A NOVEL MICRO-FLUIDIC WHOLE CELL BIOSENSOR FOR WATER TOXICITY ANALYSIS USING BIOLUMINESCENCE DETECTION Hadar Ben-Yoav 1 , Svyatoslav Yorish 1 , Tal Elad 2 , Sefi Vernick 1 , Shimshon Belkin 2 and Yosi Shacham-Diamand 1 1 Department of Electrical Engineering and Physical Electronics, Tel Aviv University, ISRAEL and 2 Institute of Life Sciences, The Hebrew University of Jerusalem, ISRAEL ABSTRACT A novel micro-fluidic whole cell biosensor for toxicity analysis based on bioluminescence detection was developed. The optical part of the biochip was modelled and simulated to optimize the total light collection efficiency and the system response. The optimization elucidated some of the optical aspects of the biochip. A study evaluating the bioluminescence reaction kinetics was performed and revealed the interdependence between the detected bioluminescence and the physical parameters of the introduced toxin. Keywords: Whole-cell biosensor, Water toxicity, Bioluminescence, Stray light analysis 1. INTRODUCTION Bioluminescent microbes are used as sensors for acute toxicity in water [1]. Genetically engineered E. coli (Strain DPD2794 carrying a recA::luxCDABE fusion) emit light once they are exposed to toxic materials. The microbes are integrated onto bio chips and in this paper we describe the basic chip integration and the optimization of the optical systems using ray tracing algorithms simulated by the ASAP TM software [2]. 2. THEORY Ray tracing methods were used to model the light collection efficiency by the solid state optical detector. The collection efficiency is defined as: e c o N N = η (1) when represents the total number of collected photons and represents the total number of emitted photons. The total number of emitted photons by the E. coli is a function of their interaction with the toxic materials. We model their emission as a uniformly distributed light emitting media. Since we have about 10 c N e N 7 -10 8 microbes per cm 3 we assume a uniform nondirectional emission uniformly distributed over 4π radians for every volume unit. We also assume a constant absorption length, α, due to intrinsic absorption by the microbes. We did not take internal scattering into consideration since we assume that it did not change neither the light intensity nor its spatial distribution. Finally we assume ray reflectance and transmittance specified by Fresnel's equations;