This PDF file contains the front matter associated with SPIE Proceedings Volume 6659, including the Title Page, Copyright information, Table of Contents, Introduction (if any), and the Conference Committee listing.

In this paper we propose totally flexible organic field effect transistors (OFETs) assembled on plastic films as sensors for physiological parameters monitoring. In the first part, mechanical sensors for pressure and bending detection are presented and some biomedical sensing applications are illustrated. A sharp and reversible sensitivity of the output current of the device to an elastic deformation induced by means of a mechanical stimulus on the device channel is observed. In the second part, the possibility of using similar devices for bio- and chemo-detection is described. By exploiting the properties of the basic structure, the device can be combined with any kind of substrate to detect for instance the 3D bending of a flexible surface and/or for detecting pH of sweat. Robot skin and wearable electronics seem to be promising applications for this emerging technology.

A bipyridazine fluorophore, DHP2, was explored as a pH sensor. A solution of bipyridazine showed fluorescence intensity decrease as acid was added to the solution. The fluorescence intensity of the solution containing DHP2 was highly sensitive to acidic solution in the range from 2 to 9.7, with a Stern-Volmer quenching constant of K'_acid as 9.7. However, the fluorescence intensity of DHP2 dissolved solution was not significantly changed by the addition of base. DHP2 was successfully doped in a transparent polymer to afford a thin film sensor. The fluorescent polymer film sensor was able to detect pH in the range from 3 to 12.

Recent developments in the structurally integrated OLED-based platform of luminescent chemical and biological sensors are reviewed. In this platform, an array of OLED pixels, which is structurally integrated with the sensing elements, is used as the photoluminescence (PL) excitation source. The structural integration is achieved by fabricating the OLED array and the sensing element on opposite sides of a common glass substrate or on two glass substrates that are attached back-to-back. As it does not require optical fibers, lens, or mirrors, it results in a uniquely simple, low-cost, and potentially rugged geometry. The recent developments on this platform include the following: (1) Enhancing the performance of gas-phase and dissolved oxygen sensors. This is achieved by (a) incorporating high-dielectric TiO₂ nanoparticles in the oxygen-sensitive Pt and Pd octaethylporphyrin (PtOEP and PdOEP, respectively)- doped polystyrene (PS) sensor films, and (b) embedding the oxygen-sensitive dyes in a matrix of polymer blends such as PS:polydimethylsiloxane (PDMS). (2) Developing sensor arrays for simultaneous detection of multiple serum analytes, including oxygen, glucose, lactate, and alcohol. The sensing element for each analyte consists of a PtOEP-doped PS oxygen sensor, and a solution containing the oxidase enzyme specific to the analyte. Each sensing element is coupled to two individually addressable OLED pixels and a Si photodiode photodetector (PD). (3) Enhancing the integration of the platform, whereby a PD array is also structurally integrated with the OLED array and sensing elements. This enhanced integration is achieved by fabricating an array of amorphous or nanocrystalline Si-based PDs, followed by fabrication of the OLED pixels in the gaps between these Si PDs.

A compact, photoluminescence (PL)-based sensor array, utilizing tris(quinolinolate) Al OLED pixels as the excitation sources, for sequential or simultaneous monitoring of dissolved oxygen (DO), glucose, lactate, and alcohol, is described. The DO is monitored through its effect on the PL lifetime of the oxygen-sensitive dye Pt octaethylporphyrin (PtOEP) embedded in a polystyrene film. The other analytes are monitored through their oxidation, catalyzed by an appropriate oxidase, which reduces the amount of DO in their vicinity. The OLED pixels are fabricated on a glass substrate; each pixel is typically 2×2 mm², with a 2 mm gap between the pixels. Two OLED pixels are associated with the detection of each of the analytes. The pixels are individually addressable, enabling consecutive detection of the different analytes within a few minutes utilizing a single photodetector (PD). Simultaneous detection is achieved by using an array of PDs. The OLED-based sensing array is compact and uniquely simple in its ease of fabrication and integration. Its performance attributes are comparable to those obtained for a single analyte using any excitation source. The potential of small-size, multi-color OLED pixel arrays for multianalyte detection is also discussed.

The introduction in the market of ubiquitous sensing applications relies heavily on the availability of affordable sensors. Key in the cost of a sensor is its modus of manufacture. In this paper a sensing scheme is presented, in which the signal transduction is based on an induced change in the optical path between an organic light emitting diode (OLED) and an organic photovoltaic (OPV) array. Using this platform, several aspects of cost efficient manufacturing technology are investigated. These aspects include the intrinsic printability of the active (OLED, responsive coating and OPV) components, which allows control of the local sensor functionality and sensitivity. It offers a large amount of freedom in sensor layout, while using relatively few process steps. Also investigated is the ability to realize the active devices on foil, which enables high throughput processing (e.g. in a reel-to-reel scheme). Moreover, the presented generic sensing scheme is of a modular design. It allows easy switching of the sensor functionality mostly by simply changing the transduction module. Since this does not affect the production parameters of the other components, these may be standardized, thus invoking favorable economies of scale.

We demonstrate the feasibility of organic semiconductor lasers as light sources for lab-on-a-chip systems. These lasers are based on a 1D- or 2D-photonic crystal resonator structure providing optical feedback in the active laser material that is deposited on top, e.g. aluminum tris(8-hydroxyquinoline) (Alq₃) doped with the laser dye 4-dicyanomethylene-2-methyl-6-(p-dimethylaminostyryl)-4H-pyran (DCM). We investigated different fabrication methods for the resonator structures, like thermal nanoimprint, UV nanoimprint, and laser interference lithography. Different substrate materials commonly used in lab-on-a-chip systems, e.g. PMMA, Topas, and Ormocer were deployed. By changing the distributed feedback grating periodicity, we demonstrate a tuning range for a single material system of more than 120 nm. The investigated organic semiconductor lasers are optically pumped. External optical pumping provides a feasible way for one-time-use chips. Our recent success of pumping organic lasers with a low-cost laser diode also renders hand-held systems possible. As a further step towards the integration of organic lasers in sensor systems, we demonstrate the coupling of an organic laser into polymeric waveguides which can be combined with microfluidic channels. The integrated organic lasers and the waveguides are both fabricated on the same polished PMMA substrate using thermal nanoimprint lithography and deep-UV modification, respectively. We could demonstrate the guiding of the laser light in single-mode waveguides.

Organic thin film transistor (OTFT) sensors are capable of fast, sensitive and reliable detection of a variety of analytes. They have been successfully tested towards many chemical and biological "odor" molecules showing high selectivity, and displaying the additional advantage of being compatible with plastic technologies. Their versatility is based on the possibility to control the device properties, from molecular design up to device architecture. Here phenylene-thiophene based organic semiconductors functionalized with ad hoc chosen side groups are used as active layers in sensing OTFTs. These materials, indeed, combine the detection capability of organic molecules (particularly in the case of bio-substituted systems) with the electronic properties of the conjugated backbone. A new OTFT structure including Langmuir-Schäfer layer by layer organic thin films is here proposed to perform chemical detection of organic vapors, including vapor phase chiral molecules such as citronellol vapors, with a detection limit in the ppm range. Thermally evaporated α6T based OTFT sensors are used as well to be employed as standard system in order to compare sensors performances.

Ionic self-assembled multilayers (ISAMs) adsorbed on long period fiber gratings (LPGs) can serve as an inexpensive, robust, portable, biosensor platform. The ISAM technique is a layer-by-layer deposition technique that creates thin films on the nanoscale level. The combination of ISAMs with LPGs yields exceptional sensitivity of the optical fiber transmission spectrum. We have shown theoretically that the resonant wavelength shift for a thin-film coated LPG can be caused by the variation of the film's refractive index and/or the variation of the thickness of the film. We have experimentally demonstrated that the deposition of nm-thick ISAM films on LPGs induces shifts in the resonant wavelength of > 1.6 nm per nm of thin film. It has also been shown that the sensitivity of the LPG to the thickness of the ISAM film increases with increased film thickness. We have further demonstrated that ISAM-coated LPGs can function effectively as biosensors by using the biotin-streptavidin system and by using the Bacillus anthracis (Anthrax) antibody- PA (Protective Antigen) system. Experiments have been successfully performed in both air and solution, which illustrates the versatility of the biosensor. The results confirm that ISAM-LPGs yield a reusable, thermally-stable, and robust platform for designing and building efficient optical biosensors.

Steps towards the improvement of a compact photoluminescence (PL)-based sensor array that is fully structurally integrated are described. The approach is demonstrated for oxygen sensing, which can be monitored via its effect on the PL intensity I or decay time τ of oxygen-sensitive dyes such as Pt octaethylporphryn (PtOEP) and its Pd analog (PdOEP). The integrated components include (1) an organic light emitting device (OLED) excitation source, which is an array of coumarin-doped tris(quinolinolate) Al (Alq₃) pixels, (2) the sensor film, i.e., PdOEP embedded in polystyrene, and (3) the photodetector (PD), which is a plasma-enhanced CVD-grown p-i-n or n-i-p structure, based on amorphous or nanocrystalline (Si,Ge):H. These components are fabricated on common or separate substrates that are attached back-to-back, resulting in sensors with a thickness largely determined by that of the substrates. The fully integrated oxygen sensor is demonstrated first by fabricating each of the three components on a separate substrate. The PD was placed in front of a flow cell containing the sensor film, while the OLED array was "behind" the sensor film. This design showed the expected trend in monitoring different concentration of O₂ via their effect on I, with improved detection sensitivity achieved by shielding the electromagnetic noise synchronous with the pulsed OLED. The detection sensitivity using the I monitoring mode is expected to further increase by reducing the OLED tail emission. The issue of the OLED background can be eliminated by monitoring the oxygen concentration via its effect on τ, where the OLED is pulsed and τ is measured while the OLED is off. Steps therefore focused also on shortening the response time of the PDs, and understanding the factors affecting their speed. Development of a sensor array, where the PD pixels are fabricated between the OLED pixels on the same side of a common substrate, is also discussed.