Germanium Plasmon Enhanced Resonators for Label-Free Terahertz Protein Sensing

Abstract

A Terahertz protein sensing concept based on subwavelength Ge resonators is presented. Ge bowtie resonators, compatible with CMOS fabrication technology, have been designed and characterized with a resonance frequency of 0.5 THz and calculated local intensity enhancement of 10.000. Selective biofunctionalization of Ge resonators on Si wafer was achieved in one step using lipoic acid-HaloTag ligand (LA-HTL) for biofunctionalization and passivation. The results lay the foundation for future investigation of protein tertiary structure and the dynamics of protein hydration shell in response to protein conformation changes.

Terahertz subwavelength sensing with bio-functionalized germanium fano-resonators

“…After 10 min of plasma treatment, PLL-PEG-HTL in aqueous solution is rapidly adsorbed electrostatically to the negatively charged Si 3 N 4 layer. This way, surface functionalization of Ge resonators becomes much faster and easier to handle compared to functionalization with α-lipoic acid established in previous work [10,11]. The obtained PLL-PEG-HTL-functionalized Ge wafers can be employed for site-specific, covalent capturing of HaloTagfusion proteins.…”

“…The spectral response of the n-Ge antennas in the THz range can be reliably simulated by solving Maxwell's equations using a Finite Element Method (FEM), with input data such as geometry, density, arrangement and stack materials [10,13]. Comprehensive FEM simulations have been made, using the method and parameters as described in [10]. The designed (theoretical) resonance frequency (f 0 ) of the plasmonic antennas is mainly governed by their arm length.…”

“…This implies that the amount of analyte required to obtain a detectable signal could be drastically reduced, while simultaneously decreasing the overall device size. Due to their higher skin depth, caused by lower conductivity, semiconductor-based LSPR has the advantage over their metallic counterparts of a larger field penetration into the material [10]. Since LSPR are responsive to changes in their immediate surroundings, they can be used as a sensing platform.…”

“…In previous studies, we have presented the sensing capability of semiconductor-based LSPR devices [10,13,14].…”