Atomically Precise Noble Metal Cluster-Assembled Superstructures in Water: Luminescence Enhancement and Sensing

We present an example of host-guest complexes of atomically precise noble metal nanoparticles with cucurbit[7]uril (CB) in water, specifically concentrating on Ag29(LA)12 (where LA is α-lipoic acid), a well-known red luminescent silver cluster. Such host-guest interactions resulted in enhanced luminescence of about 1.25 times for the modified system, compared to the parent cluster. We extended our study to cyclodextrins (CDs), where about 1.5 times enhanced luminescence was estimated compared to the parent cluster. The formation of supramolecular complexes was confirmed using high-resolution electrospray ionization mass spectrometry (HRESI MS) and nuclear magnetic resonance spectroscopy. Molecular docking and density functional theory calculations supported our experimental results and showed that while CB formed inclusion complexes by encapsulation of one of the LA ligands of the cluster, CD formed supramolecular adducts by interaction with the cavity built by the ligands on the cluster surface. The complexation was favored by geometrical compatibility. Consequently, these superstructures are labeled as Ag29LA12∩CBn and Ag29LA12@CDn (n = 1-3), where ∩ and @ indicate the inclusion complex and supramolecular adduct, respectively. Solution-phase Ag29LA12@CDn complexes were employed to detect dopamine (10 nM). Luminescent Ag29LA12@CDn and Ag29LA12∩CBn complexes in water could be potential candidates for organic pollutant sensing and biomedical applications.