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In this work, a new and convenient fabrication process for screen-printed reduced graphene oxide-molybdenum disulfide electrode (SPrGO-MoS2E) was proposed. Reduced graphene oxide-molybdenum disulfide (rGO-MoS2) composite was hydrothermally synthesized and then dispersed in deionized water and ethanol with a ratio of 2:3 (v/v) to form a conductive suspension. The suspension was then blended with carbon paste at a ratio of 0.1:9.9 (g/g) to obtain a screen-printable rGO-MoS2 conductive ink. An electrochemical sensing electrode was formed by screening this conductive ink onto a polyethylene terephthalate substrate. The characteristics of this electrode were investigated by scanning electron microscopy, energy-dispersive X-ray spectrometry, X-ray diffractometry, Raman spectroscopy, and electrochemical impedance spectroscopy. Overall, the conductive suspension comprising the rGO-MoS2 composite showed higher electrochemical sensing performance compared with electrodes containing only rGO or MoS2. Cyclic voltammetry revealed that the SPrGO-MoS2 electrode exhibited excellent electrochemical sensing performance toward several electroactive species, namely, potassium hexacyanoferrate (III) ([Fe(CN6)]3−/4−), nicotinamide adenine dinucleotide (NAD+/NADH), and hydrogen peroxide (H2O2) dissolved in 0.1 M PBS (pH 7.4). The limits of detection for [Fe(CN6)]3−/4−, NAD+/NADH, and H2O2 were 0.34, 0.25, and 1.36 μM, respectively. In addition, the reproducibility, repeatability, and stability determined from the relative standard deviations (RSDs, n = 7) of these analytes were less than 12.1 %, 8.6 %, and 7.4 %, respectively. Therefore, the ready-to-use SPrGO-MoS2E could be an alternative material for advanced chemical and biological sensing applications.

In this work, a highly sensitive and disposable screen-printed ionic liquid-graphene electrode (SPIL-GE) was developed for electrochemical sensing. The paste for screen printing was facilely prepared by mixing IL with electrolytically exfoliated graphene in poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (GP/PEDOT/PSS) and carbon paste (CP) via ball milling. The IL-GP paste was then screen printed to form working and counter electrodes (WE & CE) followed by screen printing of Ag/AgCl reference electrode and insulator layer on a polyethylene substrate. Electrode geometries were optimized for electrochemical sensing, arriving at an optimal design with an overall electrode length of 25 mm, and CE and WE active areas of 15.70 and 12.57 mm2, respectively. SPIL-GEs employing six ILs with imidazolium and pyridinium cations were assessed for electrochemical sensing of K3Fe(CN)6. The pyridinium-type IL, namely 3-methyl-1-propylpyridinium bis(trifluoromethyl sulfonyl)imide (PMPlm), was found to exhibit the highest CV peak currents compared with other ILs at an optimal PMPlm content of 1.0% (w/w). Characterization with scanning electron microscopy and Fourier-transform infrared spectroscopy confirmed the presence of PMPlm, GP/PEDOT/PSS and CP in SPIL-GEs. The electrochemical performance of the optimal SPIL-GE towards the three common analytes including ferri/ferro cyanide (Fe(CN)6)3-/4- redox couple, dopamine and hydroquinone were compared with the screen-printed carbon and graphene electrodes (SPCE & SPGE). From the results, the SPIL-GE demonstrated larger anodic currents with lower oxidation potentials for the three analytes than SPGE and SPCE, respectively. Therefore, the SPIL-GE could be a potential candidate for advanced electrochemical sensing applications.