Terahertz particle-in-liquid sensing with spoof surface plasmon polariton waveguides

Zhijie Ma,Paloma Arroyo Huidobro,Norbert Klein,Minghui Hong,Stefan A Maier,Yandong Gong,Stephen M Hanham

doi:10.1063/1.4998566

Abstract

We present a highly sensitive microfluidic sensing technique for the terahertz (THz) region of the electromagnetic spectrum based on spoof surface plasmon polaritons (SPPs). By integrating a microfluidic channel in a spoof SPP waveguide, we take advantage of these highly confined electromagnetic modes to create a platform for dielectric sensing of liquids. Our design consists of a domino waveguide, that is, a series of periodically arranged rectangular metal blocks on top of a metal surface that supports the propagation of spoof SPPs. Through numerical simulations, we demonstrate that the transmission of spoof SPPs along the waveguide is extremely sensitive to the refractive index of a liquid flowing through a microfluidic channel crossing the waveguide to give an interaction volume on the nanoliter scale. Furthermore, by taking advantage of the insensitivity of the domino waveguide’s fundamental spoof SPP mode to the lateral width of the metal blocks, we design a tapered waveguide able to achieve further confinement of the electromagnetic field. Using this approach, we demonstrate the highly sensitive detection of individual subwavelength micro-particles flowing in the liquid. These results are promising for the creation of spoof SPP based THz lab-on-a-chip microfluidic devices that are suitable for the analysis of biological liquids such as proteins and circulating tumour cells in buffer solution.

Highlights

The terahertz (THz) region of the electromagnetic spectrum, lying between microwaves and infrared light, is an important band for sensing due to its non-ionizing nature and the many intermolecular vibrational and rotational modes of polar molecules present
We demonstrate how a change in the refractive index of liquid flowing through the micro-capillary or a single micro-particle passing through it affects the transmission of the spoof surface plasmon polaritons (SPPs) waves on the domino waveguide, which can be used for sensing applications
It is shown that when no capillary is inserted, the spoof SPP wave can propagate on the waveguide with nearly no radiative loss over the propagation band, maintaining a high transmission rate over 90%, until it meets the cutoff frequency of 0.23 THz where no spoof SPP mode can propagate

Summary

INTRODUCTION

The terahertz (THz) region of the electromagnetic spectrum, lying between microwaves and infrared light, is an important band for sensing due to its non-ionizing nature and the many intermolecular vibrational and rotational modes of polar molecules present. In the THz regime, spoof SPPs provide the advantage of shrinking the relatively long wavelength of THz waves to a subwavelength scale comparable with the dimension of biological analyte targets. All these properties, together with the capability of guiding electromagnetic energy with spoof SPP waveguides, provide a new operating principle for optofluidic sensors, which combine the advantages of compact and rapid handling of microfluidics and the high detection sensitivity of the optical analysis. The proposed sensing platform has the advantage that the liquid samples are completely contained in the microfluidic system, which can be useful for integrated lab-on-chip sensing devices in the future

THEORY AND MODEL

RESULTS AND DISCUSSION

CONCLUSION