Page 199 - Organic Electronics in Sensors and Biotechnology

176 Chapter Five

FIGURE 5.10 Mixed OLED platforms of green (outer four pixels in the arrays) and
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blue OLEDs. The array on the right is encapsulated. The pixel size is 2 × 2 mm .
(See also color insert.)

(Fig. 5.5), which would be excited by rubrene-doped Alq OLED pixels.
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The arrays of mixed OLED pixels can also include adjacent blue and
green pixels based on, e.g., DPVBi or Alq , respectively. Such pixels will
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enable the use of Ru dye- or PtOEP- and PdOEP-based sensors, respec-
tively. Such a mixed array of blue OLEDs (peak EL at ~460 nm) and
green OLEDs (peak EL at ~530 nm) is shown in Fig. 5.10.
In such arrays, typically 2 to 4 pixels excite a given sensing film.
Thus, through consecutive or simultaneous excitation of such small
groups of OLED pixels, O can be detected by different sensing films
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that exhibit linear calibration plots and sensitivities suitable for dif-
ferent ranges of O levels. This approach provides the basis for sensor
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(micro)arrays for multianalyte detection, including using an array of
OLEDs emitting at various wavelengths. Such arrays were recently
fabricated using combinatorial methods. 35, 36
In summary, the example of the O sensor demonstrates that the
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use of OLEDs’ as excitation sources in PL-based chemical sensors is
promising. The ease of OLED fabrication and OLED/sensing compo-
nent integration result in compact modules, which are expected to be
inexpensive and suitable for real-world applications. The example of
oxygen sensing demonstrates the advantageous decay time detection
mode. The results also demonstrate the promise of the OLED pixel
platform for developing sensor arrays for multiple analyses of a sin-
gle analyte or for detection of multiple analytes, as shown next. In
evaluating the OLED-based platform for oxygen sensing, a new
assessment of PtOEP-based sensors in terms of PtOEP aggregation
and the effects of film composition and measurement temperature on
the PL lifetime was obtained. 17
We note that OLED-based O sensors are currently evaluated for
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potential commercialization. The main issues that face such devices are
the OLED’s long-term stability and large-scale availability. Figure 5.11
shows a structurally integrated OLED/PtOEP:PS/Si photodiode sen-
sor operating in the back detection geometry.