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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 microRaman 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.

The application of organic thin films as transducer elements in electronic devices has been widely exploited, with the electrostatic layer-by-layer (LbL) technique being one of the most powerful tools to produce such films. The conventional LbL method, however, is restricted in many cases to water soluble compounds. Here, an alternative way to produce LbL films containing iron phthalocyanine (FePc) in non-aqueous media (chloroform) is presented. This film fabrication was made possible by exploiting the specific interactions between Fe and NH(2) groups from PAH, poly(allylamine hydrochloride) used as the supporting layer, leading to the formation of bilayers structured as (PAH/FePc)(n). We have also incorporated silver nanoparticles (AgNPs) in LbL films with (PAH/FePc/AgNP)(n) trilayers, making it possible to achieve the surface-enhanced Raman scattering (SERS) phenomenon. The molecular architecture of the LbL films was determined through different techniques. The growth was monitored with UV-Vis absorption spectroscopy, their morphology characterized by optical and scanning electron (SEM) microscopes, and their molecular organization determined using FTIR. The electrochemical properties of the LbL films were successfully applied in detecting dopamine in KCl aqueous solutions at different concentrations using cyclic voltammetry. The results confirmed that the LbL films from FePc in non-aqueous media keep their electroactivity, while showing an interesting electrocatalytic effect. The SERS phenomenon suggested that FePc aggregates might be directly involved in the maintenance of the electroactivity of the LbL films.

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O resíduo (lodo) gerado nos decantadores das Estações de Tratamento de Água (ETA) possui composição variada, de acordo com a região onde ela está localizada, com o mês de coleta e com o coagulante usado. Neste trabalho foram feitas caracterizações, física, química e mineralógica, deste lodo e ensaios tecnológicos em corpos de prova, com a finalidade de avaliar a possibilidade de incorporação deste resíduo em massa cerâmica para produção de tijolos. Retração linear, absorção de água, porosidade e massa específica aparente e ensaios de resistência à flexão em corpos-de-prova, com diferentes concentrações de lodo, foram avaliadas. Também, foi avaliado o efeito do tipo de floculante usado na ETA, sobre as propriedades dos corpos-de-prova. A análise mineralógica mostrou que estes lodos apresentaram composição parecida com as das argilas usadas pelas cerâmicas. Em geral, a adição destes materiais à massa cerâmica piorou suas propriedades, entretanto, os valores obtidos para as propriedades tecnológicas ainda permaneceram dentro dos valores limites aceitáveis para a produção de tijolos, dependendo da temperatura de queima e da concentração na mistura. O lodo obtido com floculante à base de alumínio, em geral, prejudicou mais as propriedades cerâmicas do que aqueles à base de ferro. Os resultados indicaram que o lodo de ETA pode ser incorporado à massa cerâmica para produzir material cerâmico.

The surface-enhanced Raman scattering (SERS) effect and sensor and biosensor analyses are widely applied to investigate drug-biomolecule interactions or to detect trace amount of analytes. In this work, surface-enhanced resonance Raman scattering (SERRS) and an electronic tongue system using impedance spectroscopy were brought together, combining sensitivity and structural level information. Taking advantage of the use of layer-by-layer (LbL) films of phospholipids as biological membrane mimetic systems, cardiolipin (CLP) and dipalmitoyl phosphatidyl glycerol (DPPG) were applied as transducers onto Pt interdigitated electrodes forming an array of sensing units. This e-tongue system was able to detect the phenothiazine methylene blue (MB) below nanomolar concentrations. SERRS was applied to investigate the MB molecular arrangement (monomers or aggregates) when in contact with the phospholipids at trace levels of concentration. The key point was the adsorption of Ag nanoparticles (AgNPs) within the phospholipid LbL films. This approach did not compromise the e-tongue performance and allowed the recording of in situ SERRS spectra for the LbL films after immersion into MB aqueous solutions. The detection of MB through SERRS gave similar results to those reported in the literature but now with an unprecedented sensitivity.

The synergistic effect produced by nanoparticles when incorporated into different systems used as analytical tools represents a growing research field nowadays. On the other hand, the study of interactions involving pharmacological drugs and biological membranes using phospholipids as mimetic systems is a research field already well established. Here, we combine both the anionic phospholipid dipalmitoyl phosphatidyl glycerol (DPPG) and negative Ag nanoparticles (AgNP) to form layer-by-layer (LbL) multilayered films using the cationic polymer poly(allylamine hydrochloride) (PAH) as the supporting polyelectrolyte, which were further investigated in the presence of a phenothiazine compound (methylene blue -MB). The molecular architecture of the LbL films in terms of controlled growth, morphology with micro and nanometer spatial resolutions, and dispersion of both AgNP and MB within the DPPG matrix was determined combining spectroscopy [ultraviolet-visible (UV-Vis) absorption and micro-Raman spectroscopy] and microscopy [scanning electron microscopy (SEM) and atomic force microscopy (AFM)].The results showed that the LbL films can be grown in a controlled way at nanometer thickness scale with the surface morphology susceptible to the presence of both AgNP and MB. The surface-enhanced phenomenon was applied to investigate the LbL films taking the advantage of the strong surface-enhanced resonance Raman scattering (SERRS) signal presented by the MB molecules. Besides, as MB is a pharmacological drug of interest, its molecular arrangements when dispersed in LbL films containing DPPG, which is the biological membrane mimetic system here, were investigated. In this case, the AgNP played a key role in achieving the MB SERRS signal.