Flexible sweat sensors for non-invasive optimization of lithium dose in psychiatric disorders

Lithium is the main drug in the prophylaxis of Bipolar Disorder (BD) as it acts as a mood stabilizer. However, due to its narrow therapeutic range, patients are obliged to frequent check-ups in hospital to control their lithium blood level and optimize the dose.In this paper, we propose for the first time a wearable electrochemical sensor for the non-invasive decentralized Therapeutic Drug Monitoring (TDM) of lithium in sweat. The system is made of a platinum potentiometric sensor with an electrochemically nanostructured solid-contact and a silver Reference Electrode (RE). The optimal coverage and successful nanostructuration of the working electrode, useful to significantly reduce drift, is confirmed by Scanning Electron Microscopy (SEM). The integrated flexible RE is chemically chlorinated and covered with a PVC membrane doped with an Ionic Liquid (IL) to improve its stability. The sensing system is then tested both in aqueous solution and in sweat, showing quasi-Nernstian slope (56.8±3.9 mV /decade) in the range of clinical interest.