Page 278 - Organic Electronics in Sensors and Biotechnology

An Intr oduction to Or ganic Photodetectors 255

Basic blood chemistry panels comprising 10 to 20 quantitative tests
are typically analyzed using automated benchtop instruments located
in a centralized laboratory. The ability to replace such instruments
with low-cost disposable devices would transform modern health
care, allowing immediate on-the-spot testing. Immunoassays are
readily integrated into microfluidic devices 94–96 and, importantly, can
be implemented using capillarity-based fluid delivery schemes that
passively draw the sample into the chip from an entry port without
the need for external pumps. The microfluidic platform is therefore a
promising basis for an entirely self-contained diagnostic device.
Microfluidic devices have shown themselves to be highly effec-
tive for laboratory-based research, where their superior analytical
performance has established them as efficient tools for complex tasks
in genetic sequencing, proteomics, and drug discovery applications.
However, to date they have not been well suited to point-of-care or
in-the-field applications, where cost and portability are of primary
concern. Although the chips themselves are cheap and small, they are
generally used in conjunction with bulky (off-chip) optical detectors,
which are needed to quantify the optical signal. Although there have
been some attempts to integrate optics within the chip structure itself,
few have demonstrated the high levels of integration demanded of a
point-of-care stand-alone system.
One promising option for creating integrated light sources and
detectors is the use of organic semiconductor devices. 97–99 In use, the
organic light-emitting diode (OLED) and photodetector are arranged
in a face-on geometry on the top and bottom surfaces of a microflu-
idic chip with a channel in between (Fig. 6.33): biolabels present in
the detection volume of the channel absorb photons from the LED
which they may subsequently reemit as lower-energy photons.

Detector

Glass
Light

Glass
Light
pLED

FIGURE 6.33 Detection geometry for integrated emission and absorption
measurements in microfl uidic devices.