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...

Polaritons in 2D materials exhibit extensive optical phenomena, such as an ultrahigh field confinement and tunability and, thus, have been attracting increasing attentions. Many different methods have been developed to characterize and manipulate polaritons, which in turn has promoted a steady booming of this field. Here, the significant progress made in probing polaritons in 2D materials based on the characterization method, i.e., optical far‐field, optical near‐field, and (opto)electronic methods is reviewed. Perspectives on the potential development and applications of these methods are also discussed.

Nanoscale Fourier transforms infrared spectroscopy (nano-FTIR) based on scanning probe microscopy enables identification of chemical composition and structure of surface species with a high spatial resolution (~10 nm), which is...