  Flexible and epidermal sensing devices are becoming vital to enable precision
medicine and telemonitoring systems. The NFC (Near Field Communication)
protocol is also becoming increasingly important for this application since it
is embedded in most smartphones that can be used as pervasive and low-cost
readers. Furthermore, the responder can be passive and can harvest enough power
to perform electromagnetic sensing. Finally, the NFC coils are robust to
bending and to the human body's presence. This contribution details the design
of a new flexible device, including an electrochemical sensor communicating
through the NFC protocol. A spiral NFC antenna is designed, and a manufactured
prototype is experimentally tested to quantify the robustness to the
inter-wearer variability and the bending. Lastly, the sensory data retrieval is
validated by comparison with a portable potentiostat. The realized sensor can
be comfortably worn and be easily read by smartphones independently from the
wearer and from the point of application and could be used in future for
estimating the user's psycho-physical health by analyzing the body's sweat.
