Page 189 - Organic Electronics in Sensors and Biotechnology

166 Chapter Five

PL-based chemical and biological sensors, which are often uti-
lized for monitoring a single analyte, are sensitive, reliable, and
suitable for the wide range of applications in areas such as environ-
mental, medical, food and water safety, homeland security, and the
1–8
chemical industry. The sensors are typically composed of an analyte-
sensitive luminescent sensing component, a light source that excites
the PL, a photodetector (PD), a power supply, and the electronics
for signal processing. Recent compact light sources include diode
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lasers and LEDs, but their integration with the sensing element,
microfluidic architectures, and/or the PD is intricate, and not nearly
as simple and potentially low-cost as that of the OLED-based plat-
form. Based on the need and challenges, our goal is to develop a
flexible, lightweight, compact, portable, and low-cost platform of
sensor arrays, eventually miniaturized and usable for multiana-
lytes, in which the light source, the sensing component, and eventu-
ally a thin-film PD are structurally integrated in the uniquely simple
design described below. Indeed, the results reported to date on the
OLED-based platform are very promising for developing miniatur-
ized sensor arrays for the above-mentioned applications, including
for high-throughput multianalyte analysis. 10–20
This chapter reviews the recent advances in the development of such
PL-based chemical and biological sensors, where an array of OLED
pixels serves as the excitation source. This pixel array is structurally
integrated with the sensing element to generate a compact, eventually
miniaturized, sensor module. Advanced integration includes addition-
ally an array of p-i-n, thin-film PDs that are based on hydrogenated
amorphous Si (a-Si:H), a-(Si,Ge):H, or nanocrystalline Si. Organic PDs
are also suitable for this advanced structural integration.
OLED attributes that are attractive for sensing applications
include their simple and easy fabrication in any two-dimensional
shape, including on flexible plastic substrates, their uniquely simple
integration with a sensing component, and compatibility with micro-
fluidic structures. Additionally, OLEDs consist of individually
addressable pixels that can be used for multiple analytes, they can be
operated at an extremely high brightness, they consume little power
and dissipate little heat, and their cost will likely drop to disposable
levels.
SMOLEDs are typically fabricated by thermal vacuum evaporation
of the small molecules; polymer OLEDs (PLEDs) are typically fabri-
cated by spin-coating or inkjet printing of the polymer-containing solu-
tions. They have dramatically improved over the past decade, 22–26 and
21
commercial products incorporating them are proliferating rapidly.
Their inherent advantages include the ability to fabricate them on glass
and flexible plastic; electrophosphorescent red-to-green OLEDs with
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external quantum efficiencies η > 17 % and blue OLEDs with η ≈
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ext ext
11% have been reported. They can be easily fabricated in sizes ranging
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