Molecular Rotors Image Intracellular Viscosity

This review describes a new method for quantitative measurement and spatial imaging of microviscosity within individual domains of live cells. The method is based on fluorescence detection from small synthetic molecules termed 'molecular rotors', which are characterised by a strong response of fluorescence lifetimes or spectra to the viscosity of their immediate environment. We have demonstrated that the quantitative determination of viscosity is possible using lifetime-based molecular rotors and ratiometric molecular rotors. The ratiometric imaging of viscosity benefits from a very fast signal acquisition. We have illustrated this advantage by monitoring changes in intracellular viscosity during photodynamic therapy, which is a clinically utilised modality for the treatment of neoplastic disease

Advantages of extracurricular drama activities in foreign language teaching

Culture is a very valuable part of society. The study of a foreign language not only teaches the language itself, but it also introduces information on another culture, moral values and attitudes. Improving the quality of foreign language education is important. Demanding course content, low proficiency and foreign language learning anxiety discourage students from learning. Difficulty in communicating in the target language reduces their self-confidence. The use of drama could be one of the possible means to increase motivation and self-esteem and to improve foreign language skills and cultural awareness. The authors share their experience in using drama in extracurricular activities with students studying English as a foreign language at the Institute of Non-Destructive Testing, National Research Tomsk Polytechnic University

Rapid fragmentation during seeded lysozyme aggregation revealed at the single molecule level

Protein aggregation is associated with neurodegenerative disorders such as Alzheimer's and Parkinson's diseases. The poorly understood pathogenic mechanism of amyloid diseases makes early stage diagnostics or therapeutic intervention a challenge. Seeded polymerization that reduces the duration of the lag phase and accelerates fibril growth is a widespread model to study amyloid formation. Seeding effects are hypothesized to be important in the "infectivity" of amyloids and are linked to the development of systemic amyloidosis in vivo. The exact mechanism of seeding is unclear yet critical to illuminating the propagation of amyloids. Here we report on the lateral and axial fragmentation of seed fibrils in the presence of lysozyme monomers at short time scales, followed by the generation of oligomers and growth of fibrils

Molecular rheometry: direct determination of viscosity in L-o and L-d lipid phases via fluorescence lifetime imaging

Understanding of cellular regulatory pathways that involve lipid membranes requires the detailed knowledge of their physical state and structure. However, mapping the viscosity and diffusion in the membranes of complex composition is currently a non-trivial technical challenge. We report fluorescence lifetime spectroscopy and imaging (FLIM) of a meso-substituted BODIPY molecular rotor localised in the leaflet of model membranes of various lipid compositions. We prepare large and giant unilamellar vesicles (LUVs and GUVs) containing phosphatidylcholine (PC) lipids and demonstrate that recording the fluorescence lifetime of the rotor allows us to directly detect the viscosity of the membrane leaflet and to monitor the influence of cholesterol on membrane viscosity in binary and ternary lipid mixtures. In phase-separated 1,2-dioleoyl-sn-glycero-3-phosphocholine-cholesterol–sphingomyelin GUVs we visualise individual liquid ordered (Lo) and liquid disordered (Ld) domains using FLIM and assign specific microscopic viscosities to each domain. Our study showcases the power of FLIM with molecular rotors to image microviscosity of heterogeneous microenvironments in complex biological systems, including membrane-localised lipid rafts

Linker length affects photostability of protein-targeted sensor of cellular microviscosity.

Viscosity sensitive fluorophores termed 'molecular rotors' represent a convenient and quantitative tool for measuring intracellular viscosity via Fluorescence Lifetime Imaging Microscopy (FLIM). We compare the FLIM performance of two BODIPY-based molecular rotors bound to HaloTag protein expressed in different subcellular locations. While both rotors are able to penetrate live cells and specifically label the desired intracellular location, we found that the rotor with a longer HaloTag protein recognition motif was significantly affected by photo-induced damage when bound to the HaloTag protein, while the other dye showed no changes upon irradiation. Molecular dynamics modelling indicates that the irradiation-induced electron transfer between the BODIPY moiety and the HaloTag protein is a plausible explanation for these photostability issues. Our results demonstrate that binding to the targeted protein may significantly alter the photophysical behaviour of a fluorescent probe and therefore its thorough characterisation in the protein bound form is essential prior to any in vitro and in cellulo applications

Quantitative sensing of microviscosity in protocells and amyloid materials using fluorescence lifetime imaging of molecular rotors

Molecular rotors are fluorophores that have a fluorescence quantum yield that depends upon intermolecular rotation. The fluorescence quantum yield, intensity and lifetime of molecular rotors all vary as functions of viscosity, as high viscosities inhibit intermolecular rotation and cause an increase in the non-radiative decay rate. As such, molecular rotors can be used to probe viscosity on microscopic scales. Here, we apply fluorescence lifetime imaging microscopy (FLIM) to measure the fluorescence lifetimes of three different molecular rotors, in order to determine the microscopic viscosity in two model systems with significant biological interest. First, the constituents of a novel protocell - a model of a prebiotic cell - were studied using the molecular rotors BODIPY C10 and kiton red. Second, amyloid formation was investigated using the molecular rotor Cy3.</p

Dynamic viscosity mapping of the oxidation of squalene aerosol particles.

Organic aerosols (OAs) play important roles in multiple atmospheric processes, including climate change, and can impact human health. The physico-chemical properties of OAs are important for all these processes and can evolve through reactions with various atmospheric components, including oxidants. The dynamic nature of these reactions makes it challenging to obtain a true representation of their composition and surface chemistry. Here we investigate the microscopic viscosity of the model OA composed of squalene, undergoing chemical aging. We employ Fluorescent Lifetime Imaging Microscopy (FLIM) in conjunction with viscosity sensitive probes termed molecular rotors, in order to image the changes in microviscosity in real time during oxidation with ozone and hydroxyl radicals, which are two key oxidising species in the troposphere. We also recorded the Raman spectra of the levitated particles to follow the reactivity during particle ozonolysis. The levitation of droplets was achieved via optical trapping that enabled simultaneous levitation and measurement via FLIM or Raman spectroscopy and allowed the true aerosol phase to be probed. Our data revealed a very significant increase in viscosity of the levitated squalene droplets upon ozonolysis, following their transformation from the liquid to solid phase that was not observable when the oxidation was carried out on coverslip mounted droplets. FLIM imaging with sub-micron spatial resolution also revealed spatial heterogeneity in the viscosity distribution of oxidised droplets. Overall, a combination of molecular rotors, FLIM and optical trapping is able to provide powerful insights into OA chemistry and the microscopic structure that enables the dynamic monitoring of microscopic viscosity in aerosol particles in their true phase.MKK is thankful to the EPSRC for the Career Acceleration Fellowship (EP/I003983/1). CF thanks NERC for a personal studentship NE/J500070/1. CF and MK were supported by ERC grant 279405. We are thankful to the CLF RAL for a programmed access grant LSF1207 (FLIMOLA)

Designing infrared probes of DNA damage

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