Fundamental studies of molecular detection schemes enable the practical application of science with important implications for measurement of species relevant to the environment, national security, and clinical diagnostics. Essentially, these schemes rely on (1) specific interactions between synthetic host molecules and their targeted analytes and (2) an indicator that the molecules are interacting. Halogen bonding (XB)—an orthogonal, electrostatic interaction between a region of positive electrostatic potential (δ+) on a halogen atom (XB donor) and a Lewis base (δ–) (XB acceptor)—can serve as the specific interaction. Herein, a thiolate molecule/ligand with strong XB-donor moiety (–C6F4I) is successfully synthesized and characterized with NMR, IR, and HRMS. The XB-donor ligand is then used to functionalize hexanethiolate-protected gold nanoparticles (AuNPs) through place-exchange reactions. The XB-functionalized AuNPs (XB-fAuNPs) can engage in strong XB interactions with XB-acceptor analytes, which results in AuNP aggregation events (measured via UV-Vis, TEM imaging, and DOSY NMR measurements) with a limit of detection in the nanomolar range. In an application, these XB-fAuNPs are shown to engage in XB interactions with select neonicotinoid pesticides (XB acceptors) implicated in the rapid decline of insect populations. XB-acceptor capabilities of neonicotinoids are computationally and experimentally explored using density functional theory (DFT) calculations, 19F NMR, and DOSY NMR. TEM imaging and UV-Vis measurements are used to show XB-induced aggregation events between XB-fAuNPs and select neonicotinoids. This study further supports using XB-fAuNPs in XB-based molecular detection schemes.

Halogen-bonding capable functionalized gold nanoparticles: An avenue for molecular detection schemes

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