The development of carbon nanomaterials enhanced potassium sensor and glucose sensor for applications in wearable sweat-based sensing

Inkjet printed graphene (IPG) has recently shown tremendous promise in reducing the cost and complexity of graphene circuit fabrication. In this work, we fabricate an ion selective electrode (ISE) with IPG for the first time. A thermal annealing process in a nitrogen ambient environment converts the IPG into a highly conductive electrode (sheet resistance changes from 52.8 ± 7.4 MΩ/☐ for unannealed graphene to 172.7 ± 33.3Ω/☐ for graphene annealed at 950°C). Raman spectroscopy and field emission scanning electron microscopy (FESEM) analysis reveals that the printed graphene flakes begin to smooth at an annealing temperature of 500°C and then become more porous and more electrically conductive when annealed at temperatures of 650°C and above. The resultant thermally annealed, IPG electrodes are converted into potassium ISEs via functionalization with a polyvinyl chloride (PVC) membrane and valinomycin ionophore. The developed potassium ISE displays a wide linear sensing range (0.01mM to 100mM), a low detection limit (7 μM), minimal drift (8.6  10 V/s), and a negligible interference during electrochemical potassium sensing against the backdrop of interfering ions [i.e., sodium (Na), magnesium (Mg), and calcium (Ca)] and artificial eccrine perspiration. Thus, the IPG ISE shows potential for potassium detection in a wide variety of human fluids including plasma, serum, and sweat.