Comparison of emission filters for imaging DNA gels with a smartphone

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Jo Long — Thu, 2013-06-27 17:09

When carrying out gel electrophoresis of DNA samples, you will often want to take an image of the final stained gel. Most gel documentation systems require the use of a permanent camera set-up with an emission filter centered around the wavelength of the dye emission to reduce background from the excitation light source. Some of the most common dyes used for staining agarose DNA gels are ethidium bromide (595nm em) and a number of dyes emitting at ~530 nm (e.g. SYBR® Safe). We have recently been testing three emission filters with center wavelengths 535 nm, 570nm and 590 nm. Each has a bandwidth of 100 nm ( +/- 50 nm around the center wavelength). For our purposes we wanted to be able to use a smartphone camera to take our images, so we used small filters cut to a 11.5 mm diameter which can easily fit over the camera on most smartphones.

The images below show the resulting gel images from testing these filters using a Smartphone camera (Samsung Galaxy Nexus). Note: DNA samples (1kb DNA ladder, NEB Cat # N0468S) were run on 1.2% agarose gels and stained after electrophoresis by soaking the gel in buffer in diluted dye.

1) UV-B Transilluminator with Ethidium bromide Gel Stain:

For imaging ethidium bromide stained DNA with the UV transilluminator, we found the best results with the 590 nm emission filter. DNA bands are very bright with this filter and background is pretty uniform.

2) UV-B Transilluminator (amber lid) with GreenView Plus (Andy Gold^TM) Gel Stain:

As expected, the 535nm emission filter performs the best for these stained gels, removing any background from the UV light as seen in the images where no filter is used, and has the best background and band brightness. The 590nm filter gels look similar to the gels with no filter and the 570nm reduced band brightness.

3) UV-B Transilluminator (amber lid) with SYBR® Safe DNA Gel Stain:

Similar results as the GreenView Plus gels.

In addition, we also checked with the GreenView Plus and SYBR Safe gels on the Blue LED transilluminator with all 3 emission filters.

1) Blue LED Transilluminator with GreenView Plus (Andy Gold^TM) Gel Stain:

In general, the blue LED transilluminator has a more even but brighter background than the UVB transilluminator. Without any filter, the images from the smartphone for both the Andy Gold and SYBR Safe gels (see below) were pretty good. While both of the 535nm and 570 nm filters gave similar results the 570nm filter does a great job at reducing the background.