Ultrasensitive plasmonic biosensors based on halloysite nanotubes/MoS2/black phosphorus hybrid architectures

Layered black phosphorus (BP) has triggered enormous research interest due to its moderate band gap and pronounced in-plane anisotropy. In particular, its optical birefringence in the visible region and low toxicity in biological tissues make BP a promising candidate in biophotonic devices. Herein, we proposed a highly anisotropic, ultrasensitive plasmonic biosensor via vertically stacking halloysite nanotubes (HNTs), MoS2 and BP atomic layers on gold films. We show that the proposed biosensor surpasses previously reported biosensors (merely consisting of 2D materials and metal films) in terms of both the angular and phase detection sensitivities. In particular, the biosensor composed of 400 nm HNTs/1L MoS2/3L BP/40 nm Au presents angular and phase detection sensitivities up to SA = 77.0548 per RIU and Sp = 1.60595 × 105 per RIU, respectively. These SA and Sp values show the highest enhanced folds of 127 and 1.51 × 104 compared to those with only 2D materials and metal films used in plasmonic biosensors. The ultrahigh sensing performance could be closely related to the excellent features of HNTs (e.g., good biocompatibility, negatively charged surface, and large surface area), excitonic resonance enhanced local field induced by MoS2, and the work function difference driven charge transfer. Benefiting from the optical anisotropy of BP, the proposed plasmonic biosensor exhibits optically tunable detection sensitivity. Additionally, evolution of surface plasmon resonance angles, and angular and phase detection sensitivities with biosensor structural parameters such as the thicknesses of HNTs, MoS2, BP, and gold films is also discussed in detail.