Microneedle‐Based Transdermal Sensor for On‐Chip Potentiometric Determination of K+

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.