OLED microdisplays control cell behavior through optogenetics

M.C. Gather acknowledges funding from Marie Curie Career Integration Grant (PCIG45-GA-2012-334407), from the Scottish Funding Council (via SUPA), and from the RS Macdonald Charitable Trust.OLED microdisplays are introduced as a microscopic illumination platform for cell biology. The μm-scale dimensions of each pixel and the μm-thin encapsulation enable controlled light exposure of individual live cells. This breakthrough is facilitated by recent progress in ultrathin metal electrodes and by quality control via high resolution hyperspectral imaging.PostprintPeer reviewe

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

Optimizing the internal electric field distribution of alternating current driven organic light-emitting devices for a reduced operating voltage

This work was funded with financial means of the European Social Fund and the Free State of Saxony through the OrthoPhoto project.The influence of the thickness of the insulating layer and the intrinsic organic layer on the driving voltage of p-i-n based alternating current driven organic light-emitting devices (AC-OLEDs) is investigated. A three-capacitor model is employed to predict the basic behavior of the devices, and good agreement with the experimental values is found. The proposed charge regeneration mechanism based on Zener tunneling is studied in terms of field strength across the intrinsic organic layers. A remarkable consistency between the measured field strength at the onset point of light emission (3-3.1 MV/cm) and the theoretically predicted breakdown field strength of around 3 MV/cm is obtained. The latter value represents the field required for Zener tunneling in wide band gap organic materials according to Fowler-Nordheim theory. AC-OLEDs with optimized thickness of the insulating and intrinsic layers show a reduction in the driving voltage required to reach a luminance of 1000 cd/m2 of up to 23% (8.9 V) and a corresponding 20% increase in luminous efficacy.Publisher PDFPeer reviewe

Integration of spectral coronagraphy within VIPA-based spectrometers for high extinction Brillouin imaging

This work was supported in part by the National Institutes of Health (K25EB015885, R33CA204582, U01CA202177); National Science Foundation (CMMI-1537027) and Human Frontier Science Program (Young Investigator Grant RGY0074).VIPA (virtually imaged phase array) spectrometers have enabled rapid Brillouin spectrum measurements and current designs of multi-stage VIPA spectrometers offer enough spectral extinction to probe transparent tissue, cells and biomaterials. However, in highly scattering media or in the presence of strong back-reflections, such as at interfaces between materials of different refractive indices, VIPA-based Brillouin spectral measurements are limited. While several approaches to address this issue have recently been pursued, important challenges remain. Here we have adapted the design of coronagraphs used for exosolar planet imaging to the spectral domain and integrated it in a double-stage VIPA spectrometer. We demonstrate that this yields an increase in extinction up to 20 dB, with nearly no added insertion loss. The power of this improvement is vividly demonstrated by Brillouin imaging close to reflecting interfaces without index matching or sample tilting.PostprintPeer 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

Organic lasers: recent developments on materials, device geometries, and fabrication techniques

MCG acknowledges financial support through the ERC Starting Grant ABLASE (640012) and the European Union Marie Curie Career Integration Grant (PCIG12-GA-2012-334407). AJCK acknowledges financial support by the German Federal Ministry for Education and Research through a NanoMatFutur research group (BMBF grant no. 13N13522).Organic dyes have been used as gain medium for lasers since the 1960s, long before the advent of today’s organic electronic devices. Organic gain materials are highly attractive for lasing due to their chemical tunability and large stimulated emission cross section. While the traditional dye laser has been largely replaced by solid-state lasers, a number of new and miniaturized organic lasers have emerged that hold great potential for lab-on-chip applications, biointegration, low-cost sensing and related areas, which benefit from the unique properties of organic gain materials. On the fundamental level, these include high exciton binding energy, low refractive index (compared to inorganic semiconductors), and ease of spectral and chemical tuning. On a technological level, mechanical flexibility and compatibility with simple processing techniques such as printing, roll-to-roll, self-assembly, and soft-lithography are most relevant. Here, the authors provide a comprehensive review of the developments in the field over the past decade, discussing recent advances in organic gain materials, which are today often based on solid-state organic semiconductors, as well as optical feedback structures, and device fabrication. Recent efforts toward continuous wave operation and electrical pumping of solid-state organic lasers are reviewed, and new device concepts and emerging applications are summarized.PostprintPeer reviewe

Segment-specific optogenetic stimulation in Drosophila melanogaster with linear arrays of organic light-emitting diodes

This research was financially supported by the EPSRC NSF-CBET lead agency agreement (EP/R010595/1, 1706207), the DARPA-NESD programme (N66001-17-C-4012) and the Leverhulme Trust (RPG-2017-231). C.M. acknowledges funding from the European Commission through a Marie Skłodowska Curie individual fellowship (703387). S.R.P acknowledges funding from the Biology and Biotechnology Research council (BB/M021793). M.C.G. acknowledges funding from the Alexander von Humboldt Stiftung (Humboldt-Professorship).Optogenetics allows light-driven, non-contact control of neural systems, but light delivery remains challenging, in particular when fine spatial control of light is required to achieve local specificity. Here, we employ organic light-emitting diodes (OLEDs) that are micropatterned into linear arrays to obtain precise optogenetic control in Drosophila melanogaster larvae expressing the light-gated activator CsChrimson and the inhibitor GtACR2 within their peripheral sensory system. Our method allows confinement of light stimuli to within individual abdominal segments, which facilitates the study of larval behaviour in response to local sensory input. We show controlled triggering of specific crawling modes and find that targeted neurostimulation in abdominal segments switches the direction of crawling. More broadly, our work demonstrates how OLEDs can provide tailored patterns of light for photo-stimulation of neuronal networks, with future implications ranging from mapping neuronal connectivity in cultures to targeted photo-stimulation with pixelated OLED implants in vivo.Publisher PDFPeer reviewe

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