Surface plasmon resonance fiber sensor for in situ monitoring of the deposition of nm-scale polymer films Y. Shevchenko a , N. U. Ahamad b , G. Galway b , A. Ianoul b and J. Albert a a Department of Electronics, Carleton University, Ottawa, ON, Canada b Department of Chemistry, Carleton University, Ottawa, ON, Canada ABSTRACT This paper presents a Surface Plasmon Resonance (SPR) fiber sensor capable of monitoring the deposition of thin nm-scale polymer films. The sensor was used for in situ monitoring of the adsorption of 30 mono-layers of oppositely charged polyelectrolytes with an overall thickness of each individual monolayer less than 0.55 nm. The in situ monitoring of the formation of multi-layer structures was implemented through the excitation of SPR on the surface of a gold-coated fiber with a Tilted Fiber Bragg Grating (TFBG) written in the core of the optical fiber. Keywords: Surface Plasmon Resonance, fiber sensor, chemical sensing, polyelectrolyte, Bragg Grating. 1. INTRODUCTION Polyelectrolytes are an important class of macromolecules that have the unique ability to assemble multi-layer structures by adsorbing on oppositely charged substrates. These multi-layer structures can be made by repetitively immersing a charged substrate in solutions of oppositely charged polymers, through a technique known as Layer-by- Layer (LbL) deposition 1 . LbL deposition has attracted considerable attention as a relatively simple method to manufacture high quality thin films due to the possibility to adjust the thickness and composition of the deposited layer by varying such parameters as the pH level of the polymer solutions, the temperature and other assembling conditions 2 . This has created a considerable interest in polyelectrolyte films for applications such as the design of drug delivery systems, biocompatible surfaces for implantable devices, and for sensing applications 3 . The monitoring of assembled polyelectrolyte structures on solid surfaces can be performed using a variety of traditional techniques, including UV-vis absorption, Atomic Force Microscope (AFM) and Scanning Electron Microscope (SEM). Quartz Crystal Microbalance (QCM) and Surface Plasmon Resonance (SPR) are two techniques which are more promising compared to conventional techniques due to their ability to monitor and provide information pertaining to several measured parameters of the deposited films such as the thickness, viscosity and density of the films. While most SPR measurements reported in the literature are performed using the traditional Kretchmann configuration [Fig.1b], this paper presents a fiber-based SPR sensor. This SPR sensor platform is implemented using a standard telecommunication optical fiber and hence has advantages over the traditional prism-based SPR configuration for in situ sensing in small closed volumes, as well as a very simple design, fabrication technique, and interrogation method.. This study presents an SPR platform that can be used to monitor the periodic adsorption of positively and negatively charged polyelectrolyte films on the surface of a gold-coated sensor. During the experiment the gold coating of the sensor was covered with 30 mono-layers of cationic polyelectrolyte Polydiallyl Dimethyl Ammonium Chloride (PDADMAC) and anionic polyelectrolyte Sodium Polystyrene Sulfonate (PSS). The SPR in situ monitoring of the polyelectrolyte adsorption was complemented using AFM scanning of the sensor’s surface to confirm the thickness of the multi-layer structures. Overall it was found that an SPR measurement calibrated by AFM data can be used as a powerful technique for in situ characterization of the deposition of nm-thick films. 20th International Conference on Optical Fibre Sensors, edited by Julian Jones, Brian Culshaw, Wolfgang Ecke, José Miguel López-Higuera, Reinhardt Willsch, Proc. of SPIE Vol. 7503, 750311 © 2009 SPIE · CCC code: 0277-786X/09/$18 · doi: 10.1117/12.835144 Proc. of SPIE Vol. 7503 750311-1