SensLED: An Electro‐Optical Active Probe for Oxygen Determination

Abstract

Optical sensors have been a field of intensive academic as well as industrial research over the last three decades. Clark-type electrodes, [1] for example, have been a standard for many years in oxygen detection; however, they are more and more replaced by optical sensors. Different optical sensor systems, e.g., fiber optic [2] or planar waveguide [3] based platforms, were developed using the optical properties of the analyte itself as well as changes of the optical properties of an intermediate indicator molecule (e.g., organometallic compounds) for analyte detection.To yield analyte information, most common optical transduction techniques used in optical chemical sensors are based on fluorescence [4] or absorption measurements (e.g., nondispersive infrared sensors [5] ). In this context, the class of so-called direct sensors uses a modification of an intrinsic optical property of the analyte, whereas in the case of inappropriate intrinsic optical properties an intermediate analyte-sensitive dye molecule has to be added. The presence of the corresponding analyte alters the optical properties of the indicator dye, thus allowing its detection. Such a sensing technique requires, depending on the phase of the analyte, in most cases an immobilization of the dye within a matrix layer, which provides analyte accessibility but prevents leaching effects. Different approaches for immobilization of indicators within a matrix material have been realized up to now, such as covalent [6,7] bonding or simple encapsulation.[8] Apart from analyte diffusion coefficients within the matrix, [9] sensitivity as well as sensor response time strongly depend on indicatormatrix interactions.[10] Due to these interactions, spectroscopic shifts [11] and enhanced or reduced excited state lifetimes [12,13] are frequently observed in the solid state compared to solution. Nevertheless, embedding the dye molecule within a rigid matrix enhances the photostability due to reduced ligand photodegradation. [14] Along this line, optical oxygen probes commonly use platinum [15] or palladium [16] based organometallic complexes as indicator molecules. Spin orbit coupling is enhanced because of the metal ion within the organic complex; this enables an efficient radiative decay from the lowest triplet state to the singlet ground state of the molecule (phosphorescence). Because spin orbit coupling is weak in fluorescent materials, a radiative decay from an excited triplet state is unlikely. The phosphorescence lifetime of organometallic complexes is, depending on the transient metal complex and the matrix material, in the range of microseconds, which is several orders of magnitude larger than the fluorescent excited state lifetime. Most reagent-mediated optical oxygen sensors use dynamic interactions between the excited state of the dye molecule and the analyte. Since molecular contact is required for this kind of interaction, the analyte has to reach the immobilized dye molecule within its excited state lifetime. Taking into consideration the physical para...

Organic Light‐Emitting Diode Sensing Platform: Challenges and Solutions

“…As examples, luminescent conjugated polymers have been used to gain insight into biology and pathology of protein aggregation diseases,2 and for designing electrochemical switches and ion pumps for cell biology studies 3, 4. Organic thin film transistors (OTFTs) were implemented to develop cost‐effective and label‐free DNA or protein sensor chips,5 and organic light‐emitting diodes (OLEDs) have been evaluated as excitation sources in photoluminescence (PL)‐based sensing of analytes such as oxygen, ethanol, glucose, lactate, and cholesterol 1, 6–13. Other examples of the use of OLEDs (including polymer LEDs (PLEDs)) in sensing applications include an integrated PL‐based oxygen and pH sensor, utilizing an OLED as the light source and an organic photodetector (PD);13, 16 two polarizers were used for separating the PL and the OLED's electroluminescence (EL) 13.…”

“…As such, the potential of OLEDs to be used in badge‐size and miniaturized sensor arrays surpasses that of other excitation sources. Indeed, compact structures with OLEDs and thin‐film Si‐ or organic‐based PDs have been demonstrated, including with operation in the time domain 6–11, 23–25 . Figure a shows schematically the integrated OLED/sensing film configuration operated in the back‐detection geometry, with the photomultiplier tube (PMT) PD behind the OLED pixels.…”

“…The detection of oxygen in this work is based on monitoring O 2 ‐induced changes in the PL intensity ( I ) or PL decay time ( τ ) of the oxygen sensitive dye Pt octaethylporphyrine (PtOEP) embedded in a polystyrene (PS) matrix 1, 6–11, 23–25, 33, 34. Analysis was based on the well known Stern‐Volmer (SV) equation 1, 6…”

Direct Sub‐Micrometer‐Patterning of Conjugated Polymers and Polymer Light‐Emitting Devices by Electron Beam Lithography

“…Up to now a multitude of possible applications, like polymer light emitting diodes (PLEDs) [1] and light sources, [2] light emitting electrochemical cells (LECs), [3] optically pumped lasers, [4] solar cells, [5] active sensor devices, [6] photo detectors, [7] and field effect transistors [8] have been realized. Nevertheless, one of the greatest benefits of polymeric materials simultaneously limits their applicability for the fabrication of patterned and integrated devices: because of the commonly used solution-based deposition methods,…”

A method to determine the presence of oxygen in organic light-emitting diodes (OLEDs)

“…the host. A device with poly(N-vinylcarbazole) (PVK) as an emitting host was doped with PtOEP and sensed dry O 2 in lifetime and intensity modes(22). Great care was taken to ensure oxygen permeation into the PtOEP/PVK emitting layer, by excluding transport and blocking layers that could impede the oxygen from reaching the PVK/PtOEP layer and by depositing an aluminum cathode with very narrow dimensions.…”