Potassium Ion-selective Electrode with a Sensitive Ion-to-Electron Transducer Composed of Porous Laser-induced Graphene and MoS2 Fabricated by One-step Direct Laser Writing

In this study, an ion-selective electrode with a sensitive ion-to-electron transducer composed of porous laser-induced graphene (LIG) and MoS2 (LIG-MoS2/ISE) was fabricated to measure the potassium ion concentration in a greenhouse nutrient solution for soilless culture. Additionally, a more effective and low-cost method was proposed for the large-batch production and manufacture of potassium ion-selective electrodes (K+-ISEs) using the direct laser writing technique, which differs considerably from existing methods. Moreover, the sensing mechanism of the proposed LIG-MoS2/ISE for potassium ion detection was investigated. The morphology and physical properties of the LIG-MoS2/SC-K+-ISEs were studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), Raman spectroscopy and energy-dispersive spectroscopy. Potentiometric measurements, chronopotentiometry, potentiometric water layer tests, cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were used to evaluate the analytical performance of the newly developed K+-ISEs. A Nernstian slope of 30.1 mV/decade for the activity of potassium ions in a concentration range from 10(-7) to 10(-2) M was determined. The EIS and chronopotentiometry results revealed that the LIG-MoS2/SC-K+-ISE had a larger resistance and double-layer capacitance than the LIG/SC-K+-ISE. The ion-selective membrane (ISM) and solid-contact layer did not have any water film between them, according to the potentiometric water layer test. The results proved that the LIG-MoS2 nanocomposite could possibly be used as a sensitive ion-to-electron transducer to fabricate K+-ISEs. The K+-ISE fabrication method using the direct laser writing technique had a higher efficiency, enabling its broad application prospects in agriculture.