With recent developments, terahertz (THz) technology has attracted great interest in many different fields of research and application. In particular, biosensors that detect a thin film of captured pathogens are in high demand for rapid diagnosis. Based on the interaction between analytes under test and electromagnetic (EM) field, THz resonators are sensitive to changes in the permittivity of the analyte and have the potential to become sensitive thin-film sensors. However, conventional metamaterial methods have low Q factors, leading to small amplitude variations and ambiguous detection. Here, we present a photonic crystal (PhC)–based resonator with a high Q factor that is sensitive to a monolayer of beads in the µm size range. The PhC resonator made of high resistivity silicon (HRSi) shows a Q factor of 750, which is much higher compared to metamaterial-based methods. Its resonance shift is linearly related to the coverage of the micron-sized beads on its surface. Moreover, simulation results with a thin film model of a single layer of the beads showed agreement with the experimental results. Although the achieved sensitivity needs to be improved by enhancing the field concentration on the analyte, our results suggest that THz PhC resonators with high Q factor are promising for biosensing applications. We anticipate our work to be a starting point for biochips with improved sensing capabilities and more functionality.

Abstract Point-of-care (POC) devices are essential for rapid testing of samples for early diagnosis of diseases. The accuracy and the sensitivity of the POC device depend mainly on the biosensors. The currently used POC devices require specialized operating personnel, long sample preparation time and high equipment costs. We aim to explain a bio-sensing concept using a photonic crystal (PC) resonator that would mitigate the drawbacks of the present sensing techniques. Photonic crystals consist of spatially arranged dielectric materials presenting a band gap that prevents electromagnetic waves of certain frequency range to propagate through it. PC resonators have shown to have very high sensitivities for bio-sensing applications at THz frequencies. A PC resonator with a high Q-factor is designed and simulated to detect the changes in the surrounding dielectric permittivity. As an application for detecting specific biomolecules, a protocol for surface functionalization has been explained. This will enable the selective binding of biomolecules from the sample. Shift in resonant frequency and attenuation in magnitude at the peak resonant frequency can be observed from the simulation results. These changes in the resonator properties can be indicative of the presence of a particular biomolecule or pathogen and its concentration within the sample.

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