Two- and three-photon induced luminescence from graphene oxide quantum dots for bioimaging applications
Shu-Bai Liu1*, Kuang-I Lin**1, Chiao-Yi Teng2, Chi-Hsiang Lien3, Hsisheng Teng1,2, Shean-Jen Chen1,3, Chih-Ching Chang1,4, Yu-Shuan Tian1, Yun-Ching Lee1
1Center for Micro/Nano Science and Technology, National Cheng Kung University, Tainan, Taiwan
2Department of Chemical Engineering, National Cheng Kung University, Tainan, Taiwan
3Department of Engineering Science, National Cheng Kung University, Tainan, Taiwan
4Department of Environmental and Occupational Health, National Cheng Kung University, Tainan, Taiwan
* presenting author:劉淑白, email:sbliu@mail.ncku.edu.tw
Fluorescent carbon materials have attracted considerable attention due to their low toxicity, excellent biocompatibility, low cost, high resistance to photobleaching, and an abundance of raw materials in nature [1]. Recently, graphene oxide quantum dots (GOQDs) were reported as efficient two-photon fluorescent probes for cellular and deep-tissue imaging [2,3]. In this study, GOQDs are prepared using a modification of Hummers’ method with natural graphite powder. Graphite powder and NaNO₃ are added to a solution of concentrated H₂SO₄ in an ice bath. KMnO₄ is gradually added under stirring with the temperature of the mixture held below 20 °C. The precipitate of the final slurry is dried at 40 °C for 24 h to obtain the GOQDs specimens [4]. Cells are incubated with GOQDs. We use a Ti:sapphire laser and an OPO as excitation source with 120 fs pulse width, and excitation wavelengths are 730 and 1260 nm for two-photon and three-photon luminescence, respectively. The GOQDs can emit quite strong two-photon induced luminescence. Two-photon luminescence images of A549 cells treated with GOQDs and of mice lung tissue are demonstrated. Furthermore, we observed three-photon induced luminescence from the GOQDs. When the laser excitation wavelength is 1260 nm, the luminescence is in the blue light region (about 450 nm). The luminescence intensity is proportional to the cube of the excitation power, which confirms the three photon excitation process. Therefore, the GOQDs are expected to achieve a large imaging depth with longer wavelength excitation, significantly extending the fundamental two-photon imaging depth limit.
[1] J. Peng et al., Nano Lett. 12, 844 (2012). [2] Q. Liu et al., Nano Lett. 13, 2436 (2013). [3] J. Qian et al., Angew. Chem. Int. Ed. 51, 10570 (2012). [4] T. F. Yeh et al., Adv. Mater. 26, 3297 (2014).
Funding: MOST102-2112-M-006-018 and MOST103-2112-M-006-002
**corresponding author:林光儀, email: kilin@mail.ncku.edu.tw


Keywords: Graphene oxide quantum dots, Femtosecond laser, Multiphoton excitation, Luminescence , Bioimaging