The green bandpass barrier filter option for the Stereo Microscope Fluorescence Adapter isolates the green part of the spectrum and is for use with the Royal Blue excitation source. While our other barrier filters are longpass filters, transmitting all wavelengths longer than the filter’s cutoff, this new filter transmits in the restricted range from approximately 500 to 560nm.
The longpass filter has served well for most users who need to visualize green fluorescent protein (GFP), and if you are exploring fluorescence in nature it is preferable. A primary motivation for adding the green-only filter to the line-up was for the benefit of researchers using GFP in plants such as Arabidopsis thaliana, a common research model. Plants contain chlorophyll, which has a distinctive red fluorescence that can sometimes mask the GFP emission, making it harder to see and photograph. The filter can also be useful for other viewing situations in which background autofluorescence reduces viewing contrast. For example, we have found that many users prefer the bandpass when working with transgenic C. elegans. We have an article about the trade-offs between a longpass and bandpass filter.
We tested this new barrier filter with Arabidopsis supplied by Dr. John Celenza (Department of Biology, Boston University). These plants express GFP in the roots and vasculature. The images below show examples of plants photographed with the long-pass filter (left) and green bandpass filter (right). There is no chlorophyll in the roots so the GFP is evident there in both images, but the weaker expression in the leaves is much more apparent in the images on the right.
(Click on images for larger view)