2D Transition Metal Dichalcogenides and Their Composites with Carbon-Based Materials: Applications in the Electrochemical Detection of Antimicrobial Drugs in Aquatic Environments
Authors: Luo Yiran , Barwa Tara N , Dempsey Eithne , Breslin Carmel B 
Published: August 2024

The 2D layered transition metal dichalcogenides (TMDs), often described as analogues of graphene, are envisioned as the next generation of 2D nano-layered materials in the development of electrochemical-based sensors. Molybdenum disulfide, MoS2, is one of the best known and has received considerable attention, being considered as a semi-metal, with good conductivity, high surface area and low cost. In this study, MoS2 was chosen for its high mechanical strength, high surface area, and good charge carrying properties. The MoS2 was exfoliated into a few layered sheets using tannic acid to give an environmentally acceptable exfoliation routine. It was then combined with a carbon material and employed as a sensor for an antimicrobial drug in aquatic environments.
The accumulation of antimicrobials in the aquatic environment is now a major concern with increasing evidence to show that they are contributing to the spread of antimicrobial resistance. There are a wide variety of antimicrobial drug families and one well known family is the sulfonamides. These synthetic drugs have the general formula R−SO2NH−R1, where R is an p-aminobenzoyl ring and the family differ in terms of the R1 substituent, which may be H or a 6− or 5−membered heterocyclic ring. They have the capacity to act on a wide range of bacterial infections and are employed in the fight against these infections. They are not easily biodegradable and therefore have the potential to accumulate in aquatic environments. Indeed, sulfonamides have been observed in rivers and coastal waters and concerning levels of sulfonamide resistant bacteria have also been reported in these environments [1]. Sulfanilamide (SFD) was chosen as the sulfonamide drug as it not only can be used to treat bacterial infections, but it is one of the main intermediates in the degradation of other family members [2]. The existing sensors for SFD have limited linear ranges in the vicinity of 1 to 100 mM and the LOD values are typically in the mM range and are not sufficiently low to detect low levels of SFD. Therefore, the aim of this study is to design an electrochemical sensor with a more extended linear region combined with a lower detection limit for the analysis of SFD in aqueous environments.
Exfoliated MoS2 sheets were combined with reduced graphene oxide (rGO) and graphite flakes. The addition of the graphite flakes enhanced the overall stability of the sensor, making it more superior and efficient than the corresponding sensor fabricated with pure rGO. The rGO/G was firstly formed using electrodeposition from a slightly acidified sulfate solution and the exfoliated MoS2 sheets were then drop cast over the wrinkled rGO/G surface to form the final sensor, GCE/rGO/G/MoS2. The fabricated sensor exhibited an extended linear range from 0.1 to 566 μM, with a LOD of 86 nM, with good selectivity in the presence of various salts found in water and structurally related drugs from the sulfonamide family. The sensor showed very good reproducibility with the RSD at 0.39%, repeatability and acceptable long term stability over a 10-day period with good recovery from both tap and river water. This approach, combining exfoliated MoS2 sheets with rGO and graphite, has the potential to be used in formulating sensors for other analytes.

References

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