Sensitive optical bio-sensing of p-type WSe₂ hybridized with fluorescent dye attached DNA by doping and de-doping effects

Layered transition metal dichalcogenides, such as MoS₂, WSe₂ and WS₂, are exciting two-dimensional (2D) materials because they possess tunable optical and electrical properties that depend on the number of layers. In this study, the nanoscale photoluminescence (PL) characteristics of the p-type WSe₂ monolayer, and WSe₂ layers hybridized with the fluorescent dye Cy3 attached to probe-DNA (Cy3/p-DNA), have been investigated as a function of the concentration of Cy3/DNA by using high-resolution laser confocal microscopy. With increasing concentration of Cy3/p-DNA, the measured PL intensity decreases and its peak is red-shifted, suggesting that the WSe₂ layer has been p-type doped with Cy3/p-DNA. Then, the PL intensity of the WSe₂/Cy3/p-DNA hybrid system increases and the peak is blue-shifted through hybridization with relatively small amounts of target-DNA (t-DNA) (50-100 nM). This effect originates from charge and energy transfer from the Cy3/DNA to the WSe₂. For t-DNA detection, our systems using p-type WSe₂ have the merit in terms of the increase of PL intensity. The p-type WSe₂ monolayers can be a promising nanoscale 2D material for sensitive optical bio-sensing based on the doping and de-doping responses to biomaterials.