New filter designed for optimal image clarity
Michelle Cayouette Jane Moores
A new optical filter has been developed for the Eagle Eye II Still Video System that increases contrast and sensitivity when imaging silver-stained protein gels.
The Eagle Eye II Still Video System is currently sold with an optical filter optimized for imaging nucleic acid gels stained with ethidium bromide. Because the system is also frequently used to image silver-stained SDS-PAGE gels,1 we designed an optical filter to improve contrast and sensitivity when imaging these gels. Thus, Stratagenes optical filter line now comprises ethidium bromide, SYBR Green,2 Coomassie Blue,3 and silver-stain filterseach customized for different applications. All filters are coated to ensure high image quality.
SDS-PAGE protein gels were silver stained using standard procedures and were then used to compare the performances of the silver-stain and ethidium bromide filters. A stained gel was first positioned on a white-light transilluminator and imaged with the Eagle Eye II Still Video System, using each filter in turn. The same gel was then positioned on a piece of shiny, white plastic and imaged using the overhead white lights in the Eagle Eye cabinet. In each case, the f-stop was adjusted until the displayed image represented the gel as well as possible.
Figure 1 shows a gel as imaged by the system using either the ethidium bromide (panel A) or silver stain (panel B) optical filter with transillumination. Figure 2 shows an image of the gel obtained using the same filters but with overhead illumination. Using either transillumination or overhead illumination, the images captured using the silver-stain filter demonstrate an increased contrast over images obtained using the standard Eagle Eye filter; consequently, certain faint bands were more easily visualized. For example, proteins migrating at about 40 kDa are clearly visible in lanes 4 and 5 (earlier-eluting column fractions) when the silver-stain filter was used but do not become visible until lanes 7 and 8 (later-eluting fractions) when the ethidium bromide filter was used. The bands recorded using the silver-stain filter closely reflect what can be seen on the gel by eye. Although contrast and sensitivity were enhanced for most protein bands on the gel, those with a brown-orange tone showed the greatest improvement.
The silver-stain optical filter can improve image contrast when imaging silver-stained gels with the Eagle Eye II Still Video System. Using this filter can lead to improved visualization of faint bands, which increases the sensitivity of the imaging system or may reduce the amount of protein required for analysis.
The authors thank Frances Bai and Brad Scott for providing silver-stained SDS PAGE gels for imaging.