Design of Nanomaterial-Based Sensors for Enhanced Halogen Bonding.

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.