Absolute quantum efficiency measurements of electrochemiluminescent devices through electrical impedance spectroscopy

Funding: This work was financially supported by the Alexander von Humboldt Foundation (Humboldt Professorship to M.C.G.). C.K.M. acknowledges funding from the European Commission through a Marie Skłodowska Curie individual fellowship (101029807).AC-operating electrochemiluminescent devices (ECLDs) have recently shown a substantial increase in brightness, making them potentially relevant for applications in lighting and displays. To further improve the performance of these liquid-state light-emitting devices, it is essential to reliably assess the absolute quantum efficiency of electrochemiluminescence and the electrochemical reactions leading to exciton formation. However, significant non-faradaic currents occurring under the AC operation schemes make it challenging to quantify the number of charges involved in the electrochemical reactions. Here, faradaic and non-faradaic currents in sandwich-type ECLDs are analysed by electric impedance spectroscopy and to assess the absolute quantum efficiency of the electrochemiluminescence (ΦECL). An equivalent circuit model enables analysis of the current at different voltage amplitudes and operating frequencies. The analysis reveals that non-faradaic currents stem primarily from capacitive currents associated with the formation of electric double-layers near liquid/electrode interfaces. Their contribution to the total current increases at high operating frequencies and low voltages. For ECLDs operating based on an exciplex-formation and energy transfer pathway, the estimated ΦECL and resulting exciton formation efficiency are 0.53% and 27%, respectively. Reverse redox reactions are identified as a significant loss factor, thus indicating potential avenues for future improvements.Peer reviewe

Carpe lucem: harnessing organic light sources for optogenetics

With the advent of optogenetics, numerous functions in cells have been rendered responsive to the experimental delivery of light. The most common implementation of this technique features neurons genetically modified to express light-sensitive ion channel proteins, which open specifically in response to pulses of blue light, triggering electrical impulses in neurons. Optogenetics now has matured to a point where in addition to answering fundamental questions about the function of the brain, scientists begin to consider clinical applications. Further progress in this field however will require new ways of delivering light. One of these involves the use of organic light-emitting diodes (OLEDs), a display technology increasingly common in modern-day smart phones, for the optical stimulation of cells.Postprin

Cellular dye lasers : lasing thresholds and sensing in a planar resonator

This research was supported in part by the U.S. National Science Foundation (ECCS-1101947, ECCS-1505569) and National Institutes of Health (P41 EB015903). M.H. was supported in part by the Marie Curie International Outgoing Fellowship N° 627274 within the 7th European Community Framework Programme. M.C.G. was supported in part by the Starting Grant N° 640012 within the H2020 European Community Framework Programme.Biological cell lasers are promising novel building blocks of future biocompatible optical systems and offer new approaches to cellular sensing and cytometry in a microfluidic setting. Here, we demonstrate a simple method for providing optical gain by using a variety of standard fluorescent dyes. The dye gain medium can be located inside or outside a cell, or in both, which gives flexibility in experimental design and makes the method applicable to all cell types. Due to the higher refractive index of the cytoplasm compared to the surrounding medium, a cell acts as a convex lens in a planar Fabry-Perot cavity. Its effect on the stability of the laser cavity is analyzed and utilized to suppress lasing outside cells. The resonance modes depend on the shape and internal structure of the cell. As proof of concept, we show how the laser output modes are affected by the osmotic pressure.Publisher PDFPeer reviewe

White top-emitting organic light-emitting diodes with solution-processed nano-particle scattering layers

The authors are grateful to Novaled GmbH (Dresden) for financial support and material supply. M. C. Gather acknowledges financial support from the Scottish Founding Council through SUPA.A random scattering approach to enhance light extraction in white top-emitting organic light-emitting diodes (OLEDs) is reported. Through solution processing from fluorinated solvents, a nano-particlescattering layer (NPSL) can be deposited directly on top of small molecule OLEDs without affecting their electrical performance. The scattering length for light inside the NPSL is determined from transmission measurements and found to be in agreement with Mie scattering theory. Furthermore, the dependence of the light outcoupling enhancement on electron transport layer thickness is studied. Depending on the electron transport layer thickness, the NPSL enhances the external quantum efficiency of the investigated white OLEDs by between 1.5 and 2.3-fold. For a device structure that has been optimized prior to application of the NPSL, the maximum external quantum efficiency is improved from 4.7% to 7.4% (1.6-fold improvement). In addition, the scattering layer strongly reduces the undesired shift in emission color with viewing angle.Publisher PDFPeer reviewe

High-brightness organic light-emitting diodes for optogenetic control of Drosophila locomotor behaviour

We thank Simone Lenk and Tobias Günther (TU Dresden) for fruitful discussions and technical support with OLED preparation. We are grateful for financial support from the Scottish Funding Council (through SUPA), Human Frontier Science Program (RGY0074/2013), Wellcome Trust Institutional Strategic Support Fund St Andrews and the RS Macdonald Charitable Trust. C.M. acknowledges funding by the European Commission through a Marie Sklodowska-Curie Individual Fellowship (703387).Organic light emitting diodes (OLEDs) are in widespread use in today’s mobile phones and are likely to drive the next generation of large area displays and solid-state lighting. Here we show steps towards their utility as a platform technology for biophotonics, by demonstrating devices capable of optical controlling behaviour in live animals. Using devices with pin OLED architecture, sufficient illumination intensity (0.3 mW.mm-2) to activate channelrhodopsins (ChRs) in vivo was reliably achieved at low operating voltages (5 V). In Drosophila melanogaster third instar larvae expressing ChR2(H134R) in motor neurons, we found that pulsed illumination from blue and green OLEDs triggered robust and reversible contractions in animals. This response was temporally coupled to the timing of OLED illumination. With blue OLED illumination, the initial rate and overall size of the behavioural response was strongest. Green OLEDs achieved roughly 70% of the response observed with blue OLEDs. Orange OLEDs did not produce contractions in larvae, in agreement with the spectral response of ChR2(H134R). The device configuration presented here could be modified to accommodate other small model organisms, cell cultures or tissue slices and the ability of OLEDs to provide patterned illumination and spectral tuning can broaden their utility in optogenetics experiments further.Publisher PDFPeer reviewe

Snapshot hyperspectral imaging of intracellular lasers

This work received financial support from a UK EPSRC Programme Grant (EP/P030017/1). PW was supported by the 1851 Research Fellowship from the Royal Commission. KD acknowledges support from the Australian Research Council (FL210100099). MCG acknowledges support from the Alexander von Humboldt Foundation (Humboldt professorship).Intracellular lasers are emerging as powerful biosensors for multiplexed tracking and precision sensing of cells and their microenvironment. This sensing capacity is enabled by quantifying their narrow-linewidth emission spectra, which is presently challenging to do at high speeds. In this work, we demonstrate rapid snapshot hyperspectral imaging of intracellular lasers. Using integral field mapping with a microlens array and a diffraction grating, we obtain images of the spatial and spectral intensity distribution from a single camera acquisition. We demonstrate widefield hyperspectral imaging over a 3 × 3 mm2 field of view and volumetric imaging over 250 × 250 × 800 µm3 (XYZ) volumes with a lateral (XY) resolution of 5 µm, axial (Z) resolution of 10 µm, and a spectral resolution of less than 0.8 nm. We evaluate the performance and outline the challenges and strengths of snapshot methods in the context of characterizing the emission from intracellular lasers. This method offers new opportunities for a diverse range of applications, including high-throughput and long-term biosensing with intracellular lasers.Publisher PDFPeer reviewe

Snapshot hyperspectral imaging of intracellular lasers

This work received financial support from a UK EPSRC Programme Grant (EP/P030017/1). PW was supported by the 1851 Research Fellowship from the Royal Commission. KD acknowledges support from the Australian Research Council (FL210100099). MCG acknowledges support from the Alexander von Humboldt Foundation (Humboldt professorship).Intracellular lasers are emerging as powerful biosensors for multiplexed tracking and precision sensing of cells and their microenvironment. This sensing capacity is enabled by quantifying their narrow-linewidth emission spectra, which is presently challenging to do at high speeds. In this work, we demonstrate rapid snapshot hyperspectral imaging of intracellular lasers. Using integral field mapping with a microlens array and a diffraction grating, we obtain images of the spatial and spectral intensity distribution from a single camera acquisition. We demonstrate widefield hyperspectral imaging over a 3×3 mm2 field of view and volumetric imaging over 250×250×800 µm3 volumes with a spatial resolution of 5 µm and a spectral resolution of less than 0.8 nm. We evaluate the performance and outline the challenges and strengths of snapshot methods in the context of characterising the emission from intracellular lasers. This method offers new opportunities for a diverse range of applications, including high-throughput and long-term biosensing with intracellular lasers.Preprin

Open-source tools for the fabrication and characterization of organic electronics

Funding: J.F.B. acknowledges funding from Beverly and Frank MacInnis via the University of St Andrews. This work was supported by the Alexander von Humboldt Foundation (Humboldt Professorship to M.C.G.) and the DFG-funded Research Training Group “Template-Designed Organic Electronics (TIDE)” (RTG2591).By promoting collaborative sharing of knowledge, the open-source movement has catalyzed substantial progress across diverse fields, including software development and artificial intelligence. Similarly, the concept of openly shared hardware has gained attention, due to its cost-effectiveness and the prospect of improved reproducibility. A major motivation for the development of organic electronics is its promise to deliver substantial advantages in price and manufacturability relative to its inorganic counterpart. Here, two open-source tools for organic electronics are introduced: a dip-coating device designed for thin film fabrication and a four-point probe for precisely measuring the resistance of thin films. These tools only cost a fraction of comparable commercial devices and run with open-source software to ensure a user-friendly experience. A case study demonstrates the optimization of simple fluorescent organic light-emitting diodes (OLEDs) using these open-source tools achieving 4% external quantum efficiency (EQE). To characterize these OLEDs, a previously reported open-source setup for accurate efficiency measurements is used. A substantial software upgrade to this setup, which speeds up the characterization of electroluminescence, is also repor. This work contributes open-source hardware and software to the field of organic electronics, thereby lowering the entrance barrier to the field and fostering the involvement of scientists with diverse scientific backgrounds.Peer reviewe

A highly stable and efficient organic microcavity polariton laser

Funding: The authors acknowledge support by the Deutsche Forschungsgemeinschaft (Research Training Group “TIDE”, RTG2591). M.C.G. and F.L.R. acknowledge funding from the Alexander von Humboldt Foundation (Humboldt Professorship to M.C.G. and Humboldt Fellowship to F.L.R.). A.M. acknowledges funding from the European Union’s Horizon 2020 research and innovation programme under Marie Skłodowska-Curie grant agreement No. 101023743 (PolDev). M.C.G. acknowledges funding from the European Research Council under the European Union's Horizon Europe Framework Programme/ERC Advanced Grant agreement No. 101097878 (HyAngle).With their remarkably low thresholds, organic polariton lasers are a promising alternative to organic photonic lasers. However, device stability remains a challenge, in part due to material degradation during deposition of the top dielectric mirror. We demonstrate polariton lasers based on 4,4´-Bis(4-(9H-carbazol-9-yl)styryl)biphenyl (BSBCz) as active material that achieve a low lasing threshold of 8.7 μJ/cm2, and we show that a ZrO2 protection layer between active layer and top mirror significantly improves stability. Optimized devices exhibit minimal degradation after 100,000 excitation pulses at 3.8 times above threshold. Our findings establish BSBCz as an attractive candidate for future injection driven polariton lasers.Peer reviewe