Entries in webcam (1)

Friday
Dec162011

Cheap, LED gel-doc using a webcam - updated

A gel-doc is an essential item in any molecular biology laboratory, however a ready-made gel doc can cost a lot and will likely use UV lamps.  UV lamps are bigger and heavier than available LED technology and also may induce damage to your DNA samples, especially when using long exposures for band cutting.  Cheap blue LEDs are now widely available emitting in the 450-490 nm range and arrays of small LEDs are bright enough for gel imaging.  The blue light emitted is safe to view and does not risk DNA photodamage.

I bought a new Syngene Ultraslim LED transilluminator which has two 54 diode arrays of 470nm LEDs - this illuminates the central area very evenly.  Whilst not super-cheap, at £300 it still beats a UV transilluminator by some margin.  If you wanted to go really cheap you could get a blue LED grow light (check hydroponic suppliers) or do a full DIY installation of LEDs from an electronics supplier.

SYBR-Safe stained gel image taken with cellphone camera - note reflection due to high ambient light and original shiny base surface. Gel courtesy of Dr Bill Wickstead.The LEDs easily illuminate gels stained with SYBR-Safe or similar dyes - see the photo taken with my phone camera.  The dark orange lid filters out all the blue light, giving a really "constrasty" picture.  You can partially replicate this effect with LEE 12 (yellow) or 15 (dark yellow) filters, but you might have to stack them to get the best effect.

The built-in filter allows you to use any unfiltered camera for image capture and so we purchased a cheap webcam and fitted it into an insulated shipping box.  The white interior of the box gave us problems with stray light, leading to strong reflections of the camera on the filter glass.  Also the base of the trans was a sheet of clear acrylic over black, the shiny acrylic was also too reflective.  Gel doc showing black lining and webcam, the orange filter lid is raised.

 Both of these problems were solved by the application of matte black surfaces - black plastic card to the base of the trans (cheap, waterproof and replaceable), and matte self-adhesive vinyl to the box interior (Avery vinyl is used for sign-making and is widely available on e-Bay or at model/craft shops).  The resultant enclosure is very black and reflections are absent.

Since the webcam is a tiny, cheap sensor images are quite noisy.  However it is possible to collect images at 10 fps or higher, therefore we collect 20+ images and average them together to generate low-noise final images. This is currently accomplished using ImageJ, Virtual-Dub and the ImageJ Video capture macro.

Gel images from the final setup to follow.