Fluorescence Enhancement of Adamantane-Modified Dyes in Aqueous Solution via Supramolecular Interaction with Methyl--cyclodextrin and Their Application in Cell Imaging

The fluorescence of functional dyes was generally quenched in aqueous solution, which hindered their application in water-bearing detections. In this work, a novel strategy based on host-guest interaction was provided for the purpose of fluorescence enhancement in aqueous solution and cell imaging. Three adamantane-modified fluorescent dyes (Coum-Ad, NP-Ad, NR-Ad) with coumarin, 1,8-naphthalimide and Nile Red as fluorophores were initially designed and prepared. The ((adamantan-1-yl)methyl)amino group, as the auxochrome of those dyes, complexed with methylated beta-cyclodextrin (M-beta-CD) via supramolecular interaction, and then fluorescent supramolecular nanoparticles (FSNPs) were formed by self-assembly in water. The inclusion equilibrium constant (K) could be as high as 3.94x10(4) M-1. With the addition of M-beta-CD, fluorescence quantum yields of these dyes were separately improved to 69.8 %, 32.9 % and 41.3 %. Inspired by the above satisfactory results, six adamantane-modified probes organelle-NPAds with organelle-targeting capability were further obtained. As the formation of hydrogen bonds between organelle-NPAd2 and M-beta-CD verified by theoretical calculation, K of organelle-NPAd2 (5.13x10(4) M-1 similar to 4.53x10(5) M-1) with M-beta-CD was higher than that of organelle-NPAd1 (1.15x10(4) M-1 similar to 3.66x10(4) M-1) and their fluorescence quantum yields increased to 32.8 %similar to 83.6 % in aqueous solution. In addition, fluorescence enhancement was realized in cell imaging with the addition of M-beta-CD.