Development of Two-Dimensional (2D) Sensing Materials

In recent years, two-dimensional (2D) materials have gained crucial interest in several fields. This interest is noted after the discovery of graphene in 2004 using the scotch tape exfoliation method. Among the synthesized 2D materials, we are interested in transition metal dichalcogenides (TMDCs) thanks to their fascinating features citing the indirect-to-direct bandgap crossover, large surface-to-volume area, high carrier mobility... The most studied TMDCs material is molybdenum disulphide (MoS2). Actually, researchers are also paying attention to tungsten disulfide (WS2) and molybdenum selenide (MoSe2) illustrating a wide potential of applications, especially as chemical sensors. Indeed, the sensing field become more significant due to its use in daily and practical life. In this thesis, we are interested in the development of two different types of sensors; electrochemical and plasmonic-based on the 2D-TMDCs nanosheets (NS). Herein, we have exfoliated MoS2, WS2, and MoSe2 NS using the liquid phase exfoliation (LPE) technique. By using these nanosheets, we have created different nanocomposites which were used later as sensing layers for different analytes. For electrochemical sensors, we have chosen a low-cost, simple-to-use device known as a screen-printed carbon electrode (SPCE) where the working electrode is modified with several modifiers. Two different fields of application were our focus: medicine and agriculture user cases. For the first one, we chose folic acid (FA) and dopamine (DA) as analytes. Regarding FA known also as vitamin B9, its determination was on the AuNPs-MoS2 system showing a new sensing mechanism. Indeed, the FA molecules are strongly adsorbed on the surface leading to the decrease of the anodic current peak instead of its increase when adding FA concentration. This fact was referred to as the reduction of gold nanoparticles (AuNPs) active sites number. Moreover, the determination of DA has occurred by using SPCE modified with nanocomposite based on MoSe2 and green synthesized AuNPs (AuNPs-MoSe2). An outstanding improvement in the DA Faradic current was noted and inferred to the band between DA and AuNPs surface. For the agricultural field user case, we used the modified SPCE with graphene oxide-tungsten disulphide (GO-WS2) for the determination of a fungicide known as Thiram. Herein, we observed a good performance toward this analyte at low concentrations. Thus, we studied the effect of the variation of the GO to WS2 ratio on the electroanalytical behaviour. For the plasmonic sensors, we have used the exfoliated nanosheets coated with noble metal for the detection of different analytes using enhanced Raman spectroscopies (ERS): surface-enhanced Raman spectroscopy (SERS), and photo-induced enhanced Raman spectroscopy (PIERS). Indeed, the Au-MoS2 sensing layer was used to determine 4-mercaptobenzoic acid (MBA) and FA where we noticed a good performance. Moreover, the MBA molecules were used also to check the efficiency of the Au-WS2 substrate where the PIERS performance of this prior was found to be better than that of SERS. This fact is owing to the charge transfer from WS2 nanosheets and AuNPs owing to the UV-C pre-irradiation step in PIERS. The last substrate used as a plasmonic sensor is made of MoSe2 and gold nanorods (AuNRs) that were used to detect methylene blue (MB) pigment. From this test, the SERS performance was improved and we noted a strong enhancement in the Raman signals while with the PIERS we observed better behaviour with significant improvement. All of these investigations are either published or submitted in journals with high impact factors. This work is only the initiative of a deeper work that will be accomplished after the thesis.