Q: What applications need a 6285 rather than the 6280 or 6270?
A: The 6285 has a sensitive photomultiplier tube (PMT) to detect the fluorescence down to <1ng/ml coupled with a wide spectrum pulsed xenon lamp that can be used for assays from 190 to 850nm. The 6280 also has a PMT, but is limited to 650nm so is not suitable for those assays performed at a longer wavelength. The 6270 has a silicon diode detector that allows detection at the µg/ml level which makes it ideal for those assays with higher levels of fluorescence.
Q: What are the differences between interference, bandpass and cut-off filters?
A: Bandpass filters allow all the light between the specified wavelengths to pass through them, making them ideal for excitation filters, but normally unsuitable for emission filters. Cut-off and interference filters are more commonly used for this purpose. The cut-off filters allow all the light above the specified wavelength to pass through and the interference only allow a very narrow range of light to pass through. Typically this is 10nm, +/-5nm of the specified wavelength, with the selected wavelength close to the emission maxima. Using interference filters for excitation and emission would ensure a very specific assay with only a small possibility of interference from other fluorescing molecules, but the assay is likely to have a lower overall fluorescence as very little light is allowed through the filters.
Q: Is it possible to control the temperature of the sample in the Jenway fluorimeters?
A: Yes, there are 2 options; firstly the sipper pump which also transfers multiple samples from their containers into the flow cell and flushes the cell before the next sample is taken up. Secondly, the electrically heated cell system which heats the sample in position within the fluorimeter, making it the best option for longer enzyme kinetic assays.
Q: What is the gain feature?
A: This feature is only found on the 6280 and 6285; the gain is the sensitivity of the photomultiplier tube (PMT) and this can be turned down if the samples are very concentrated and turned up to 100% using the entire PMT capacity if the sample is of a low concentration. The idea is to use as much of the PMT range for the particular set of samples to get the most accurate results.
Q: Is it possible to measure DNA and RNA samples using the Jenway fluorimeters?
A: Yes, DNA can be measured with the Quant-iT PicoGreen kit and RNA with the RiboGreen Quant-iT from Invitrogen. Specific filters are required and Jenway recommends the interference filters 490nm (part code 627 169) for excitation and 520nm (part code 627 172) for emission. DNA can also be quantitated using Hoechst dye. Applications notes are available from the Technical Support team at firstname.lastname@example.org
Q: What is the difference between a spectrophotometer and fluorimeter cuvette?
A: In a spectrophotometer a certain amount of light is passed through the sample and the amount absorbed by the sample is measured by the detector. This requires that the detector is in line with the light source and sample therefore the windows of spectrophotometer cuvettes are on opposite walls of the cuvette. In a fluorimeter, the fluorescence of the sample is measured at 90º to the incident light otherwise the detector will see light from the lamp which is not due to fluorescence of the actual sample. Therefore fluorimeter cuvettes have windows on adjacent walls.