Inkjet-printed polymer composites for the detection of volatile organic compounds

Sensors capable of detecting and classifying volatile organic compounds (VOC) have been gaining more attention by the advent of internet-of-things (IoT) enabled devices and integration of various sensing elements into hand-held and portable devices. The recent applications of VOC sensors call for detectors that operate with low power consumption as well as fabrication techniques that allow integration of sensing elements with devices. Hence, in this dissertation, the application of chemiresistive sensing elements based on polymer nanocomposites, which operate at near room temperature, for low-power detection of VOCs was investigated. As a versatile fabrication method, drop-on-demand inkjet printing (DoD IJP) was used to transfer the sensing material onto the sensor platform. A group of commercially available polymers with representative solubility parameters were selected to detect a wide range of chemically diverse analytes. A highly conductive high-structure carbon black (CB) was used as the conductive filler. The inkjet inks containing different polymers and CB were then formulated via solution mixing. Due to various constraints on the physical properties of inkjet inks, a systematic process for ink formulation had to be established, especially when formulating inks that contained multiple components. For this aim, a systematic approach consisting of successive characterization steps, including assessment of rheology, evaporation profile, and CB particle size distribution was proposed. At the end of this step, inkjet inks containing different polymer composites were formulated, allowing stable droplet jetting and deposition of uniform sensory films. The effect of ink formulation on the sensing performance of the printed sensors was investigated. It was demonstrated that by changing CB concentration in the composite, the sensor sensitivity varied. Lower CB loading resulted in better sensitivity (55% higher sensitivity to pentane for 3.3 vol% compared to 8.3 vol% CB loading) but inferior baseline noise (45% increase in baseline noise for 3.3 vol% compared to 8.3 vol% CB loading). By optimizing the CB concentration, high sensitivity with an improved limit of detection (LoD) was obtained as demonstrated by comparing the LoD of composites containing 3.3, 5.5, and 8.3 vol% CB to pentane, which was approximately 80, 20, and 90~ppm, respectively. The concentration dependence of the sensor response upon exposure to chemically diverse analytes, namely water, ethanol, acetone, pentane, and heptane, was studied. It was shown that the sensor response to each analyte was in line with the analyte-polymer affinity expected from their respective solubility parameters. In the studied concentration range, all sensors showed a linear response to the concentration change of those analytes to which they were sensitive, allowing to extract the sensor sensitivity and expected LoD. The sensor LoD values appeared to be in the range of few to tens of ppm, depending on the analyte and the printing parameters. By performing the principal component analysis (PCA), it was demonstrated that using three principal components would allow the classification of the tested analytes. Overall, the methods, materials, and results of this work demonstrated the potential of DoD IJP for the fabrication of versatile and sensitive low-temperature VOC detectors, paving the way to fully printed low-cost and low-power electronic nose devices.

Study of the pO2-sensitivity of the dendrimeric and free forms of Pd-meso-tetra(4-carboxyphenyl)porphyrin, incorporated or not in chitosan-based nanoparticles

Peter Käuper, Patrycja Nowak-Sliwinska, Hubert van den Bergh, Georges Wagnières

The concentration of oxygen and its rate of consumption are important factors in certain medical treatments, such as radiotherapy and photodynamic therapy (PDT). Measuring the tissue concentration of oxygen or its partial pressure (pO2) can be achieved by taking advantage of the oxygen-dependent luminescence lifetime of certain molecules, including metallo-porphyrin derivatives, due to the oxygen-dependent quenching of their triplet state. Unfortunately, most of these porphyrin derivatives are phototoxic due to the O2 1Δ produced in the pO2 measurement procedure. The aim of this work was to characterize new nanoparticle oxygen sensors, where the palladium-porhyrin molecule (Pd-meso-tetra(4- carboxyphenyl)porphyrin) or its dendrimer form, is incorporated into an oxygen permeable matrix of chitosan-based colloidal particles. It was hypothesized that the reactive O2 1Δ produced during the pO 2 measurement would react inside the particle thus reducing its toxicity for the surrounding tissue, whereas the 3Σ ground state of O2, that is to be measured, would diffuse freely in the peptide. We observed that the incorporation of the porphyrin in the nanoparticles resulted in a reduction of the phosphorescence lifetime sensitivity to pO2 by about one order of magnitude. Our studies of these new sensors indicate that the oxygen concentration can be measured in aqueous solutions with a precision of ±20% for oxygen concentrations ranging between 0% and 25%. © Schweizerische Chemische Gesellschaft.

Schweizerische Chemische Gesellschaft2011

Printed Polymer Composite Sensors for Low-Power, Near Room-Temperature Detection and Classification of VOCS

Jürgen Brugger, Mohammadmahdi Kiaee, Thomas Maeder

We demonstrate the application of inkjet-printed near room-temperature chemiresistors composed of polymer-carbon black (CB) composites for detecting and classifying volatile organic compounds (VOC). Our results demonstrate that the printed sensors can selectively detect the target analytes at 28°C. The sensor’s selectivity is correlated to their Hansen solubility parameters (HSP), and their response dynamic is adjusted by the polymer glass transition temperature (T g ). Using the principal component analysis (PCA), we demonstrate that the selected polymers can successfully discriminate between chemically diverse analytes. Hence, showing the potential of inkjet-printable polymer composites with representative HSPs as low power and cost-effective VOC sensors. Such sensors can be readily integrated with wearable and flexible electronics.

IEEE2021