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The development and analytical characterization of a novel ion-selective potentiometric cell in a temporary-transfer tattoo platform for monitoring ammonium levels in sweat is presented. The fabrication of this skin-worn sensor, which is based on a screen-printed design, incorporates all-solid-state potentiometric sensor technology for both the working and reference electrodes, in connection to ammonium-selective polymeric membrane based on the nonactin ionophore. The resulting tattooed potentiometric sensor exhibits a working range between 10(-4) M to 0.1 M, well within the physiological levels of ammonium in sweat. Testing under stringent mechanical stress expected on the epidermis shows that the analytical performance is not affected by factors such as stretching or bending. Since the levels of ammonium are related to the breakdown of proteins, the new wearable potentiometric tattoo sensor offers considerable promise for monitoring sport performance or detecting metabolic disorders in healthcare. Such combination of the epidermal integration, screen-printed technology and potentiometric sensing represents an attractive path towards non-invasive monitoring of a variety of electrolytes in human perspiration.

Instrumental approaches to remotely and wirelessly monitoring chemical species are increasingly needed. Together with the electronic developments, efforts to optimize and validate the performance of these new devices are required. In this work, the analytical performance of a recently developed potentiometer-radiofrequency tag connected to ion- selective electrodes is evaluated. This credit card sized and extremely low power consumption device yield results that are comparable to those obtained with more sophisticated, lab-based tools. Advantages such as portability and autonomy, together with unique features, such as the ability to be read through the walls in a closed vessel are demonstrated. Future perspectives opened by this new generation of devices, such as their use in wearable devices and in decentralized settings are discussed.