# Design of Nanomaterial-Based Sensors for Enhanced Halogen Bonding

## TL;DR

This paper explores how nanomaterial-based sensors using halogen bonding can detect trace amounts of nonvolatile explosives more effectively.

## Contribution

The study introduces functionalized nanomaterials with optimized halogen bonding geometries for enhanced sensing performance.

## Key findings

- Halogen bond donor ligands on gold nanoparticles significantly improve detection of cyclohexanone.
- The sensing interface achieved detection limits below 10 ppm for cyclohexanone in both solution and gas phases.
- Nanomaterial composites with halogen bonding show promise for rapid and sensitive explosive detection.

## Abstract

Halogen bonding is a highly directional, noncovalent,
intermolecular
interaction which has been harnessed for a variety of applications,
including sensor design. A halogen bond (XB) is formed between a region
of positive electrostatic potential on a halogen atom (X) and electron
rich portions of target molecules. The strength of XB interactions
relies on shorter XB bond distances and more linear R–X···B
bond angles, which facilitate stronger, more negative binding energies.
While prior studies have sought to maximize interactions, few have
explored or experimentally demonstrated how geometries and bond angles
can enhance XB interactions. Herein, fundamental studies are conducted
at self-assembled monolayers (SAMs) and gold nanoparticle (Au-NP)
interfaces that are functionalized to engage in XB interactions. Alkanethiolate-stabilized
Au-NPs, known as monolayer-protected gold clusters (MPCs), were enhanced
with XB-donor capability by incorporating specialized XB donor thiol
ligands including halogen terminated perfluorinated straight chain
and rigid perfluoro-aromatic amide ligandsboth of which were
used within nanomaterial composite films of single-walled carbon nanotubes
(SWCNTs) as a sensing interface in both solution and the gas phase.
DFT and vapor studies targeting cyclohexanone (CH), a known byproduct
of hard-to-detect, nonvolatile explosives (e.g., RDX), produced a
sensing interface that achieved detection limits of CH (<10 ppm)
that markedly outperform similar systems. The materials and methods
presented in this study further demonstrate the potential of XB systems
as a rapid and sensitive step toward developing field sensors for
explosives.