journal homepage: www.elsevier.com/locate/nanoenergy Available online at www.sciencedirect.com RAPID COMMUNICATION Water-resistant flexible GaN LED on a liquid crystal polymer substrate for implantable biomedical applications Sang Yong Lee a , Kwi-Il Park a , Chul Huh b , Min Koo a , Hyeon Gyun Yoo a , Seungjun Kim a , Chil Seong Ah b , Gun Yong Sung b,n,1 , Keon Jae Lee a,nn,1 a Department of Materials Science and Engineering, Korea Advanced Institute of Science and Technology (KAIST), 291 Daehak-ro, Yuseong-gu, Daejeon 305-701, Republic of Korea b Biosensor Research Team, BT Convergence Technology Research Department, Electronics and Telecommunications Research Institute (ETRI), 138 Gajeong-dong, Yuseong-gu, Daejeon 305-700, Republic of Korea Received 25 June 2011; received in revised form 9 July 2011; accepted 9 July 2011 Available online 21 July 2011 KEYWORDS Flexible GaN LED; White LED; Biosensor; PTFE; Liquid crystal polymer substrate Abstract A flexible GaN light-emitting diode (LED) has been fabricated on a liquid crystal polymer (LCP) substrate for biomedical applications. The bending radius and fatigue tests demonstrated the mechanically and optically stable characteristics of the GaN LEDs on the flexible substrates. A white light-emitting phosphor-coated GaN LED showed its potential as a next-generation flexible light source. A water-resistant and biocompatible polytetrafluoroethylene (PTFE) coated flexible LED detected prostate-specific antigen (PSA), which is expected to be used in future biomedical devices. & 2011 Elsevier Ltd. All rights reserved. 1. Introduction Light-emitting diodes (LEDs) have superior characteristics, such as long-term stability, high efficiency, and strong brightness compared to conventional incandescent lamps. With these advantages, LEDs have been developed and explored for not only consumer electronics such as energy efficient light lamp, back-light unit (BLU), and active matrix organic LED (AMOLED) but also medical applications, including body composition detectors (e.g., hemoglobin [1], human body fat [2], prostate- specific antigen (PSA) [3], and cholesterol [4]), and therapy devices (e.g., sterilization [5], skin homeostasis [6], and operation lamps [7]). In particular, flexible LEDs, which can conformally contact on curvilinear surface, have intrigued researchers in the field of biosensors and micro-sized surgery robots for non-bleeding diagnoses and treatment. 2211-2855/$ - see front matter & 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.nanoen.2011.07.001 n Corresponding author. Tel.: +8242 860 5698; fax: +8242 860 6594. nn Corresponding author. Tel.: +8242 3503343; fax: + 8242 350 3310. E-mail addresses: gysung@etri.re.kr (G.Y. Sung), keonlee@kaist.ac.kr (K.J. Lee). 1 These corresponding authors have equally contributed. Nano Energy (2012) 1, 145–151