Two-photon absorption and sensitivity to DNA of dye molecule-driven CdSe quantum dots

Abstract

Two photons are simultaneously absorbed by a molecule when their frequencies correspond exactly to the energy between two eigenstates. In a medium, however, homogeneous and inhomogeneous broadenings strongly hinder this two-photon absorption. By compensating for the impedance mismatch between visible wavelengths and intense laser pulses, CdSe quantum dots can enhance light-matter interactions over a broad frequency range. We used CdSe quantum dots to enhance two photon absorption statistics of dye molecules. Qualitative agreement between the measured enhancement and the theoretically forecast enhancement indicate that the two-photon absorption cross-section (σ) can be increased by 500 GM (1 GM = 1 × 10⁻⁵⁰ cm⁴ s per photon). The interactions between the chromophore and calf thymus DNA were investigated by UV-visible absorption experiments. The results show that the chromophore could interact with DNA in an intercalation mode and could therefore potentially be used in cell imaging applications.