The%20most%20recent%20application%20of%20OLEDs:%20Structurally-integrated%20OLED-based%20luminescent%20chemical%20

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The most recent application of OLEDsStructurally
-integrated OLED-basedluminescent chemical
biological sensorsRuth Shinar Microelectronics
Research Center ECpE Dept, ISUIntegrated
Sensor Technologies, Inc. (ISTI) Joseph
ShinarAll of the aforementioned ISTI
Support by DOE, NASA, NSF, NIH also gratefully
acknowledged
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Outline

• Photoluminescence (PL)-based sensors issues,
  goal
• Approach
• Structural integration OLED excitation source
  and sensing component
• Applications
• Single analyte detection
• Multianalyte detection
• Advanced structural integration OLED/sensing
  component/thin film-based
• photodetector
• Application example O2
  sensing

Joseph Shinar and Ruth Shinar, Organic
Light-Emitting Devices (OLEDs) and OLED-Based
Chemical and Biological Sensors An Overview,
J. Phys. D Appl. Phys. 41, 133001 (2008).
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Components of PL-Based Sensors

• Excitation source lasers, inorganic LEDs, lamps
• Sensing element a porous film with an embedded
  luminescent dye, surface immobilized
• species, or microfluidic channels with
  recognition elements in solution
• Photodetector photomultiplier tube, Si
  photodiode
• Electronics and readout
• 
  Not Integrated
• Issues
• Light-source is either bulky, or the integration
  with the sensing element/microfluidics involves
  intricate design (fibers, lens)
• Sensors are often immobile, costly
• Sensors are limited in use for real-world
  applications often used for single analyte
  detection

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Long-Term Goal
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OLEDs Advantages for Sensor Applications

• Are simple to fabricate and uniquely simple to
  integrate with a sensing component
• Can be easily fabricated in any 2-D shape
• Are compatible with microfluidic structures
• Can be fabricated on plastic substrates
• Can be operated at an extremely high brightness
• Consume little power and dissipate little heat
• Cost is expected to drop to a near-disposable
  level

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OLED/Sensing Component Integration
Approach structural integration of two
components
OLEDs are easily fabricated as an array of pixels
Back-detection mode using an array of OLED pixels

• Sensor operation modes
• monitoring changes in I
• monitoring changes in t

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1. Oxygen Sensor R. Shinar et al., Anal. Chim.
Acta 568, 190 (2006)

• Principle of operation
• An oxygen sensitive dye is embedded in a thin
  film matrix or dissolved in solution
• Collisions of O2 with the dye result in quenching
  of the PL intensity I and shortening of the PL
  decay time t
• Stern-Volmer (SV) equation
• I0/I t0/t 1 KSVO2
• I0 and t0 unquenched PL intensity and decay
  time KSV - Stern-Volmer constant
• Sensor operation modes (1) monitoring changes
  in I
• (2) monitoring changes in t
• The need for optical filters and frequent
  calibration
• is eliminated when using the PL decay time mode.

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Results for Gas-Phase OxygenIntegrated
OLED/sensing element back-detectionGreen OLED
(Alq3)/Pt octaethylporphyrin (PtOEP) in a
polystyrene film
I0/I t0/t 1 KSVO2
PtOEP
emission 635 nm
S t0/t(100 O2)30-50
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Results for Gas-Phase OxygenIntegrated
OLED/sensing element back-detectionRubrene
(0.5)-doped Alq3/Pd octaethylporphyrin (PdOEP)
in a polystyrene film
PdOEP
emission 645 nm
S t0/t(100 O2)240
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Results for Dissolved OxygenIntegrated
OLED/sensing element back-detectionAlq3/PtOEP
in a polystyrene film or in solution
I0/I t0/t 1 KSVO2
water
toluene 0.01 mg/mL PtOEP
ethanol
water
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Long-term stability gas-phase oxygen
Long-term stability dissolved oxygen
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2. Recent Improvements in OLED-Based Oxygen
Sensors Dispersion of TiO2 Particles in the
PSPtOEP Film Enables use of reduced
brightness for enhanced OLED lifetime and reduced
photo-degradation Zhou et al., Adv.
Func. Mater. 17, 3530 (2007)

• A uniquely simple approach, using 360 nm-diameter
  TiO2 particles.
• Enhancement is due to light scattering by the
  high refractive index particles, possibly by
  voids induced by the particles.

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Typically, the sensor films were prepared by drop
casting 40-60 mL of the solution onto the glass
substrate the resulting films were all 8 mm
thick
(a)
(b)

• SEM images of PS films doped with PtOEP and
  titania particles
• 2 mg/mL TiO2 in the solution used for film
  fabrication, (b) 8 mg/mL particles.

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In Air
The PL spectra in air, excited at 535 nm by the
Alq3 OLED, of PtOEPPS doped with different
concentrations of TiO2, measured in reflection
geometry.
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Gas-Phase
The effect of titania particles on the PtOEPPS
PL decay curves and on the EL of the Alq3 OLED in
a 100 gas-phase Ar environment at 295 K. Shown
is the intensity measured by the PD during and
following the 50 ms Alq3 OLED pulse at titania
particle concentrations of 0, 1.5, 2, 4, and 8
mg/mL. A 610 nm long-pass filter was placed in
front of the PD, so that only a small fraction of
the OLED emission reached the PD. Inset the PL
signal enhancement vs. the titania particle
concentration.
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DO in Water
(a)
The PL decay curves in Ar- and O2-saturated
solutions for (a) PtOEP and (b) PdOEP with and
without titania doping the exponential (Ar) and
bi-exponential (O2) fitting are also shown.
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Example of sensor design operation Green
OLED/PtOEP embedded in polystyrene
Green Alq3 OLED/PtOEP

• The green Alq3 OLED array is behind the
  PtOEP-film, which is largely confined to a region
  in front of the middle two OLED pixels.
• The green emission from these pixels combines
  with the red PL of the PtOEP dye to produce the
  observed yellowish spots.
• The photodetector is located behind the OLED
  array.

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3. Oxidases-Based Multianalyte Sensor Array
(based on the preceding O2 sensor)
Choudhury et al., J. Appl. Phys. 96, 2949 (2004).
glucose O2
H2O2 gluconic acid
glucose oxidase PtOEP normal
level100 mg/dL (5.5 mM)
O
ethanol O2
alcohol oxidase PtOEP Legal limit 0.1 0.1
mg/dL (2.2 mM)
lactate O2
H2O2 pyruvic acid
lactate oxidase
PtOEP Normal level Venous blood 4.5-19.8 mg/dL
(0.56-2.46 mM) Arterial blood 4.5-14.4 mg/dL
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Multianalyte Sensor in Operation consecutive
sensing using a single photodetector
R. Shinar et al., SPIE Conf. Proc. 6007, 600710-1
(2005).
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Multianalyte Sensor Array simultaneous monitoring
Y. Cai et al., Sensors Actuators B 134, 727
(2008).

• small-size sensor array (e.g., total size
  1.5x1.5 cm2)
• sensing element O2-sensitive dye (PtOEP) and an
  analyte-specific oxidase enzyme
• each sensing element is associated with 2 OLED
  pixels
• sensing of the different analytes in a single
  sample is obtained by addressing the appropriate
  OLED pixels
• simultaneous sensing of the different analytes in
  a single sample is obtained when all OLED pixels
  are lit simultaneously, and the PL of each
  analyte is monitored by its associated Si
  photodiode. A Labview program enables such
  simultaneous monitoring via separate channels.

silicon photodiode array
6 mm
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Sensing in Sealed Wells Assessing the limit of
detection
In reactions performed in sealed wells, where
there is no replenishing of O2, and the initial
concentration of the analyte does not exceed that
of the initial DO (0.25 mM in water at 23oC)
37oC cell open to air lactate monitoring
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Multianalyte mixture sensing sequential
monitoring simultaneous monitoring
23oC sealed containers
circles ethanol squares lactate triangles
glucose
LOD 0.02 mM dynamic range 0.25 mM at 23oC in
the final, diluted sample.
Modified SV equation I0/I t0/t 1
kSVDOinitial analyteinitial
Simultaneous detection using a 55 mm2 Si
photodiode array.
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• 4. Bacillus Anthracis (Anthrax) Lethal Factor
  (LF)
• Principle of Operation
• R. T. Cummings et al. Proc. Nat. Acad. Sci.
  99, 6603 (2002)
• The LF enzyme, one of three proteins of the
  Anthrax toxin, a Zn-dependent metalloprotease,
  cleaves certain peptides at specific sites.
• Fluorescence detection of LF is therefore
  possible by using a peptide- based
  FluorescenceResonance Energy Transfer (FRET)
  assay.

FRET-labeled peptide sequence (donor)-Nle-K-K-K-K
-V-L-P--I-Q-L-N-A-A-T-D-K- (acceptor) G-G-NH2
cleaving site

• Peptides with donor and acceptor on either side
  of the cleaving site are synthesized
• In this D-A configuration, the fluorescence of
  the donor is quenched by the acceptor
• Following exposure to LF, the peptide is
  cleaved the donor and acceptor are
• separated, resulting in an increase in the
  detected intensity of the donor fluorescence.

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Selected examples showing the effect of the
concentration of the peptide on the
photoluminescence using 25 nM LF
The maximal increase in the PL following exposure
of the labeled peptide to LF was by a factor of 2
at 37 oC
To improve sensitivity, need to eliminate OLED
tail that overlaps the donor emission. Turn to Ru
dye (?exc385 nm, red emission) bis(2,2-bipyridi
ne)-4-methyl-4-carboxybipyridine-Ru N
succinimidyl ester-bis(hexafluorophosphate)
QSY21 quencher.
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5. Hydrazine (N2H4)
S. Rose-Pehrsson and G. E. Collins, US Patent
5,719,061)

• Highly toxic but popular NASA monopropellant
  common precursor in the synthesis of some
  polymers, plasticizers and pesticides
• M. P. 2C, B. P. 113.5C, room temp vapor
  pressure 14.4 torr
• Govt recommended exposure limit is 10 ppb for 8
  hrs
• Immediately dangerous to life or health at 50
  ppm
• Detection based on reaction of hydrazine with
• anthracene 2,3-dicarboxaldehyde (ADA).

• Reaction product emits at 549 nm (?exc 476 nm)
• Signal proportional to N2H4 concentration
• Good for air, solution
• Fast and very selective response

H
H
ADA
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Hydrazine
The limit of detection (LOD) is 60 ppb in 1
min, or 1 ppb in 1 h, exceeding the OSHA-
allowed limit of 10 ppb over 8 hrs by a factor of
80
PL change upon ADA exposure to 60 ppb hydrazine
in Ar
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6. Enhanced Integration OLED/Sensing
Element/Photodetector
Back Detection
sensing component
band-pass filter over OLED pixels
glass
(thin) glass
OLED
OLED
PD
PD
PD
long-pass filter (large gap cuts blue)
nanocrystalline or a-(Si,Ge)H low-gap PD
Envisioned fully integrated OLED/sensing
film/thin film PD array in a back detection
configuration. Grounded Al stripes between the
OLEDs and PDs will block the edge EL and the
synchronous electromagnetic noise generated by
modulated OLEDs.
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Towards complete integration front detection
long-pass filter
low gap a-(Si,Ge)H PD
transparent cover
glass/PDMS
wells or microfluidic channels
Band-pass filter over OLED pixels
glass
OLED
OLED
OLED
OLED
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OLED/Sensing Component/Photodetector Integration
R. Shinar et al., J. Non Cryst. Solids 352, 1995
(2006).
First Step Structural integration of two
components the sensing element and an a-Si thin
film-based photodetector Second Step single
element front detection structural integration
of three components OLED/sensing element/PD I
mode of operation The three-component
integration is attractive due to the potential
for miniaturization of sensor arrays, their
fabrication on flexible substrates, and
integration with microfluidics
PD
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• PDs
• PECVD-grown p-i-n and n-i-p structures, based
  on a-Si and a-(Si,Ge), or nc-Si.
• The p-i-n structures were fabricated on an
  ITO-coated glass substrate the ITO was protected
  from reduction by the hydrogen plasma with a 0.1
  ?m thick ZnO layer grown by RF sputtering.
• The composition and thickness of the p i
  layers were tuned to increase the sensitivity at
  wavelengths matching the emission band of the
  oxygen-sensitive dye and to reduce the
  sensitivity to the OLED background.
• The emphasis was on
• improving the O2 detection sensitivity by
  improving the PDs reducing the synchronous
  OLED-generated electromagnetic noise
• understanding factors that affect the speed of
  the PDs

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TUNING of the PDs
The PDs were first tuned for high sensitivity at
the PtOEP/PdOEP emission wavelength (635/650 nm)
and minimal response at the OLED excitation (535
nm). The a-(Si,Ge)-based PDs are preferred due to
their match with the dye PL, and lower response
at the EL band. However, their dark current was
higher and their speed lower.
(0.5 mm) 0.15 mm p-layer
0.3 mm p-layer 1.6 Ge in p-layer 10 Ge in
i-layer
PtOEP
emission 635 nm
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Sensor Film/Photodetector Integration
Detection of the photoluminescence of PtOEP
embedded in polystyrene by the a-(Si,Ge)H- based
photodetector, using a 600 nm long-pass filter
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O2 sensor lamp-monochromator/ PtOEP-based sensor
film/thin-film PD
I0/I t0/t 1 KSVO2
I0/I
S I0/I(100 O2)23
Detection of the photoluminescence of PtOEP
embedded in polystyrene by the a-(Si,Ge)H- based
photodetector using a 620 nm band-pass filter to
reduce the background, and therefore increase the
sensitivity.
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OLED/Sensing Component/Thin-Film Photodetector
Integration
Single element front detection

• Initial integration resulted in low S attributed
  to a large background stemming
• from the broad OLED EL, and high PDs dark
  current.
• A major reason to the low S is the synchronous
  electromagnetic (EM) noise from
• the pulsed OLED when using lockin detection
  of the intensity.
• S improved significantly by shielding the OLED.

• To shield the PD from this EM noise, a grounded
  150 nm thick ITO-coated glass was placed above
  the OLED.

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O2 sensor, I mode operation OLED/PdOEPPS/thin-fi
lm PD Examples of SV plots of different sensors,
each with the three-component integration, i.e.,
unshielded and shielded Alq3 OLED/PdOEPPS/a-(Si,G
e) PD, and double-shielded coumarin-doped Alq3
OLED/PdOEPPS/nc-Si PD
Shielding the PD improved the response. The best
results were obtained for the double shielded,
coumarin-doped Alq3 S 47, improved strongly
over the value of 7 achieved with unshielded
Alq3 OLEDs.
Towards operation in the t mode
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Concluding Remarks

• OLED science and technology is undergoing
  explosive growth
• Structurally integrated OLED-based sensors are
  very promising
• Organic photovoltaics organic field-effect
  transistors are also growing at an extremely
  rapid clip. They deserve a separate treatment.
  See Sumit Chaudharys ECpE course on Organic
  Electronics.