Plasmonics–Nanofluidics Hydrid Metamaterial: An Ultrasensitive Platform for Infrared Absorption Spectroscopy and Quantitative Measurement of Molecules

Abstract

One of the most attractive potentials of plasmonic metamaterials is the amplification of intrinsically weak signals such as molecular infrared absorption or Raman scattering for detection applications. This effect, however, is only effective when target molecules are located at the enhanced electromagnetic field of the plasmonic structures (i.e., hot-spots). It is thus of significance to control the spatial overlapping of molecules and hot-spots, yet it is a long-standing challenge, since it involves the handling of molecules in nanoscale spaces. Here a metamaterial consisting of a nanofluidic channel with a depth of several tens of nanometers sandwiched between plasmonic resonators and a metal film enables the controllable delivery of small molecules into the most enhanced field arising from the quadrupole mode of the structures, forming a plasmon-molecular coupled system. It offers an ultrasensitive platform for detection of IR absorption and molecular sensing. Notably, the precise handling of molecules in a fixed and ultrasmall (10-100 nm) gap also addressed some critical issues in IR spectroscopy such as quantitative measurement and measurement in aqueous solution. Moreover, a drastic change in the reflectance characteristic resulting from the strong coupling between molecules and plasmonic structures indicates that molecules can also be utilized as triggers for actively switching the optical property of metamaterials.

Leveraging of MEMS Technologies for Optical Metamaterials Applications

“…Copyright 2019, The American Association for the Advancement of Science. (f) Reproduced with permission . Copyright 2017, American Chemical Society.…”

“…However, there is a tradeoff between near‐field intensity and hotspot area in planar metamaterial resonators. To further enhance sensitivity, the nanofluidic approach was presented by Le et al With the aid of the bottom gold mirror, quadrupolar resonance mode is excited in the metal‐insulator‐metal (MIM) structure, bringing a large area hotspot with an enhanced near‐field intensity inside the nanometer‐scale liquid chamber. As shown in Figure f, the analyte solution was filled in the hotspot generated by the nano‐gapped MIM structure with high near‐field enhancement, which results in strong plasmon‐phonon interaction.…”

MIR plasmonic liquid sensing in nano-metric space driven by capillary force

“…Hence, identification of molecular fingerprint can be achieved without the labeling process in a non-destructive manner [9][10][11][12]. Despite the advantages that MIR spectroscopy provides in the detection of biochemical samples, the weak interaction between the incident light and the molecular vibrational modes leads to low absorption/scattering cross sections [13]. This limits the sensitivity and thus prevents the application of vibrational spectroscopies to practical use.…”

Bonding and Antibonding Modes in Metal–Dielectric–Metal Plasmonic Antennas for Dual‐Band Applications

“…The observed significant fingerprint enhancement justifies the use of our dual‐band dimer SPP antenna for surface‐enhanced spectroscopy. Notice that from the practical point of view, the delivery of the sensed materials in between the gold disks, as well as around the antenna, can potentially be realized via nanofluidics …”