Emerson M. Girotto

Nanoholes as nanochannels: flow-through plasmonic sensing.

We combine nanofluidics and nanoplasmonics for surface-plasmon resonance (SPR) sensing using flow-through nanohole arrays. The role of surface plasmons on resonant transmission motivates the application of nanohole arrays as surface-based biosensors. Research to date, however, has focused on dead-ended holes, and therefore failed to harness the benefits of nanoconfined transport combined with SPR sensing. The flow-through format enables rapid transport of reactants to the active surface inside the nanoholes, with potential for significantly improved time of analysis and biomarker yield through nanohole sieving. We apply the flow-through method to monitor the formation of a monolayer and the immobilization of an ovarian cancer biomarker specific antibody on the sensing surface in real-time. The flow-through method resulted in a 6-fold improvement in response time as compared to the established flow-over method.

Attomolar Protein Detection Using in-Hole Surface Plasmon Resonance

An in-hole nanohole surface plasmon resonance sensing scheme is demonstrated. Arrays of periodic nanoholes milled through thin layers of SiO(x) and gold were used to detect the binding of organic and biological molecules inside the nanoholes, while blocking the gold surfaces outside the holes. This new approach is more efficient than the previous nanohole array method, where the response was related to binding events taking place inside of the holes and on the top gold surface. The improved sensitivity to binding events and lower detection limit are related to resonant surface plasmon enhanced transmission through the arrays of nanoholes. The sensitivity was found to be 650 nm/RIU and the detection of three attomoles of proteins was estimated from this scheme.

Hydrogels based on PAAm network with PNIPAAm included: hydrophilic–hydrophobic transition measured by the partition of Orange II and Methylene Blue in water

Abstract This work describes the transition from hydrophilic to hydrophobic in hydrogels of Polyacrylamide (PAAm) having Poly(N-isopropylacrylamide) (PNIPAAm) included. The transition was measured through the partition coefficient, K, Orange II and Methylene Blue dyes at several temperatures, using different amount of Acrylamide (AAm), Methylene-bis-acrylamide (MBAAm), as cross-linking agent, and PNIPAAm. The dye concentration in the gel and the solution were measured using UV–Vis spectroscopy. Values of partition coefficient, K, were determined as the ratio of the dye concentration in hydrogel relative to water. Methylene Blue, the less hydrophilic dye, showed higher K values when compared to Orange II, more hydrophilic one. Value of K depends on the temperature and on the PNIPAAm content. The PNIPAAm chains are solvated by water and randomly distributed at temperatures below 32 °C, the LCST of PNIPAAm, but collapse near or above the LCST. The collapsed PNIPAAm chains induce a more hydrophobic environment that increases the solubility of Methylene Blue and decreases the solubility of Orange II in the hydrogels of PAAm with PNIPAAm included. These hydrogels show potential application concerning the separation processes, where the temperature and/or the hydrophilicity control the diffusion.

Transport properties of V2O5/polypyrrole nanocomposite prepared by a sol-gel alkoxide route

Nanocomposites of V2O5 xerogel and polypyrrole (Ppy) were prepared from a vanadyl tris(isopropoxide) precursor and pyrrole monomer by in situ oxidative polymerization of the pyrrole in the sol stage followed by gelation. Unlike previous sol-gel nanocomposite synthetic routes, the gel forms a stable solution from which thin homogeneous films can be cast. The nanocomposite was characterized by XRD, FTIR and electrochemical measurements. Three different thin film types with different spatial arrangements were used to characterize the compensation of charge. X-ray diffraction reveals that the Ppy chains are intercalated within the interlayer region of the V2O5, leading to an increase in the d-spacing from 11.85 Afor V2O5 to 13.8 Afor the nanocomposite. Electrogravimetric results showed that electroneutrality during charging and discharging is achieved predominantly by Litransport. EQCM studies of a bilayer film arrangement with the nanocomposite cast over an electropolymerized film of Ppy revealed that the nanocomposite is an effective barrier for anion transport. The nanocomposite showed a higher specific capacity (283 A h kg � 1 ) than that of V2O5 (236 A h kg � 1 ). This result was attributed to differences in structure between the two materials. The galvanostatic intermittent titration technique (GITT) was used to obtain the diffusion coefficients of Liin the nanocomposite and the V2O5 xerogel. These values range from 2� /10 � 11 to 3 � /10 � 13 cm 2 s � 1 , decreasing as the amount of intercalated Liis increased. For V2O5 the Lidiffusion coefficient ranged from 1� /10 � 12 to 8 � /10 � 14 cm 2 s � 1 , also decreasing as the amount of intercalated Liincreased. In situ resistance measurements revealed a very high conductivity over the potential range of 0.4 to � /0.7 V( vs. Ag/AgNO3) for the nanocomposite, more than a factor of five larger than that for V2O5. # 2002 Elsevier Science B.V. All rights reserved.

Surface spin disorder effects in magnetite and poly(thiophene)-coated magnetite nanoparticles

Chemically synthesized magnetite and poly(thiophene)-coated magnetite nanoparticles and the correlations between their magnetic, structural, and microstructural properties are investigated. A typical superparamagnetic behavior was observed for faceted nanoparticle agglomerates of magnetite and nanocomposite. In nanocomposites, the polymer layer causes a sharp decrease in the spin disorder, which reduces the anisotropy constant significantly. This happens because the intimate contact between magnetite and poly(thiophene) leads to charge transfer from the polymer to the core via polaron interactions, causing a structural rearrangement of the nanoparticles and suppression of the spin movement at the surface. As this dynamic interaction can tune the core dimensions, the magnetic properties of nanocomposites can be tuned by controlling the core size through polymer coating. These characteristics can be exploited to design high-performance magnetically tunable nanodevices and applied in many areas of biomedicin...

Preparation and cytotoxicity of N,N,N-trimethyl chitosan/alginate beads containing gold nanoparticles

Polyelectrolyte complex beads based on N,N,N-trimethyl chitosan (TMC) and sodium alginate (ALG) were obtained. This biomaterial was characterised by FTIR, TGA/DTG, DSC and SEM analysis. The good properties of polyelectrolyte complex hydrogel beads were associated, for the first time, with gold nanoparticles (AuNPs). Through a straightforward methodology, AuNPs were encapsulated into the beads. The in vitro cytotoxicity assays on the Caco-2 colon cancer cells and healthy VERO cells showed that the beads presented good biocompatibility on both cell lines, whereas the beads loaded with gold nanoparticles (beads/AuNPs) was slightly cytotoxic on the Caco-2 and VERO cells.

Synthesis of Ag-PVA and Ag-PVA/PET-s20 composites by supercritical CO2 method and study of silver nanoparticle growth

Supercritical CO2 has been used to prepare silver polymer composites, silver/poly(vinyl alcohol) and silver/poly(vinyl alcohol)/sulfonated poly(ethylene terephthalate) through impregnation of a silver precursor in solid-state polymeric matrices followed by thermal reduction of the silver precursor. X-ray diffraction, scanning electron microscopy, energy dispersive spectroscopy, atomic force microscopy, thermogravimetric analysis and UV/vis spectroscopy indicate that synthesis conditions and polymeric matrix composition affect silver particle size, shape and distribution in polymeric matrices. Silver particles are smaller, have a more uniform shape and present narrower size distribution in PVA-rich than in PETs-rich composites.

Polyelectrolyte complex containing silver nanoparticles with antitumor property on Caco-2 colon cancer cells.

Polyelectrolyte complex (beads) based on N,N,N-trimethyl chitosan/alginate was successful obtained and silver nanoparticles (AgNPs) were loaded within beads. In vitro cytotoxicity assays using beads/silver nanoparticles (beads/AgNPs) provided results, indicating that this material significantly inhibited the growth of colon cancer cells (Caco-2). In vitro release studies showed that the beads stabilized AgNPs and repressed Ag(0) oxidation under gastric conditions (pH 2.0). On the other hand, at physiological condition (pH 7.4) the beads/AgNPs released 3.3 μg of Ag(+) per each beads milligram. These studies showed that the concentration of Ag(+) released (3.3 μg) was cytotoxic for the Caco-2 cells and was not cytotoxic on healthy VERO cells. This result opens new perspectives for the manufacture of biomaterials based on beads/AgNPs with anti-tumor properties.

A urethane-based multimethacrylate mixture and its use in dental composites with combined high-performance properties

OBJECTIVES To synthesize and characterize different molar weight urethane multimethacrylates with a single stage (one-pot) procedure. To prepare and characterize the properties of related composites. METHODS Two methacrylate precursors were initially synthesized. Then, these precursors and the multimethacrylate system formed by their coupling were characterized by FTIR and (1)H NMR. The final product was used as a matrix (with TEGDMA and SiO2 silanized microparticles) in the preparation of composites and their physical and mechanical properties were compared to those of a bis-GMA-based resin. Water sorption and solubility measurements of the composites were also performed. RESULTS FTIR and NMR suggested that the proposed synthesis route yields a mixture of mainly urethane-di, -tri, and tetramethacrylates. The composites presented low polymerization shrinkage (e.g. 1.88±0.08% for a resin with 70% of SiO2) and high flexural strength (e.g. 124.74±9.68 MPa for a resin with 65% of SiO2) when compared to the bis-GMA based resin and other composites found to date. Water sorption and solubility results show that the composites were deemed compliant with ISO 4049 requirements. SIGNIFICANCE The mixture containing different molar weight of urethane multimethacrylates showed to be an excellent substitute for bis-GMA, achieving an equilibrium of properties (unlike reports elsewhere which show the enhancement of some parameters in detriment to others) and composites with low polymerization shrinkage, suitable microhardness and degree of conversion, and up to standard water sorption/solubility and flexural strength.

Chemical characterization of BiFeO3 obtained by Pechini method

This work describes the synthesis and characterization of BiFeO3 obtained by the Pechini route using bismuth nitrate and iron nitrate as precursors. The powders were annealed at 800 °C in air for 2 h. X-ray diffraction patterns showed that the material presents two phases, BiFeO3 (95%) and α-Bi2O3 (5%). The ferroelectric transition of the sample at 821 °C was detected by differential thermal analysis. Results of analyses by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and energy dispersive X-ray fluorescence (EDX) showed that the sample is chemically homogeneous. Transmission electron microscopy images revealed that the sample is uniform and contains spherical particles with an average size of 30 nm.