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

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

Accurate efficiency measurements of organic light-emitting diodes via angle-resolved spectroscopy

Funding: EPSRC NSF-CBET lead agency agreement (EP/R010595/1, 1706207), the Leverhulme Trust (RPG-2017-231), the Volkswagen Foundation (No. 93404), and the Alexander von Humboldt Stiftung (Humboldt-Professorship to M.C.G.). C.K. acknowledges support from the Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education (2017R1A6A3A03012331). Diese Arbeit wurde mitfinanziert durch Steuermittel auf der Grundlage des vom Sächsischen Landtag beschlossenen Haushaltes.The accurate characterization of thin-film LEDs – including organic light emitting diodes (OLEDs), perovskites and quantum dot LEDs – is crucial to our understanding of the factors that influence their efficiency and thus to the fabrication of LEDs with improved performance and stability. In addition, detailed information about the angular characteristics of LED emission is useful to assess the suitability of individual architectures, e.g. for display applications. Here, the implementation of a goniometer-based measurement system and corresponding protocol are described that allow to accurately determine the current-voltage-luminance characteristics, external quantum efficiency and luminous efficacy of OLEDs and other emerging thin-film LEDs. The system allows recording of angle-resolved electroluminescence spectra and accurate efficiency measurements for devices with both Lambertian and non-Lambertian emission characteristics. A detailed description of the setup and a protocol for assembling and aligning the required hardware are provided. Drawings of all custom parts and the open-source Python software required to perform the measurement and to analyze the data are included.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

Orientation of OLED emitter molecules revealed by XRD

We thank Dr. Lutz Wilde at Fraunhofer IPMS, Center Nanoelectronic Technologies, Dresden for carrying out the GIXRD measurements. CM acknowledges funding by the Graduate Academy of the TU Dresden and by the European Commission through a Marie Skłodowska Curie individual fellowship (703387).Thin films of the phosphorescent emitters Ir(ppy)3 and Ir(ppy)2(acac) are investigated by GIXRD and GIWAXS. Both molecules form crystalline grains and exhibit a preferred orientation that is pertained even when doped into a host.Postprin

Improving the thermal stability of top-emitting organic light-emitting diodes by modification of the anode interface

This research was financially supported by the EPSRC NSF-CBET lead agency agreement (EP/R010595/1, 1706207), the DARPA-NESD program (N66001-17-C-4012) and the Leverhulme Trust (RPG-2017-231). Y.D. acknowledges a stipend from the Chinese Scholarship Council (CSC). C.K. acknowledges support from the Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education (2017R1A6A3A03012331). M.C.G. acknowledges support from the Alexander von Humboldt Stiftung through the Humboldt-Professorship.Top‐emitting organic light‐emitting diodes (OLEDs) are of interest for numerous applications, in particular for displays with high fill factors. To maximize efficiency and luminance, molecular p‐doping of the hole transport layer (p‐HTL) and a highly reflective anode contact, for example, made from silver, are used. Atomic layer deposition (ALD) is attractive for thin film encapsulation of OLEDs but generally requires a minimum process temperature of 80 °C. Here it is reported that the interface between the p‐HTL and the silver anode of top‐emitting OLEDs degrades during an 80 °C ALD encapsulation process, causing an over fourfold reduction in OLED current and luminance. To understand the underlying mechanism of device degradation, single charge carrier devices are investigated before and after annealing. A spectroscopic study of p‐HTLs indicates that degradation is due to the interaction between diffusing silver ions and the p‐type molecular dopant. To improve the stability of the interface, either an ultrathin MoO3 buffer layer or a bilayer HTL is inserted at the anode/organic interface. Both approaches effectively suppress degradation. This work shows a route to successful encapsulation of top‐emitting OLEDs using ALD without sacrificing device performance.Publisher PDFPeer reviewe

A substrateless, flexible, and water-resistant organic light-emitting diode

This research was financially supported from the Leverhulme Trust (RPG-2017-231), the EPSRC NSF-CBET lead agency agreement (EP/R010595/1, 1706207), the DARPA NESD programme (N66001-17-C-4012) and the RS Macdonald Charitable Trust. C.K. acknowledges support from the Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education (2017R1A6A3A03012331). C.M. acknowledges funding from the European Commission through a Marie Skłodowska Curie individual fellowship (703387). A.M. acknowledges funding through an individual fellowship of the Deutsche Forschungsgemeinschaft (404587082). M.C.G. acknowledges funding from the Alexander von Humboldt Stiftung (Humboldt-Professorship).Despite widespread interest, ultrathin and highly flexible light-emitting devices that can be seamlessly integrated and used for flexible displays, wearables, and as bioimplants remain elusive. Organic light-emitting diodes (OLEDs) with µm-scale thickness and exceptional flexibility have been demonstrated but show insufficient stability in air and moist environments due to a lack of suitable encapsulation barriers. Here, we demonstrate an efficient and stable OLED with a total thickness of ≈ 12 µm that can be fully immersed in water or cell nutrient media for weeks without suffering substantial degradation. The active layers of the device are embedded between conformal barriers formed by alternating layers of parylene-C and metal oxides that are deposited through a low temperature chemical vapour process. These barriers also confer stability of the OLED to repeated bending and to extensive postprocessing, e.g. via reactive gas plasmas, organic solvents, and photolithography. This unprecedented robustness opens up a wide range of novel possibilities for ultrathin OLEDs.Publisher PDFPeer reviewe

Organic light-emitting diodes for optogenetic stimulation of Drosophila larvae

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, the RS Macdonald Charitable Trust, and EPSRC via grant EP/J01771X/1. CM acknowledges funding by the European Commission through a Marie Skłodowska Curie individual fellowship (703387).Optogenetics is an emerging method in biology that enables controlling neurons with light. We use organic light-emitting diodes to stimulate neurons in Drosophila larvae and investigate subsequent behavioral changes at different light intensities.Postprin

Infrared organic light-emitting diodes with carbon nanotube emitters

This research was financially supported by the Volkswagen Foundation (93404), the European Research Council under the European Union's Seventh Framework Programme (FP/2007-2013)/ERC Grant Agreement No. 306298 (EN-LUMINATE) and by EPSRC (EP/R010595/1). C.M. acknowledges funding by the European Commission through a Marie Skłodowska Curie Individual Fellowship (703387). J.Z. thanks the Alfried Krupp von Bohlen und Halbach-Stiftung via the “Alfried Krupp Förderpreis für junge Hochschullehrer” for general support.While organic light-emitting diodes (OLEDs) covering all colors of the visible spectrum have been demonstrated, suitable organic emitter materials in the near-infrared (nIR) beyond 800 nm are still lacking. Here, we demonstrate the first OLED based on single-walled carbon nanotubes (SWCNTs) as the emitter. By using a multi-layer stacked architecture with matching charge blocking and charge transport layers, we achieve narrow band electroluminescence at wavelengths between 1000 nm and 1200 nm, with spectral features characteristic of excitonic and trionic emission of the (6,5) SWCNTs used. We investigate the OLED performance in detail and find that local conduction hot-spots lead to pronounced trion emission. Analysis of the emissive dipole orientation shows a strong horizontal alignment of the SWCNTs with an average inclination angle of 12.9° with respect to the plane, leading to an exceptionally high outcoupling efficiency of 49 %. Our SWCNT-based OLEDs represent a highly attractive platform for emission across the entire nIR.PostprintPeer reviewe

Investigating the molecular orientation of Ir(ppy)3 and Ir(ppy)2(acac) emitter complexes by X-ray diffraction

This work received funding from the European Community Seventh Framework Programme under Grant Agreement No. FP7 267995 (NUDEV) and from the European Social Fund and the Free State of Saxony through the OrganoMechanics project. CM acknowledges funding from the Graduate Academy of the TU Dresden and by the European Commission through a Marie Skłodowska-Curie Individual Fellowship (703387).We study thermally evaporated thin films of Ir(ppy)3 and Ir(ppy)2(acac) by means of grazing incidence X-ray diffraction (GIXRD) and grazing incidence wide-angle X-ray scattering (GIWAXS). Ir(ppy)3 and Ir(ppy)2(acac) are both widely used as phosphorescent green emitter molecules in organic light-emitting diodes (OLEDs) and it was previously found that differences in their average transition dipole orientation affect the light extraction efficiency in OLEDs. Here we show that in pure films both materials form crystalline grains and that these grains exhibit a preferred orientation with respect to the substrate. When doped into an amorphous host, both the orientation and formation of the crystallites remain nearly unchanged for the concentration range accessible with GIXRD and GIWAXS. This is remarkable given that the transition dipole moments have found to be oriented only for Ir(ppy)2(acac) but isotropic for Ir(ppy)3. Analysis of the crystallite size indicates that the tendency to form crystallites is stronger for Ir(ppy)3 than for Ir(ppy)2(acac). From a comparison of the thin-film diffraction data of Ir(ppy)3 to its powder pattern, we infer that Ir(ppy)3 molecules are oriented with their permanent dipole moment roughly parallel to the substrate. Our findings will guide the further understanding of the mechanisms controlling transition dipole orientation and may thus lead to further improvements in device efficiency.PostprintPeer reviewe