Direct Drawing Method of Graphite onto Paper for High-Performance Flexible Electrochemical Sensors

-A simple and fast fabrication method to create high-performance pencil -drawn electrochemical sensors is reported for the first time. The sluggish electron- transfer observed on bare pencil -drawn surfaces was enhanced using two electrochemical steps: first oxidizing the surface and then reducing it in a subsequent step. The heterogeneous rate constant was found to be 5.1 x 10(-3) cm s(-1), which is the highest value reported so far for pencil-drawn surfaces. We mapped the, origin of such performance by atomic force microscopy, X-ray photoelectron spectroscopy, and Raman spectroscopy.- Our results suggest that the oxidation process leads to 'chemical land structural transformations on. the surface. As a proof -of -concept, we modified the pencil -drawn surface with, Meldola's blue to electrocatalytically detect nicotinainide adenine dinucleotide (NADH). The electrochemical device exhibited the highest catalytic,constant 41.7 X 10(5) L mol(-1) s(-1)) and the -lowest detection potential for NADH reported so far in -paper -based electrodes.