Water-soluble cationic branched phenylene-ethynylene as fluorescent probes for supramolecular interaction

Abstract

Five amphiphilic fluorophores (N⁰N⁺, N⁺, 2N⁺, 3N⁺ and 6N⁺) with phenylene-ethynylene fluorogenic units are employed as the fluorescent probes for investigation of fluorescence responses in nano-confined environments of DNAs, BSA protein, surfactants and cyclodextrins in aqueous media. 3N⁺ represents one of the most responsive probes to all analytes. For example, the strong fluorescence enhancement of 3N⁺ by γ-cyclodextrin is due to a 1:1 stable inclusion complexation (K[subscript b] = 3.0x10⁴ M⁻¹). The discovery of fluorescence enhancement of 3N⁺ via charge interaction with ssDNA chain leads to the design of selective and sensitive potassium ion fluorescence aptasensing system. Strong fluorescence response to BSA protein suggest effective self-quenching prevention probably via both hydrophobic and hydrophilic interaction (K[subscript b] = 6.7x10⁵ M⁻¹). 3N⁺ is also used as a fluorescence micellization probe to determine CMC of surfactants. In the case of 6N⁺, the fluorescence enhancement becomes apparent only for BSA protein and surfactants. The interaction with ssDNA is proven by FRET signals which are useful for DNA sequence detection.