A review on thin films, conducting polymers as sensor devices

Thin film sensors are used to monitor environmental conditions by measuring the physical parameters. By using thin film technology, the sensors are capable of conducting precise measurements. Moreover, the measurements are stable and dependable. Furthermore, inexpensive sensor devices can be produced. In this paper, thin film technology for the design and fabrication of sensors that are used in various applications is reviewed. Further, the applications of thin film sensors in the fields of biomedical, energy harvesting, optical, and corrosion applications are also presented. From the review, the future research needs and future perspectives are identified and discussed.

Combinatorial selectivity with an array of phthalocyanines functionalized TiO2/ZnO heterojunction thin film sensors

The development of electronic noses requires the control of the selectivity pattern of each sensor of the array. Organic chemistry offers a manifold of possibilities to this regard but in many cases the chemical sensitivity is not matched with the response of electronic sensor. The combination of organic and inorganic materials is an approach to transfer the chemical sensitivities of the sensor to the measurable electronic signals. In this paper, this approach is demonstrated with a hybrid material made of phthalocyanines and a bilayer structure of ZnO and TiO2. Results show that the whole spectrum of sensitivity of phthalocyanines results in changes of the resistance of the sensor, and even the adsorption of compounds, such as hexane, which cannot change the resistance of pure phthalocyanine layers, elicits changes of the sensor resistance. Furthermore, since phthalocyanines are optically active, the sensitivity in dark and visible light are different. Thus, operating the sensor in dark and light two different signals per sensors can be extracted. As a consequence, an array of 3 sensors made of different phthalocyanines results in a virtual array of six sensors. The sensor array shows a remarkable selectivity respect to a set of test compounds. Principal component analysis scores plot illustrates that hydrogen bond basicity and dispersion interaction are the dominant mechanisms of interaction.

Humidity Dependence of Commercial Thick and Thin-Film MOX Gas Sensors under UV Illumination

Enhancing the performance of a chemo-resistive gas sensor is often challenging due to environmental humidity influencing its sensitivity and baseline resistance. One of the most promising ways of overcoming this challenge is through ultraviolet (UV) illumination of the sensing material. Most research has focused on using UV with in-house developed sensors, which has limited their widespread use. In this work, we have evaluated if UV can enhance the performance of commercially available MOX-based gas sensors. The performance of five different MOX sensors has been evaluated, specifically SGX Microtech MiCS6814 (thin-film triple sensor), FIGARO TGS2620 (n-type thick film), and Alphasense VOC sensor (p-type thick film). These sensors were tested towards isobutylene gas under UV light at different wavelengths (UV-278 nm and UV-365 nm) to investigate its effect on humidity, sensitivity, baseline drift, and recovery time of each sensor. We found the response time of thin-film sensors for reducing gases was improved by 70 s under UV- 365 nm at normal operating temperatures. In addition, all the sensors were left in a dirty environment and the humid-gas testing was repeated. However, due to their robust design, the sensitivity and baseline drift of all the sensors remained the same. This indicates that UV has only limited uses with commercial gas sensors.

Self-made 3D-printed encapsulation of thin-film transducers for reliable force measurement in biomedical applications

In biomedical studies as well as in clinical trials, it is often useful to have a reliable measure of the force exerted by the body(eg. clenching force at the teeth or pinch force at fingertips) or on the body by external stimuli (eg. taps to elicit reflexes orlocal pressure for nociceptive stimulation). Thin-film sensors such as FlexiForce ® provide a very handy and versatile solutionfor these application, but can be easily damaged and offer poor accuracy and repeatability, being heavily affected by thesurface material they get in contact with. The aim of the study is the realization of a 3D-printed cover that completely embedsthe sensor, thus providing mechanical protection and increasing reliability of the measurement. The increasing availability of3D printers and of printing materials for medical use allows the user to shape the cover according to specific needs, with shortdeveloping time and low cost.

Development and Characterization of Integrated Nano-Sensors for Organic Residues and pH Field Detection

Meeting global water quality standards is a real challenge to ensure that food crops and livestock are fit for consumption, as well as for human health in general. A major hurdle affecting the detection of pollutants in water reservoirs is the lapse of time between the sampling moment and the availability of the laboratory-based results. Here, we report the preparation, characterization, and performance assessment of an innovative sensor for the rapid detection of organic residue levels and pH in water samples. The sensor is based on carbonaceous nanomaterials (CNMs) coated with an intrinsically conductive polymer, polyaniline (PANI). Inverse emulsion polymerizations of aniline in the presence of carbon nanotubes (CNTs) or graphene were prepared and confirmed by thermogravimetric analysis and high-resolution scanning electron microscopy. Aminophenol and phenol were used as proxies for organic residue detection. The PANI/CNM nanocomposites were used to fabricate thin-film sensors. Of all the CNMs, the smallest limit of detection (LOD) was achieved for multi-walled CNT (MWCNT) with a LOD of 9.6 ppb for aminophenol and a very high linearity of 0.997, with an average sensitivity of 2.3 kΩ/pH at an acid pH. This high sensor performance can be attributed to the high homogeneity of the PANI coating on the MWCNT surface.