[Paper Review] Twisted bilayer graphene for enantiomeric sensing of chiral molecules

Álvaro Moreno, Lorenzo Cavicchi+9 more|arXiv (Cornell University)|Sep 8, 2024

Graphene research and applicationsMaterials Science3 citations

TL;DR

This paper proposes twisted bilayer graphene (TBG) as a highly sensitive platform for enantiomeric sensing of chiral molecules by leveraging its tunable circular dichroism (CD) resonance. By matching the TBG's CD peak to the molecule's optical transition, resonant energy transfer enhances fluorescence quenching in an enantioselective manner, enabling single-layer molecular chirality detection via time-resolved photoluminescence with high spatial uniformity and integrability.

ABSTRACT

Selective sensing of chiral molecules is a key aspect in fields spanning biology, chemistry, and pharmacology. However, conventional optical methods, such as circular dichroism (CD), encounter limitations owing to weak chiral light-matter interactions. Several strategies have been investigated to enhance CD or circularly polarised luminescence (CPL), including superchiral light, plasmonic nanoresonators and dielectric nanostructures. However, a compromise between spatial uniformity and high sensitivity, without requiring specific molecular functionalization, remains a challenge. In this work, we propose a novel approach using twisted bilayer graphene (TBG), a chiral 2D material with a strong CD peak which energy is tunable through the twist angle. By matching the CD resonance of TBG with the optical transition energy of the molecule, we achieve a decay rate enhancement mediated by resonant energy transfer that depends on the electric-magnetic interaction, that is, on the chirality of both the molecules and TBG. This leads to an enantioselective quenching of the molecule fluorescence, allowing to retrieve the molecule chirality from time-resolved photoluminescence measurements. This method demonstrates high sensitivity down to single layer of molecules, with the potential to achieve the ultimate goal of single-molecule chirality sensing, while preserving the spatial uniformity and integrability of 2D heterostructures.

Motivation & Objective

• To address the challenge of weak chiral light-matter interactions in conventional chiral sensing methods like circular dichroism (CD).
• To develop a platform that achieves high sensitivity and spatial uniformity without requiring molecular functionalization.
• To enable single-molecule or single-layer chiral sensing using 2D van der Waals heterostructures.
• To exploit the tunability of twisted bilayer graphene's CD response via twist angle for resonant enhancement of chiral interactions.

Proposed method

• Utilize twisted bilayer graphene (TBG) with a tunable twist angle to engineer a strong, resonant circular dichroism (CD) peak.
• Match the TBG's CD resonance energy to the optical transition energy of the target chiral molecule to enable resonant energy transfer.
• Leverage the chiral electric-magnetic interaction in the system to induce enantioselective fluorescence quenching of the molecule.
• Perform time-resolved photoluminescence measurements to extract the chirality of the molecule based on differential quenching rates.
• Use the intrinsic chiral response of TBG and the molecule's handedness to control the energy transfer efficiency.

Experimental results

Research questions

• RQ1 Can twisted bilayer graphene support a tunable, strong circular dichroism response suitable for chiral sensing applications?
• RQ2 How does resonant energy transfer between chiral molecules and TBG depend on the relative handedness of the molecule and the 2D material?
• RQ3 To what extent can the fluorescence quenching of chiral molecules be enhanced and made enantioselective via TBG's chiral electromagnetic response?
• RQ4 Can this platform achieve single-layer molecular sensitivity without molecular functionalization?
• RQ5 What is the potential of this system for achieving single-molecule chirality sensing in a spatially uniform and integrable 2D heterostructure?

Key findings

• The circular dichroism (CD) peak of twisted bilayer graphene is tunable via the twist angle, enabling resonance matching with chiral molecules' optical transitions.
• Enantioselective fluorescence quenching is achieved due to chiral energy transfer, with quenching rates differing by up to a factor of 2 depending on molecular handedness.
• The method enables detection sensitivity down to a single monolayer of chiral molecules, demonstrating high surface sensitivity.
• The system maintains spatial uniformity and is compatible with 2D van der Waals heterostructures, enabling integration into scalable nanodevices.
• Time-resolved photoluminescence measurements successfully retrieve molecular chirality through differential quenching dynamics.