Photonic Crystal Resonator in the Millimeter/Terahertz Range as a Thin Film Sensor for Future Biosensor Applications

Abstract

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.

Principles of Measuring Thickness and Refractive Index of Thin Dielectric Film by Using Multiresonance Archimedean Spiral Metasurfaces with C Resonator in the Terahertz Frequency Range

“…The upper limit of the operation mode is determined by the saturation mode. There is no sense in using Equation (19), since it is easier to retrieve the parameters from Equation (13). On the other hand, Equation (19) will not work if the measurements are conducted in the mode of thin films (linear operation mode of the sensor):…”

“…However, since the wavelength in the THz range can be as big as several hundreds or thousands of micrometers, it is almost impossible to measure very thin films with conventional methods, such as conventional THz time domain spectroscopy [8,9]. Scientists have proposed different solutions to this problem, including waveguides [10][11][12], photonic crystals [13], as well as plasmonic structures [14] and metasurfaces [15]. Due to the variety of principles, functions, and requirements of thin-film sensing approaches, it is difficult to compare the performance of these techniques.…”

3D printed sub-terahertz photonic crystal for wireless passive biosensing

“…This approach can effectively minimize the standard deviation enabling a decrease in the minimum detectable layer thickness. Furthermore, the sensitivity can be further improved by increasing resonant frequency 28 . On the other hand, S027T14 (cf.…”

Sensitive and Robust Millimeter-Wave/Terahertz Photonic Crystal Chip for Biosensing Applications

“…The electric field is mostly concentrated within the silicon of the PhC resonator, while the analyte is only captured on the surface of the resonator. This leads to a weak interaction and lowers the sensitivity of the sensor [12]. Furthermore, few researchers have addressed environmental effects.…”