Martin Tscherner

Opto-chemical method for ultra-low oxygen transmission rate measurement

A highly sensitive alternative to established methods for measuring oxygen transmission rates of ultra-barrier membranes is presented. The key idea is the employment of an opto-chemical sensor (a luminescent dye immobilized in a matrix) which has vital advantages over electrochemical sensors, such as consumption-less detection and extraordinary sensitivity. The luminescent response to modulated light, which is altered in the presence of oxygen, is recorded by an opto-electronic instrument in a non-invasive manner. Provided with said sensing system, a reusable stand-alone permeation cell was developed. Unlike in conventional devices, the permeating oxygen is accumulated while being simultaneously monitored. The demonstrator unit achieves a limit of detection in the 10−5 cm3 m−2 day−1 bar−1 regime. It is therefore among the most sensitive O2 permeability testers, outperforming commercial instruments by two orders of magnitude, yet offering reusability and similar convenience in operation.

Synthesis and characterization of naphthalimide-functionalized polynorbornenes

Highly fluorescent and photostable (2-alkyl)-1H-benzo[de]isoquinoline-1,3(2H)-diones with a polymerizable norbornene scaffold have been synthesized and polymerized using ring-opening metathesis polymerization. The monomers presented herein could be polymerized in a living fashion, using different comonomers and different monomer ratios. All obtained materials showed good film-forming properties and bright fluorescence caused by the incorporated push–pull chromophores. Additionally, one of the monomers containing a methylpiperazine functionality showed protonation-dependent photoinduced electron transfer which opens up interesting applications for logic gates and sensing.Graphical abstract

Simultaneously monitoring of tissue O 2 and CO 2 partial pressures by means of miniaturized implanted fiber optical sensors

A novel opto-chemical sensor instrumentation based on fiber optical micro-sensors for the simultaneous detection of pO2 and pCO2 in tissues is presented. The adopted sensing principle for both parameters is the measurement of luminescence lifetime via phase modulation fluorometry. Respect to currently used blood-gas analysers that require blood sampling and are associated with blood loss, this instrumentation allows on-line continuous measurements. Compared to electrochemical micro sensors, it is advantageous because of intrinsic higher sensitivity, no analyte consumption and less electromagnetic interferences. The results of the laboratory characterization and of tests in in vivo experiments of the proposed instrumentation are reported.

Dye functionalized-ROMP based terpolymers for the use as a light up-converting material via triplet–triplet annihilation

In this paper we introduce and compare different terpolymers comprising covalently attached sensitizer and emitter chromophores for the use as a light up-converting material via triplet–triplet annihilation (TTA). Using the advantages of ring opening metathesis polymerisation it was possible to prepare five different polymer architectures in order to investigate the influence of polymer architecture and chromophore arrangement on the photon up-conversion behaviour. First, two new monomers containing the chromophores have been synthesized and characterized in regard to their photophysical characteristics suitable for triplet–triplet annihilation dye pair. For this purpose, a derivative of Pt(II) meso-tetraphenyltetra(tert-butyl)benzoporphyrin as sensitizer and a perylenediester as emitter were attached to norbornene moieties via ester linkages. Polymerisations of these monomeric chromophores were performed in combination with dimethyl 5-norbornene-2,3-dicarboxylate as matrix monomer. Depending on the location of the dye molecules on the polymer chain, large differences in the TTA efficiency were observed. The best quantum yields have been achieved with a completely statistically distributed terpolymer showing an up-conversion quantum yield of up to 3% in solution.

Optochemical sensor based on screenprinted fluorescent sensorspots surrounded by organic photodiodes for multianalyte detection

A compact, integrated photoluminescence based oxygen sensor, utilizing an organic light emitting device (OLED) as the light source and an organic photodiode (OPD) as the detection unit, is described. The detection system of the sensor array consists of an array of circular screen-printed fluorescent sensor spots surrounded by organic photodiodes as integrated fluorescence detectors. The OPD originates from the well-known Tang photodiode, consisting of a stacked layer of copper phthalocyanine (CuPc, p-type material) and perylene tetracarboxylic bisbenzimidazole (PTCBi, n-type material). An additional layer of tris-8-hydroxyquinolinatoaluminium (Alq3, n-type material) was inserted between the PTCBi layer and cathode. An ORMOCERR layer was used as encapsulation layer. For excitation an organic light emitting diode is used. The sensor spot and the detector are processed on the same flexible substrate. This approach not only simplifies the detection system by minimizing the numbers of required optical components - no optical filters have to be used for separating the excitation light and the luminescent emission-, but also has a large potential for low-cost sensor applications. The feasibility of the concept is demonstrated by an integrated oxygen sensor, indicating good performance. Sensor schemes for other chemical parameters are proposed.

Optochemical sensors based on polymer nanofibers with ultra-fast response characteristics

For most “simple” analytes (e.g. oxygen), the actual sensing element of optochemical sensors consists of a luminescent dye embedded in a polymeric matrix whose luminescence intensity and decay time correlates with the analyte concentration. The response characteristics of these sensors are limited by the time requirement for diffusion and equilibration of the analyte in the bulk of the matrix material. Traditionally, the sensor formulation is cast onto a substrate as a compact layer. Thin layers result in good response speed but poor signal intensity and signal-to-noise ratio, respectively. By means of electrospinning, many polymers can be processed to nanofibers, resulting in a highly-porous textile-like layer with high surface-to-volume ratio and superb analyte accessibility. Doped with fluorescent dyes, such fiber layers are well suited for fast sensing applications where the response time is a critical issue. It was shown that by electrospinning of a typical oxygen sensor formulation (PtTFPP immobilized in polystyrene), that the response time t90 can be accelerated from several seconds to less than 40ms at comparable general sensor performance. This work focuses on the long-term operational stability of such nanofiber based optical sensors. No pronounced tendency for degradation could be observed in long-term stress tests.

A study on Aerosol jet printing technology in LED module manufacturing

State of the art fabrication of LED modules based on chip-on-board (COB) technology comprises some shortcomings both with respect to the manufacturing process itself but also with regard to potential sources of failures and manufacturing impreciseness. One promising alternative is additive manufacturing, a technology which has gained a lot of attention during the last years due to its materials and cost saving capabilities. Especially direct-write technologies like Aerosol jet printing have demonstrated advantages compared to other technological approaches when printing high precision layers or high precision electronic circuits on substrates which, as an additional advantage, also can be flexible and 3D shaped. Based on test samples and test structures manufactured by Aerosol jet printing technology, in this context we discuss the potentials of additive manufacturing in various aspects of LED module fabrication, ranging from the deposition of the die-attach material, wire bond replacement by printed electrical connects as well as aspects of high-precision phosphor layer deposition for color conversion and white light generation.