4. Characterization of components for the on-chip
fluorescence sensor
4.1. OLEDs characteristics
The emission spectral and intensity characteristics of the blue
and green OLEDs are illustrated in Fig. 3. Emission peak wavelengths
are at 480 nm and 515 nm for blue and green OLEDs,
respectively (Fig. 3a). The peak position depends on the organic
materials used for the emitting layer, which in this case is DPVBi
for blue OLED and Alq3 for green OLED. We can easily tune the
emission wavelengths by changing the organic molecules in the
OLED organic structure. The fabricated OLEDs show broad emission
spectra with a typical spectral width of 87–90 nm.
The intensity of the OLED depends on the operating voltage as
shown in Fig. 3b. Components exhibited maximal luminance of
more than 25,000 Cd/m2 for green OLEDs and over 10,000 Cd/m2
for the blue OLED. Such high luminance values allow OLED to be
utilized for fluorescence detection.
We also tested the durability of these devices. Tests were made
by applying pulses of voltage to the devices at 12V for blue OLED
(for a luminance of 4700 Cd/m2) and 18V for green OLED (for
a luminance of 20,700 Cd/m2) and no reduction of the emission
intensity was observed after several tens of pulses. However, a significant
reduction of emission appeared at higher applied voltages.
Since current flows through the organic molecules,there is a significant
degradation of the devices, particularly at very high voltages,
and the OLED lifetime decreases rapidly in this condition.
Fig. 4 shows the blue and green OLEDs fabricated on the same
glass substrate and is an example of the great potential of integration
of different OLEDs with different spectral characteristics.
It is noteworthy that the emission of OLED pixels corresponds to
the zone where the aluminum cathode and ITO anode are crossing.
Moreover, OLEDs areplanar like amicrofluidic chip. Thismeans that
the geometry and size of OLEDs’ pixels can be designed according to
the geometry of microfluidic detection chambers. Then, OLEDs are
fully compatible with microfluidic for their integration for optical
detection.