There is increasing interest in the utilisation of medical gases, such as ozone, for the treatment of herniated disks, peripheral artery diseases, and chronic wounds, and for dentistry. Currently, the in situ measurement of the dissolved ozone concentration during the medical procedures in human bodily liquids and tissues is not possible. Further research is necessary to enable the integration of ozone sensors in medical and bioanalytical devices. In the present review, we report selected recent developments in ozone sensor technology (2016–2020). The sensors are subdivided into ozone gas sensors and dissolved ozone sensors. The focus thereby lies upon amperometric and impedimetric as well as optical measurement methods. The progress made in various areas—such as measurement temperature, measurement range, response time, and recovery time—is presented. As inkjet-printing is a new promising technology for embedding sensors in medical and bioanalytical devices, the present review includes a brief overview of the current approaches of inkjet-printed ozone sensors.

Ozone therapy is established in clinical applications since many decades, such as treatment of infections or herniated discs. However, in-line monitoring of ozone concentrations is challenging and therefore not performed by default. We developed an experimental setup to measure the in-line ozone concentration in water in real-time with a spectroscopic sensor. Thereby, the experimental setup enables the calibration and evaluation of newly evolved ozone sensors. The results for ozone concentration measurement with the spectroscopic sensor and the colorimetric photometer show a very good correlation. Furthermore, the ozone decay curves measured with our experimental setup highly correlate with those of previous research.

The biocompatibility of medical sensors is of great importance. In order to prevent harm of the patient during measurement, this aspect must be considered throughout the entire design process. Biocompatibility can be achieved by various methods. For example, the sensor can be encapsulated, only biocompatible materials can be used for the sensor, or anti-inflammatory agents can be applied to the surface of the sensor. In this paper the focus is on sensors fully fabricated from biocompatible materials. Two exemplary inkjet-printed amperometric and impedimetric sensors are systematically assessed regarding their biocompatibility. Both sensors can be used for the measurement of dissolved ozone during oxygen-ozone injection therapy. For the sensors each material is evaluated with respect to the international standard ISO 10993. Overall, many amperometric and impedimetric sensors are fabricated from a small set of materials. The assessment reveals that for this specific application an amperometric sensor consisting of gold and silver nanoparticle inks, inkjet-printed on a polydimethylsiloxane membrane, and passivated with SU-8 ink offers the highest biocompatibility and reaches a good compliance with other important requirements. In addition, biological characterization tests are required for the specific medical application to validate the biocompatibility. From this study, it can be concluded that the findings on biocompatibility can also be transferred to other sensors that are made of the same set of materials but are for other applications. This applies to oxygen, glucose, pH, hydrogen peroxide, sweat lactate, and acetone sensors.

Body energy harvesting (BEH), especially for wearable devices, is an emerging and promising technology to improve the battery capacity and to avoid regular maintenance in terms of energy supply. A broad application of BEH increases sustainability and thus offers an advantage from an environmental point of view. We present a light weight BEH device for non-resonant arm and leg swing motions. The design was kept as simple and robust as possible and is based on an electrical generator. The generator is moved by an oscillating mass, which was previously simulated in a model, so that in this generator model, the kinetic energy is optimally transformed into electrical energy. Additionally, an ultra-low voltage power conditioning circuit, based on a step-up converter, was adapted to the BEH generator. The BEH generator and the power conditioning circuit were evaluated in a real test setup for arm and leg movements during walking and jogging with the BEH device worn on the wrist or ankle. An effective power of ∼11.3 mW was generated. This provides a constant voltage to charge a battery or supercapacitor.