Perena Gouma

Comparison of sol-gel and ion beam deposited MoO3 thin film gas sensors for selective ammonia detection

Abstract This paper presents a comparative study of the gas-sensing behavior of MoO3 thin films prepared by ion beam deposition and sol–gel techniques, respectively. The sensing response of these films to ammonia in the presence of interfering gases (such as NO2) is assessed. The microstructural characteristics of the sensing materials prepared by these two techniques are determined using electron microscopy and microanalysis techniques. MoO3 is shown to be highly sensitive to ammonia, and the sensitivity depends on processing. The sensing properties of MoO3 thin films and the origin of the p–n-type transition occurring in sol–gel processed films are correlated with the type of the MoO3 polymorph(s) used for sensing.

Nanosensor and Breath Analyzer for Ammonia Detection in Exhaled Human Breath

The detection and monitoring of gases in exhaled human breath up to date has been limited by the lack of appropriate materials and technologies which could rapidly and selectively identify the presence and monitor the concentration of trace levels of specific analytes-biomarkers. We present a metal oxide-based nanosensor that is highly specific to ammonia gas in breath-simulating environments at low part-per-billion concentrations. The design of a handheld breath analyzer for gas detection in exhaled human breath is described. Semiconducting ceramics are presented as suitable sensor materials for easy and affordable noninvasive diagnostics.

An Acetone Nanosensor For Non‐invasive Diabetes Detection

Diabetes is a most common disease worldwide. Acetone in exhaled breath is a known biomarker of Type‐ 1 diabetes. An exhaled breath analyzer has been developed with the potential to diagnose diabetes as a non‐invasive alternative of the currently used blood‐based diagnostics. This device utilizes a chemiresistor based on ferroelectric tungsten oxide nanoparticles and detects acetone selectively in breath‐simulated media. Real‐time monitoring of the acetone concentration is feasible, potentially making this detector a revolutionary, non‐ invasive, diabetes diagnostic tool.

An overview of the translation of selective semiconducting gas sensors from first results to automotive exhaust gas monitors to a platform for breath-based diagnostics

Metal oxide-based resistive gas sensors with inherent selectivity to gases exhaled in a human breath were developed in a scalable and affordable manner. The developments in the tailored synthesis and scalable nanomanufacturing of polymorphs of binary metal oxide gas-sensing elements, together with the publication of guidelines from the medical community for the measurement of breath gases in exhaled breath, have opened the pathway for personalized diagnostic breathalyzers, as described here.

Selective Crystal Structure Synthesis and Sensing Dependencies

Chemo-resistive sensors utilizing meal oxides form a very important type of sensors for gas detection. They are based on the interaction between gas molecules and surface ionosorbed oxygen species accompanied by electron transfer, which eventually leads to the change of material resistance. This process is controlled by a few external parameters (working temperature) and internal parameters (microstructure, chemical composition and crystal structure). While most parameters have been paid sufficient attention to, the influence of crystal structures is still largely unexplored. On the other hand, metal oxides exist in more than one crystalline form. The structural and property difference between different structures is expected to affect the sensing behavior of the material. Taking TiO2 and WO3 as examples, this chapter reviews how to selectively synthesize desired crystal structures and how they are related to the performance as agas sensor. TiO2 exists in two major polymorphs, with rutile being the thermodynamically stable phase and anatase being the metastable one. Compared to rutile, anatase is more open-structured and more chemically active and has lower surface energy. The hydrothermal method has been proved to be very effective in anatase synthesis as long as particle size is well controlled (normally under 20 nm) and dopants could stabilize this phase. Studies have found that anatase shows higher sensitivity as a gas sensor which is believed to be attributed to its higher chemical activity.WO3 undergoes a series of phase transition when it is cooled down and γ-WO3 is usually the room-temperature (RT) stable phase. The low-temperature stable phase, e-WO3, is the least symmetric among all the phases and is the only one with a ferroelectric feature. By a rapid solidification method called flame spray pyrolysis, e-WO3 is able to be synthesized in high purity at RT. Doping with silicon and chromium could effectively stabilize this phase up to 500 °C by forming boundary domains or surface layers. The dopant-stabilized e-WO3 shows high sensitivity and unique selectivity to polar gas molecules, esp. acetone, which may be due to the strong interaction between the e-WO3 surface dipole and polar molecules.

A low-power wide-dynamic-range readout IC for breath analyzer system

We present a low-power wide-dynamic-range readout circuit that directly interfaces a selective metal-oxide gas sensor. The proposed novel readout architecture implements an adaptive baseline compensation and limits the sensor current. The readout IC can interface the sensors with the baseline resistance from 1 kΩ to 100 MΩ and measures the gas induced resistance change in the range from 0.05% to 10% of the baseline resistance. The simulations demonstrate the 166 dB dynamic range of the readout circuit and 113 μW power consumption amenable to the sensors that can operate at room temperature for the application of the proposed system in portable breath analyzers.

Flame Spray Synthesis and Ammonia Sensing Properties of Pure α-MoO3 Nanosheets

This paper highlights the flame spray synthesis of α-MoO3 using ammonium molybdate as precursor. The as-synthesized particles obtained were found to be ammonium molybdenum oxide and belonged to the triclinic crystal system. The particles crystallized to α-MoO3 upon thermal treatment at 500°C. Sensors were prepared by drop coating the powders onto alumina substrates coated with platinum electrodes and sensing tests were conducted evaluating the detection of ammonia concentrations down to ppb level concentration in air. The flame synthesized α-MoO3 based sensors show high sensitivity towards ammonia and may potentially be used in breath ammonia gas diagnostics.

Guest Editorial - Special issue on machine olfaction

This year is the 10th anniversary of the first special issue on machine olfaction of the IEEE SENSORS JOURNAL. During this past decade, the field has grown in a number of exciting directions, including spectroscopic and olfactory receptorbased sensing, computational models of olfactory processing, and mobile and distributed sensing. This second special issue provides a timely update on advances during the past decade (as well as a vantage point from which to evaluate the last 30 years) in the field and, more importantly, the challenges that still lie ahead. It includes invited papers based upon presentations give at the International Symposium on Olfaction and Chemical Sensing (ISOCS) that was held in New York Digital Object Identifier 10.1109/JSEN.2012.2215434 City in 2011 (see www.olfactionsociety.org). To provide a balanced view of the various advances in the field, the special issue is organized into six distinct topic areas: biological sensors, chemical sensors, sensor systems, data processing, and electronic nose applications. The topic area of biological sensors recognises the fact that considerable effort is being directed towards improving the capability of artificial olfactory sensors by exploring more closely the biological system and seeking to mimic it more closely.

Sol-gel processed MoO3 and WO3 thin films for use as selective chemosensors

Selective detection of small amounts of toxic gases, such as ammonia and CO is very important to environmental monitoring as well as for medical diagnoses. MoO3 and WO3 have been identified as suitable materials for detecting these gases with high sensitivity. Sol-gel processed thin films of MoO3, WO3 and their combination have been prepared at SUNY Stony Brook by the hydrolysis of metal alkoxide precursors followed by spin coating and were deposited on alumina heater/electrode containing substrates that were produced by the Brescia group. Sensing tests were carried out in the state-of-the-art gas sensor testing facilities available in Brescia, where the electrical resistance of sensor arrays was recorded as a function of gas concentration, for various combinations of gases (including ammonia, CO, NO2, Methanol, isoprene, etc) at 10% relative humidity and at temperatures ranging from 400-500°C. The MoO3-WO3 composite system showed the best stability at the highest testing temperature. The sensing results obtained are correlated with the structural characteristics of the sensing films. This work has been carried out as a joint collaboration between the Advanced Materials Characterization Laboratory of SUNY Stony Brook (USA) and the Sensor Lab at the University of Brescia (Italy) and was funded by a NSF-AAAS (WISC) grant awarded to Perena Gouma.

A PANI–Cellulose acetate composite as a selective and sensitive chemomechanical actuator for acetone detection

Abstract This study addresses the role of PANI–CA composites in the detection of acetone vapors with high sensitivity and selectivity in the presence of alcohols. The PANI–CA composites were fabricated by the solution-casting method and were cut to 4 cm × 3 mm rectangular strips of about 20-μm thickness. The composite strips behave as gas sensors/chemoactuators and respond to gaseous species by converting their relative concentration to a corresponding mechanical motion (bending). The bending-recovery responses of PANI/CA sensor was examined thoroughly by exposing it to varying headspace concentrations of acetone and alcohols, and by removing the analyte once the sensor reached its maximum bending angle. Sensitivity was determined by comparing the bending response of the composite strips to different headspace concentrations of acetone. Selectivity was determined through analysis of the angle change in 50/50 ml solutions of four different (potentially interfering) chemicals. The results indicate that the sensor highly discriminates between acetone and alcohols making it a potential wearable acetone skin sensor for indirect measurement of glucose in the blood for diabetics. Graphical abstract