Emiliano Zampetti

Biomimetic sensing layer based on electrospun conductive polymer webs

The aim of the present study is to combine a bio-inspired nanofibrous artificial epithelium to the electronic nose (e-nose) principles. The sensing device set up was an electronic nose consisting of an array of 9 micro-chemoresistors (Cr-Au, 3×3) coated with electrospun nanofibrous structures. These were comprised of doped polyemeraldine base blended with 3 different polymers: polyethylene oxide, polyvinilpyrrolidone and polystyrene, which acted as carriers for the conducting polymer and were the major responsible of the features of each fibrous overlay (electrical parameters, selectivity and sensitivity ranges). The two sensing strategies here adopted and compared consisted in the use of 2 different textural coatings: a single- and a double-overlay, where the double-overlay resulting from overdeposition of 2 different polymer blends. Such e-nose included a plurality of nanofibres whose electrical parameters were at the same time depending on each polymer exposure to analytes (NO(2), NH(3)) and on the spatial distribution of the interlacing fibres. The morphology of the coating arrangements of this novel e-nose was investigated by scanning electron microscopy (SEM) and its sensor responses were processed by multicomponent data analyses (PCA and PLS) reporting encouraging results for detection and recognition of analytes at ppb levels.

Large-Scale Chemical Sensor Array Testing Biological Olfaction Concepts

Biological olfactory systems are characterized by a large number of sensors with broad overlapping specificities. The sensitivity and selectivity of the system may be enhanced by the huge redundancy of the olfactory receptor neurons (ORNs). A European project, NEUROCHEM, was devoted to test computational models of the olfactory system of vertebrates and insects. To test these models, a realistic artifact of the olfactory epithelium was developed as a large sensor array mimicking some features of biological ORNs, in particular, the broad and overlapping selectivity to many odors, the combinatorial response, the high level of redundancy, and the different dynamic ranges exhibited by same types of ORNs. The sensor array is composed of 16 384 elements arranged in four smaller arrays of 64 × 64 interdigitated electrodes deposited on a borosilicate substrate. To mimic the redundancy of the biological ORNs, tens of organic conductive polymers were chosen as active sensing materials because of their broad and diverse, but overlapping, specificity to different classes of volatile organic compounds. These sensors were characterized by their responses to varying concentrations of test analytes. The collected sensor data were processed with standard multivariate techniques and the results are reported in this paper.

On-chip fabrication of ultrasensitive NO2 sensors based on silicon nanowires

We report a very simple, robust, and reliable on-chip fabrication method of a chemoresistive sensor based on silicon nanowires (NWs). Our method permits the use of nanowires without the need of their removal and transfer to a support different from the growth substrate. Our method, completely based on the silicon technology platform, exploits nanowires directly grown onto a selected area, over and between pre-patterned, interdigitated electrodes defined on oxidized silicon. The fabricated sensor is capable to detect NO2 down to a few ppb levels operating at room temperature. The sensor characteristics benefit of the presence of self-welded nanowires.

Alcohol vapor sensory properties of nanostructured conjugated polymers

The response to relative humidity (RH) and alcohol vapors of resistive-type sensors based on nanobeads of conjugated polymers, namely polyphenylacetylene (PPA) and copolymer poly[phenylacetylene-(co-2-hydroxyethyl methacrylate)] (P(PA/HEMA)), were investigated. Sensors based on ordered arrays of these nanostructured polymeric materials showed stable and reproducible current intensity variations in the range 10–90% of relative humidity at room temperature. Both polymers also showed sensitivity to aliphatic chain primary alcohols, and a fine tuning of the sensor response was obtained by varying the chain length of the alcohol in relation to the polarity. The nanostructured feature of polymeric-based membranes seems to have an effect on the sensing response and an enhancement of the sensitivity was observed for the response to water and alcohol vapor variations with respect to previous studies based on amorphous polyphenylacetylene. High stability of the polymeric nanostructured membranes was detected with no aging after two weeks in continuum stressing measurement conditions.

Enhanced Sensory Properties of a Multichannel Quartz Crystal Microbalance Coated with Polymeric Nanobeads

In this study the sensorial performances of a four-channel quartz crystal microbalance implemented on a single quartz plate are reported and compared with those of four independent quartz crystal microbalances. Particular attention has been devoted to both cross talk in responses and sensor sensitivity. A recently synthesized nanostructured polymer, poly[phenylacetylene-(co-2-hydroxyethyl methacrylate)], has been used as chemical interactive material. The interactions of our sensor system with relative humidity are also reported. The multichannel device shows a better homogeneity of the mass sensitivity with a spread of the values less then 4% compared to a 50% spread observed in the set of four microbalances.

Electrospinning for High Performance Sensors

Due to rapid growth of industrialization, urbanization and modern agricultural development, there has resulted a heavy backlog of gaseous and liquid pollution in all over the world and threated the health of human beings. Driven by the actual demand, the sensors possess good portability, easy usability, excellent selectivity and sensitivity for water and air pollution monitoring are highly desirable. Among versatile sensing platforms, quartz crystal microbalance sensors and colorimetric sensor gained increasing attention for their easy accessibility, favorable expansibility and good associativity. Based on above two platforms, nanofibrous materials have been choose as an idea substrate to either capture the marker or amplify the signal associated with detection. In this chapter, we reviewed recent progress in the development of electrospun nanofibrous materials having applications in two predominant sensing approaches (quartz crystal microbalance and colorimetric sensors), illustrate them with current examples showing how they have been applied, optimized and discuss their intrinsic fundamentals and optimal designs. Moreover, we will also highlight gaps requiring further research.

Very large chemical sensor array for mimicking biological olfaction

Olfactory receptor neurons (ORN) in the mammalian olfactory system, transduce molecular properties of the odorants into electrical signals and project these into the olfactory bulb (OB). In the biological system several millions of receptor neurons of a few hundred types create redundancy and the massive convergence of the ORNs to the OB, is thought to enhance the sensitivity and selectivity of the system. To explore this concept, the NEUROCHEM project will build a polymeric chemical sensor array consisting of 216 (65536) sensors with tens of different types. To interface such a large sensor array, a topological array configuration with n rows and m columns, has been adopted, to reduce the total wiring connections to n+m. A method of addressing a single element in the array in isolation of the rest of the network has been developed. Over the array ten different conductive polymers with different sensing characteristics will be deposited by means of electrodeposition and inkjet printing. A smaller prototyp...

Interdigitated sensorial system on flexible substrate

In this paper we present the design and fabrication of two flexible sensor devices: humidity sensor and ammonia sensor integrated with electronic circuit interface on thin flexible substrate (8 mum). The transducers layout has been optimized by means of numerical simulations. A thin layer of Bisbenzocyclobytene (BCB) is used as dielectric sensitive material in humidity sensor. Conversely a mixed polymer layer based on polyaniline emeraldine base (PANi-EB) is used as sensing conductive polymer for ammonia.

Temperature and flow velocity control for quartz crystal microbalances

Although quartz microbalances (QMBs) are widely used, controlling their temperature is a challenge. Here a slightly modified quartz microbalance, driven by an original SigmaDelta electronic interface, acts as temperature sensor, flow sensor, heater, and resonator; no interference between the oscillator circuit and the SigmaDelta interface has been observed. In comparison with traditional solutions, the proposed approach is more accurate, faster, cheaper, more flexible, and more power efficient. As an additional, unique advantage of our system, the flow velocity is automatically measured by the QMB sensor itself. The technological and circuit solutions reported here are general and may be useful in other applications where temperature and/or flow velocity must be controlled

Photoconductive Electrospun Titania Nanofibres to Develop Gas Sensors Operating at Room Temperature

The use of nanostructured materials, such as those based on metal or metal oxides, has opened a new way to enhance the performances of chemical sensors making them able to detect gases at ppb level. In this type of sensors, the conductance is modulated by the presence of analytes that interact through physical-chemical processes of absorption and desorption, inducing changes in mobility or carriers density. The nano-scale dimensions of these materials enhance the interaction phenomena in terms of time and responses. In order to activate the physical/chemical interaction processes of the sensors based on oxide materials, an high operating temperature (200–400 °C) is required, resulting in significant power consumption. In this chapter, we report our recent studies on the possibility to exploit the titania photoconduction to develop gas sensor devices working at room temperature. We present the characterization of two different photoconductive Electrospun sensing layers: the first one is composed of titania nanofibres (TiO2 NFs) and the second of TiO2 NFs decorated with Pt nanoparticles (PtNPs) ranging from 5 to 10 nm.