Antonio Riul - Academia.edu (original) (raw)

Papers by Antonio Riul

2012 11th International Conference on Machine Learning and Applications, 2012

The correct classification of sugar according to its physico-chemical characteristics directly in... more The correct classification of sugar according to its physico-chemical characteristics directly influences the value of the product and its acceptance by the market. This study shows that using an electronic tongue system along with established techniques of supervised learning leads to the correct classification of sugar samples according to their qualities. In this paper, we offer two new real, public and non-encoded sugar datasets whose attributes were automatically collected using an electronic tongue, with and without pH controlling. Moreover, we compare the performance achieved by several established machine learning methods. Our experiments were diligently designed to ensure statistically sound results and they indicate that k-nearest neighbors method outperforms other evaluated classifiers and, hence, it can be used as a good baseline for further comparison.

Journal of nanoscience and nanotechnology, 2007

Nanostructured films of lignin (macromolecule extracted from sugar cane bagasse), polypyrrole (co... more Nanostructured films of lignin (macromolecule extracted from sugar cane bagasse), polypyrrole (conducting polymer) and bis butylimido perylene (organic dye) were used in the detection of trace levels of fluorine (from H2SiF6), chlorine (from NaClO), Pb(+2), Cu(+2), and Cd(+2) in aqueous solutions. Langmuir monolayers on ultrapure water were characterised by surface pressure-mean molecular area (II-A) isotherms. Langmuir-Blodgett (LB) films were transferred onto gold interdigitated electrodes and used as individual sensing units of an electronic tongue system. Impedance spectroscopy measurements were taken with the sensor immersed into aqueous solutions containing the ions described above in different molar concentrations. Fourier transform infrared absorption (FTIR) was employed to identify possible interactions between the LB films and the analytes in solution, and no significant changes could be observed in the FTIR spectra of BuPTCD and Ppy. Therefore, the results for lignin poin...

Synthetic Metals, 2005

Langmuir films of a tetracarboxylic perylene derivative and polypyrrole display condensed surface... more Langmuir films of a tetracarboxylic perylene derivative and polypyrrole display condensed surface pressure isotherms that are shifted when Cu 2+ ions are added to the ultrapure water subphase. These films were transferred onto interdigitated gold electrodes leading to Y-type Langmuir-Blodgett (LB) films. The electrodes modified with 5-layer LB films were immersed into a flask with ultrapure water and water containing Cu 2+ ions at concentrations ranging from mM to M. Impedance measurements indicated a distinct electrical response for the two types of films. Although the materials chosen have no specificity for ionic metals, they can be combined for detecting trace levels of Cu 2+ , which may be exploited in water quality monitoring.

Applied Surface Science, 2014

Alternative energy sources are on a global demand, with fuel cells as promising devices from mobi... more Alternative energy sources are on a global demand, with fuel cells as promising devices from mobile to stationary applications. Nafion ® is at the heart of many of these appliances, being mostly used due to its high proton conduction and good chemical stability at ambient temperature in proton exchange membranes (PEM). Therefore, methanol permeation throughout Nafion ® films reduces drastically the performance of direct methanol fuel cells (DMFC). We present here the deposition of layer-by-layer (LbL) nanostructured thin films of poly(allylamine hydrochloride) (PAH) and poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS) onto commercial Nafion ® 212 membranes. It was observed a good adherence of the LbL films onto Nafion ® 212, with UV-vis results displaying a linear characteristic growth, indicative that the same amount of material was deposited at each deposition step during the layer-bylayer assembly. In addition, the LbL films also act as a good barrier to avoid methanol crossover, with an observed reduction in the methanol permeation from 5.5 × 10 −6 cm 2 s −1 to 3.2 × 10 −6 cm 2 s −1 , respectively to pristine Nafion ® 212 and a 5-bilayer PAH/PEDOT:PSS LbL film deposited on Nafion ® 212. The measured power density in a DMFC set-up was not significantly changed (∼12 mW cm −2 ) due to the LbL films, since the PAH/PEDOT:PSS nanostructure is impeding water and ion transport, consequently affecting the proton conduction throughout the membrane.

Sensors and Actuators B: Chemical, 2015

Fast, simple inspection of liquids such as coffee, wine and body fluids is highly desirable for f... more Fast, simple inspection of liquids such as coffee, wine and body fluids is highly desirable for food, beverage and clinical analysis. Electronic tongues are sensors capable of performing quantitative and qualitative measurements in liquid substances using multivariate analysis tools. Earlier attempts to fulfil this task using only a few drops (microliters) of sample did not yield rational results with non-electrolytes e.g. sucrose (sweetness). We report here the fabrication and testing of a microfluidic e-tongue able to distinguish electrolytes from non-electrolytes, covering also the basic tastes relevant to human gustative perception. The sensitivity of our device is mainly attributed to the ultrathin nature of an array formed by non-selective sensing units. The electronic tongue is composed of an array of sensing units designed with a microchannel stamped in a poly(dimethylsiloxane) (PDMS) matrix and sealed onto gold interdigitated electrodes (IDEs). The IDEs are then coated in situ with a 5-bilayer film deposited by the layer-by-layer (LbL) technique. The cationic layer is derived from polyallylamine chloride (PAH). The anionic layer is either poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) PEDOT:PSS, polypyrrole or nickel tetrasulfonated phthalocyanine. When compared to a conventional electronic tongue our system is three times faster and requires only microliters of sample. Applying Principal Component Analysis to the data yields a high correlation for all substances tested. This microfluidic e-tongue has the potential for producing low-cost, easily integrated, multi-functional sensor for food, beverages, in addition to clinical and environmental applications.

Optics & Laser Technology, 2015

ABSTRACT Electronic tongue (e-tongue) sensors based on impedance spectroscopy have emerged as a p... more ABSTRACT Electronic tongue (e-tongue) sensors based on impedance spectroscopy have emerged as a potential technology to evaluate the quality and chemical composition of food, beverages, and pharmaceuticals. E-tongues usually employ transducers based on metal interdigitated electrodes (IDEs) coated with a thin layer of an active material, which is capable of interacting chemically with several types of analytes. IDEs are usually produced by photolithographic methods, which are time-consuming and costly, therefore, new fabrication technologies are required to make it more affordable. Here, we employed femtosecond laser ablation with pulse duration of 50 fs to microfabricate gold IDEs having finger width from 2.3 μm up to 3.2 μm. The parameters used in the laser ablation technique, such as light intensity, scan speed and beam spot size have been optimized to achieve uniform IDEs, which were characterized by optical and scanning electron microscopy. The electrical properties of gold IDEs fabricated by laser ablation were evaluated by impedance spectroscopy, and compared to those produced by conventional photolithography. The results show that femtosecond laser ablation is a promising alternative to conventional photolithography for fabricating metal IDEs for e-tongue systems.

VII Brazilian Symposium on Neural Networks, 2002. SBRN 2002. Proceedings., 2002

... Humberto Costa de Sousa André CPLF Carvalho Instituto de Ciências Matemáticas e de Computaç .... more ... Humberto Costa de Sousa André CPLF Carvalho Instituto de Ciências Matemáticas e de Computaç ... Antonio Riul Jr Luiz HC Mattoso EMBRAPA Instrumentaçao Agropecuária CP 741, 13560 ... and variety (Cabernet Sauvignon), but different brand - classes A and C; same variety ...

International Journal of Molecular Sciences, 2013

We report on optimized architectures containing layer-by-layer (LbL) films of natural rubber late... more We report on optimized architectures containing layer-by-layer (LbL) films of natural rubber latex (NRL), carboxymethyl-chitosan (CMC) and magnetite (Fe 3 O 4 ) nanoparticles (MNPs) deposited on flexible substrates, which could be easily bent by an external magnetic field. The mechanical response depended on the number of deposited layers and was explained semi-quantitatively with a fully atomistic model, where the LbL film was represented as superposing layers of hexagonal graphene-like atomic arrangements deposited on a stiffer substrate. The bending with no direct current or voltage being applied to a supramolecular structure containing biocompatible and antimicrobial materials represents a proof-of-principle experiment that is promising for tissue engineering applications in biomedicine.

Thin Solid Films, 2008

The selective determination of alcohol molecules either in aqueous solutions or in vapor phase is... more The selective determination of alcohol molecules either in aqueous solutions or in vapor phase is of great importance for several technological areas. In the last years, a number of researchers have reported the fabrication of highly sensitive sensors for ethanol detection, based upon specific enzymatic reactions occurring at the surface of enzyme-containing electrodes. In this study, the enzyme alcohol dehydrogenase (ADH) was immobilized in a layer-by-layer fashion onto Au-interdigitated electrodes (IDEs), in conjunction with layers of PAMAM dendrimers. The immobilization process was followed in real time using quartz crystal microbalance (QCM), indicating that an average mass of 52.1 ng of ADH was adsorbed at each deposition step. Detection was carried out using a novel strategy entirely based upon electrical capacitance measurements, through which ethanol could be detected at concentrations of 1 part per million by volume (ppmv).

Thin Solid Films, 1996

The surface pressure rr of two component monolayers of stearic acid (SA) and 3,4-didecyloxy-2,5-d... more The surface pressure rr of two component monolayers of stearic acid (SA) and 3,4-didecyloxy-2,5-di(4-nitrophenylazomethine) thiopbene (DNAT) has been measured at the air water interface by the Wilhelmy method as a function of mean molecular area at various compositions. The surface properties of these mixed films were interpreted in terms of both the additivity rule of molecular areas and the two-dimensional phase rule applied to collapse pressures. Results indicate that SA is miscible with DNAT to up to XSA = 0.5. At XSA > 0.5 phase separation occurs and at rt > 14 mN m ~ DNAT is ejected from the highly ordered SA film matrix. The index of refraction and thickness of these films dielectrics were determined through surface plasmon (SP) measurements on approximately 500 • thick silver substrates. Horizontal lifting was used to transfer the Langmuir Blodgen monolayers to glass slides coated with silver. Mixed solid films of DNAT up to 10% (by weight) in polystyrene matrices with thicknesses ranging from 4 to 12/am were also prepared, indices and thicknesses being measured using the m-line technique. This allowed us to estimate the index of pure DNAT as a cross-check on the SP results. Since index determinations from these techniques are in essential agreement in terms of linear refractivity, we are able to discuss the structural implications of the SP-measured monolayer film thicknesses.

The Journal of Physical Chemistry B, 2008

The possibility of generating distinct film properties from the same material is crucial for a nu... more 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.

The Journal of Physical Chemistry B, 2002

ABSTRACT A molecular-level interaction between biphosphine ruthenium complexes and stearic acid h... more ABSTRACT A molecular-level interaction between biphosphine ruthenium complexes and stearic acid has been observed in Langmuir and Langmuir−Blodgett (LB) films. Similar results were obtained for the ruthenium complexes mer-[RuCl3(dppb)(4-Mepy)] (dppb = PPh2(CH2)4PPh2; 4-Mepy = 4-methylpyridine) (Rupic) and mer-[RuCl3(dppb)(py)], (pyridine) (Rupy), which differ by the substituent group in the pyridine ring. The interaction was manifested in the Langmuir films by a nonlinear increase in the area per molecule and in surface potential with the relative concentration of the ruthenium complex in the mixture. In the LB films, interaction with stearic acid occurred via complexation with Rupy or Rupic, even though the latter are not charged. It is suggested that one of the chlorides is labilized, thus promoting complexation and keeping the Ru(III) oxidation state for the complex. Complexation was confirmed through FTIR data. Interaction with stearic acid enhanced the color change characteristic of biphosphine ruthenium complexes, which may be associated with an order-induced effect or with the exposure to the water subphase in the LB film preparation. In addition, X-ray diffraction experiments failed to detect separate domains of cadmium stearate, which is also attributed to the molecular-level interaction that prevents separate stearic acid or cadmium stearate domains from being formed.

The Analyst, 2010

This minireview describes the main developments of electronic tongues (e-tongues) and taste senso... more This minireview describes the main developments of electronic tongues (e-tongues) and taste sensors in recent years, with a summary of the principles of detection and materials used in the sensing units. E-tongues are sensor arrays capable of distinguishing very similar liquids employing the concept of global selectivity, where the difference in the electrical response of different materials serves as a fingerprint for the analysed sample. They have been widely used for the analysis of wines, fruit juices, coffee, milk and beverages, in addition to the detection of trace amounts of impurities or pollutants in waters. Among the various principles of detection, electrochemical measurements and impedance spectroscopy are the most prominent. With regard to the materials for the sensing units, in most cases use is made of ultrathin films produced in a layer-by-layer fashion to yield higher sensitivity with the advantage of control of the film molecular architecture. The concept of e-tongues has been extended to biosensing by using sensing units capable of molecular recognition, as in films with immobilized antigens or enzymes with specific recognition for clinical diagnosis. Because the identification of samples is basically a classification task, there has been a trend to use artificial intelligence and information visualization methods to enhance the performance of e-tongues.

Synthetic Metals, 2003

An electronic tongue composed of six different sensing units: a bare interdigitated electrode, an... more An electronic tongue composed of six different sensing units: a bare interdigitated electrode, and interdigitated electrodes coated with stearic acid (SA), a polyaniline oligomer (16-mer), polypyrrole (PPy) and mixtures (1:1, w/w) of 16-mer/SA and PPy/SA, was able to distinguish salt, sweet, bitter and acidic solutions. The films were deposited by the Langmuir-Blodgett (LB) technique onto interdigitated electrodes, and impedance studies were performed over the frequency range 20-10 5 Hz. The sensor is able to distinguish between different brands of mineral water, tea and coffee and can also differentiate tastants below the human detection threshold, proving that conducting polymers are useful sensing materials and transducers for this sort of application. #

Sensors and Actuators B: Chemical, 2004

... 4. Yet, one would need, ideally, a complete library with the response of wines. Given a sampl... more ... 4. Yet, one would need, ideally, a complete library with the response of wines. Given a sample of any wine already studied, one could then determine its brand, variety and vintage. Therefore, we need to go beyond PCA analysis for this purpose. ...

Review of Scientific Instruments, 2009

We present a compact and easy to handle instrument developed to perform rapid analysis of liquids... more We present a compact and easy to handle instrument developed to perform rapid analysis of liquids utilizing an &amp;amp;amp;amp;amp;amp;amp;amp;amp;quot;electronic tongue&amp;amp;amp;amp;amp;amp;amp;amp;amp;quot; system. Briefly, the e-tongue used here is based on impedance measurements of an array of sensing units fabricated with ultrathin films of different materials deposited onto gold interdigitated electrodes. The instrument has the capability of measuring up to eight different sensor sets, each comprising an array of eight sensing units, and can perform a series of measurements in less than half of an hour. Additionally, there is a user-friendly software interface for instrument control, allowing the statistical correlation of samples using principal component analysis.

Polymer, 2003

Langmuir -Blodgett (LB) films from a ruthenium complex, mer-[RuCl 3 (dppb)(py)] (dppb ¼ PPh 2 (CH... more Langmuir -Blodgett (LB) films from a ruthenium complex, mer-[RuCl 3 (dppb)(py)] (dppb ¼ PPh 2 (CH 2 ) 4 PPh 2 ; py ¼ pyridine) (Rupy), and from mixtures with varied amounts of polyaniline (PANi) were fabricated. Molecular-level interactions between the two components are investigated by surface potential, dc conductivity and Raman spectroscopy measurements, particularly for the mixed film with 10% of Rupy. For the latter, the better miscibility led to an interaction with Rupy inducing a decrease in the conducting state of PANi, as observed in the Raman spectra and conductivity measurement. The interaction causes the final film properties to depend on the concentration of Rupy, and this was exploited to produce a sensor array made up of sensing units consisting of 11-layer LB films from pure PANi, pure Rupy and mixtures with 10 and 30% of Rupy. It is shown that the combination of only four non-specific sensing units allows one to distinguish the basic tastes detected by biological systems, viz. saltiness, sweetness, sourness and bitterness, at the mM level. q

Materials Science and Engineering: C, 2014

The introduction of spraying procedures to fabricate layer-by-layer (LbL) films has brought new p... more The introduction of spraying procedures to fabricate layer-by-layer (LbL) films has brought new possibilities for the control of molecular architectures and for making the LbL technique compliant with industrial processes. In this study we show that significantly distinct architectures are produced for dipping and spray-LbL films of the same components, which included DODAB/DPPG vesicles. The films differed notably in their thickness and stratified nature. The electrical response of the two types of films to aqueous solutions containing erythrosin was also different. With multidimensional projections we showed that the impedance for the DODAB/DPPG spray-LbL film is more sensitive to changes in concentration, being therefore more promising as sensing units. Furthermore, with surface-enhanced Raman scattering (SERS) we could ascribe the high sensitivity of the LbL films to adsorption of erythrosin.

Materials Science and Engineering: C, 2012

The Layer-by-Layer (LbL) technique via spraying (spray-LbL) has been applied as new and alternati... more The Layer-by-Layer (LbL) technique via spraying (spray-LbL) has been applied as new and alternative methodology to fabricate ultrathin films due to its versatility in relation to the conventional dipping-LbL method, mainly in terms of faster layer deposition and larger coated area. In this work, the possibility of immobilizing vesicles of dipalmitoyl phosphatidyl glycerol (DPPG) phospholipid onto alternating layers of the polyelectrolyte poly(allylamine hydrochloride) (PAH) using the spray-LbL method was investigated, being the results compared to the conventional dipping-LbL method. The growth of (PAH/DPPG) n spray-LbL films was systematically monitored by quartz crystal microbalance (QCM) and ultraviolet-visible (UV-vis) absorption spectroscopy, revealing a linear increase of the absorbance vs deposited layers. In relation to a possible electrostatic interaction between the groups PO 4 − (DPPG) and NH 3 + (PAH), it was observed through Fourier transform infrared (FTIR) absorption spectroscopy that the spectrum recorded for the spray-LbL film is basically a simple superposition of the FTIR spectra from PAH and DPPG casting films. The latter indicates a weak interaction between both materials, differently of the trend observed for (PAH/DPPG) n grown via dipping-LbL method. Atomic force microscopy (AFM) images of spray-LbL films showed evidences that the DPPG vesicles present in the aqueous dispersion are not destroyed when submitted to pressure conditions during the spray deposition. However, comparing to dipping-LbL, the DPPG vesicles do not cover completely the PAH layer for the spray-LbL film, which was further confirmed by surface-enhanced Raman scattering (SERS) measurements. Moreover, the AFM analysis showed that the spray-LbL deposition led to thicker PAH/DPPG bilayers in average than via dipping-LbL for the same concentrations of PAH solution and DPPG dispersion, which is consistent with QCM and UV-vis absorption results. PAH/DPPG films deposited by dipping-and spray-LbL techniques and also by Langmuir-Blodgett (LB) onto Pt interdigitated electrodes composing an array of sensing units (e-tongue) were applied in the detection of a xanthene derivate (eosin) in diluted solutions (10 − 9 , 10 − 7 and 10 − 6 M). Despite the LB and LbL films are formed by the same materials (PAH and DPPG), it was found that their different molecular architectures play an important role on the electrical response of Pt interdigitated electrodes in impedance spectroscopy measurements. The high sensitivity reached by these sensing units was intimately related to changes in the film morphology caused by the adsorption of the eosin molecules onto the film surfaces during electrical measurements, as evidenced by micro-Raman technique.