ABSTRACT Fluorescence immunoassay is a sensitive technique that can be used in the measurement of many compounds, including drugs, hormones, and proteins; in the identification of antibodies; and in the quantification of antigens such as viral particles and, potentially, bacteria. Homogeneous fluorescence immunoassay, fluorescent excitation transfer immunoassay, fluorescence polarization immunoassay, solid-phase "dipstick" immunoassay, solid-phase microbead fluorescence immunoassay, substrate-labeled fluorescence immunoassay, and fluorescence immunoassays using internal reflectance spectroscopy or phycobiliprotein conjugates are reviewed.
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ABSTRACT: This article presents a microfluidic device (so called concentrator) for rapid and efficient concentration of micro/nanoparticles using direct current dielectrophoresis (DC DEP) in continuous fluid flow. The concentrator is composed of a series of microchannels constructed with PDMS-insulating microstructures to focus efficiently the electric field in the flow direction to provide high field strength and gradient. Multiple trapping regions are formed within the concentrator. The location of particle trapping depends on the strength of the electric field applied. Under the experimental conditions, both streaming movement and DEP trapping of particles simultaneously take place within the concentrator at different regions. The former occurs upstream and is responsible for continuous transport of the particles, whereas the latter occurs downstream and rapidly traps the particles delivered from upstream. The observation agrees with the distribution of the simulated electric field and DEP force. The performance of the device is demonstrated by successfully and effectively concentrating fluorescent nanoparticles. At the sufficiently high electric field, the device demonstrates a trapping efficiency of 100%, which means downstream DEP traps and concentrates all (100%) the incoming particles from upstream. The trapping efficiency of the device is further studied by measuring the fluorescence intensity of concentrated particles in the channel. Typically, the fluorescence intensity becomes saturated in Trap 1 by applying the voltage (400V) for >2min, demonstrating that rapid concentration of the nanoparticles (107particles/ml) is achieved in the device. The microfluidic concentrator described can be implemented in applications where rapid concentration of targets is needed such as concentrating cells for sample preparation and concentrating molecular biomarkers for detection. KeywordsMicrofluidics-DC dielectrophoresis-Electrokinetics-DEP trapping-Micro/nanoparticlesMicrofluidics and Nanofluidics 01/2010; 9(2):281-291. DOI:10.1007/s10404-009-0545-z · 2.67 Impact Factor
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ABSTRACT: An immunoassay format is presented that takes advantage of the microfluidic properties of the H-FilterTM for measuring sample analyte concentration. The method relies on the diffusion of analyte particles into a region containing beads coated with specific antibody. Competitive binding of labeled analyte and sample analyte with a limited number of binding sites allows measurement of the concentration of sample analyte based on the fraction of labeled analyte bound. The fraction of labeled analyte bound can be determined with a microcytometer by measuring the bead fluorescence intensity on the microcytometer portion of an integrated microfluidic chip. It is not necessary to separate the beads from the mixture because the bead intensity can be determined above the background of unbound labeled antigens. Other advantages include the ability to eliminate large interfering particles from samples, continuous sample monitoring, and the ability to concentrate the beads. Microfluidic immunoassay formats also consume smaller volumes of costly reagents and sample.Proceedings of SPIE - The International Society for Optical Engineering 08/1999; DOI:10.1117/12.359334 · 0.20 Impact Factor