2. Principle of a fluorescence sensor with organic
optoelectronic components
The principle of a fluorescence sensor based on organic devices
is shown in Fig. 1. It consists of an excitation source, a detector and
a detection chamber. The excitation source emits photons, which
excites fluorophores (fluorescent chemical or cells) in the detection
chamber so that the sensor can collect the emitted fluorescent
photons. The excitation source and the detector are an OLED and
an OPD, respectively. Optical filters are placed on either side of the
detection chamber of the microfluidic chip in a way that the OPD
only detects the fluorescence signal.
OLEDs and OPDs are both made of layers of organic semiconductors
(about 100 nm thick), sandwiched between two
conductive electrodes. Typically, the two electrodes are a
100–150 nm thick metal cathode (e.g., Ca, Al, Ba and Ag) and a
100–150 nm indium-tin oxide (ITO) transparent anode.
OLED and OPD differ with the choice of organic semiconductors
and their mode of operation. For OLED, a positive voltage between
the two electrodes is applied in order that the organic layer emits
photons, whereas the organic layer of OPD absorbs photons and
converts them into current signal. Thus, spectral characteristics
of organic devices thoroughly depend on organic materials that
compose them. In both devices, organic semiconductors can be
either small molecules or polymers. They can be deposited by liquid
process (e.g., ink-jet printing and spin coating) or by vacuum
evaporation.
Fluorescence emission is isotropic. This feature provides thatthe
excitation source and detector can locate independently in space.
Generally, these two components are placed at 90◦ in standard laboratory
equipmentinorder to avoid saturationofthe photodetector
by the excitation source. As OLED and OPD are planar technologies,
three configurations could be possible, as shown in Fig. 2. Among
these three arrangements, it has been chosen to place the OLED and the OPD in the same vertical direction on either side of the
detection chamber in order to maximize the fluorescence signal to
be detected (configuration a). However, in this configuration, the
OPD detects all OLED photons, too. Therefore, such configuration
requires the integration of optical filters in order to detect only
the fluorescence signal coming from the analyzed sample without
interfering signal coming directly from OLED and reaching the OPD
(Fig. 1). First, an excitation filter is placed between the OLED and the
detection chamber in order to cutoff the portion of the OLED emission
signal that could overlap the fluorescence signal of the sample.
In addition, a second filter (emission filter) is disposed between the
sensor chamber and the photodetector to avoid that unabsorbed
OLED photons to reach the OPD. The integration of the two optical
filters allows the device to detect only pure fluorescence signal
emitted by fluorophores.
2. Principle of a fluorescence sensor with organicoptoelectronic componentsThe principle of a fluorescence sensor based on organic devicesis shown in Fig. 1. It consists of an excitation source, a detector anda detection chamber. The excitation source emits photons, whichexcites fluorophores (fluorescent chemical or cells) in the detectionchamber so that the sensor can collect the emitted fluorescentphotons. The excitation source and the detector are an OLED andan OPD, respectively. Optical filters are placed on either side of thedetection chamber of the microfluidic chip in a way that the OPDonly detects the fluorescence signal.OLEDs and OPDs are both made of layers of organic semiconductors(about 100 nm thick), sandwiched between twoconductive electrodes. Typically, the two electrodes are a100–150 nm thick metal cathode (e.g., Ca, Al, Ba and Ag) and a100–150 nm indium-tin oxide (ITO) transparent anode.OLED and OPD differ with the choice of organic semiconductorsand their mode of operation. For OLED, a positive voltage betweenthe two electrodes is applied in order that the organic layer emitsphotons, whereas the organic layer of OPD absorbs photons andconverts them into current signal. Thus, spectral characteristicsof organic devices thoroughly depend on organic materials thatcompose them. In both devices, organic semiconductors can beeither small molecules or polymers. They can be deposited by liquidprocess (e.g., ink-jet printing and spin coating) or by vacuum
evaporation.
Fluorescence emission is isotropic. This feature provides thatthe
excitation source and detector can locate independently in space.
Generally, these two components are placed at 90◦ in standard laboratory
equipmentinorder to avoid saturationofthe photodetector
by the excitation source. As OLED and OPD are planar technologies,
three configurations could be possible, as shown in Fig. 2. Among
these three arrangements, it has been chosen to place the OLED and the OPD in the same vertical direction on either side of the
detection chamber in order to maximize the fluorescence signal to
be detected (configuration a). However, in this configuration, the
OPD detects all OLED photons, too. Therefore, such configuration
requires the integration of optical filters in order to detect only
the fluorescence signal coming from the analyzed sample without
interfering signal coming directly from OLED and reaching the OPD
(Fig. 1). First, an excitation filter is placed between the OLED and the
detection chamber in order to cutoff the portion of the OLED emission
signal that could overlap the fluorescence signal of the sample.
In addition, a second filter (emission filter) is disposed between the
sensor chamber and the photodetector to avoid that unabsorbed
OLED photons to reach the OPD. The integration of the two optical
filters allows the device to detect only pure fluorescence signal
emitted by fluorophores.
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