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Progress and Challenges in OLED-Based Chemical and Biological Sensors 177

FIGURE 5.11 Top view of a structurally integrated OLED/sensor fi lm/PD
probe in a back detection geometry. (See also color insert.)

5.3.2 Multianalyte Sensing
Sensor arrays for detection of multiple analytes in a single sample
have been reported extensively. The sensing transduction mecha-
nisms included electrochemical, 43, 44 piezoelectric, 45, 46 electrical resis-
tance, 47, 48 and optical. 49–55 Such wide-range studies are driven by the
need for high-throughput, inexpensive, and efficient analyses of com-
plex samples. Sensor arrays are often fabricated by using photoli-
thography and soft lithography; 44, 48, 56–58 inkjet, screen, and pin print-
59
ing; and photodeposition. 49, 60, 61 These techniques frequently involve
labor-intensive multistep fabrication and require sophisticated image
analysis and pattern recognition codes, which often require relearn-
ing. The use of OLEDs as single- or multicolor excitation sources in
sensor (micro)arrays would drastically simplify fabrication, minia-
turization, and use of the PL-based sensors for sequential or simulta-
neous monitoring of multiple analytes in a single sample.
As mentioned, the OLED-based arrays are unique in their ease
of fabrication and integration of the excitation source with the sens-
ing component. The excitation source of individually addressable
OLED pixels can be based on a single-color OLED or possibly on
multicolor pixels fabricated in a combinatorial approach that results
in adjacent OLED pixels that emit at wavelengths ranging from blue
29
35
to red. OLED pixels of nanometer size, reported recently, should
be suitable for future sensor micro/nanoarrays for a wide range of
applications.
The OLED-based multianalyte sensor for DO, glucose, lactate, and
ethanol, all present in a single sample, was based on the successful