We describe chemically sensitive organic transistors in which the semiconductor film consists of a base layer of a high
mobility p- or n-channel molecular solid, and an overlayer contains analogous compounds terminated with hydroxy
functional groups. Such devices respond to dimethyl methylphosphonate at concentrations on the order of 100 ppb and
on time scales <1 minute. Semiconductor cores include diphenylbithiophene and naphthalenetetracarboxylic diimide,
with OH end groups in some cases. End groups include both alkyl and phenolic OH. Devices are as thin as four
monolayers. Sensitivity is highly gate dependent, and means of ensuring the gate setting for maximum response are
proposed. Contrasting response to dinitrotoluene, a component of nitroaromatic explosive vapors, is reported. Finally,
the influence of the channel versus near-contact regions on the vapor-induced changes in resistance is evaluated.
A first generation dendrimer comprised of a 9,9,9',9'-tetra-n-hexyl substituted 2,2'-bifluorene core, biphenyl dendrons,
and 2-ethylhexyloxy surface groups can rapidly detect high electron affinity, explosive-related analytes such as pnitrotoluene
and 2,4-dinitrotoluene. Stern-Volmer analysis of the dendrimer in solution showed that the quenching could
be either collisional or static but not a combination of the two mechanisms. The Stern-Volmer analysis was found to be
critically dependent on correcting for the absorption of the analyte at the excitation wavelength and the inner filter effect.
Films of the dendrimer were found to have a measurable decrease in the PL for all the nitroaromatic analytes in seconds.
The luminescence of the films could be recovered on removal of the analyte. It was found that both thin (25 nm) and
thick (80 nm) films showed a rapid response to the analytes but for the less volatile analytes the final level of quenching
was less for the thicker films.
Molecular probes for selective identification of biomolecular targets are important to advance our understanding of the
molecular mechanisms underlying pathological events and for clinical diagnostic of specific diseases. Luminescent
conjugated polythiophenes (LCPs) have been utilized as colorimetric and fluorescent sensing elements for the recording
of biological processes, such as DNA-hybridization and ligand-receptor interactions. However, LCPs have several
limitations for being used as real time in vivo imaging agents. In this regard, novel thiophene based molecular scaffold,
denoted luminescent conjugated oligothiophenes (LCOs) have been developed. The LCOs are chemically defined
molecules having distinct side chain functionalizations and a precise number of thiophene units. Properly functionalized
LCO showed a striking specificity and selectivity towards distinct molecular targets, such as protein aggregates under
physiological conditions. The protein aggregates were easily identified due to the conformation-dependent emission
profile from the LCOs and spectral assignment of protein aggregates both in vitro and in ex vivo tissue samples could be
obtained. It was also shown that LCOs could be used for live imaging of intracellular molecules and compartments in
cells. Overall, we demonstrate that LCOs have the potential of being utilized as powerful practical research tools for
studying biological processes in real time.
Proc. SPIE 7418, Sniffing out cancer in the breath: detection of non-polar volatile compounds through carrier scattering in random networks of carbon nanotubes, 741809 (21 August 2009); doi: 10.1117/12.824444
Exhaled breath of cancer patients contains certain nonpolar volatile organic compounds (VOCs)
which are not present in the breath of a healthy person. An electronic nose composed of an array
of random network (RN) of carbon nanotube (CNT) sensors could in principle detect cancer from
breath, but the notoriously low sensitivity of CNT sensors to nonpolar VOCs limits their accuracy.
We have achieved a marked improvement of the RN-CNT chemiresistors' response to the nonpolar
VOCs found in the breath of lung cancer patients by functionalizing them with different types of
nonpolymeric organic films as well as discontinuous films composed of sponge-like wires of
hexaperi-hexabenzocoronene (HBC) molecules. By monitoring the changes in conductance, work
function and organic film thickness during exposure we show that the enhanced sensitivity of the
functionalized RN-CNTs to nonpolar cancer biomarkers stems from carrier scattering induced by
swelling of the organic film. Based on these findings, we show that an array of RN-CNT sensors
can discriminate between the VOCs found in the breath of patients with lung cancer and in healthy
controls. Hence, controlling the carrier scattering in RN-CNTs via deliberate functionalization
with suitable organic films could become an important factor in the design of sensors for nonpolar
VOCs, which have hitherto been difficult to trace. The results presented here are an important
step towards the development of a robust, cost effective electronic nose for sniffing out nonpolar
VOCs as biomarkers for cancer in patients' breath.
We present optofluidic lab-on-a-chip devices (LOCs) for single use as disposables. In our approach we are aiming for
systems out of poly(methyl methacrylate) (PMMA) that integrate (a) organic lasers, (b) optical waveguides, (c)
microfluidic channels, (d) surface functionalization, and (e) fluorescence excitation on one single chip. We are utilizing
mass production techniques to show the applicability of this approach by avoiding electrical interconnects but using
optical and fluidic interfaces only. With our experiments we can show the feasibility of this approach by respectively
combining two consecutive elements (a - e) of the path of light: Organic semiconductor lasers are integrated by
evaporating a thin film of photoactive material on top of a distributed feedback (DFB) grating. For this purpose, grating
masters are replicated by hot embossing into PMMA bulk material. The lasing wavelength in the visible light regime is
tuned by altering the thickness of the vacuum deposited organic semiconductor active material or the DFB grating
period. Emitted light from the DFB laser is coupled into polymer strip optical waveguides realized by Deep UV
lithography. The waveguides allow optical guidance to a microfluidic channel. Tailored surface functionalization in the
microfluidic channel by Dip-Pen Nanolithography (DPN) enables the local excitation of fluorescent markers and thus a
detection of selected components in biomedical or environmentally relevant fluids.
Since oxygen concentration is a critical parameter in various applications optical gas sensors are a field of
intensive academic as well as industrial research. Nowadays indicator based optical oxygen sensors comprises in
most cases a light source an immobilized transition metal complex for analyte determination and a detector
system. In view of the fact that miniaturization of sensor elements is a key requirement, a novel electro-optical
sensor device comprising the sensing as well as the light emitting functionality within one layer is demonstrated.
This approach bridges the gap between organic light emitting devices (OLEDs), where transition metal
complexes are used for device efficiency enhancement and classical optical oxygen probes. Based on a OLEDs
comprising platinum-octaethylporphyrin immobilized in a poly(9-vinylcarbazole) we demonstrated the
versatility of this new approach. Furthermore we were able to determine the indicator analyte interaction
principle and showed the reversibility of this process.
Typical guest-host small molecular OLEDs (SMOLEDs) exhibit an emission spike at 100 - 200 ns and a tail that
extends over several μs following a bias pulse. The spike and tail are attributed to recombination of correlated
charge pairs and detrapped charges (mostly from the host shallow states), respectively. They may also be associated
with other OLED layers and other phenomena, e.g., triplet-triplet annihilation. The implications of the spike and tail
for OLED-based, photoluminescent oxygen sensors operated in the time domain are evaluated and compared to the
behavior observed when using undoped OLEDs or inorganic LEDs as the excitation sources.
A photoluminescence (PL)-based O2 sensor utilizing inorganic light emitting diode (LED) as the light source and a
polymer-based photodetector (PD) is demonstrated. The device structure is compact and the sensor integrates the sensing
element, light source, and organic PD as thin films that are attached such that the sensing element is sandwiched between
the LED and the PD. The sensing elements are based on the oxygen-sensitive dyes Pt-octaethylporphyrin embedded in a
polystyrene matrix. A green inorganic LED (peak emission ~525 nm) light source was used to excite the porphyrin dye,
which emits at ~640 nm. This emission can be measured using P3HT:PCBM bulk heterojunction photodiodes, which
have been shown earlier to have efficient photodetection at this wavelength if the active layer is sufficiently thick. The
time constant associated with sweeping out the photogenerated carriers is found to be ~ 10μs. Such a fast decay of
photocurrent is useful for oxygen monitoring, determined by measuring the Pl decay time rather than the PL intensity, of
the sensing film. This approach can eliminate the need for frequent sensor calibration and optical filters (as pulsed LED
excitation is employed in this mode) which lead to bulkier design.
We demonstrate a polymer photodetector with spectral response from 300nm to 1450nm by using a
narrow-band-gap semiconducting polymer blended with a fullerene derivative. Operating in room temperature, the polymer
photodetectors exhibit detectivity greater than 1013Jones (1Jones =1cm Hz1/2/W) from the UV well into the near-infrared
out to 1150nm and greater than 1012Jones from 1150nm to 1450nm. The linear dynamic range is over 100dB. To our
knowledge, there is no inorganic material system (not even Si-Ge alloys) capable of such high performance
photodetectivty over such a wide spectral range.
Stretchability significantly expands the scope of electronic applications-particularly large-area electronics such as
displays, sensors, and actuators-because stretchable electronics can cover arbitrary surfaces and movable parts, which is
impossible with conventional electronics. However, the realization of stretchable electronics for the manufacturing of
electrical wiring with high conductivity, high stretchability, and large-area compatibility is a major hurdle. We
manufactured printable elastic conductors comprising single-walled carbon nanotubes (SWNTs) uniformly dispersed in
fluorinated rubber. Using ionic liquid and jet milling, we produced longer and finer SWNT bundles that formed
well-developed conducting networks in rubber. A conductivity and stretchability greater than 100 S/cm and 100%,
respectively, were obtained. In order to demonstrate the feasibility of the elastic conductors for electrical wiring, we
manufactured a rubber-like large-area organic transistor active matrix comprising printed organic transistors and elastic
conductors. The effective area of the matrix was 20 × 20 cm2. The active matrix sheet was uniaxially and biaxially
stretched to 70% without incurring mechanical or electrical damage. Furthermore, we constructed a rubber-like
stretchable active matrix display comprising integrated printed elastic conductors, organic transistors, and organic
light-emitting diodes. The display could stretch by 30-50% and spread over a hemisphere without being mechanically or
Organic light-emitting diode (OLED)-based sensing platforms are attractive for photoluminescence (PL)-based
monitoring of a variety of analytes. Among the promising OLED attributes for sensing applications is the thin and
flexible size and design of the OLED pixel array that is used for PL excitation. To generate a compact, fielddeployable
sensor, other major sensor components, such as the sensing probe and the photodetector, in addition to
the thin excitation source, should be compact. To this end, the
OLED-based sensing platform was tested with
composite thin biosensing films, where oxidase enzymes were immobilized on ZnO nanoparticles, rather than
dissolved in solution, to generate a more compact device. The analytes tested, glucose, cholesterol, and lactate, were
monitored by following their oxidation reactions in the presence of oxygen and their respective oxidase enzymes.
During such reactions, oxygen is consumed and its residual concentration, which is determined by the initial
concentration of the above-mentioned analytes, is monitored. The sensors utilized the oxygen-sensitive dye Pt
octaethylporphyrin, embedded in polystyrene. The enzymes were sandwiched between two thin ZnO layers, an
approach that was found to improve the stability of the sensing probes.