A facile method for the assessment of DNA damage induced by UV-activated nanomaterials.

Fluorescent microscopy observation of gene-size DNA (T4 phage DNA or λ phage DNA) was used to assess DNA damage induced by UV irradiation in the presence of nanomaterials, such as QDs (quantum dots: CdSe/ZnS semiconductor nanoparticles), the water-soluble fullerene derivative C(60)(OH)(n) (n = 6-12) and titanium oxide nanoparticles of 25 nm in diameter. The magnitude of DNA damage could be simply evaluated based on the degree of shortening of the stretched DNA image. This method showed that DNA damage was amplified by the action of QDs under irradiation by C-band (λ(max) = 254 nm) or B-band (λ(max) = 303 nm) UV. Smaller QDs that emitted higher-energy fluorescence (λ = 565 nm) induced more severe damage than medium- and larger-size QDs that emitted longer-wavelength fluorescence (λ = 605 and 705 nm, respectively). The fullerene derivative and TiO(2) nanoparticles caused DNA damage even under irradiation by A-band UV (λ(max) = 365 nm) and showed more severe DNA damage than QDs under similar conditions.

Assessment of the DNA damage using the fluorescence microscope.

DNA damage was monitored by fluorescent microscopy observations of DNA fluorescent images after hydrodynamic stretching on a microscope glass. DNA double-strand breaks lead to a decrease of the average length of observed fluorescent DNA molecules. Compared to conventional methods such as electrophoresis, the proposed method allows for the analysis of the DNA damage at very low DNA breaking frequency. In particular, this method was used to study DNA damage by weak UV irradiation in solutions of quantum dots.