Tunable excitonic emission of monolayer WS₂ for the optical detection of DNA nucleobases

Two-dimensional transition metal dichalcogenides (2D TMDs) possess a tunable excitonic light emission that is sensitive to external conditions such as electric field, strain, and chemical doping. In this work, we reveal the interactions between DNA nucleobases, i.e., adenine (A), guanine (G), cytosine (C), and thymine (T) and monolayer WS₂ by investigating the changes in the photoluminescence (PL) emissions of the monolayer WS₂ after coating with nucleobase solutions. We found that adenine and guanine exert a clear effect on the PL profile of the monolayer WS₂ and cause different PL evolution trends. In contrast, cytosine and thymine have little effect on the PL behavior. To obtain information on the interactions between the DNA bases and WS₂, a series of measurements were conducted on adenine-coated WS₂ monolayers, as a demonstration. The p-type doping of the WS₂ monolayers on the introduction of adenine is clearly shown by both the evolution of the PL spectra and the electrical transport response. Our findings open the door for the development of label-free optical sensing approaches in which the detection signals arise from the tunable excitonic emission of the TMD itself rather than the fluorescence signals of label molecules. This dopant-selective optical response to the DNA nucleobases fills the gaps in previously reported optical biosensing methods and indicates a potential new strategy for DNA sequencing.