Bio-dot® Microfiltration Apparatus From Bio-Rad

The Bio-dot® Microfiltration Apparatus from Bio-Rad is designed to enable binding of nucleic acid, protein or protein complexes to a membrane by vacuum filtration. Potential applications include immunoassays, DNA and RNA blotting and hybridization. The Bio-dot® Microfiltration Apparatus is in a 96 well-plate format, allowing analysis of many small samples at once. As the sample is concentrated in a small area, this format also allows easy quantification of samples using a densitometer or the Odyssey Imaging system.

The unit consists of a vacuum manifold base with reservoir, a gasket support plate, gasket, and sample template. A short length of tubing and three-way valve provide the connection to the vacuum source. All components are made out of tough plastic or silicone, and can be autoclaved, decontaminated and cleaned for RNAses using standard lab procedures. The manual supplied with the product is comprehensive, and provides protocols for a number of applications.

To use the unit, place the gasket support plate in the reservoir, and lay the clean, dry gasket over the top. A presoaked membrane can then be applied, covering all the holes. Using clean tweezers or a glass pipette, carefully roll out any air bubbles under the membrane then add the template. Tighten the screws in a diagonal fashion to ensure a tight fit before applying a vacuum to the system and retightening – the better the seal, the more efficient the vacuum will be, and the less the chance of cross contamination. Rehydrate the membrane with the buffer of your choice by filling the wells of the template with a multichannel pipette, then apply the vacuum and pull the buffer through the membrane. Repeat the procedure with your samples, gently pipetting up and down any samples that pull through slowly to remove any membrane blockages. Repeat the buffer wash several times before removing the last traces of liquid by allowing the vacuum to run for a few seconds. To retrieve the membrane, leave the vacuum on and remove the template. Take a firm hold on one corner with tweezers, and remove quickly and cleanly to prevent splashback from the reservoir.

While setting up the unit is simple, a little time must be taken to familiarize oneself with how it works; otherwise, you risk cross contamination. It is also useful to prepare your samples in a U-bottom 96-well plate before starting, and transfer across with a multichannel pipette. Note that samples that are viscous or containing cell debris will not pull thought the membrane well, and may require dilution or centrifugation before use. Unused wells must be taped off or filled with buffer to prevent loss of vacuum. We have used this apparatus for over a year, and found it to be an excellent tool for quantifying protein expression in cell supernatants. The unit is tough, and even the softer gasket has stood up to over a year of decontamination and general lab handling.