Ultrasensitive Mid‐Infrared Biosensing in Aqueous Solutions with Graphene Plasmons

Abstract

nanomedicine targeting effects are at the nanoscale level. [2] Thus, it is important to develop in situ and noninvasive methods with nanoscale resolutions to understand biological processes in physiological environments. [3] Along these lines, Fourier transform infrared (FTIR) spectroscopy serves as a label-free, noninvasive, and fast method for identifying biomolecules by detecting their molecular vibrational fingerprints. [4] However, achieving FTIR in aqueous solutions with nanoscale sensitivity remains a challenge since the strong and broad IR band of water (H 2 O) always masks the vibrational fingerprints of the biomolecules, especially in the mid-IR range. [5] Many efforts have been made to implement the vibrational fingerprints masked by H 2 O. For example, alternative solvents (e.g., D 2 O, CCl 4 , and CS 2 ) are used in FTIR measurements since their IR absorption bands are shifted away from the absorption band of H 2 O. [4] Another potential route is to shorten the effective IR optical path in an aqueous solution to suppress the interference of H 2 O, such as the attenuated total reflectance (ATR). [6] Nevertheless, neither solvent replacement nor ATR can enhance the FTIR sensitivity to the nanoscale due to the weak light-matter interaction. Therefore, the surface-enhanced infrared absorption (SEIRA) technique is developed for in situ probing nanoscale samples through the enhanced near-field of the surface plasmons. [7] Although the metal-antenna-based SEIRA has already achieved high sensitivity, the detection limit is ultimately restricted to monolayer molecules by the relatively poor light confinement of metal in the mid-IR.The extremely high light confinement of graphene plasmon renders it attractive for SEIRA applications. [8] The sensitivity of graphene-plasmon-enhanced FTIR can reach sub-nanometer scale, which has been demonstrated in identifying molecules in the solid phase and the gas phase. [8a,9] In addtion, graphene can increase the IR absorption of molecules in aqueous solution in the inner reflection process, [10] but the lack of tunability as well as the utilization of bulky ATR instrumentation prevents it from practical use. [11] In this work, we develop a tunable graphene-plasmonenhanced FTIR technology to identify nanoscale proteins in physiological conditions. Specifically, the interference of H 2 O outside the graphene plasmon hotspots is eliminated Identifying nanoscale biomolecules in aqueous solutions by Fourier transform infrared spectroscopy (FTIR) provides an in situ and noninvasive method for exploring the structure, reactions, and transport of biologically active molecules. However, this remains a challenge due to the strong and broad IR absorption of water which overwhelms the respective vibrational fingerprints of the biomolecules. In this work, a tunable IR transparent microfluidic system with graphene plasmons is exploited to identify ≈2 nm-thick proteins in physiological conditions. The acquired in situ tunability makes it possible to eliminate the IR absorption of...

2D Material Infrared Photonics and Plasmonics

“…The tunability of graphene plasmons makes it viable to detect multiple parts of biomolecules with a single device, thus providing a more comprehensive understanding of the molecular structures. More recently, by using a similar plasmonic mechanism, Wu et al demonstrated a MIR graphene-based plasmonic biosensor that was capable of detecting proteins under aqueous conditions. This is conventionally difficult as a result of the broadband and strong absorption of water in the IR region.…”

“…This is conventionally difficult as a result of the broadband and strong absorption of water in the IR region. By tuning the gate voltage, background signals unrelated to the plasmonic response could be removed and the IR absorption of water could be eliminated …”

“…The tunability of graphene plasmons makes it viable to detect multiple parts of biomolecules with a single device, thus providing a more comprehensive understanding of the molecular structures. More recently, by using a similar plasmonic mechanism, Wu et al 251 plasmonic response could be removed and the IR absorption of water could be eliminated. 251 Non-Graphene-Based Plasmonics.…”

“…More recently, by using a similar plasmonic mechanism, Wu et al 251 plasmonic response could be removed and the IR absorption of water could be eliminated. 251 Non-Graphene-Based Plasmonics. 2D Transition Metal Dichalcogenide Plasmonics.…”

Graphene Coated Dielectric Hierarchical Nanostructures for Highly Sensitive Broadband Infrared Sensing

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The nfrared (IR) band contains rich matter information, and has great scientific interest and technological importance in practical applications in various fields, [1] such as thermal imaging, [2] chemical sensor, [3,4,5] optical communication, [6] and medical diagnosis. [7] IR plasmonic nanostructures [8,9] supporting IR light-matter interaction in nanoscale, which contribute strongly enhanced local electromagnetic field, are essential for ultrasensitive IR spectroscopy, photodetections, modulation, and generation.Strong IR absorption can be achieved by exploiting the strong optical near-field in the vicinity of resonant metallic nanostructures.

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