Photothermal Therapy Gold Nanorod–Photosensitizer Complex Obtained by Layer-by- Layer Method for Photodynamic/Photothermal Therapy In Vitro Seung Beom Kim, Tae Heon Lee, Il Yoon,* Young Key Shim,* and Woo Kyoung Lee* [a] Abstract: Gold nanorod (GNR)–photosensitizer (PS) com- plex was prepared using anionic PS (sodium salt of pur- purin-18) and cationic poly(allylamine hydrochloride) by layer-by-layer method, and was characterized by transmis- sion electron microscopy, UV-vis spectroscopy, and zeta potential. The GNR–PS complex is a promising agent for synergistic (photothermal and photodynamic) therapy (PTT/PDT), in which PTT generates heat as well as oper- ates the PS release which maximize the following PDT ac- tivity. The combined dual therapy, PTT followed by PDT, exhibits a significantly higher photocytotoxicity result based on synergistic effect of hyperthermia from PTT as well as singlet oxygen photogeneration from PDT. Photodynamic therapy (PDT) is a promising non-invasive and patient-specific anticancer therapy, which consists of the ad- ministration and selective accumulation of photosensitizer (PS) in target tumor tissues, followed by reactive oxygen species (e.g., singlet oxygen, 1 O 2 ) photogeneration by irradiation with light of appropriate wavelength in the presence of tissue oxygen. [1] Photothermal therapy (PTT), a minimally invasive cancer therapy to convert photon energy into sufficient heat, using near infrared (NIR) wavelength (700–850 nm) absorption to the nanoparticles (NPs) has shown enhanced hyperthermia effect, resulting in an increased temperature (> 43 8C) to de- stroy tumor cells with no significant heating of normal tis- sues. [2] Gold NPs (nanospheres, [3] nanoshells, [4] nanorods, [5] nanocages, [6] etc.) can induce surface plasmon resonance (SPR) and can possess enhanced optical and electronic properties as well as good biocompatibility and easy penetration into the tumor tissues through enhanced permeability and retention, [7] making them useful in biological and medical applications. [8] Among them, gold nanorods (GNRs) are the most interesting NPs for PTT treatment to generate heat in cancer therapy. [2, 9] PDT or PTT alone in vivo reduces the number of tumor cells through photodamage of cellular components, however, it often does not achieve complete tumor eradication. [1b, 4b, 5a, 10] Therefore, new synergistic treatment modalities are developed which combine PDT and PTT to achieve enhanced anticancer efficacy. [11] In this report, we have used a combined synergistic therapy using PTT followed by PDT, in which PTT mediated the PS release from the GNR–PS complex in a layer-by-layer (LbL) system [12] to maximize the following PDT activity. Although there are many reports on either individual PDT or PTT alone, only few reports about a combination therapy of PDT and PTT for anticancer treatment have been publish- ed. [4b, 6a, 11, 13] It is still a great challenge to develop an optimal combined method of PDT and PTT with high efficiency and compatibility through maximized synergistic PDT/PTT treat- ment. [11] Especially, there are very rare examples for operating PS or drug release system from the GNR surface by PTT treat- ment. [13, 14] Recently, Jang et al. reported a combination dual therapy of PTT/PDT using a negatively charged GNR–PS com- plex containing a metallophthalocyanine derivative. [13] To the best of our knowledge, this report is the first example of a combination therapy of PTT followed by PDT using an anionic chlorin derivative PS by the LbL method to build a posi- tively charged GNR–PS complex which is suitable for drug de- livery systems for PDT, in which PTT controls the PS release op- eration to maximize photogeneration of 1 O 2 for subsequent PDT, with very low side-effects. GNRs are generally prepared by using a seed-mediated growth method with hydrogen tetrachloroaurate(III) trihydrate (HAuCl 4 ·3H 2 O) and cetyl trimethylammonium bromide (CTAB). [5] However, CTAB is cytotoxic, thus preventing the direct clinical application of GNRs, as CTAB is required to modify the surface of the GNRs (GNR–CTAB). [15] Thus, we chose the LbL method to overcome the cytotoxicity of CTAB using a cationic and bio- compatible polymer, poly(allylamine hydrochloride) [16] (PAH). In this report, it is noted that the LbL method has two important roles: 1) to avoid the cytotoxicity of CTAB in the GNR–CTAB (l max = 800 nm) and 2) to load the PS to prepare a dual therapy system (PTT/PDT). The target compound of the GNR–PS complex (GNR–PS/PAH in Scheme 1) was successfully prepared by the LbL method using electrostatic interactions between cationic CTAB and anionic PS (sodium salt of purpurin-18, l max = 668 nm, Scheme S1 in the Supporting Information) layers as well as be- tween anionic PS and cationic PAH layers. [a] S. B. Kim, T. H. Lee, Prof. I. Yoon, Prof. Y. K. Shim, Prof. W. K. Lee Photodynamic Therapy Institute and School of Nano System Engineering Inje University 197 Injero, Gimhae, Gyeongnam 621-749 (Republic of Korea) E-mail : yoonil71@inje.ac.kr ykshim@inje.ac.kr wlee@inje.ac.kr Supporting information for this article is available on the WWW under http ://dx.doi.org/10.1002/asia.201403193. Chem. Asian J. 2015, 10, 563 – 567  2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim 563 Communication DOI: 10.1002/asia.201403193