Dry paper-based test strip potassium assay

A test strip comprising a layered structure comprising a top layer, a bottom layer, and active layers positioned between the top and bottom layers, the active layers including:

• a filter layer adapted to separate a drop of plasma from components of a drop of whole blood from a single fingerstick;
• optionally an interference mitigation composition positioned between the top layer and the bottom layer in a configuration where it contacts the whole blood and/or the drop of plasma to deplete or reduce endogenous substances therein;
• an optical analysis layer comprising an enzymatic cascade detection system and adapted to receive the drop of plasma from the filter layer,
• wherein the optical analysis layer is accessible to spectroscopic interrogation,
• wherein the enzymatic cascade detection system includes phosphoenolpyruvate or a phosphoenolpyruvate salt, a pyruvate kinase that converts the phosphoenolpyruvate into pyruvate, and an enzyme readout system that generates a detectable chromophore from the pyruvate,
• wherein the pyruvate kinase is a first stage of an enzymatic cascade,
• wherein potassium concentration within the drop of plasma can be extracted from a rate of generation of the detectable chromophore from the enzymatic cascade detection system,
• wherein the detectable chromophore has an absorbance peak that does not overlap with any oxyhemoglobin absorbance peak.