Venkataragavalu Sivagnanam

On-Chip Immunoassay Using Electrostatic Assembly of Streptavidin-Coated Bead Micropatterns

We propose an original concept for a sandwich immunoassay that is completely performed on-chip using streptavidin-coated beads as substrate. The latter are electrostatically self-assembled on aminosilane micropatterns at the bottom of a microfluidic channel. We use mouse IgG diluted in phosphate buffered saline (PBS) with 1% bovine serum albumin (BSA) solution as target antigen. The fluorescent sandwich immunocomplex is formed on the beads during the operation of the chip both in stop-flow and continuous-flow modes. Target mouse IgG antigen is detected down to a concentration of 15 ng/mL in stop-flow mode and 250 pg/mL in continuous-flow mode, using only 1300 nL of sample volume. We also demonstrate the possibility of simultaneous detection of two different antigens in a PBS-BSA solution using a dual microfluidic channel structure.

Exploring Living Multicellular Organisms, Organs, and Tissues Using Microfluidic Systems

Reference EPFL-ARTICLE-188561doi:10.1021/cr200432qView record in Web of Science Record created on 2013-09-19, modified on 2017-08-07

Selective Breast Cancer Cell Capture, Culture, and Immunocytochemical Analysis Using Self-Assembled Magnetic Bead Patterns in a Microfluidic Chip

Separation and subsequent culturing of MCF-7 breast cancer cells on self-assembled protein-coated magnetic beads in a microfluidic chip is demonstrated. The beads were patterned in situ inside a sealed microfluidic channel using magnetic-field-assisted electrostatic self-assembly. Hereafter, they were grafted by exposure to a solution of 5D10 monoclonal antibodies (mAb) and fibronectin (FN), with the first being used for immunospecific cell capture and the latter being used for cell adhesion and growth. A solution of target MCF-7 cells mixed with Jurkat cells was brought inside the microchannel, leading to specific MCF-7 cell capture; the latter were then cultured and evidenced by cell immuno-luminescence.

Microfluidic Protein Preconcentrator Using a Microchannel-Integrated Nafion Strip: Experiment and Modeling

We propose a simple microfluidic device for protein preconcentration based on the electrokinetic trapping principle. It comprises a narrow Nafion strip that is simply cut from a commercial membrane and is integrated into a molded poly(dimethylsiloxane) (PDMS) microfluidic structure using a guiding channel. Mechanically clamping the PDMS/Nafion assembly with a glass substrate results in a rapid prototypable, leak-tight, and easily disposable device. Our device preconcentrates negatively charged fluorescent proteins located at the anodic microfluidic compartment side of the Nafion strip within a few minutes and up to a concentration factor of 10(4). Moreover, we present a numerical study of the preconcentration effect by solving the coupled Poisson, Nernst-Planck, and Navier-Stokes equations for our type of device, which provides microscopic insight into the mechanism of preconcentration. The electrical field across the ion-permselective Nafion generates concentration polarization, i.e., ion depletion at the anodic side and ion enrichment at the cathodic side for both types of ions, with a local excess of mobile positive ions in the depleted concentration polarization zone, inducing a nonequilibrium electrical double layer in close proximity to the Nafion membrane. A voltage difference applied over the anodic compartment is used to generate the electrophoretic flow velocity of the negatively charged tracer biomolecules. This, in combination with the electroosmotic flow in the opposite direction, which originates from the fixed charges on the channel walls and the induced space charge near the membrane, provides the basis for the local preconcentration of the negative tracer biomolecules.

Time-resolved lanthanide luminescence for lab-on-a-chip detection of biomarkers on cancerous tissues

PDMS-based microfluidic devices combined with lanthanide-based immunocomplexes have been successfully tested for the multiplex detection of biomarkers on cancerous tissues, revealing an enhanced sensitivity compared to classical organic dyes.

High-performance protein preconcentrator using microchannel-integrated nafion strip

A microfluidic device for protein preconcentration based on the electrokinetic trapping principle is proposed. It comprises a Nafion strip which is simply cut from a commercially available membrane and integrated into a polydimethylsiloxane (PDMS) microfluidic structure using a guiding channel. By applying low voltage (<15 V), the device exhibits a preconcentration factor of >103 of fluorescently labeled bovine serum albumin (BSA) within a few minutes. Moreover, a numerical study of the preconcentration effect is presented to microscopically understand the phenomenon in our type of device.

Ultra-thick micro-optical components using the PRISM photosensitive flexopolymer

We present the photosensitive flexopolymer PRISM as a new promising material for the realization of thick optical components. The PRISM flexopolymer can be directly polymerized using conventional UV exposure and is simply developed in a water-based solution. A casting method is used to realize flexopolymer layers of a few millimetres thickness in a single application step. Optical components as thick as 2 mm have been fabricated using an exposure time of less than 1 min and a development time below 3 min. No baking process is required, making the process very fast and avoiding any temperature-induced stress problems. Due to its elastomeric nature, the material can be easily applied either on rigid or flexible supports. The good optical transmission of the PRISM flexopolymer in the 400–800 nm spectral range makes it a promising material for optical applications. Refractive index measurements are performed at different wavelengths in the UV–visible range and the flexopolymer refractive index dispersion behaviour is determined. Optical components such as right-angle prisms, penta-prisms and cylindrical lenses with thicknesses up to a few mm have been successfully fabricated.

Study of Spatio-Temporal Immunofluorescence on Bead Patterns in a Microfluidic Channel

We performed a direct immunoassay inside a microfluidic channel on patterned streptavidin‐coated beads, which captured fluorescently‐labeled biotin target molecules from a continuous flow. We arranged the beads in a dot array at the bottom of the channel and demonstrated their position‐ and flow rate‐dependent fluorescence. As the target analyte gets gradually depleted from the flow when passing downstream the channel, the highest fluorescence intensity was observed on the most upstream positioned dot patterns. We propose a simple analytical convection model to explain this spatio‐temporal fluorescence.