Specific biosensing with non-linear metamaterials

The studentship is part of the UK’s Centre of Doctoral Training in Metamaterials (XM2) based in the Departments of Physics and Engineering on the Streatham Campus in Exeter. Its aim is to undertake world-leading research, while training scientists and engineers with the relevant research skills and knowledge, and professional attributes for industry and academia.

The ability to monitor and detect biochemical signatures is of vital importance to public health and well-being, affecting areas such as food quality assurance, medical diagnostics and drug development. This has driven the rapid development of nanophotonic biosensors, which can reach single molecule sensitivity [1], but lack the ability to arbitrarily differentiate one molecular species from another and instead rely on the use of bio-receptors for specificity. On the other hand, the vibrational modes of molecular bonds provide a unique fingerprint of the chemical structure, but interact very weakly with infrared radiation. This interaction can be greatly improved using mid-IR metamaterials, where the strong optical near-field significantly enhances the light-matter interaction, a technique known as surface-enhanced infrared absorption (SEIRA), resulting in improvements in sensitivity of five orders of magnitude [2]. A major drawback of SEIRA is that it requires bulky and expensive infrared spectrometers, thus limiting the scope of applications.

This project aims to combine the advantages of optical biosensors with the specificity of SEIRA to develop an integrated spectroscopic sensing platform. To achieve this, the student will investigate the photonic integration of 2D materials as a platform for efficient non-linear frequency conversion [3]. The initial emphasis will be on graphene, where nonlinearities are predicted to be very large, even down to single photon level [4]. However, other materials, such as boron nitride and transition metal dichalcogenides will also be investigated. To maximise the efficiency of the non-linear processes, the electric field must be enhanced at both the infrared and optical frequencies. This will be achieved through the integration of 2D materials with infrared metamaterials and visible integrated photonics, to realise a novel doubly resonant photonic platform.

[1] F. Vollmer & S. Arnold, Nat. Methods 5, 591 (2008).
[2] F. Neubrech et al., Phys. Rev. Lett. 101, 157403 (2008).
[3] T. J. Constant et al., Nat. Physics 12, 124 (2016); X. Yao et al., Phys. Rev. Lett. 112, 055501 (2014).
[4] M. Gullans et al., Phys. Rev. Lett. 111, 247401 (2013).