The prion fragment PrP106-127 adopts a secondary structure typical of aggregated fibrils in langmuir monolayers of brain lipid extract.

Understanding protein aggregation is essential to unveil molecular mechanisms associated with neurodegenerative diseases such as Alzheimer's, Huntington's and spongiform encephalopathy, particularly to determine the role of interaction with cell membranes. In this study, we employ Langmuir monolayers as cell membrane models to mimic interaction with the peptide KTNMHKHMAGAAAAGAVVGGLG-OH, a fragment from the human prion protein including residues 106-127, believed to be involved in protein aggregation. Using in situ polarization-modulated infrared reflection adsorption spectroscopy (PM-IRRAS) for Langmuir monolayers and FTIR for solid films, we found that PrP106-127 adopts mainly ß-sheets, random coils and ß-turns in Langmuir monolayers and in Langmuir-Blodgett (LB) and cast films. This also applies to monolayers and solid films made with PrP106-127 and a brain total lipid extract (BTLE). In contrast, some α-helices are observed in the secondary structure of PrP106-127 in monolayers, and especially in solid films, of 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC). In summary, in a model representing brain cells (BTLE), the secondary structure of PrP106-127 is typical of fiber aggregates, while aggregation is unlikely if PrP106-127 interacts with a membrane model (DOPC) characteristic of mammalian cells.

Evolution of Electronic Circuits using Carbon Nanotube Composites.

Evolution-in-materio concerns the computer controlled manipulation of material systems using external stimuli to train or evolve the material to perform a useful function. In this paper we demonstrate the evolution of a disordered composite material, using voltages as the external stimuli, into a form where a simple computational problem can be solved. The material consists of single-walled carbon nanotubes suspended in liquid crystal; the nanotubes act as a conductive network, with the liquid crystal providing a host medium to allow the conductive network to reorganise when voltages are applied. We show that the application of electric fields under computer control results in a significant change in the material morphology, favouring the solution to a classification task.

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%.

Layer-by-layer technique as a new approach to produce nanostructured films containing phospholipids as transducers in sensing applications.

Phospholipids are widely used as mimetic systems to exploit interactions involving biological membranes and pharmacological drugs. In this work, the layer-by-layer (LbL) technique was used as a new approach to produce multilayered thin films containing biological phospholipids applied as transducers onto Pt interdigitated electrodes forming sensing units of an electronic tongue system. Low concentrations (nM level) of a phenothiazine compound were detected through impedance spectroscopy. Both negative 1,2-dipalmitoyl-sn-3-glycero-[phosphor-rac-(1-glycerol)] (DPPG) and zwitterionic l-alpha-1,2-dipalmitoyl-sn-3-glycero-phosphatidylcholine (DPPC) phospholipids were used to produce the LbL films, whose molecular architecture was monitored combining spectroscopy and microscopy at micro and nanoscales. The sensor array was complemented by Langmuir-Blodgett (LB) monolayers of DPPG and DPPC deposited onto Pt interdigitated electrodes as well. It was found that the distinct molecular architecture presented by both LbL and LB films plays a key role on the sensitivity of the sensor array with the importance of the LbL films being demonstrated by principal component analysis (PCA).

Sensor array made with nanostructured films to detect a phenothiazine compound.

The detection of trace amounts of phenothiazines with fast, direct methods is important for medical applications and the pharmaceutical industry. In this paper we explore the concept of an electronic tongue to detect methylene blue (MB), with a sensor array comprising 6 units. These units were a bare Pt electrode, and Pt electrodes coated with 1-layer LB films of dipalmitoyl phosphatidylcholine (DPPC) and dipalmitoyl phosphatidylglycerol (DPPG), a 5-layer LB film of stearic acid, and 10 nm PVD films of bis benzimidazo perylene (AzoPTCD) and iron phthalocyanine (FePc). The electrical response obtained with impedance spectroscopy varied with the sensing unit, in spite of the small film thickness, thus indicating good cross-sensitivity. Upon treating the capacitance data at 1 kHz with Principal Component Analysis (PCA), the sensor array was capable of distinguishing MB solutions from ultrapure water down to 1 nM. This unprecedented high sensitivity was probably due to strong interactions between MB and DPPC and DPPG, as the sensing units of these phospholipids gave the most important contributions to the PCA plots. Such strong interaction was not manifested in the surface pressure-area isotherms of co-spread monolayers of MB and DPPC or DPPG, which emphasizes the high sensitivity of the electrical measurements in ultrathin films in contact with liquids, now widely exploited in electronic tongues.

Exploiting distinct molecular architectures of ultrathin films made with iron phthalocyanine for sensing.

The possibility of generating distinct film properties from the same material is crucial for a number of applications, which can only be achieved by controlling the molecular architecture. In this paper we demonstrate as a proof-of-principle that ultrathin films produced from iron phthalocyanine (FePc) may be used to detect trace amounts of copper ions in water, where advantage was taken of the cross sensitivity of the sensing units that displayed distinct electrical properties. The ultrathin films were fabricated with three methods, namely physical vapor deposition (PVD), Langmuir-Blodgett (LB), and electrostatic layer-by-layer (LbL) techniques, where for the latter tetrasulfonated phthalocyanine was used (FeTsPc). PVD and LB films were more homogeneous than the LbL films at both microscopic and nanoscopic scales, according to results from micro-Raman spectroscopy and atomic force microscopy (AFM), respectively. From FTIR spectroscopy data, these more homogeneous films were found to have FePc molecules oriented preferentially, tilted in relation to the substrate surface, while FeTsPc molecules were isotropically distributed in the LbL films. Impedance spectroscopy measurements with films adsorbed onto interdigitated gold electrodes indicated that the electrical response depends on the type of film-forming method and varies with incorporation of copper ions in aqueous solutions. Using principal component analysis (PCA), we were able to exploit the cross sensitivity of the sensing units and detect copper ions (Cu(2+)) down to 0.2 mg/L, not only in ultrapure water but also in distilled and tap water. This level of sensitivity is sufficient for quality control of water for human consumption, with a fast, low-cost method.

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).