The determination of electrolytes is invaluable for point of care diagnostic applications. An ion selective transdermal microneedle sensor is demonstrated for potassium by integrating a hollow microneedle with a microfluidic chip to extract fluid through a channel towards a downstream solid-state ion-selective-electrode (ISE). 3D porous carbon and 3D porous graphene electrodes, made via interference lithography, are compared as solid-state transducers for ISE's and evaluated for electrochemical performance, stability, and selectivity. The porous carbon K+ ISE's show better performance than the porous graphene K+ ISE's, capable of measuring potassium across normal physiological concentrations in the presence of interfering ions with greater stability. This new microfluidic/microneedle platform shows promise for medical applications.A new integrated microneedle-based microfluidic platform
is described for in vivo potassium sensing. Fluid can be extracted through a hollow microneedle and run over a downstream porous carbon solid state ion selective electrode to detect physiological levels of potassium.