New approach to terahertz sensing offers detection of circulating tumor cells

Terahertz sensing provides information on materials and processes occurring at length scales down to the nanometer range. Terahertz technology has developed in recent decades for biological sensing applications like tumor detection, but circulating fluid applications pose substantial challenges.

In APL Photonics, researchers from Imperial College London and the National University of Singapore report a highly sensitive microfluidic sensing technique for the terahertz frequency range. The study is part of a larger research project called Teracell, whose goal is to develop terahertz- and microwave-based biosensors for the label-free detection of circulating tumor cells.

The novel approach integrates a microfluidic channel in a spoof surface plasmon polariton (SPP) domino waveguide. The waveguide consists of a periodic array of standing metallic blocks which gradually narrow in width along a metal surface. The wave, known as a spoof SPP for terahertz field excitations, is bound to its surface and propagates with a much smaller wavelength than in free space. A liquid sample, like blood, introduced into the focused SPP field changes the refractive index, inducing a detectable shift in the transmission spectrum.

In addition to the theory, the authors report on their electromagnetic simulation modeling for the design and analysis. The model simplifies the cancer cell detection problem, simulating a dielectric particle flowing in a liquid-filled capillary. The results reveal that the technique could detect particles in an extremely small volume of liquid, less than one nanoliter.

Detecting circulating tumor cells in blood samples has important implications for improving cancer diagnosis and the development of personalized cancer therapies. According to author Stephen Hanham, the long-term goal is to develop the terahertz biosensing technology to the point where it can be tested in clinical trials.

Source: “Terahertz particle-in-liquid sensing with spoof surface plasmon polariton waveguides,” by Zhijie Ma, Stephen M. Hanham, Paloma Arroyo Huidobro, Yandong Gong, Minghui Hong, Norbert Klein, and Stefan A. Maier, APL Photonics (2017). The article can be accessed at https://doi.org/10.1063/1.4998566 .