Detection of DNA damaging agents using layer-by-layer assembly

The layer-by-layer (LBL) electrostatic deposition method was used to fabricate multilayer films of pentaerythritol-based metallodendrimer with Ru^II terpyridine subunits (RuDen) that has a positive charge and ds-DNA (ds, double-stranded) that has a negative charge due to its phosphate backbone. Evidence of assembly was obtained by fabrication of (DNA | RuDen)_n on quartz treated with poly(diallyldimethylammonium chloride), PDDA. The absorbance at 263 nm varied linearly with n in the range 1-6. For electrochemical monitoring of damage by styrene oxide, the assembly was on a glassy carbon electrode that was coated with a monolayer of aminobenzoic acid. The measurement was based upon the RuDen-catalyzed oxidation of sites, e.g. guanine, that are exposed when ds-DNA is damaged. The peak current at 1.07 V versus Ag | AgCl in square wave voltammetry increases with incubation time for 30 min. The process was also monitored by the shift in the spectrum of a long period grating (LPG) fiber coated with (DNA | RuDen)₅. A typical shift, which is due to changes in the refractive index of the coating, was 0.3 and 1.8 nm for 5 and 30 min exposures, respectively, using an algorithm that can measure a shift of 10⁻⁴ nm.