Extremely High Two-Photon Absorbing Graphene Oxide for Imaging of Tumor Cells in the Second Biological Window Avijit Pramanik, Suhash Reddy Chavva, Zhen Fan, Sudarson Sekhar Sinha, Bhanu Priya Viraka Nellore, and Paresh Chandra Ray* Department of Chemistry and Biochemistry, Jackson State University, Jackson, Mississippi 39217, United States ABSTRACT: Cancer, a life-threatening disease, has become a global pandemic. Targeted tumor imaging using near-infrared (NIR) light is the key to improve the penetration depth and it is highly promising for clinical tumor diagnostics. Driven by this need, in this Letter we have reported aptamer conjugated graphene oxide-based two-photon imaging of breast tumor cells selectively. Reported data indicate that there is an extremely high two- photon absorption from aptamer conjugated graphene oxide (σ 2PA = 46890 GM). Experimental data show that two-photon luminescence signal remains almost unchanged even after 2 h of illuminations. Reported results show that S6 RNA aptamers conjugated graphene oxide-based two-photon fluorescence can be used for selective two-photon imaging of SK-BR-3 breast tumor cell in second biological transparency windows using 1100 nm wavelength. Experimental data demonstrate that it is highly capable of distinguishing targeted breast cancer SK-BR-3 cells from other nontargeted MDA-MB-231 breast cancer cells. SECTION: Physical Processes in Nanomaterials and Nanostructures C ancer has been known for more than 3000 years, but still in the 21st century, it is one of the most life-threatening diseases, causing 1 in 8 deaths worldwide. 1-5 Breast cancer is the second leading cause of cancer deaths in women today, after lung cancer. 6-10 Although we all know that early detection is the key for survival, it is still an important challenge for society. 1-10 For in vivo cancer imaging without surgery, near- infrared (NIR) light between 650-950 nm for the first NIR window and 1000-1350 nm for the second NIR window must be used to avoid absorption by physiological fluids. 6-11 Since human blood exhibits transparency from 1000 to 1350 nm, the second window thus provides a maximum radiation penetration through tissue. 12-18 Despite huge advances in organic fluorescence probes in the last several decades, still today the fluorescence imaging using second NIR window light remains a huge challenge. 6-13 Two-photon fluorescence (TPF) imaging has been introduced as an alternative for NIR imaging. 11-18 TPF has several advantages for tumor imaging and these are larger penetration depth, minimized tissue autofluorescence background, and reduced photodamage. 11-18 The efficiency of TPF imaging is highly dependent on the two-photon absorption cross sections in water and also on long time photostability. However, the rapid photobleaching and low two-photon absorption cross-section (50 Goeppert-Mayer (GM)) use of organic dyes for TPF has been hampered for real-life imaging. 11-18 For a finding better two-photon luminescence imaging platform, the current Letter reports on a water-soluble S6 RNA aptamer-conjugated graphene oxide (GO)-based two-photon photoluminescence probe for targeted bioimaging of SK-BR-3 breast cancer cells in second biological transparency window using 1100 nm wavelength, as shown in Scheme 1. To demonstrate the selectivity, we have used SK-BR- 3 and MDA-MB-231, breast cancer cell lines, where the first one is targeted and the second one is nontargeted. For the past decade, after its discovery in 2004, graphene has revolutionized the scientific community due to its remarkable Received: May 17, 2014 Accepted: June 6, 2014 Scheme 1. Schematic Representation Showing Aptamer- Bound Graphene Oxide-Based Two-Photon Luminescence Imaging Platform for Selective Cancer Cell Imaging Letter pubs.acs.org/JPCL © XXXX American Chemical Society 2150 dx.doi.org/10.1021/jz5009856 | J. Phys. Chem. Lett. 2014, 5, 2150-2154