Molecular Imager ChemiDoc XRS System From Bio-Rad

The Bio-Rad ChemiDoc XRS System is Bio-Rad’s most advanced imaging system. The system is able to image chemiluminescent, fluorescent and colorimetric samples and comes complete with a compact darkroom, transilluminator and supercooled high resolution 1.44 megapixel CCD camera. The entire system is controlled by the provided Quantity One 1-D analysis software with additional controls on the compact darkroom to control focus, aperture and zoom. Consequently, the ChemiDoc XRS system is extremely flexible and can be used for imaging a diverse range of applications such as Western blotting, DNA/RNA gel electrophoresis, 2-D gel electrophoresis, densitometry, etc. The system is able to detect HRP and AP chemiluminescence, ethidium bromide, SYBR® Green, green fluorescent protein, silver stain and Coomasie brilliant blue staining to name but a few that are frequently used with the above applications. The system features flat fielding technology which allows for superior uniformity and quantification. Flat-fielding is a technique that corrects for pixel-to-pixel variations by dividing the gain variations out of an image, thus flattening the relative response for each pixel.

Operation of the system is very simple. The gel or membrane is placed on the transilluminator, which is set into a drawer which can be moved in and out of the darkroom, facilitating placement of the gel or membrane. Once the gel or membrane is placed, it and the transilluminator are returned to the darkroom and the door closed. With the Epi-illumination switched on, the aperture, zoom and focus are adjusted using the touchpad on the darkroom and viewed on the computer monitor until the desired position, size and focus of the gel are achieved. To acquire the image, the appropriate light source for the gel or membrane is selected and the software is used to select an integration time. Using the Quantity One software, the image is frozen when a satisfactory image is acquired. The Quantity One 1-D image analysis software aids the user in obtaining the best images possible from the gel or membrane. The software is user-friendly and equipped with built-in quick guides and wizards to facilitate the optimization of images and printouts. The software is compatible with both Microsoft® Windows® and Macintosh® platforms. The Quantity One 1-D software is used for analysis of 1-D electrophoresis gels, Western blotting membranes, Coomassie-stained SDS-PAGE gels, etc. whereas the PDQuest 2-D analysis software is also available and is intended to be used for comparative analysis where many 2-D gels are analyzed at once.

In our laboratory, we have used the ChemiDoc XRS system primarily for the imaging and digital documentation of DNA electrophoresis gels stained with ethidium bromide or SYBR® Green as well as for imaging and digital documentation of SDS-PAGE gels stained with Coomassie brilliant blue (using the white light conversion screen which can be purchased separately from Bio-Rad). The software is very flexible and allows the image to be optimized for analysis and record keeping. The many features of the software are beyond the scope of this review but, for example, within our laboratory, the software is frequently used to perform molecular weight determinations of gel bands using a molecular weight ladder as a reference. We also use the software to make semi-quantitative determinations of the amount of DNA or protein present in bands following DNA gel electrophoresis and SDS-PAGE. In addition to these applications, we also use the ChemiDoc XRS System to image Western blots stained with HRP-conjugated antibodies and the Visualizer Spray-And-Glow ECL Western blotting detection system from Upstate. We have found the system sensitive enough for this purpose. In summary, the ChemiDoc XRS System is an effective, flexible documentation and imaging system.