Graphene/Titanium Nitride Hybrid Nano-cuboid Plasmonic Metamaterial–Based Biosensor for Highly Sensitive and Tunable Infrared Detection

Abstract

In this paper, we propose a new plasmonic metamaterial-based biosensor using graphene-coated titanium nitride nano-cuboids with a tunable absorbance peak for the use in the first biological window in the infrared region between 830 and 950 nm. Using the finite element simulations, we study the absorbance of the proposed graphene/TiN hybrid metamaterial and demonstrate the possibility of achieving narrow and sensitive peaks to ambient medium index of refraction. The proposed nanostructure is highly tunable across the first biological window as the optical response of the metamaterial can be simply adjusted by varying the bias voltage of graphene nano-films. We demonstrate that graphene coating of the titanium nitride nano-films not only introduce tunability in the structure, but also improves the average absorption of the metamaterial by more than 20%, and the sensitivity by more than double while acting as a surface protection layer for the TiN nano-cuboids. The optimized structure demonstrates an average linear spectral sensitivity of 1014 nm/RIU, and a detection limit of 9.86 × 10^–6 RIU has been obtained for RI variations between 1.3 and 1.42. The proposed structure also demonstrates an amplitude sensitivity of 5 RIU⁻¹ with 850 nm excitation in IR region for liquid analytes. We also showed that the proposed sensor has a linear response for small variations in analyte RI with a tunable peak in IR region. This enables the development of a highly tunable and accurate refractometer for the detection of biomaterials, biological molecules, and liquid analytes in the infrared region. Finally, we demonstrate that small variation in design parameters due to fabrication-induced imperfection does not change the sensing performance of the proposed biosensor, resulting in a viable platform for sensing and narrowband applications with higher stability, sensitivity, and durability than previously reported structures based on traditional plasmonic materials like gold and silver.