Corrado Di Natale

DATA ANALYSIS FOR CHEMICAL SENSOR ARRAYS

Arrays were introduced in the mid-eighties as a method to counteract the cross-selectivity of gas sensors. Their use has since become a common practice in sensor applications. [1]. The great advantage of this technique is that once arrays are matched with proper multivariate data analysis, the use of non-selective sensors for practical applications becomes possible. Again in the eighties, Persaud and Dodds argued that such arrays has a very close connection with mammalian olfaction systems. This conjecture opened the way to the advent of electronic noses [2], a popular name for chemical sensor arrays used for qualitative analysis of complex samples. It is worth remarking that a gas sensor array is a mere mathematical construction where the sensor outputs are arranged as components of a vector. Arrays can also be utilized to investigate the properties of chemical sensors, or even better, the peculiar behaviour of a sensor as a component of an array. In this chapter, the more common sensor array methodologies are critically reviewed, including the most general steps of a multivariate data analysis. The application of such methods to the study of sensor properties is also illustrated through a practical

Volatile Compounds Detection by IR Acousto-Optic Detectors

Many important gasses and liquids, including the aggressive or anomalous ones for which our attention is higher, have strong absorption lines in the near and mid infrared spectral range. Infrared sensors exploit the fact that most gasses and liquids present unique infrared signatures in the 2–14 μm wavelength region. Due to this uniqueness infrared sensors provide conclusive identification and measurement of the target sample with little interference from other unwanted volatile compounds. Infrared sensors have the characteristics of being highly accurate, reliable, and, in general, low noise devices. In this chapter we will consider the most important infrared sources and sensors as well as the absorption techniques employed in this context. Furthermore the acousto-optic principle will be presented and discussed in some detail as the promoter of a multi-wavelength infrared generator. Finally system performance and data on gas detection will also be introduced and commented upon.

Sensor arrays and Self-Organizing Maps for Odour Analysis in Artificial Olfactory Systems

Our studies have regarded bio-inspired adaptive artificial olfactory systems composed of a sensor array for gas sensing and an artificial neural network, Self-Organizing Topology Preserving Map (SOM), introduced by T. Kohonen (Kohonen, 1989). In order to state the main working principles, Fig. I shows an overview of the digital version of a system for odour classification. The information flows from the left-hand side to the right-hand side: the gas mixtures in the environment determine the m sensor outputs which are sampled and converted into the digital stream z at each clock time. The module implementing the SOM network accepts a sequence of samples by a delay line, classifies the pattern according to its internal class models, and provides a class label as output (Davide et al.,1992 I,II,III).

Fiber optic multimeter for interrogating an array of absorption-based optochemical sensors

A fiber optic multimeter is presented, consisting of a platform for interrogating an array of absorption-based chemical sensors. It has been validated on a set of porphyrin-based materials having gas-sensor potential. Discrimination between different kinds of gases has been demonstrated.

E-tongue based on Porphyrin Electropolymers for Apulian Red Wines Defects Detection

An application of e-tongue based on porphyrin electropolymers for the detection of Primitivo and Negroamaro wines defects related to the presence of “off-odor” methiol (3-(methylthio)-propanol), isoamyl alcohol fusel oil, the marker of the yeast activity benzaldehyde and vinegar formation marker acetic acid was investigated. The best results were obtained for acetic acid and isoamyl alcohol. Further the Soft Independent Modelling by Class Analogy, SIMCA, classification models and Partial Least Squares-Discriminant Analysis, PLS-DA, were employed to distinguish real wine samples with different (permitted and alarm levels) fault compounds content as far as two types of wines among them.

Electronic tongue based on porphyrins for Apulian red wines defects detection

Electronic tongue based on porphyrin coatings obtained by electrochemical polymerization process was employed for the detection of Apulian wines (Primitivo and Negroamaro) defects related to the presence of “off-odor” methiol (3-(methylthio)-propanol) and ethyl phenol compounds, isoamyl alcohol fusel oil, the marker of the yeast activity benzaldehyde and vinegar formation marker acetic acid. The satisfactory prediction with R2 0.989 and 0.732 for isoamyl alcohol and acetic acid were obtained for in real wine samples. Moreover, the possibility to distinguish wine samples on the base of permitted levels of fault compounds content was shown.

Sensing materials with a concurrent sensitivity: design, synthesis and application in multisensory systems

A series of novel sensing materials with concurrent sensitivity, namely the porphyrins [free‐base, Mn(III) and Fe(III) complexes], functionalized with crown‐ether or aza‐crown (cyclam) pendant groups, were synthesized and tested as ionophores for polymeric membrane electrodes. Several aspects were studied in order to evaluate the functionality and the desired sensitivity of resulting crown‐porphyrins hyphenated ionophores, among them the nature and the size of crown fragment cavity, the length of the alkyl pendant incorporating the crown‐ether unit, the presence and the nature of central metal ion both in porphyrin and crown macrocycles.

Photo-assisted chemical sensors

The interplay between photosensitivity and chemical sensitivity can give rise to a number of properties that can extend the sensitivity in each separate context. Here we illustrate how the sensitivity to visble light of porphyrins coated ZnO nanorods can modify the gas detection enhancing the sensitivity in particular towards electron donor species.

An Analog Automatic Lock-In Amplifier for the Accurate Detection of Very Low Gas Concentrations

We propose here a new analog lock-in amplifier to be utilized in sensor interfaces for the detection of very low quantity of dangerous gases. When compared to other commercial systems in the literature, the proposed scheme shows an automatic operation, consisting in the self-alignment of the relative phase between input and reference signals. This functionality is continuously guaranteed, both at power-on and for any variation of the input noisy signal phase and amplitude during the working time. The proposed lock-in has been designed to work at a specified reference frequency (77 Hz), suitable for gas sensor applications and that avoids interferences with 50 Hz net frequency and its harmonics. The system has been tested using the carbon monoxide as gas to be revealed. With respect to the simple resistive gas sensor interface implemented by a resistive voltage divider, the improvement given by the proposed lock-in amplifier for the system sensitivity is of a factor of about 80, while the resolution, starting from about 5 ppm, has been enhanced to a theoretical value of about 0.05 ppm.