic chains which self-assemble in polar solvent mixtures into unprecedented hierarchical superstructures analogous to known ionic block copolymer aggregates but with complex organizations of nanoparticles in three dimensions. Electrostatic repulsion between hydrophilic chains forces nonequilibrium pathways to variable kinetic structures with internal lamellar organization of nanoparticles; however, decreasing electrostatic interactions through salt or acid addition allows tunable equilibrium assemblies, including supermicelles and bilayer vesicles of nanoparticles, to be formed. The application of ionic block copolymer assembly principles and mechanisms opens a new chemical toolbox for the organization of nanoparticles into functional assemblies.

A hybrid material assembled by anthocyanins from açaí fruit intercalated between niobium lamellar oxide.

Organic-inorganic hybrid materials can be prepared dispersing organic species into well-defined inorganic nanoblocks. This paper describes the immobilization of natural dyes from the extract of the Brazilian açaí-fruit into two types of layered hexaniobate precursors derived from H(2)K(2)Nb(6)O(17): (i) colloidal dispersion of niobate exfoliated nanoparticles and (ii) niobate pre-intercalated with tetraethylammonium cations (TEA(+)). The restacking of exfoliated particles in the presence of açaí anthocyanins promotes their intercalation and produces stacked layers showing large basal spacing (ca. 50 A). The TEA(+) pre-intercalated niobate provides particles with lower content of dye species than the exfoliated precursor but with higher degree of organization and regularity according to X-ray diffraction data and images obtained by electron microscopies. Vibrational (FTIR and Raman) and (13)C NMR spectroscopies indicate the presence of flavylium cations in the hybrid materials and spectral profiles characteristic of glycosylated anthocyanidins. According to thermal analysis results, the purplish hybrids materials are more stable than the free açaí-dyes. One hybrid sample was heated under air up to 170 degrees C and maintained at this temperature for 240 min. No weight loss events were observed and the sample retained its original color, indicating that the intercalation of anthocyanin into hexaniobate increases its thermal stability. Considering the structural, chemical, optical and thermal properties of the synthesized hybrid materials, they might be good candidates to be investigated for future specialized applications.

Polyaniline/layered zirconium phosphate nanocomposites: secondary-like doped polyaniline obtained by the layer-by-layer technique.

In the present work, nanocomposites of polyaniline (PANI) and layered alpha-Zr(HPO4)2 x H2O (alpha-ZrP) were prepared using two different approaches: (i) the in situ aniline polymerization in the presence of the layered inorganic material and (ii) the layer-by-layer (LBL) assembly using an aqueous solution of the polycation emeraldine salt (ES-PANI) and a dispersion of exfoliated negative slabs of alpha-ZrP. These materials were characterized spectroscopically using mainly resonance Raman scattering at four exciting radiations and electronic absorption in the UV-VIS-NIR region. Structural and textural characterizations were carried out using powder X-ray diffraction (XRD) and scanning electron microscopy (SEM). The polymer obtained by the in situ aniline polymerization is located primarily in the external surface of the inorganic material although aniline monomers were intercalated between alpha-ZrP interlayer regions before oxidative polymerization. Through resonance Raman spectroscopy, it was observed that the formed polymer has semiquinone units (ES-PANI) and also azo bonds (-N=N-), showing that this method results in a polymer with a different structure from the usual "head-to-tail" ES-PANI. The LBL assembly of pre-formed ES-PANI and exfoliated alpha-ZrP particles produces homogeneous films with reproducible deposition from layer to layer, up to 20 bilayers. Resonance Raman (lambda0 = 632.8 nm) spectrum of PANI/ZrP LBL film shows an enhancement in the intensity of the polaronic band at 1333 cm(-1) (upsilonC-N*+) and the decrease of the band intensity at 1485 cm(-1) compared to bulk ES-PANI. Its UV-VIS-NIR spectrum presents an absorption tail in the NIR region assigned to delocalized free charge carrier. These spectroscopic features are characteristic of highly conductive secondary doped PANI suggesting that polymeric chains in PANI/ZrP LBL film have a more extended conformation than in bulk ES-PANI.

The role of cross-linking structures to the formation of one-dimensional nano-organized polyaniline and their Raman fingerprint.

In the present work, the resonance Raman, UV-vis-NIR and scanning electron microscopic (SEM) data of nanorods (about approximately 300 nm in diameter) and nanofibers (about approximately 93 nm in diameter) of PANI are presented and compared. The PANI samples were synthesized in aqueous media with dodecybenzenesulfonic acid (DBSA) and beta-naphtalenesulfonic acid (beta-NSA) as dopants, respectively. The presence of bands at 578, 1400 and 1, 632 cm(-1) in the Raman spectra of PANI-NSA and PANI-DBSA shows that the formation of cross-linking structures is a general feature of the PANI chains prepared in micellar media. It is proposed that these structures are responsible for the one-dimensional PANI morphology formation. In addition, the Raman band at 609 cm(-1) of PANI fibers is correlated with the extended PANI chain conformation.

Surface-enhanced resonance Raman scattering of polyaniline on silver and gold colloids.

The interaction of emeraldine base (PANI-EB) with silver and gold colloids was probed by using Surface-Enhanced Resonance Raman Scattering (SERRS) at 3 different exciting radiations. Due to the great sensitivity of SERRS technique the detection limit of PANI-EB concentration was ca. 2 x 10(-7) mol L(-1) in Ag and Au colloidal suspensions. The UV-vis-NIR spectra of metal colloids in function of PANI-EB concentrations showed that gold colloids present a higher degree of aggregation than silver colloids. SERRS of PANI-EB on metal colloids allowed the study of the polymeric species formed primarily on the metallic surface. The polymer formed after the adsorption of PANI-EB on metallic nanoparticles is strongly dependent on the nature of the metal colloids. The oxidation of PANI-EB to pernigraniline occurred for silver colloids, while a doping process of PANI-EB on Au nanoparticles was evidenced through the observation of the characteristic SERRS spectrum of emeraldine salt at 1064nm.

Spectroscopic characterization of polyaniline formed by using copper(II) in homogeneous and MCM-41 molecular sieve media.

This work emphasizes the important role of the synthetic parameters in the structure of the polymeric material obtained in the aniline polymerization. The polymers formed by the oxidative polymerization of aniline by copper(II) ions in acidic aqueous solution, acetonitrile/water medium, and also copper(II) acetate complex encapsulated into MCM-41 molecular sieve were characterized by resonance Raman spectroscopy using three exciting laser lines and other techniques such as UV-vis, FTIR, and XANES (Nitrogen K edge). Additionally the products were investigated by thermogravimetric analysis and powder X-ray diffraction. When Cu(II) ions in acidic aqueous medium are used, emeraldine salt (ES-PANI) is formed through the usual head-to-tail polymerization mechanism, while in acetonitrile/water medium a polymer is observed having mainly phenazine-like rings, quinonediimine, and/or phenylenediamine segments in the chains, suggesting that a distinct mechanism is operating. The average molecular weights of the free polymers synthesized in water and in acetronile/water were, respectively, ca. 37 300 and 16 900 Da. The encapsulated polymer synthesized in Cu(II)-MCM-41 is a polymeric mixture of (i) ES-PANI and (ii) the polymer obtained when this metal cation was used as oxidant in acetonitrile/water medium. All the characterization data were compared to those ones obtained for standard free polyaniline and also for the encapsulated polymer into mesoporous MCM-41 formed by using persulfate in acidic aqueous medium as oxidant.

Synthesis and photophysical study of highly luminescent coordination compounds of rare earth ions with thenoyltrifluoroacetonate and AZT.

This work presents the study of the interaction between zidovudine (AZT) and rare earth (RE) ions with thenoyltrifluoroacetonate (TTA). The complexes [RE(TTA)(3) x (AZT)(2)] (where RE(III)=Eu and Gd) were prepared by reaction between the [RE(TTA)(3) x (H(2)O)(2)] precursors and AZT dissolved in acetone in the molar ratio 1:2. The obtained luminescent materials were characterized by microanalyses (C, H, N), complexometric titration, IR spectroscopy, X-ray powder diffraction and thermal analysis (DSC and TG/DTG). The luminescence data indicate that the substitution of the two water molecules by AZT in the europium complex causes an intensification of luminescence corresponding to the (5)D(0) -->(7)F(J) (J=0-4) transitions associated with one of the site symmetries. Based on the luminescence spectrum of the Eu(III)-compound the Omega(lambda) experimental intensity parameters (lambda=2 and 4) were calculated for the electronic transitions (5)D(0)-->(7)F(2, 4). The Omega(2) intensity parameter for this new compound is higher than for the precursor compound, suggesting an effective interaction between the AZT and the chemical environment of the Eu(III) ion. Luminescence data confirm that the AZT complex and precursor compound have a comparable emission quantum efficiency.