Biology subjects

Hayden, O.

Publications and source records attributed to Hayden, O..

3 recordsLinked to original sources

bioRxiv2025

Fabry-Perot Microscopy for Improved Contrast Enhancement and 3D Cellular Imaging

Fabry-Perot Microscopy (FPM) integrates a lab-on-a-chip optical cavity and tunable light source in a label-free imaging technique that enhances contrast and enables pseudo-three-dimensional imaging in transparent biological samples. By integrating a fixed-length Fabry-Perot cavity into a coated microfluidic cell, FPM selectively highlights structures of defined optical thickness through resonance-based interference. We demonstrate that this architecture preserves lateral resolution while providing up to 20-fold contrast enhancement compared to conventional wide-field microscopy. Using human epithelial cells, blood components, and E. coli bacteria, we show that FPM enables clear visualization of subcellular features and discrimination of cell types. Spectrally resolved image stacks are used to extract pixel-wise optical thickness maps, from which physical thickness and refractive index can be derived. These parameters reveal nanoscale structural differences and offer routes to biophysical characterization. Notably, the system operates without mechanical scanning the cavity, using spectral tuning alone to generate images. FPM is compatible with standard microscope optics, and functions under static or flow-compatible conditions, making it suitable for high-throughput cytometry and in vitro diagnostics. These results establish FPM as a versatile extension to wide-field microscopy, enabling contrast-tunable, quantitative imaging of biomedical specimen.

biophysics↗

bioRxiv2024

Spatiotemporal control of a multilayered co-axial flow in a 3D printed microchannel with cascaded nozzles

Sculpting and stopping multilayered co-flowing streams is challenging due to inhomogeneous pressure distribution within a fluidic circuit composed of multiple interconnected microchannels having variable flow resistances. Here, we have investigated three different flow control methods to effectively stop a multilayered flow inside a 3D-printed microfluidic channel by bringing the average flow velocity from >100 mm s-1 to below a critical velocity of 200 {micro}m s-1 within a certain delay time tD of [~]2s. Firstly, we 3D printed a sequence of three concentric nozzles ([~]75 {micro}m) embedded serially inside the microchannel ([~]200 {micro}m) using a two-photon polymerization (2PP) method. Secondly, we used the 2PP-based 3D printed device to produce a structured coaxial flow of four streams with individual layer thicknesses of O(10 {micro}m) within the outlet section of the microchannel. Thirdly, we removed the pressure gradient across the fluidic circuit, from > 2 bar to [~]0 bar, to stop the multilayered flow and measured tD to assess the performance of the three stop flow methods. During the stop-flow phase, an inhomogeneous pressure gradient across different inlets resulted in a backflow to inlet channels with lower pressures. In the three stop-flow methods investigated, we systemically managed the fluidic capacitance to minimize a dimensionless backflow index (BFI) value from [~]0.3 (worst case) to [~]0.03 (best case) for a total flow rate ranging from 16.8 {micro}l min-1 to 168 {micro}l min-1. Finally, we have recommended the best stop-flow conditions, which resulted in a minimal delay time of tD [~] 2s and a BFI < 0.05.

bioengineering↗

bioRxiv2024

Quantitative Magnetic Flow Cytometry in High Hematocrit Conditions for Point-of-Care Testing

Quantitative cell analysis in liquid biopsies is essential for many clinical decisions, but it is primarily tied to centralized laboratories. However, access to these laboratories is limited in low-resource settings or for immobile patients, highlighting the urgent need for Point-of-Care (POC) testing infrastructure. Magnetic flow cytometers (MFC) offer a solution, albeit sample processing steps like cell lysis or washing crucially disrupt POC-capable MFC workflows. Here, we investigate conditions for immunomagnetic labeling and direct cell quantification in a streamlined workflow suitable for high hematocrit environments. Magnetic nanoparticles (MNP) are characterized by their size, magnetic moment, and potential to generate signal noise, favoring small (< 50 nm) MNPs. Theoretical models provide the framework for quantifying bound MNPs per cell, revealing labeling quality and giving insight into system requirements for reliable cell detection. Temporal labeling dynamics show suboptimal binding kinetics in whole blood (WB), leading to long incubation periods and only 50% recovery of optically determined concentrations. Besides showing quantitative MFC in WB with biomimetic microbeads, we finally quantify CD14+ monocytes in WB with our streamlined workflow, achieving an intra-assay coefficient of variation (CV) of 0.11 and a CV across multiple donors of 0.10, demonstrating reliable POC flow cytometry close to regulatory standards.

bioengineering↗