“NMR Chemosensing” Using Monolayer-Protected Nanoparticles as Receptors

Abstract

A new sensing protocol based on NMR magnetization transfer sequences and the molecular recognition abilities of nanoparticles allows the detection and identification of organic molecules in complex mixtures.

Nanoparticle-Based Receptors Mimic Protein-Ligand Recognition

“…In this regard, some of us recently proposed nuclear magnetic resonance (NMR) chemosensing as a protocol that exploits the molecular recognition ability of monolayer-protected gold nanoparticles (AuNPs, about 2 nm core diameter) in order to detect target analytes 21, 22, 23, 24. Typically, these analytes are small organic molecules such as salicylate.…”

“…1 -AuNPs, reported in Scheme 1, detect salicylate (2-hydroxybenzoate, 3 ; Scheme 1) in water with a remarkable selectivity with respect to many other aromatic anions of a similar structure, including 3- and 4-hydroxybenzoate ( 4 and 5 ; Scheme 1) and 4-methylbenzenesulfonate ( 6 ; Scheme 1). 21 Within this group, salicylate is the molecule with the highest octanol/water partition coefficient ( P ow ) and the most retained in reversed-phase chromatography. Selective recognition could hence simply arise from the hydrophobic interaction with the inner part of the nanoparticle-coating monolayer.…”

“…Interestingly, when we elongated the alkyl portion of 1 by four carbon atoms, we obtained 2 -AuNPs (Scheme 1), which could detect 4-methylbenzenesulfonate in addition to salicylate. Nevertheless, 2 -AuNPs could not detect the less hydrophilic 3- and 4-hydroxybenzoate 21 . This result demonstrated that other factors were at play in determining the monolayer's binding selectivity.

Scheme 1The NMR Chemosensing Machinery for Analyte DetectionUpper: the monolayer-protected nanoparticles (ligands 1 and 2 ) and analytes ( 3 – 6 ) investigated in early studies 21

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Simultaneous Identification of Neutral and Anionic Species in Complex Mixtures without Separation

“…The high sensitivity of fluorine NMR shifts to the local environment and the low level of interfering background signals allows this chemosensory platform to operate on complex mixtures without the need of separation, wherein both neural and ionic species with minute structural differences are simultaneously identified in complex mixtures. [4][5][6] We view the amide-based palladium pincer complexes (Scheme 1b) to be versatile scaffolds because metallation of the ligand creates a confined binding cleft with a Lewis acidic metal, and also has a structure wherein fluorine probes can be positioned in close proximity to analytes bound in the cleft. [7] Another appealing feature of these complexes is the ability to undergo facile ligand exchange at only one coordination site, but also exhibit analyte bound complexes that are static on the NMR timescale.…”

19F NMR indicator displacement assay using a synthetic receptor with appended paramagnetic relaxation agent

“…For example, NMR spectroscopy has greater signal dispersion, which favors the creation of multiplex sensing assays. 7 In addition, the ability to manipulate NMR spin states using multipulse sequences allows selective signal detection and spectral editing. Furthermore, the ability of MRI to visualize signals that are spatially deep within physical objects, including living subjects, raises the intriguing idea of buried IDAs that are detected remotely.…”