Silver Nanoclusters Regulated By Polymorphic DNA Templates: Fluorescent Properties And Cellular Imaging Applications

Fluorescent metal nanoclusters (FMNCs) are molecular aggregate containingfrom several to dozens of noble metal atoms. As a novel class of fluorescent materials,FMNCs have unique optical and photophysical properties, which are used in analytesdetection and celluar imaging. Particularly, DNA-templated silver nanoclusters (AgNCs), with the advantages of facile synthesis, tunable fluorescence emission, andgood biocompatibility, have attracted increasing interests in biosensing andbionanotechnology. However, it is so far elusive yet what the relationships arebetween the structural composition of DNA sequences and the fluorescent propertiesof Ag NCs. The preparation Ag NCs with desirable properties through designingsuitable DNA templates have became a hot topic in the scientific community.In this article, interactions of Ag+with polymorphic DNA templates involvingG-quadruplex, i-motif, C-rich strand, and duplex were investigated through ITC. Theformation of different DNA-Ag+complexes is a strongly enthalpy driven process. Thebinding ratio for the duplex is the highest, and the binding ratio for G-quadruplex ismuch samller. The binding affinities of Ag+greatly depend on the secondarystructures of DNA templates, with a decreasing order: C-rich strand> i-motif>duplex> G-quadruplex. Fluorescent Ag NCs prepared using these DNA templatespossess the emission wavelength from538nm to706nm. Among them,[C4A4C3]-Agexhibit the highest fluorescent quantum yield of37%. Their fluorescence stabilitiesare associated with the binding affinities between DNA templates and Ag+, e.g.,C4A4C3with the highest binding constant (40.2×105M1) stabilizes Ag NCs for over300h, while G4T4G4with the lowest binding constant (0.64×105M1) generates AgNCs with the shortest shelf-life (50h). In addition, HeLa cells were successfullylabeled by using Lipofectamine as a transfection agent to incorporate the red emitting[C4A4C3]-Ag and the NIR emitting [G4T4G4-C4A4C4]-Ag, which are better than thefluorescent image of pancreatic cancer.