Available online at www.sciencedirect.com Sensors and Actuators B 130 (2008) 758–764 Enhanced oxygen detection using porous polymeric gratings with integrated recognition elements Sung Jin Kim a , Vamsy P. Chodavarapu b , Alexander N. Cartwright a,∗ , Mark T. Swihart c , Timothy J. Bunning d a Department of Electrical Engineering, University at Buffalo, The State University of New York, Buffalo, NY 14260, United States b Department of Electrical and Computer Engineering, McGill University, Montreal, QC H3A 2A7, United States c Department of Chemical and Biological Engineering, University at Buffalo, The State University of New York, Buffalo, NY 14260, United States d Air Force Research Laboratory, Materials and Manufacturing Directorate, Wright-Patterson Air Force Base, OH 45433, United States Received 14 February 2007; received in revised form 13 October 2007; accepted 23 October 2007 Available online 17 November 2007 Abstract The development of ordered porous nanostructured materials, such as polymeric Bragg gratings, offers an attractive platform for the encapsulation of chemical and biological recognition elements. To date, various types of polymer gratings have been developed with several demonstrated applications in switching, lasing, and display devices. Here, we focus on a new class of holographically ordered porous polymer (HOPP) gratings that are an extension of holographic polymer dispersed liquid crystal (H-PDLC) structures. We present biochemical sensing using HOPP gratings that include a volatile solvent as the phase separation fluid. The resulting HOPP gratings are simple to fabricate, chromatically tunable, highly versatile, and can be employed as a general template for the encapsulation of recognition elements. As a prototype, we developed an oxygen (O 2 ) sensor by encapsulating the fluorophore (tris(4,7-diphenyl-1,10-phenathroline)ruthenium(II) within these nanostructured materials. The resulting O 2 sensors performed across the full-scale range (0–100%) of oxygen in nitrogen, with a response time of less than 1 s. The O 2 sensor system uses a LED excitation source and a silicon photodiode detector. The ability of these HOPP reflection gratings to transmit or reflect a particular wavelength range, based on the grating spacing, enables us to selectively enhance the detection efficiency for the wavelengths of interest. Published by Elsevier B.V. Keywords: HPDLC gratings; Porous structures; Fluorometry; Optical sensors; Reflection gratings; Nanostructured sensors; Oxygen sensors; Biosensors; Biochemical sensors 1. Introduction Nanostructured materials are playing an increasingly impor- tant role in the advancement of optical science and technology in various application areas including light emitting devices, biomedical diagnostics and imaging, sensing, information storage, and communications [1]. Here, we describe the devel- opment of sensors using nanostructured materials that act as an encapsulation template for biochemical recognition elements. This approach exploits unique optical properties of these struc- ∗ Corresponding author. Tel.: +1 716 645 3115x1205. E-mail address: anc@buffalo.edu (A.N. Cartwright). tures. There have been numerous examples of chemical and biochemical sensors that have used nanotechnology to enhance sensitivity, selectivity, and dynamic response [2–6]. In this paper, we describe the development of nanosensors based on optical (fluorescence) sensing mechanisms. Fluorescence spectroscopy is a well-known and useful modality for highly selective and sen- sitive chemical and biochemical sensors [7]. Fluorescence based sensing offers several advantages including fast response times, easy implementation, and stand-off detection. Typically, fluores- cence based sensors excite optically active recognition elements that are selective to particular analyte(s) of interest. Emission from the recognition element, at wavelengths longer than the excitation wavelength, is monitored and provides information regarding the concentration of the analyte(s). Thus, in this tech- 0925-4005/$ – see front matter. Published by Elsevier B.V. doi:10.1016/j.snb.2007.10.073