Scalable and Contactless Optical Dye Sensors Based on Differential Reflectivity of Excitonic Peaks by MoS₂ Nanostructures

Due to their excellent optoelectronic properties, two-dimensional nanomaterials are becoming key in developing various sensors for detecting harmful environmental pollutants. In this study, we present an approach for detecting methylene blue (MB) pollutants using a contactless optical sensor based on molybdenum disulfide (MoS 2 ) nanostructures. Our approach involves exploiting the interaction between the optical absorption of MB and the excitons of MoS 2, considered as markers, to monitor the presence of the MB contaminant at various concentrations. For this purpose, MoS 2 nanostructures are deposited onto a quartz substrate via chemical vapor deposition, exhibiting exceptional crystalline quality and a triangular-like morphology. We demonstrate a high-sensitivity (with a limit of detection as low as 1 ng·L –1 ) dynamic response for the MoS 2 /quartz-based device in reflectivity measurements from MoS 2 nanostructure excitons as a function of the MB concentration variation. Specifically, we show that the reflectivity intensity ratio at A and B exciton positions is directly related to the change in MB concentration in the analyte. Furthermore, the proposed sensor device features highly persistent reusability, owing to its contactless configuration with the MB pollutant, which preserves the MoS 2 sensing layer from poisoning and/or alteration. Our findings provide valuable insights for potential developments aimed at achieving highly accurate and reliable next-generation optical sensors based on two-dimensional nanomaterials.