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.