Page 309 - Organic Electronics in Sensors and Biotechnology

286 Chapter Seven

The integration of conventional laser systems on a chip-based
analyzing system is not applicable. Studies on miniaturizing dye
73
lasers may be an alternative. These laser sources are optically
pumped and can be integrated directly on the chip with the possibil-
24
ity of the integration with rib waveguides. However, this approach
still requires a costly pump laser source, and the achievable spectral
emission range is limited.
Microfluidics
Many lab-on-a-chip designs make use of microfluidic systems. Basic
components are microfluidic channels with widths ranging from 5 to
100 μm. The substance to analyze is handled in these channels by
using pump systems or electrophoretic methods. 74–76 The use of micro-
fluidics promises a fast and precise analysis with small amounts of
needed substances. This is especially important in the field of DNA
and high-throughput screening. 14, 77 By joining different system com-
ponents for handling, mixing, and dosing, many tasks required for
the preparation of the analyte can be done directly on the chip. With
the combination of such systems with waveguide-based optical sen-
sors, highly integrated analytic devices can be realized. 78

7.4.2 Integration of Organic Lasers in Optical
Sensor Systems
It has been shown that in principle OLEDs are possible light sources
to excite a fluorophore. However, OLEDs have decisive drawbacks in
comparison to organic lasers. First, their large spectral emission width
is disadvantageous for fluorescence excitation, because the excitation
light has to be eliminated from the measurement signal by complex
methods. Second, even though coupling to waveguides is possible,
the efficiency of the coupling is weak.
An organic laser is a monochromatic light source with a wide tun-
ing range. Optical pumping of the laser allows operation without the
need for electrical contacts. In comparison to dye-doped polymer
lasers organic semiconductor lasers have certain advantages. The
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use of Förster energy transfer systems allows organic lasers to be effi-
ciently pumped with only one light source in the UV range and to
emit laser light in the whole visible spectrum.
A scheme of the proposed integration of organic lasers as light
sources in lab-on-a-chip systems is shown in Fig. 7.20. Light of the opti-
cally pumped organic lasers is coupled into a polymeric waveguide.
The laser light is guided to the detection area, being a cross section of
the waveguide and a microfluidic channel. The resulting optical signal,
e.g., a change in the absorption pattern or a laser-induced fluorescent
signal, is then detected by an integrated photodiode.
In conventional chemical analysis systems, often several solid state or
gas lasers are needed to generate light at different wavelengths, rendering