Phase‐Change‐Material‐Based Low‐Loss Visible‐Frequency Hyperbolic Metamaterials for Ultrasensitive Label‐Free Biosensing

Hyperbolic metamaterials (HMMs) have emerged as a burgeoning field of research over the past few years as their dispersion can be easily engineered in different spectral regions using various material combinations. Even though HMMs have comparatively low optical loss due to a single resonance, the noble‐metal‐based HMMs are limited by their strong energy dissipation in metallic layers at visible frequencies. Here, the fabrication of noble‐metal‐free reconfigurable HMMs for visible photonic applications is experimentally demonstrated. The low‐loss and active HMMs are realized by combining titanium nitride (TiN) and stibnite (Sb2S3) as the phase change material. A reconfigurable plasmonic biosensor platform based on active Sb2S3–TiN HMMs is proposed, and it is shown that significant improvement in sensitivity is possible for small molecule detection at low concentrations. In addition, a plasmonic apta‐biosensor based on a hybrid platform of graphene and Sb2S3–TiN HMM is developed and the detection and real‐time binding of thrombin concentration as low as 1 × 10−15 m are demonstrated. A biosensor operating in the visible range has several advantages including the availability of sources and detectors in this region, and ease of operation particularly for point‐of‐care applications.