How to Choose Excitation and Emission Filters for the 62 Series Fluorimeter
Jenway offers a simple benchtop fluorimeter, Jenway 6280, which uses drop in intelligent filters, however which filters should you choiose as there seems to be a lot of options to choose from?
Optical filters are chosen to suit the requirements of each application. Often this choice will be a balance between the sensitivity and specificity requirements of the application.
Bandpass filters pass a broad band of light. For example, a 627 126 UG1 bandpass filter will transmit light from 320 – 380nm while blocking light with wavelengths shorter than 320nm and longer than 380nm.
Interference filters pass a narrow band of light, typically 10nm. For example, a 627 140 – 350nm filter with a bandpass of 10nm will pass light from 345 – 355nm (5nm on either side of 350nm).
Cut-off filters are used to block light that is shorter than a specified wavelength. A 475nm cut-off filter will allow transmission of light that is longer than 475nm, but it will block light that is shorter than 475nm.
An excitation filter should only allow light which excites the molecule of interest to reach the sample. The emission filter should allow the fluorescence from the sample to pass to the detector whilst blocking stray light from the light source or any interfering components in the sample.
Bandpass filters are often used for the excitation wavelengths in an application as they provide the required selectivity without compromising the sensitivity of the application. If the excitation wavelength is not covered by one of the available bandpass filters an interference filter will be required.
The emission filter is usually either an interference or cut-off type filter. These types of filter are able to isolate the fluorescence signal of interest from interferences that may be present in the sample. Using interference filters, with their narrow bandpass specification, may reduce the sensitivity of an application method; however the specificity is generally increased.
Choosing Optical Filters for the 62 Series Fluorimeter
1. Identify the optimum excitation and emission wavelengths for your application. A table of common fluorochromes is available here.
2. Select a bandpass or interference filter which brackets the excitation wavelength required. (The measurements sensitivity will be reduced when using an interference filter rather than a bandpass filter.)
3. Select an interference or cut-off filter which brackets the emission wavelength required. (The measurements sensitivity will be reduced when using an interference filter rather than a cut-off filter.)
4. Ensure that the transmitted wavelengths of the filters selected in 2 and 3 do not overlap as this may reduce the measurements sensitivity.
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