Development of tattoo-based wearable electrochemical devices for health status monitoring

One of the main goals of scientific research regards taking care of people’s health, therefore the need to monitor the body status for accurate and rapid management of critical health conditions has become a priority. Many electrochemical systems have been developed to monitor important biomarkers and the world of sensors for healthcare is wide1. Scientific interest is moving nowadays towards the design of wearable and non-invasive devices for continuous monitoring and many technological challenges are still unaddressed. The activity of our research group is focused on the development of wearable sensing platforms based on both OECTs2 (Organic ElectroChemical Transistors) and amperometric sensors configuration fabricated by ink-jet printing technique3 and applied on the skin likewise a temporary tattoo. The matrix selected for the detection is not blood, which would require an invasive sampling, but the interstitial fluid (ISF) which is the biofluid present between cells and tissues. ISF is an interesting option because its composition reflects blood and it can be extracted through the skin without the use of needles, e.g. by reverse iontophoresis. The first step of the project has been the development and optimization of a glucose sensor printed on a flexible plastic support. Soft materials were selected to print and pattern the connections and the active parts of the electrochemical devices. In particular, the organic semiconductor PEDOT (poly(3,4-ethylenedioxy-thiophene)) doped with PSS (poly(styrene sulfonate)) was chosen as the electrochemical transducer and was then functionalized with the proper enzyme (glucose oxidase) in order to make the device sensible to glucose. This procedure comprises the platinization of the PEDOT film, the following enzyme deposition by drop-casting and finally its immobilization with cross-linkers. Two sensing structures are currently under development, e.g. amperometric and transistor-based, showing sensitivities of 1.35·10-3 and 2.81·10-4 µM-1, respectively, in the concentration range of interest for glucose detection in extracted ISF (10-1000 µM). Figure 1 reports the real-time response of a printed amperometric flexible biosensor to increasing glucose additions and the correspondent calibration curve. The following steps will be focused on selectivity investigation, taking into consideration the interference of different analytes, and the evaluation of temperature’s impact on the device performance.