A two bead immunoassay in a micro fluidic device using a flat laser intensity profile for illumination

Abstract

Recently it was demonstrated that a collimated Gaussian beam can be converted to a flattop beam using a Keplerian beam reshaper consisting of two aspheric lenses. Here, using the same optical system, we demonstrate that this flattop profile can be maintained when used in a confocal detection system that focuses the laser beam into a diameter of only 33 microm. The intensity profile of the reshaped beam was determined by imaging the excitation of a constant stream of fluorescein inside a microfluidic device. The resulting shape had a 6.38% RSD intensity across the flat profile when imaged with a CCD camera. This flat illumination profile was then used in a two bead multiplex immunoassay where the colour combination and/or the intensities can be used to determine the presence of an antigen. Detection limits of TNF-alpha and IL-6 were comparable with standard ELISA immunoassays.

Microfabrication and Applications of Opto-Microfluidic Sensors

“…All steps can be completed in one hour, and the reagent consumption is only on the order of microliters. Roos et al [39] and Herrmann et al [40] used microspheres to support the binding, and the fluorescence signals were collected from these microbeads. These microspheres provided increased surface area to support the immune complex.…”

Simulation of advanced microfluidic systems with dissipative particle dynamics

“…In this work, we explore the DPD approach with respect to representing a realistic engineering problem involving the design process of a special type of a microfluidic chamber serving as a bead-based immunoassay. In this chamber, microspheres with immobilized capture proteins are supposed to aggregate in as regular a pattern as possible to facilitate fluorescent readout (Riegger et al 2006), see also Prerequisites for a regular and reproducible aggregation pattern are a careful design of flow geometry, the shape of the chamber and the interactions of the microspheres (Roos and Skinner 2003;Stone et al 2004). On the way to a time-dependent simulation of the aggregation process in comparison to experiments, we illustrate a possible validation process, which will indeed reveal the limitations but especially the virtues of the simulation approach.…”

“…With an increasing number of devices one attempts to manipulate these complex fluids in a controlled manner-examples are bead-based micromixers and immunoassays (Riegger et al 2006;Grumann et al 2005;Sato et al 2002;Saleh and Sohn 2003;Roos and Skinner 2003), cell sorting or DNA-separation devices (Yoshida et al 2003;Wolff et al 2003;Dittrich and Schwille 2003;Tian et al 2000;Tian and Landers 2002;Sanders et al 2003;Doyle et al 2002;Duong et al 2003). In these systems, one is dealing with rather complex situations of fluid flow.…”

Finite element simulations of hydrodynamic trapping in microfluidic particle-trap array systems

“…Most microfluidic systems involve complex mixtures of biological particles, such as functionalized microspheres or colloids 4,5 and cell suspensions. 6 Applications of these microfluidic systems include biomolecule detection and profiling, 7,8 microsphere-based micromixing and immunoassays, 9,10 and cell sorting and separation. 11,12 For example, the experiments of sorting, separation, and trapping of CTCs have been performed using microfluidic systems with similar hydrodynamically engineered configurations.…”