Alexandra Manzoli

Low-Cost Gas Sensors Produced by the Graphite Line-Patterning Technique Applied to Monitoring Banana Ripeness

A low-cost sensor array system for banana ripeness monitoring is presented. The sensors are constructed by employing a graphite line-patterning technique (LPT) to print interdigitated graphite electrodes on tracing paper and then coating the printed area with a thin film of polyaniline (PANI) by in-situ polymerization as the gas-sensitive layer. The PANI layers were used for the detection of volatile organic compounds (VOCs), including ethylene, emitted during ripening. The influence of the various acid dopants, hydrochloric acid (HCl), methanesulfonic acid (MSA), p-toluenesulfonic acid (TSA) and camphorsulfonic acid (CSA), on the electrical properties of the thin film of PANI adsorbed on the electrodes was also studied. The extent of doping of the films was investigated by UV-Vis absorption spectroscopy and tests showed that the type of dopant plays an important role in the performance of these low-cost sensors. The array of three sensors, without the PANI-HCl sensor, was able to produce a distinct pattern of signals, taken as a signature (fingerprint) that can be used to characterize bananas ripeness.

Microcantilever Sensors Coated With Doped Polyaniline for the Detection of Water Vapor

In the present work, PANI (polyaniline) emeraldine salt (doped) and base (dedoped) were used as the sensitive layer of a silicon microcantilever, and the mechanical response (deflection) of the bimaterial (coated microcantilever) was investigated under the influence of humidity. PANI in the emeraldine base oxidation state was obtained by interfacial synthesis and was deposited on the microcantilever surface by spin-coating (dedoped). Next, the conducting polymer was doped with 1 M HCl (hydrochloric acid). A four-quadrant AFM head with an integrated laser and a position-sensitive detector (AFM Veeco Dimension V) was used to measure the optical deflection of the coated microcantilever. The deflection of the coated (doped and undoped PANI) and uncoated microcantilever was measured under different humidities (in triplicate) at room pressure and temperature in a closed chamber to evaluate the sensors sensitivity. The relative humidity (RH) in the chamber was varied from 20% to 70% using dry nitrogen as a carrier gas, which was passed through a bubbler containing water to generate humidity. The results showed that microcantilevers coated with sensitive layers of doped and undoped PANI films were sensitive (12,717 ± 6% and 6,939 ± 8%, respectively) and provided good repeatability (98.6 ± 0.015% and 99 ± 0.01%, respectively) after several cycles of exposure to RH. The microcantilever sensor without a PANI coating (uncoated) was not sensitive to humidity. The strong effect of doping on the sensitivity of the sensor was attributed to an increased adsorption of water molecules dissociated at imine nitrogen centers, which improves the performance of the coated microcantilever sensor. Moreover, microcantilever sensors coated with a sensitive layer provided good results in several cycles of exposure to RH (%).

Information Visualization and Feature Selection Methods Applied to Detect Gliadin in Gluten-Containing Foodstuff with a Microfluidic Electronic Tongue

The fast growth of celiac disease diagnosis has sparked the production of gluten-free food and the search for reliable methods to detect gluten in foodstuff. In this paper, we report on a microfluidic electronic tongue (e-tongue) capable of detecting trace amounts of gliadin, a protein of gluten, down to 0.005 mg kg-1 in ethanol solutions, and distinguishing between gluten-free and gluten-containing foodstuff. In some cases, it is even possible to determine whether gluten-free foodstuff has been contaminated with gliadin. That was made possible with an e-tongue comprising four sensing units, three of which made of layer-by-layer (LbL) films of semiconducting polymers deposited onto gold interdigitated electrodes placed inside microchannels. Impedance spectroscopy was employed as the principle of detection, and the electrical capacitance data collected with the e-tongue were treated with information visualization techniques with feature selection for optimizing performance. The sensing units are disposable to avoid cross-contamination as gliadin adsorbs irreversibly onto the LbL films according to polarization-modulated infrared reflection absorption spectroscopy (PM-IRRAS) analysis. Small amounts of material are required to produce the nanostructured films, however, and the e-tongue methodology is promising for low-cost, reliable detection of gliadin and other gluten constituents in foodstuff.

Cantilever nanobiosensor using tyrosinase to detect atrazine in liquid medium

ABSTRACT The aim of this study was to develop a cantilever nanobiosensor for atrazine detection in liquid medium by immobilising the biological recognition element (tyrosinase vegetal extract) on its surface with self-assembled monolayers using gold, 16-mercaptohexadecanoic acid, 1-ethyl-3-[3-dimethylaminopropyl] carbodiimide hydrochloride/n-hydroxysuccinimide. Cantilever nanobiosensors presented a surface compression tension increase when atrazine concentrations were increased, with a limit of detection and limit of quantification of 7.754 ppb (parts per billion) and 22.792 ppb, respectively. From the voltage results obtained, the evaluation of atrazine contamination in river and drinking water were very close to those of the reference sample and ultrapure water, demonstrating the ability of the cantilever nanobiosensor to distinguish different water samples and different concentrations of atrazine. Cantilever nanosensor surface functionalization was characterised by combining polarisation modulation infrared reflection-absorption spectroscopy and atomic force microscopy and indicating film thickness in nanometric scale (80.2 ± 0.4 nm). Thus, the cantilever nanobiosensor developed for this study using low cost tyrosinase vegetal extract was adequate for atrazine detection, a potential tool in the environmental field.

Lab-made electronic-nose with polyaniline sensor array used in classification of different aromas in gummy candies

Aroma is closely related to the food product acceptability and an important product quality indicator. Electronic-nose (E-nose) systems are an interesting alternative to traditional methods of aroma analyses. A lab-made E-nose system equipped with an array of sensing units comprised by gold interdigitated microelectrodes (IDEs) using polyaniline (Pani) as sensitive layers deposited by the in situ and Layer-by-layer (LbL) methods was used to analyze aromas in gummy candies. Different concentrations from artificial aromas (apple, strawberry and grape), added to the gummy candies were evaluated. Our system presented 21.6 mV.ppb-1 sensitivity, ppb range detection limit, and good reversibility, around 97.6%. The sensitive layers of Pani films was adequate deposited on IDEs observed by the Attenuated Total Reflection/Fourier-transform infrared spectroscopy (ATR/FTIR). Linear Discriminant Analysis (LDA) was able to classify apple, strawberry, and grape aromas added to gummy candies using saturation potential values from the E-nose system, demonstrating its applicability in food matrices.

Array of Different Polyaniline-Based Sensors for Detection of Volatile Compounds in Gummy Candy

Aroma in foodstuff is considered an essential attribute since it is closely related to the consumer acceptance of foodstuffs. Electronic nose (e-nose) system is composed by an array of gas sensor and has emerged as a promising alternative for the aroma volatile compounds recognition. In this study, a lab-made e-nose system comprising of an array of different polyaniline-based sensors has been used for aroma discrimination (apple, strawberry, and grape) in gummy candy. The sensor array was comprised by interdigitated graphite electrodes, using tracing paper substrate and sensitive layer of polyaniline (Pani) obtained by in situ and interfacial synthesis deposited by the in situ adsorption polymerization of aniline and layer-by-layer (LbL) methods. The sensors were characterized in relation to humidity and the Pani-in situ/PSS LbL layer presenting the higher sensitivity, a quite interesting feature for its use as a gas sensor. It has been demonstrated that the lab-made e-nose has been highly efficient in the discrimination of different concentrations of aromas added to gummy candies with excellent sensitivity and a limit of detection in the range of parts-per-billion, so demonstrated the applicability in food matrices.

Nanosensors for detection of pesticides in water

Water is an invaluable resource for human being life and other life forms on the planet. The increasing growth of human population and chaotic spreading of agricultural lands have been endangering water supplies around the globe. The indiscriminate use of pesticides is contaminating both superficial water bodies and groundwater. Detection of such micropollutants is mandatory in order to assure the quality of water and avoid environment contamination. Recently there have been evaluated more precise and inexpensive methods of pesticide detection in water at very low concentrations. The nanossensors become an emerging and promising technology for biosensing applications, due to their small size, fast response, and high sensitivity. The aim of this review will be the description of the structure, operation, and applicability of cantilevers nanossensors for pollutants in water. Also discussed in the chapter are the following: the surface functionalization methods, limit of detection, and mechanism of pesticide recognition.

Scanning Probe Microscopy as a Tool Applied to Agriculture

The control of materials properties and processes at the molecular level inherent in nanotechnology has been exploited in many areas of science and technology, including agriculture where nanotech methods are used in release of herbicides and monitoring of food quality and environmental impact. Atomic force microscopy (AFM) and related techniques are among the most employed nanotech methods, particularly with the possibility of direct measurements of intermolecular interactions. This chapter presents a brief review of the applications of AFM in agriculture that may be categorized into four main topics, namely thin films, research on nanomaterials and nanostructures, biological systems and natural fibers, and soils science. Examples of recent applications will be provided to give the reader a sense of the power of the technique and potential contributions to agriculture.