A novel bio-photonics approach based on the nonlinear optical process of second harmonic generation by non-centrosymmetric nanoparticles is presented and demonstrated on malignant human cell lines. The proposed method allows to directly interact with DNA in absence of photosensitizing molecules, to enable independent imaging and therapeutic modalities switching between the two modes of operation by simply tuning the excitation laser wavelength, and to avoid any risk of spontaneous activation by any natural or artificial light source. ∗To whom correspondence should be addressed †Institute of Chemical Sciences and Engineering, EPFL, CH-1015, Lausanne, Switzerland ‡GAP-Biophotonics, Université de Genève, 22 chemin de Pinchat, CH-1211 Genève 4, Switzerland ¶FEE Gmbh, Struthstrasse 2, 55743 Idar-Oberstein, Germany §SYMME, Université de Savoie, BP 80439, 74944, Annecy Le Vieux Cedex, France ‖Contributed equally to this work. 1 ar X iv :1 30 6. 64 87 v1 [ ph ys ic s. bi oph ] 2 7 Ju n 20 13 We demonstrate here a novel diagnostic and therapeutic (theranostic) protocol based on the nonlinear optical process of non phase-matched second harmonic (SH) generation by non-centrosymmetric nanoparticles, referred to in the following as harmonic nanoparticles (HNPs).1,2 To date, the capability of these recently introduced nanometric probes of doubling any incoming frequency has not been employed for therapeutic use, although it presents several straightforward advantages, including i) the possibility to directly interact with DNA of malignant cells in absence of photosensitizing molecules, ii) fully independent access to imaging and therapeutic modalities, and iii) complete absence of risk of spontaneous activation by natural or artificial light sources other than pulsed femtosecond lasers. Given the unconstrained tunability of the HNPs nonlinear conversion process, this approach can be extended to selectively photo-activate molecules at the surface or in the vicinity of HNPs to further diversify the prospective therapeutic action.3 Here we show that by tuning the frequency of ultrashort laser pulses from infrared (IR) to visible (both harmless), SH generation leads respectively to diagnostics (imaging) and therapy (phototoxicity). Specifically, we report in situ generation of deep ultraviolet (DUV) radiation (270 nm) in human-derived lung cancer cells treated with bismuth ferrite (BiFeO3, BFO) HNPs upon pulsed laser irradiation in the visible spectrum, at 540 nm. We observe and quantify the appearance of double-strand breaks (DSBs) in the DNA and cell apoptosis, in the area of the laser beam. We show that DNA damages are dependent on irradiation-time, laser intensity, and NP concentration. We observe that apoptosis and genotoxic effects are only observed when visible light excitation is employed, being completely absent when IR excitation is used for imaging. HNPs, a family of NPs specifically conceived for multi-photon imaging, were introduced in 2005 for complementing fluorescence imaging labels.1,4,5 Although comparatively less bright than quantum dots, HNPs possess a series of advantageous optical properties, including complete absence of bleaching and blinking,1,6 spectrally narrow emission bands, fully coherent response,7–9 ,and UV to IR excitation wavelength tunability.10,11 These unique characteristics have been recently exploited in demanding bio-imaging applications12 including regenerative research.13 The possibility of working with long wavelengths presents clear advantages in terms of tissue pene-