High-sensitivity and versatile plasmonic biosensor based on grain boundaries in polycrystalline 1L WS films.

Structural defects play an important role in exploitation of two-dimensional layered materials (2DLMs) for advanced biosensors with the increasingly high sensitivity and low detection limit. Grain boundaries (GBs), as an important type of structural defect in polycrystalline 2DLM films, potentially provide sufficient active defect sites for the immobilization of bioreceptor units via chemical functionalization. In this work, we report the selective functionalization of high-density GBs with complementary DNA receptors, via gold nanoparticle (AuNP) linkers, in wafer-scale polycrystalline monolayer (1L) W(Mo)S films as versatile plasmonic biosensing platforms. The large surface area and GB-rich nature of the polycrystalline 1L WS film enabled the immobilization of bioreceptors in high surface density with spatial uniformity, while the AuNPs perform not only as bioreceptor linkers, but also promote detection sensitivity through surface plasmon resonance enhancement effect. Therefore, the presented biosensor demonstrated highly sensitive and selective sub-femto-molar detection of representative RNA sequences from the novel coronavirus (RdRp, ORF1ad and E). This work demonstrates the immense potential of AuNP-decorated GB-rich 2DLMs in the design of ultra-sensitive biosensing platforms for the detection of biological targets beyond RNA, bringing new opportunities for novel healthcare technologies.