A redox active and electrochemiluminescent threading bis-intercalator and its applications in DNA assays

A redox active and electrochemiluminescent (ECL) threading bis-intercalator, consisting of two N,N'-bis(3-propyl-imidazole)-1,4,5,8-naphthalene diimides (PIND) linked by a Ru(dmbpy)2(2+) (dmbpy = 4,4'-dimethyl-2,2'-bipyridine) complex (PIND-Ru-PIND), was synthesized for the first time. Its optical, electrochemical, and ECL properties were studied. UV-vis spectrophotometric measurements indicated that the two PIND groups bind to the double-stranded DNA (ds-DNA) in a threading intercalation mode, while the Ru(dmbpy)2(2+) reinforces the intercalation via electrostatic interaction with ds-DNA. An ECL DNA biosensor was fabricated using PIND-Ru-PIND. A 2000-fold sensitivity enhancement over direct voltammetry was obtained, making this an ultrasensitive system for ECL detection of DNA. Under optimized conditions, the biosensor allowed the detection of a target DNA in the range of 0.70-400 pM with a detection limit of 400 fM.