Fabrication Of Self-Supporting Nitrogen-Doped Graphene Microelectrodes For In Situ Analysis Of Salicylic Acid In Plants

A needle electrochemical sensor was developed based on a nitrogen-doped graphene (NDG) microelectrode for the analysis of salicylic acid (SA) in plants. Self-supporting NDG microelectrodes were synthesized by electron-assisted hot filament chemical vapor deposition using ethanol and nitrogen as the C and N sources, respectively. The formation mechanism of the NDG microelectrodes is discussed by analyzing the ethanol decomposition and nitrogen-doping processes. The microelectrodes were composed of few-layered NDG nanosheets, and the N content of the nanosheets varied in the 0.96 -12.5 at% range. Furthermore, a novel needle sensor was constructed based on a cylindrical three-electrode system consisting of a Pt wire, optimized NDG microelectrode, and Ti tube with diameters of approximately 0.3, 0.9, and 1.5 mm, respectively, arranged concentrically. The needle sensors were also assembled into a parallel array consisting of four sensors. At a pH range of 4.5-7.5, the NDG-microelectrode-based needle sensor array exhibited a low detection limit (0.32-0.14 mu A mu M-1 S/ N = 3), wide linear range (1-500 mu M), and excellent reproducibility, selectivity, and stability for the detection of SA. The NDG-based needle sensors and sensor arrays are reliable electrochemical platforms for the detection of SA in plant tissue both in vivo and in vitro. (C) 2021 Elsevier Ltd. All rights reserved.