Fluorescent vesicles for signal amplification in reverse phase protein microarray assays.

Developments in microarray technology promise to lead to great advancements in the biomedical and biological field. However, implementation of these analytical tools often relies on signal amplification strategies that are essential to reach the sensitivity levels required for a variety of biological applications. This is true especially for reverse phase arrays where a complex biological sample is directly immobilized on the chip. We present a simple and generic method for signal amplification based on the use of antibody-tagged fluorescent vesicles as labels for signal generation. To assess the gain in assay sensitivity, we performed a model assay for the detection of rabbit immunoglobulin G (IgG) and compared the limit of detection (LOD) of the vesicle assay with the LOD of a conventional assay performed with fluorescent reporter molecules. We evaluated the improvements for two fluorescence-based transduction setups: a high-sensitivity microarray reader (ZeptoREADER) and a conventional confocal scanner. In all cases, our strategy led to an increase in sensitivity. However, gain in sensitivity widely depended on the type of illumination; whereas an approximately 2-fold increase in sensitivity was observed for readout based on evanescent field illumination, the contribution was as high as more than 200-fold for confocal scanning.

Microarrays made easy: biofunctionalized hydrogel channels for rapid protein microarray production.

We present a simple, inexpensive, and sensitive technique for producing multiple copies of a hydrogel-based protein microarray. An agarose block containing 25 biofunctionalized channels is sliced perpendicularly to produce many identical biochips. Each microarray consists of 500 µm spots, which contain protein-coated microparticles physically trapped in porous SeaPrep agarose. Proteins diffuse readily through SeaPrep agarose, while the larger microparticles are immobilized in the hydrogel matrix. Without major assay optimization, the limit of detection is 12 pM for a sandwich assay detecting human IgG. These highly flexible, multiplexed arrays can be produced rapidly without any special instrumentation and are compatible with standard fluorescence-based read-out.

A microwell array platform for picoliter membrane protein assays.

A novel microwell chip is developed that can be used to detect protein binding in a liquid environment, together with a liquid handling system that allows the performance of assays with picoliter volumes. A PDMS well structure is cast on a planar optical waveguide, providing reaction containers combined with a high-sensitivity fluorescence readout system. Individual wells of the array can be addressed, filled, and rinsed using a contact-mode pin and ring spotter. This allows for immunoassays in a heavily multiplexed way, as all steps of the assay can be individually chosen per well. An array density of over 1000 wells cm(-2) is used for the current experiments. The wells provide a protected liquid environment in which the handling of proteins in their natural state is possible, thus maintaining their activity. The membrane protein annexin V is chosen as a model protein to demonstrate the current possibilities. Annexin V binds to phosphatidylserine (PS) head groups of lipids in a Ca(2+)-dependent manner and is often chosen as a marker for cell apoptosis. Lipid vesicles with and without PS are spotted in individual wells and spontaneously formed a planar lipid bilayer on the bottom of the buffer-filled wells. Annexin V can be used to distinguish between wells containing PS groups previously incorporated in the membrane patches and reference wells without PS head groups. Also, the dependence on the calcium concentration can be shown. Fluorescence readout of the assays is performed using a highly sensitive system based on a planar optical waveguide.