Abstract: Microfluidic, electrochemical devices are described. The microfluidic, electrochemical device may include a sample zone on a first porous, hydrophilic layer, a reference zone and a microfluidic channel, wherein the microfluidic channel provides for predominantly diffusive fluid communication between the sample zone and the reference zone; (therefore realizing a similar function of a reference electrode), a fluid-impermeable material that defines each of the sample zone, reference zone and microfluidic channel, a first electrode in fluid communication with the sample zone and a second electrode in fluid communication with the reference zone. Also described are microfluidic, electrochemical devices containing an ion-selective membrane for potentiometric ion sensing.