This application describes methods and apparatus for monitoring of fluid content that are suitable for in-situ, real time and/or continuous monitoring, especially of bodily fluids and in particular the content of sweat. The application also describes fabrication of such an apparatus. The apparatus comprises a multilayer structure comprising at least two electrode layers for detection of fluid content separated by at least one insulating layer. The multilayer structure defines at least one flow channel which provides a flow path for continuous flow of fluid in use, and the electrode layers form part of the sidewall of the flow channel(s). The flow channel(s) may run in a direction substantially perpendicular to the layers. The electrode layers may employ electrochemical detection and may comprise a reference electrode and an ion-sensitive electrode. The apparatus may be fabricated using various printing or deposition techniques.
