Fig. 7. Selective K⁺ sensing in human blood serum.

a Real time high sensitivity K⁺ detection in human blood serum. The K⁺ concentration range is 4.8 10⁻³ M – 9.6 10⁻³ M. The potassium concentration of the blood serum is increased over time by spiking small amounts of 1 10⁻¹ M KCl water solution. The measurements are performed at V_I = 0.37 V. b Measured steady-state output voltage V_O (symbols) as a function of K⁺ concentration c. Full blue line is the linear least square fit to the measurements and yields a sensitivity S_A = 662 mV dec⁻¹. c Control experiment demonstrating the selectivity against sodium in blood serum. V_O is measured over time and the Na⁺ concentration of the blood serum is systematically increased from 1.36 10⁻¹ M to 2.70 10⁻¹ M. The K⁺ concentration is constant and amounts to 4.8 10⁻³ M. f Measured (symbols) steady state V_O as a function of c^Na+. Solid line is the linear least square fit to the measurements and yields a cross-sensitivity equal to 44 mV dec⁻¹, which is more than 15-fold lower than the sensitivity of the selected K⁺ ions.