Simulation of biochemical binding kinetics on the microfluidic biochip of fiber-optic localized plasma resonance (FO-LPR) Chun-Ping Jen * , Ching-Te Huang, Yun-Hung Lu Department of Mechanical Engineering, National Chung Cheng University, 168 University Road, Min-Hsiung, Chia Yi, Taiwan, ROC article info Article history: Received 18 September 2008 Received in revised form 25 December 2008 Accepted 30 December 2008 Available online 17 January 2009 Keywords: Microfluidic Biosensor Fiber-optic localized plasma resonance abstract A reflection-based localized surface plasma resonance fiber-optic probe for chemical and biochemical sensing, called fiber-optic localized plasma resonance (FO-LPR), has been proposed in the literature. Bio-molecular recognition is detected by the unique optical properties of self-assembled gold nanoparti- cles on the unclad portions of an optical fiber whose surfaces are modified with a receptor. To enhance the performance of the sensing platform, the sensing element is integrated with microfluidic chips to reduce sample and reagent volume, to shorten response time and analysis time, as well as to increase sensitivity. The main purpose of the present study is to simulate the biochemical assays in the FO-LPR microfluidic chip and to investigate the effects parameters, such as inlet concentrations of analyte or the flowrate on the biochemical binding kinetics. The geometry of the grooved channel is also proposed to enhance the biochemical binding on the unclad optical fiber. The results reveal that the chaotic mixing generated by the grooves enhances the biochemical binding when the injected flowrate is high and, because of that, limits the performance of the molecular mixing. The enhancement of biochemical bind- ing performance was significant, especially at the low injected concentration of analyte. Ó 2009 Elsevier B.V. All rights reserved. 1. Introduction The development of biosensors is an important issue for indus- trial, environmental and clinical applications. In recent years, a reflection-based localized surface plasma resonance fiber-optic probe for chemical and biochemical sensing has been proposed [1–3]. The unclad portion of an optical fiber is modified with self-assembled gold nanoparticles which are functionalized with a receptor. Thus, bio-molecular recognition can be detected by the unique optical properties of the gold nanoparticles whose sur- faces have been modified with the receptor. The optical properties of the self-assembled nanoparticles on the optical fiber change with the adsorbate-induced refractive index change of the environ- ment near the nanoparticle surface. The realization of the biosen- sing platform is achieved via the measurement of evanescent wave absorption by the nanoparticle-modified optical fiber. Bio- sensors using the mechanism of surface plasma resonance (SPR) measurements have been widely employed. In order to enhance the performance of the sensing platform, the sensing element can be integrated with microfluidic chips to reduce sample and re- agent volume, to shorten response time and analysis time, as well as to increase sensitivity. The main purpose of the present study was to simulate the biochemical assays in the fiber-optic localized plasma resonance (FO-LPR) microfluidic chip and to investigate the effects parameters, such as the inlet concentrations of analyte or the flowrate on the biochemical binding kinetics. The mathemati- cal model for the mass-influenced binding kinetics has been inves- tigated in the literature [4]. The geometry of the grooved channel has also been proposed to enhance the biochemical binding on the unclad optical fiber. 2. Designs for the microfluidic chip of FO-LPR The schematic illustration of the FO-LPR microfluidic chip is de- picted in Fig. 1. The composition and the fluidic operation are illus- trated in Fig. 1a and b, respectively. The solution with analyte was injected into the reaction microchannel and reacted with the receptor coated on the optical fiber. This microfluidic device, as shown in Fig. 1c, was made of polymethylmethacrylate (PMMA) by microinjection molding. The reaction microchannel was 950 lm high and 950 lm wide with an effective binding length of 18.1 mm. An unclad optical fiber 400 lm in diameter was fixed at the center of the microchannel. A gold nanoparticle monolayer was coated on the unclad portion of the optical fiber [1], thus mod- ifying the receptors on the colloidal gold surface to functionalize the gold surface. The assembled microfluidic chip is shown in Fig. 1d. The value of the Reynolds number for the microchannel of the FO-LPR device was less than ten; therefore, there was laminar flow 0167-9317/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.mee.2008.12.084 * Corresponding author. Tel.: +886 5 272 0411; fax: +886 5 272 0589. E-mail address: imecpj@ccu.edu.tw (C.-P. Jen). Microelectronic Engineering 86 (2009) 1505–1510 Contents lists available at ScienceDirect Microelectronic Engineering journal homepage: www.elsevier.com/locate/mee