WS2 Nanosheets with Chemical Recognition Phase for the Detection of Salmonella

Abstract

It is of great interest to modulate the dimension and functionality of nanomaterials for designing biosensors capable of the selective and sensitive detection of target molecules without the use of expensive and fragile antibodies. Herein, I develop a new and simple approach for the exfoliation and functionalization of transition metal dichalcogenide (TMD) nanosheets for the selective and sensitive detection of Salmonella typhimurium without the use of an antibody. To this end, WS2 nanosheets are exfoliated by dextran (MW 40,000) in water via a sonication process. As-prepared WS2 nanosheets have an average lateral size of 49 nm and a thickness of 1.8 nm. In addition, the WS2 nanosheets exhibit intense Raman scattering and photoluminescence (PL) that would be exploited as a transduction signal for the optical detection of Salmonella typhimurium. The WS2 nanosheets are then functionalized with a variety of tripeptides bearing a nitrilotriacetate-copper complex (denoted as “WS2-Cu-TPs”) through coordination of the sulfur atom with the copper moiety. The resulting WS2-Cu-TPs maintain the intense Raman scattering of WS2 after functionalization in an aqueous solution, but their PL is diminished. The WS2-Cu-TP library then reacts with Salmonella typhimurium, E. coli O157:H7, and Staphylococcus (S.) aureus to select the one showing the selective recognition of Salmonella typhimurium. The intensive screening process produces WS2-Cu-CHC being able to selectively recognize Salmonella typhimurium against E. coli O157:H7, and S. aureus without the use of any antibody. The affinity of WS2-Cu-CHC to Salmonella typhimurium is found to be 76 nM, which is very comparable to that of a Salmonella-specific antibody. The mechanistic study suggests that two cysteine groups of the CHC tripeptide on the WS2 surface play an important role in the selective recognition of Salmonella typhimurium. Finally, the WS2-Cu-CHC sensor is able to detect a single copy of Salmonella typhimurium in a rapid and simple manner.