5. Optical System
70
Instructions for Use for
infinite® 200
No. 30017581 Rev. No. 1.4
2008-07
5.1.3
Fluorescence Intensity Detection
The fluorescence detection system is used for both measuring modes:
fluorescence from above (top) and below the microplate wells (bottom).
The fluorescence light is focused onto the entrance slit of the Emission
Monochromator. After passing the monochromator the light is focused onto the
detector (PMT). A filter wheel is located between the monochromator and the
PMT.
The Fluorescence Detection system is built from the following components:
•
Emission Double Monochromator
•
Filter
Wheel
PMT
•
PMT
Detector
Emission Double Monochromator
Similar to the Excitation Double Monochromator, the Emission Double
Monochromator is used to select any wavelength of the fluorescence signal.
It acts like an adjustable filter to discriminate scatter of excitation light and
nonspecific fluorescence. The wavelength range is selectable from 330 – 600 nm
in the standard instrument and from 280 – 850 nm in the spectrally enhanced
instrument. The bandwidth is 20 nm.
Filter Wheel PMT
The filter wheel contains wavelength specific optical filters, which are necessary
to block undesired diffraction orders produced by the optical gratings. The filters
are set automatically.
PMT Detector
A photo-multiplier tube (PMT) is used for the detection of such low light levels
associated with fluorescence. The
infinite
®
M200
is available in two versions: The
PMT of the standard version is sensitive up to 600 nm. The PMT of the spectrally
enhanced version of the
infinite
®
M200
is sensitive up to the near infrared (NIR)
while still having low dark current. Electronic circuitry uses analog to digital
conversion of PMT output current. Adjusting the PMT gain enables measurement
of a wide range of concentrations in lower or higher concentration domains. For
details see Section 6.3.1 Instrument Parameters.
