title: Reversible two-photon photoswitching and two-photon imaging of immunofunctionalized nanoparticles targeted to cancer cells.
abstract: Both photoswitchable fluorescent nanoparticles and photoactivatable fluorescent proteins have been used for super-resolution far-field imaging on the nanometer scale, but the photoactivating wavelength for such photochemical events generally falls in the near-UV (NUV) region (<420 nm), which is not preferred in cellular imaging. However, using two near-IR (NIR) photons that are lower in energy, we can circumvent such problems and replace NUV single-photon excitations (e.g., 390 nm) with NIR two-photon excitations (e.g., 780 nm). Thus, we have demonstrated that alternating 780 nm NIR two-photon and 488 nm single-photon excitations induces reversible on-off fluorescence switching of immunotargeted nanoparticles in the human breast cancer cell line SK-BR-3. Herein, two-photon absorption not only caused spiropyran-merocyanine photoisomerization within the particles but also imparted red fluorescence. In comparison with single-photon NUV excitations, two-photon NIR laser excitations can potentially reduce absorption-related photodamage to living systems because cellular systems absorb much more weakly in the NIR.
authors.affiliation: Wuhan National Laboratory for Optoelectronics, Huazhong University of Science and Technology, Wuhan 430074, China. mqzhu@mail.hust.edu.cn
authors.forename: Ming-Qiang
authors.initials: MQ
authors.lastname: Zhu
authors.forename: Guo-Feng
authors.initials: GF
authors.lastname: Zhang
authors.forename: Chong
authors.initials: C
authors.lastname: Li
authors.forename: Matthew P
authors.initials: MP
authors.lastname: Aldred
authors.forename: Emmanuel
authors.initials: E
authors.lastname: Chang
authors.forename: Rebekah A
authors.initials: RA
authors.lastname: Drezek
authors.forename: Alexander D Q
authors.initials: AD
authors.lastname: Li
mesh_terms: D001578:Benzopyrans / Q000737:chemistry; D045744:Cell Line, Tumor; D005453:Fluorescence; D006801:Humans; D007211:Indoles / Q000737:chemistry; D053758:Nanoparticles / Q000737:chemistry; D009369:Neoplasms / Q000473:pathology*; D009574:Nitro Compounds / Q000737:chemistry; D055668:Photochemical Processes; D017785:Photons
chemical_list: D001578:Benzopyrans; D007211:Indoles; D009574:Nitro Compounds; C548873:merocyanine; C088184:spiropyran