Core-shell Au@Cu2O-graphene-polydopamine interdigitated microelectrode array sensor for in situ determination of salicylic acid in cucumber leaves

Abstract The in situ detection of active small molecules in plants is one of the key technologies for the development of precision agriculture. An interdigitated microelectrode (IDME) array electrochemical sensor is constructed herein, with three groups of IDME arrays as a three-electrode system. The core-shell Au@Cu2O-graphene (Gr)-polydopamine (PDA) nanoparticles are densely packed on Al microelectrodes using a three-potential step pulse electrodeposition method. Each of the over 2000 individual microelectrodes is approximately 1 μm wide and 1100 μm in length. The sensor has a high response to salicylic acid (SA) due to the synergistic electrocatalysis of Au@Cu2O, Gr, and PDA, and the high-density arrangement of the three-electrode unit with microelectrodes. The sensor has a linear concentration range of 0.01–100 μM for SA and the detection limit is as low as 1.16 nM. The SA concentration in cucumber leaves is monitored from the early growth stage to the fruiting stage using the IDME array sensor, and the juice and living stems of the cucumber are detected. The flat structure of the Au@Cu2O-Gr-PDA IDME array sensor is suitable for attachment onto plant tissues, especially for the in situ detection of SA in leaves.