title: Direct detection of DNA with an electrocatalytic threading intercalator.
abstract: Herein we report the synthesis, intercalating properties, and analytical applications of an imidazole-substituted naphthalene diimide, N,N'-bis(3-propylimidazole)-1,4,5,8-naphthalene diimide (PIND), functionalized with electrocatalytic redox moieties. PIND was prepared in a single-step reaction from the corresponding dianhydride. Attachment of the redox moieties to PIND relied upon ligand exchange with one of the liable chloride ligands of an Os(bpy)2Cl2 (bpy = 2,2'-bipyridine) complex. The Os(bpy)2Cl2 complex was grafted onto PIND through coordinative bonds with the two imidazole groups at its termini, forming a PIND-[Os(bpy)2Cl]+ compound (PIND-Os). Gel electrophoretic studies revealed that PIND-Os binds more strongly to double-stranded DNA (ds-DNA) than its parent compound 1,4,5,8-naphthalene diimide. The naphthalene diimide group binds to ds-DNA in a "classical" threading intercalation mode, while the two Os(bpy)2Cl+ pendants interact with DNA via electrostatic interaction, reinforcing the intercalation by "locking up" the naphthalene diimide group in place. An electrochemical biosensor was fabricated using the redox-active and catalytic PIND-Os intercalator. An increase in sensitivity of 2500-fold over direct voltammetry was obtained in electrocatalytic amperometry, making this an interesting system for amperometric DNA sensing. Under optimized experimental conditions, the biosensor allowed the detection of a 50-mer target DNA in the range of 1.0-300 pM with a detection limit of 600 fM (1.5 amol, 23 fg).
authors.affiliation: Institute of Bioengineering and Nanotechnology, 31 Biopolis Way, Singapore 138669, Republic of Singapore.
authors.forename: Natalia C
authors.initials: NC
authors.lastname: Tansil
authors.forename: Hong
authors.initials: H
authors.lastname: Xie
authors.forename: Fang
authors.initials: F
authors.lastname: Xie
authors.forename: Zhiqiang
authors.initials: Z
authors.lastname: Gao
mesh_terms: D015374:Biosensing Techniques / Q000379:methods*; D002384:Catalysis; D004247:DNA / Q000032:analysis*; D004563:Electrochemistry; D007094:Imides; D007364:Intercalating Agents / Q000737:chemistry*; D009281:Naphthalenes; D010084:Oxidation-Reduction; D010618:Phenanthrolines / Q000737:chemistry
chemical_list: D007094:Imides; D007364:Intercalating Agents; D009281:Naphthalenes; D010618:Phenanthrolines; C542131:naphthalenediimide; D004247:DNA