Single cell induced optical confinement in biological lasers

We acknowledge financial support from the European Research Council (ERC StG ABLASE, 640012), the Scottish Funding Council (via SUPA) and the European Union Marie Curie Career Integration Grant (PCIG12-GA-2012-334407). M.K. acknowledges funding from the EPSRC DTG (EP/M506631/1). M.S. acknowledges funding from the European Commission for a Marie Sklodowska-Curie Individual Fellowship (659213). I.D.W.S. acknowledges funding from a Royal Society Wolfson research merit award.Biological single cell lasers have shown great potential for fundamental research and next generation sensing applications. In this study, the potential of fluorescent biological cells as refractive index landscapes and active optical elements is investigated using a combined Fourier- and hyperspectral imaging technique. We show that the refractive index contrast between cell and surrounding leads to three dimensional confinement of photons inside living cells. The Fourier- and real-space emission characteristics of these biological lasers are closely related and can be predicted from one another. Investigations of the lasing threshold for different energy and momentum position in Fourier-space give insight into the fundamental creation of longitudinal and transverse lasing modes within the cell. These findings corroborate the potential of living biological materials for precision engineering of photonic structures and may pave the way towards low threshold polariton lasing from single cells.Publisher PDFPeer reviewe

Red-shifted excitation and two-photon pumping of biointegrated GaInP/AlGaInP quantum well microlasers

This work received financial support from the Leverhulme Trust (RPG-2017-231), European Union’s Horizon 2020 Framework Programme (FP/2014-2020)/ERC grant agreement no. 640012 (ABLASE), EPSRC (EP/P030017/1), and the Humboldt Foundation (Alexander von Humboldt professorship). MS acknowledges funding by the Royal Society (Dorothy Hodgkin Fellowship, DH160102; Research Grant, RGF\R1\180070; Enhancement Award, RGF\EA\180051). ADF acknowledges support from European Research Council (ERC) under the European Union Horizon 2020 research and innovation program (Grant Agreement No. 819346).Biointegrated intracellular microlasers have emerged as an attractive and versatile tool in biophotonics. Different inorganic semiconductor materials have been used for the fabrication of such biocompatible microlasers, but often operate at visible wavelengths ill-suited for imaging through tissue. Here, we report on whispering gallery mode microdisk lasers made from a range of GaInP/AlGaInP multi-quantum well structures with compositions tailored to red-shifted excitation and emission. The selected semiconductor alloys show minimal toxicity and allow fabrication of lasers with stable single-mode emission in the NIR (675 – 720 nm) and sub-pJ thresholds. The microlasers operate in the first therapeutic window under direct excitation by a conventional diode laser and can also be pumped in the second therapeutic window using two-photon excitation at pulse energies compatible with standard multiphoton microscopy. Stable performance is observed under cell culturing conditions for five days without any device encapsulation. With their bio-optimized spectral characteristics, low lasing threshold and compatibility with two-photon pumping, AlGaInP-based microlasers are ideally suited for novel cell tagging and in vivo sensing applications.Publisher PDFPeer reviewe

Intersectionality as a tool for clinical ethics consultation in mental healthcare.

Bioethics increasingly recognizes the impact of discriminatory practices based on social categories such as race, gender, sexual orientation or ability on clinical practice. Accordingly, major bioethics associations have stressed that identifying and countering structural discrimination in clinical ethics consultations is a professional obligation of clinical ethics consultants. Yet, it is still unclear how clinical ethics consultants can fulfill this obligation. More specifically, clinical ethics needs both theoretical tools to analyze and practical strategies to address structural discrimination within clinical ethics consultations. Intersectionality, a concept developed in Black feminist scholarship, is increasingly considered in bioethical theory. It stresses how social structures and practices determine social positions of privilege and disadvantage in multiple, mutually co-constitutive systems of oppression. This article aims to investigate how intersectionality can contribute to addressing structural discrimination in clinical ethics consultations with a particular focus on mental healthcare. To this end, we critically review existing approaches for clinical ethics consultants to address structural racism in clinical ethics consultations and extend them by intersectional considerations. We argue that intersectionality is a suitable tool to address structural discrimination within clinical ethics consultations and show that it can be practically implemented in two complementary ways: 1) as an analytic approach and 2) as a critical practice

Preparation of WS2-PMMA composite films for optical applications

C. B. acknowledges the German research foundation DFG under Emmy-Noether grant BA4856/2-1. C. B., J. Z. and M. C. G. acknowledge the Volkswagen foundation under grant agreement no. 93404-93406. W. J. B. gratefully acknowledges support by a research grant from Science Foundation Ireland (SFI) under Grant Number 12/IA/1306.Thus far, research activities of 2D materials in optics, photonics and optoelectronics predominantly focus on micromechanically cleaved or grown nanosheets. Here, we show that high quality liquid-exfoliated nanosheets offer an alternative approach. Starting from well-defined, monolayer rich WS2 dispersions obtained after liquid exfoliation and size selection in aqueous surfactant, we present an optimised protocol facilitating transfer of the nanosheets to a polymer solution in organic media. From such dispersions, we fabricate WS2–polymer thin films by spin coating. The characteristic photoluminescence of WS2 monolayers is retained in the film at 2.04 eV without broadening (line width 40 meV) or significant changes in the line-shape. This confirms that nanosheet aggregation is efficiently prevented on transfer and deposition. The films are extremely smooth and uniform over large areas with a root mean square roughness <0.5 nm. To demonstrate the potential in optical applications, the nonlinear optical response was studied, revealing promise as optical limiter. In addition, we show that the photoluminescence can be manipulated by coupling the exciton response to cavity photons in a Ag microcavity.PostprintPeer reviewe

Advances in small lasers

M.T.H was supported by an Australian Research council Future Fellowship research grant for this work. M.C.G. is grateful to the Scottish Funding Council (via SUPA) for financial support.Small lasers have dimensions or modes sizes close to or smaller than the wavelength of emitted light. In recent years there has been significant progress towards reducing the size and improving the characteristics of these devices. This work has been led primarily by the innovative use of new materials and cavity designs. This Review summarizes some of the latest developments, particularly in metallic and plasmonic lasers, improvements in small dielectric lasers, and the emerging area of small bio-compatible or bio-derived lasers. We examine the different approaches employed to reduce size and how they result in significant differences in the final device, particularly between metal- and dielectric-cavity lasers. We also present potential applications for the various forms of small lasers, and indicate where further developments are required.PostprintPeer reviewe

Cortical cell stiffness is independent of substrate mechanics.

Cortical stiffness is an important cellular property that changes during migration, adhesion and growth. Previous atomic force microscopy (AFM) indentation measurements of cells cultured on deformable substrates have suggested that cells adapt their stiffness to that of their surroundings. Here we show that the force applied by AFM to a cell results in a significant deformation of the underlying substrate if this substrate is softer than the cell. This 'soft substrate effect' leads to an underestimation of a cell's elastic modulus when analysing data using a standard Hertz model, as confirmed by finite element modelling and AFM measurements of calibrated polyacrylamide beads, microglial cells and fibroblasts. To account for this substrate deformation, we developed a 'composite cell-substrate model'. Correcting for the substrate indentation revealed that cortical cell stiffness is largely independent of substrate mechanics, which has major implications for our interpretation of many physiological and pathological processes

Identification of the key parameters for horizontal transition dipole orientation in fluorescent and TADF organic light-emitting diodes

This research was financially supported by the Volkswagen Foundation (No. 93404), the European Commission under EU Horizon 2020 Grant Agreement No. 812872 (TADFlife), the European Research Council under the European Union's Horizon 2020 Framework Programme (FP/2014-2020)/ERC grant agreement no. 640012 (ABLASE), and The Leverhulme Trust (RPG-2016047). M.C.G. acknowledges support from the Alexander von Humboldt Stiftung through the Humboldt-Professorship. All computations were performed using resources kindly provided by the University of Mons (UMONS), supported by the Belgian National Fund for Scientific Research (FRS-FNRS). Computational resources were provided by the Consortium des Équipements de Calcul Intensif (CÉCI) funded by F.R.S.-FNRS under Grant 2.5020.11. Y.O. acknowledges funding from the FRS-FNRS under the grant F.4534.21 (MIS-IMAGINE).In organic light-emitting diodes (OLEDs), horizontal orientation of the emissive transition dipole moment (TDM) can improve light outcoupling efficiency by up to 50% relative to random orientation. Therefore, there have been extensive efforts to identify drivers of horizontal orientation. The aspect ratio of the emitter molecule and the glass-transition temperature (Tg) of the films are currently regarded as particularly important. However, there remains a paucity of systematic studies that establish the extent to which these and other parameters control orientation in the wide range of emitter systems relevant for state-of-the-art OLEDs. Here, recent work on molecular orientation of fluorescent and thermally activated delayed fluorescent emitters in vacuum-processed OLEDs is reviewed. Additionally, to identify parameters linked to TDM orientation, a meta-analysis of 203 published emitter systems is conducted and combined with density-functional theory calculations. Molecular weight (MW) and linearity are identified as key parameters in neat systems. In host–guest systems with low-MW emitters, orientation is mostly influenced by the host Tg, whereas the length and MW of the emitter become more relevant for systems involving higher-MW emitters. To close, a perspective of where the field must advance to establish a comprehensive model of molecular orientation is given.Publisher PDFPeer reviewe

Season\u27s influence on the relationship between mass concentrations of sulphur dioxide and sulphate in the air

Studiran je odnos masenih koncentracija (p) sumpor-dioksida i sulfata u prirodnim uvjetima, tj. u dvije gradske sredine s različitim razinama atmosferskog onečišćenja tijekom zimskog i ljetnog razdoblja. Na svakom mjernom mjestu tijekom sezone sakupljeno je i analizirano pedesetak uzoraka sumpor-dioksida, dima·i lebdećih čestica. U uzorcima lebdećih čestica određivana je ukupna masena koncentracija lebdećih čestica, sulfata, kalcija, olova, željeza, mangana i bakra. Studirana je korelacija po sezonama između masenih koncentracija sulfata i sumpor-dioksida, lebdećih čestica, dima, te pojedinih komponenata lebdećih čestica. Dobivena je dobra korelacija između masenih koncentracija sulfata i lebdećih čestica. Razine masenih koncentracija sumpor-dioksida, dima, sulfata i lebdećih čestica značajno su više tijekom zimskog razdoblja u obim sredinama. Na obim je mjestima dobiven gotovo jednak prosječni maseni udjel (w) sulfata (oko 10) u lebdećim česticama i tijekom zimskog i ljetnog razdoblja. Izračunate jednadžbe regresije za odnos između sulfatnog S i ukupnog S (sulfati i sumpor-dioksid) za ljetno i zimsko razdoblje međusobno se razlikuju. Izgleda da se taj sezonski utjecaj na odnos masenih koncentracija sumpor-dioksida i sulfata može dovesti u vezu s različitim porijeklom i različitim razinama masenih koncentracija lebdećih čestica u zraku.The relationship between sulphur dioxide and sulphate was studied in natural conditions, in two urban areas with different levels of air pollution during the winter and summer periods. About fifty samples of sulphur dioxide, smoke and suspended particulates were collected and analysed on each measuring site during the season. In the sample of suspended particulates the total mass concentration of suspended particulates, sulphate, calcium, lead, iron, manganese and copper was determined. The correlation between sulphate and sulphur dioxide, suspended particulates, smoke and some suspended particulate\u27s components was studied by seasons. A good correlation was found between the concentration of sulphate and suspended particulates. The concentration levels of sulphur dioxide, smoke, sulphate and suspended particulates were significantly higher during the winter period in both areas. On both locations the average mass fraction of sulphate (about 10%) in suspended particulates was nearly the same during the winter and summer periods. The calculated equation regressions for the relationship between sulphate S and total S (sulphate and sulphur dioxide) for the summer and winter period are reciprocally different. It seems that the season\u27s influence on the relationship between sulphur dioxide and sulphate might be due to a different origin and different levels of suspended particulates in the air

Flexible and ultra-lightweight polymer membrane lasers

The authors acknowledge financial support from the European Research Council (ERC StG ABLASE, 640012), the Scottish Funding Council (via SUPA) and EPSRC (EP/P030017/1). M.K. and J.M.E.G. acknowledge funding from the EPSRC DTG (EP/M506631/1 and EP/L505079/1). M.S. acknowledges funding from the European Commission for a Marie Sklodowska-Curie Individual Fellowship (659213). I.D.W.S. acknowledges funding from a Royal Society Wolfson research merit award.Organic semiconductors enable the fabrication of a range of lightweight and mechanically flexible optoelectronic devices. Most organic semiconductor lasers, however, have remained rigid until now, predominantly due to the need for a support substrate. Here, we use a simple fabrication process to make membrane-based, substrate-less and extremely thin (< 500 nm) organic distributed feedback lasers that offer ultralow-weight (m/A <0.5 gm−2) and excellent mechanical flexibility. We show operation of the lasers as free-standing membranes and transfer them onto other substrates, e.g. a banknote, where the unique lasing spectrum is readily read out and used as security feature. The pump thresholds and emission intensity of our membrane lasers are well within the permissible exposures for ocular safety and we demonstrate integration on contact lenses as wearable security tags.Publisher PDFPeer reviewe