Titanium nitride-based hyperbolic metamaterial for near-infrared ultrasensitive sensing of microbes.

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We demonstrate an ultrasensitive microbe sensor for the first time using a titanium nitride (TiN) nanowire-based hyperbolic metamaterial (HMM) structure. We detected the change in the resonance wavelength shift due to the inclusion of microbes in a freshwater environment employing the finite-difference time-domain (FDTD) method. Our proposed HMM sensor exhibits strong bulk plasmon polariton (BPP) modes in the anisotropic hyperbolic regime (λ ≥ 590 nm) and operates in the near-infrared (NIR) wavelength region. We studied the impact of structural parameters on the resonance wavelength shift, where our proposed HMM sensor structure exhibited an outstanding sensing capability of 11 nm per bacteria. A limit of detection of 0.00008 RIU was achieved for our proposed HMM sensor structure. Additionally, we verified our results theoretically to calculate mode frequency shift by solving the effective medium theory (EMT). Our study revealed that HMM is the origin of highly sensitive BPP modes. We obtained two BPP modes, where the BPP mode at a longer wavelength (q = 1) exhibited the highest resonance wavelength shift compared to the BPP mode at a shorter wavelength (q = 2). More importantly, we demonstrated numerically the point-detection capability of our proposed HMM microbe sensor structure, which was unattainable in previously reported sensor work. Moreover, this sensor can be adapted to detect different viruses and bacteria. Our proposed TiN-based HMM structure can potentially be an ultrasensitive and straightforward microbe sensor for label-free detection.