Methods, structures, devices and systems are disclosed for fabricating and implementing electrochemical biosensors and chemical sensors. In one aspect, a method of producing an epidermal biosensor includes forming an electrode pattern onto a coated surface of a paper-based substrate to form an electrochemical sensor, the electrode pattern including an electrically conductive material and an electrically insulative material configured in a particular design layout, and attaching an adhesive sheet on a surface of the electrochemical sensor having the electrode pattern, the adhesive sheet capable of adhering to skin or a wearable item, in which the electrochemical sensor, when attached to the skin or the wearable item, is operable to detect chemical analytes within an external environment.