arXiv subjects

David Regan

Publications and source records attributed to David Regan.

4 recordsLinked to original sources

arXiv2025

Understanding the mechanisms of supported lipid membrane reshaping into tubular networks using quantitative DIC microscopy

Biological membranes are known to form various structural motifs, from lipid bilayers to tubular filaments and networks facilitating e.g. adhesion and cell-cell communication. To understand the biophysical processes underpinning lipid-lipid interactions in these systems, synthetic membrane models are crucial. Here, we demonstrate the formation of tubular networks from supported lipid membranes of controlled lipid composition on glass. We quantify tube radii using quantitative differential interference contrast (qDIC) and propose a biophysical mechanism for the formation of these structures, regulated by surface tension and lipid exchange with connected supported membranes. Two lipid types are investigated, namely DOPC and DC15PC, exhibiting a liquid disordered and a solid ordered phase at room temperature, respectively. Tube formation is studied versus temperature, revealing bilamellar layers retracting and folding into tubes upon DC15PC lipids transitioning from liquid to solid phase, which is explained by lipid transfer from bilamellar to unilamellar layers. This study introduces a novel model system for bilayer tubes, allowing to elucidate the biophysics of lipid-lipid interactions governing lipid membrane reshaping into tubular structures, important for our understanding of biological membrane filaments.

cond-mat.soft↗

arXiv2025

Genetically encoding stimulated Raman-scattering probes for cell imaging using infrared fluorescent proteins

Stimulated Raman scattering (SRS) microscopy offers great potential to surpass fluorescent-based approaches, owing to the sharp linewidth of Raman vibrations amenable to super-multiplex cell imaging, but currently lacks one crucial component: genetically encodable tags equivalent to fluorescent proteins. Here, we show that infrared fluorescent proteins (IRFPs) can be used as genetically encoded SRS probes and benefit from the electronic pre-resonant SRS enhancement effect with near-infrared exciting pulses, comparable to synthetic dyes reported in the literature. SRS imaging of the nucleus in mammalian cells is demonstrated where a histone protein is fused to an IRFP. This work opens the route towards Raman-based cell imaging using genetically encoded probes, motivating efforts in solving the challenges of photostability and creating a vibrational palette.

physics.chem-ph↗

arXiv2021

Sizing individual dielectric nanoparticles with quantitative differential interference contrast microscopy

We report a method to measure the size of single dielectric nanoparticles with high accuracy and precision using quantitative differential interference contrast (DIC) microscopy. Dielectric nanoparticles are detected optically by the conversion of the optical phase change into an intensity change using DIC. Phase images of individual nanoparticles were retrieved from DIC by Wiener filtering, and a quantitative methodology to extract nanoparticle sizes was developed. Using polystyrene beads of 100 nm radius as size standard, we show that the method determines this radius within a few nm accuracy. The smallest detectable polystyrene bead is limited by background and shot-noise, which depend on acquisition and analysis parameters, including the objective numerical aperture, the DIC phase offset, and the refractive index contrast between particles and their surrounding. A sensitivity limit potentially reaching down to 1.8 nm radius was inferred. As application example, individual nanodiamonds with nominal sizes below 50 nm were measured, and were found to have a nearly exponential size distribution with 28 nm mean value. Considering the importance of dielectric nanoparticles in many fields, from naturally occurring virions to polluting nanoplastics, the proposed method could offer a powerful quantitative tool for nanoparticle analysis, combining accuracy, sensitivity and high-throughput with widely available and easy-to-use DIC microscopy

physics.optics↗

arXiv2021

Simultaneous microscopic imaging of thickness and refractive index of thin layers by heterodyne interferometric reflectometry (HiRef)

The detection of spatial or temporal variations in very thin samples has important applications in the biological sciences. For example, cellular membranes exhibit changes in lipid composition and order, which in turn modulate their function in space and time. Simultaneous measurement of thickness and refractive index would be one way to observe these variations, yet doing it noninvasively remains an elusive goal. Here we present a microscopic-imaging technique to simultaneously measure the thickness and refractive index of thin layers in a spatially resolved manner using reflectometry. The heterodyne-detected interference between a light field reflected by the sample and a reference field allows measurement of the amplitude and phase of the reflected field and thus determination of the complex reflection coefficient. Comparing the results with the simulated reflection of a thin layer under coherent illumination of high numerical aperture by the microscope objective, the refractive index and thickness of the layer can be determined. We present results on a layer of polyvinylacetate (PVA) with a thickness of approximately 80~nm. These results have a precision better than 10\% in the thickness and better than 1\% in the refractive index and are consistent within error with measurements by quantitative differential interference contrast (qDIC) and literature values. We discuss the significance of these results, and the possibility of performing accurate measurements on nanometric layers. Notably, the shot-noise limit of the technique is below 0.5~nm in thickness and 0.0005 in refractive index for millisecond measurement times.

physics.optics↗