A portable ascorbic acid in sweat analysis system based on highly crystalline conductive nickel-based metal-organic framework (Ni-MOF).

Conductive metal-organic frameworks can provide unique porous structures, large pore volumes, many catalytically active sites and high crystallinity, and so are becoming increasingly important and attractive as electrocatalytic materials. The present work synthesized nanorods of the conductive compound Ni3(2,3,6,7,10,11-hexaiminotriphenylene)2 (Ni3(HITP)2) with a high degree of crystallinity from HITP ligands and Ni2+ ions. Screen-printed electrodes made with this material were employed to fabricate an enzyme-free sensor for the detection of ascorbic acid (AA). The sensor exhibited good catalytic activity during the electrocatalytic analysis of AA in alkaline media, attributed to the synergistic effect of highly active Ni-N4 catalytic sites in the nanorods, the two-dimensional superimposed honeycomb lattice of the Ni3(HITP)2, and the large specific surface area of this material. The latter property facilitated efficient electron transfer during catalytic oxidation. A portable electrochemical AA detection system was developed using Ni3(HITP)2 as the electrode material together with application-specific integrated circuits and a smartphone application with App. Good sensing performance was obtained, including a wide linear range (2-200 µM) with high sensitivity (0.814 µA µM-1 cm-2), and low detection limit (1 µM). This system can be used to monitor AA levels and trends in sweat to assess vitamin C intake as a part of personal health management.