Rapid assessment of DNA damage induced by polystyrene nanosphere suspension using a photoelectrochemical DNA sensor

Abstract

Nanomaterials have been used increasingly in a wide variety of applications, and some of them have shown toxic effects on experimental animals and cells. In this study, a previously established photoelectrochemical DNA sensor was employed to rapidly detect DNA damage induced by polystyrene nanosphere (PSNS) suspensions. In the sensor, a double-stranded DNA film was assembled on a semiconductor electrode, and a DNA intercalator, Ru(bpy)2(dppz)2+ (bpy = 2,2′-bipyridine, dppz = dipyrido[3,2-a:2′,3′-c]phenazine) was used as the photoelectrochemical signal indicator. After the DNA-modified electrode was exposed to 2.0 mg/mL PSNS suspension, photocurrent of DNA-bound Ru(bpy)2(dppz)2+ decreased by about 20%. The decrease is attributed to the chemical damage of DNA and consequently less binding of Ru(bpy)2(dppz)2+ molecules to the electrode. Gel electrophoresis of DNA samples incubated with PSNS suspension confirmed DNA damage after the chemical exposure. However, in both photoelectrochemical and gel electrophoresis experiments, extensively washed PSNS did not induce any DNA damage, and the supernatant of PSNS suspension exhibited comparable DNA damage as the unwashed PSNS suspension. Furthermore, UV-visible absorption spectrum of the supernatant displayed a pattern very similar to that of styrene oxide (SO), a compound which has been shown to induce DNA damage by forming covalent DNA adducts. It is therefore suggested that styrene oxide and other residual chemicals in the PSNS may be responsible for the observed DNA damage. The results highlight the importance of full characterization of nanomaterials before their toxicity study, and demonstrate the utility of photoelectrochemical DNA sensors in the rapid assessment of DNA damage induced by chemicals and nanomaterials.