Design of a lab-on-a-chip for clinical tests of human physiological fluids

Abstract

Labs-on-a-chip are useful to perform in situ clinical tests with instantaneous results. In this work, the design phase of the development of a lab-on-a-chip is presented. The device will be used to perform tests on physiological fluids. It will be able to test 8 components: calcium, chloride, creatinine, glucose, magnesium, total protein, urea and uric acid. A sample of the physiological fluid reacts with several reagents and the device measures the absorbance of the reaction products. The lab-on-a-chip is composed of a microfluidic system and an optical detection system. The first contains microchannels and micro-reactors fabricated using SU-8 techniques. The second includes CMOS photodetectors and readout electronics, as well as optical filters fabricated using CMOS-compatible post-processing on top of the photodetectors. Careful design of the microfluidic system of a lab-on-a-chip requires knowledge of the transport phenomena in the microchannels. Numerical methods are used to simulate the electroosmotic flow, reaction and mixture in the system. Velocitypressure formulation of the Navier-Stokes equations is solved by a finite difference method. Mass transport equation is solved by a second order finite difference method. For enzymatic reactions, biochemical reaction kinetics is considered. Design choices are presented and explained. The final design of the microfluidic system complies with layout restriction and kinetic, mass transport and other physical limitations. The dimensions of the micro-reactors are optimized to maximize mixing. The design of the optical detection system involves selection of the dielectric layers available in the CMOS process for the photodetectors and selection of the dielectric thin-films layers for the optical filters. An array of 8 selective optical filters is designed for parallel testing of the 8 reported components. They are structurally optimized for an optical response at the absorption peak of each reaction product. The lab-on-a-chip output provides a digital signal for computer interfacing.