In process of using the Leeds Spectral Vision System (LSV), to search for bodily fluids or evidence, there may be the occasion with various fabrics, where wave-lengths and filter combinations that are normally used for specific stains, are unable to be readily visualized due to the fabric itself preventing the stain sample from being detected (either from a lack of contrast between the fabric and the sample or innate fluorescence from the fabric itself). In cases such as this, the LSV offers a very strong capability to rapidly switch between different filter and light combinations along with increased sensitivity of the camera. Through changing techniques, the LSV can help with the visualized samples that would normally be very difficult or time consuming to detect.
Tips for difficult substrates
Change your lights- Your fabric may be excited at a very specific wave-length whereas your sample may be excited more (compared to your fabric) at a separate wave-length. UV is a good place to start if you are having difficulty as many biological samples will generally fluoresce somewhat in this region.
Don’t forget to change your filters – Your fabrics emitted fluorescence spectrum may be different than that of your sample. Changing your filters can help reduce background in some cases by blocking out parts of the background fluorescence, while letting through portions of your sample’s fluorescence.
Adjust your brightness settings – Sometimes on substrates that fluoresce, the signal is so bright that your biological sample’s fluorescence gets lost in the background due to the exposure being too high. Changing the brightness/exposure of the camera can reveal details that were previously over or underexposed. This can be particularly useful for looking at pattern fabric which have both fluorescence and non-fluorescence patterns, adjusting the brightness or exposure settings for the dark and lighter sections of the background in turn.
Get in close – For fluorescence signal detection, distance plays a very important role. By bringing the lights in closer to your sample you will exponentially increase the efficiency of the fluorescence. This goes doubly for bringing the imaging head itself closer, as both the camera and lights get closer to the sample allowing greater detection of fluorescence signal. Additionally, as the efficiency increases, exposure times can be lowered (in auto exposure this will occur automatically) allowing the system to have higher frame rates for easier screening. The auxiliary lenses in the head can be switched to allow the head to get closer or further away from the sample.
Cant see a sample? Try exciting the background- Sometimes instead of trying to excite your sample, see what happens when you cause the background to fluoresce or reflect back light. Violet light with a clear filter occasionally is a good counter for fabrics which absorbs IR light similarly to blood.
Remember gain increases the camera sensitivity, which can allow you to reduce the exposure time thus increasing frame rates.
Speed – Apply settings button on captured images can save loads of time – if you find yourself searching on a material which you have already found in the past a good lens, filter, and light combination for, try opening a previously captured image from the same substrate type and hit the apply settings button. The apply settings button can let you rapidly switch not only between light and filter combinations but also zoom, focus, and auxiliary lens allowing you to quickly switch between sample types and different magnifications.
These are just some tips we have run into; if you have others, or recommended filters/lights for fabrics, please share your thoughts on this blog or feel free to contact us at 1-800-444-5333.