Dielectric measurements of nanoliter liquids with a photonic crystal resonator at terahertz frequencies

Abstract

We present a highly sensitive technique for determining the complex permittivity of nanoliter liquid samples in the terahertz band based on a photonic crystal resonator and microcapillary. Liquids are characterized by using a capillary tube to introduce a ∼4 nl liquid sample into the electromagnetic field of a resonant mode confined by an L3 resonant cavity in a high-resistivity silicon photonic crystal slab. Monitoring the perturbation of the resonant frequency and unloaded Q-factor of the resonant mode at 100 GHz and ∼5800, respectively, allows a sample's permittivity to be calculated. An analytical model describing the system response based on perturbation theory and quasi-static analysis of the electric field within the capillary is also presented and found to agree well with FEM simulations and experimental measurements of ethanol-water mixtures of various concentrations for low to moderate loss tangents of the liquid samples. We demonstrate the utility of this approach by measuring the complex permittivity of several bioliquids, including suspensions of red and white blood cells. These results represent a step towards a lab-on-a-chip device for the analysis of extremely small quantities of biological, toxic, explosive, and other liquid types at terahertz frequencies.

LED-Switchable High-QPackaged THz Microbeam Resonators

“…H IGH quality (Q-) factor resonators form the basis of millimeter and submillimeter wave system components, such as low phase-noise oscillators, impedance matching networks, and narrowband filters [1]. They can also serve as sensing platforms by enhancing light-matter interaction, allowing for highly sensitive dielectric measurements and chemical sensing [2], [3]. The system integration of these resonators will be critical to realizing advanced terahertz systems.…”

Coupled dielectric-split ring microwave resonator for liquid measurements in microfluidic channels at nanoliter volumes

“…Due to the strong interaction of water with electric fields at microwave frequencies, sensors operating in this regime have shown high sensitivity for the measurement of the complex dielectric permittivity (ε*) of small volumes of aqueous solutions [1][2][3][4][5][6][7][8][9]. This is promising for biosensing applications where most liquids to be investigated consist predominantly of water.…”

Microwave-to-terahertz dielectric resonators for liquid sensing in microfluidic systems

“…Fig. 2 from [11] shows our previous work on HRS 2D photonic bandgap defect resonators for dielectric measurement of liquids within a disposable glass capillary, which is inserted through a hole within the hexagonal photonic crystal lattice in close vicinity to the maxima of the resonant field. We have demonstrated highly accurate dielectric measurements on a variety of liquids, the actual interaction volume is only 4 nl.…”

“…2). The advanced perturbation approach described in [11] takes this effect into account and enables quantitative dielectric measurements on nanolitre samples at 100 GHz for the first time.…”