Miniaturization and reliable, real-time, non-invasive monitoring are essential for investigating microfluidic processes in Lab-on-a-Chip (LoC) systems. Progress in this field is driven by three complementary approaches: analytical modeling, computational fluid dynamics (CFD) simulations, and experimental validation techniques. In this study, we present an on-chip experimental method for estimating the slug-flow velocity in microchannels through in situ optical monitoring. Slug flow involving two immiscible fluids was investigated under both liquid–liquid and gas–liquid conditions via an extensive experimental campaign. The measured velocities were used to determine the slug length and key dimensionless parameters, including the Reynolds number and Capillary number. A comparison with analytical models and CFD simulations revealed significant discrepancies, particularly in gas–liquid flows. These differences are mainly attributed to factors such as gas compressibility, pressure fluctuations, the presence of a liquid film, and leakage flows, all of which substantially affect flow dynamics. Notably, the percentage error in liquid–liquid flows was lower than that in gas–liquid flows, largely due to the incompressibility assumption inherent in the model. The high-frequency monitoring capability of the proposed method enables in situ mapping of evolving multiphase structures, offering valuable insights into slug-flow dynamics and transient phenomena that are often difficult to capture using conventional measurement techniques.

For many synchrotron radiation experiments, it is critical to perform continuous, real-time monitoring of the X-ray flux for normalization and stabilization purposes. Traditional transmission-mode monitors included metal mesh foils and ionization chambers, which suffered from low signal stability and size constraints. Solid-state detectors are now considered superior alternatives for many applications, offering appealing features like compactness and signal stability. However, silicon-based detectors suffer from poor radiation resistance, and diamond detectors are limited in scalability and are expensive to produce. Silicon carbide (SiC) has recently emerged as an alternative to both materials, offering a high-quality mature semiconductor with high thermal conductivity and radiation hardness. This study focuses on a systematic exploration of the SiC `free-standing membrane' devices developed by SenSiC GmbH. In particular, we performed in-depth sensor-response analysis with photon energies ranging from tender (1.75 keV) to hard (10 keV) X-rays at the Four-Crystal Monochromator beamline in the PTB laboratory at the synchrotron radiation facility BESSY II, studying uniformity of transmission and responsivity compared with the state-of-the-art beam monitors. Furthermore, we theoretically evaluated the expected signal in different regions of the sensors, also taking into account the effect of charge diffusion from the SiC substrate in the case of the not-carved region.

Non-Newtonian fluids analysis in micro-devices is challenging both in biological and chemical applications. In this context, the flow velocity evaluation is crucial. This work presents a portable and disposable micro-optofluidic detector, in which micro-optical and microfluidic components are integrated and used for the real-time characterization of a sequenced flow generated by two immiscible fluids, called slug flow. The 3D-printed approach was chosen for the device fabrication, being simple, flexible, fast and low-cost, and for the possibility of exploring wider channel geometries as compared to soft lithography. In the micro optofluidic detector, the light interacts with the flow in two observation points, 1 mm apart from each other, placed along the micro-channel at 26 mm far from the T-junction. The optical signal variations, correlated to the fluids’ optical properties, were used for real-time tracking of slug frequency passage, velocity, and length by an ad-hoc signal processing procedure. Two micro-optofluidic detector prototypes were presented. One prototype was entirely made in PDMS, while in the second, the micro-optical component was made of VeroClear and the microfluidic part in PDMS. Both prototypes were successfully characterized in different hydrodynamic conditions as proof of concept of their validity as flow velocity detectors. The advantage of realizing, by using a low-cost and easy-to-use fabrication process, a micro-optofluidic device that embeds the optical monitoring elements and the micro-channels, without constraints on the localization of the observation point and micro-channel height, opens the way to the design of a great variety of Lab-on-a-chip micro-devices for complex fluids investigation.

Conventional beam intensity monitor technologies, such as `gold-meshes' and `diamond conductive thin films', currently applied to tender and soft X-ray beams, encounter numerous application challenges, including diffraction effects, low signal strength, non-uniform transparency, and lack of position information. This study explores the potential of very thin (<2 µm) silicon carbide free-standing membranes, as in-line, minimally interfering beam intensity and position monitors, with high-lateral resolution, for soft and tender X-ray beamlines. Initial experimental assessments were conducted at the NanoMAX beamline at MAX IV to analyze the performance of such very thin devices in monitoring tightly focused (<1 µm FWHM) beams. The tests revealed that employing four-quadrant sensor layouts on such thin sensors resulted in significant charge collection losses in the regions between the quadrants and, under high electric field conditions, in charge multiplication effects (avalanche effects). Through Sentaurus TCAD theoretical simulations, the limitations of the four-quadrant design for such applications and the potential of an alternative technology (resistive X-ray beam postion monitor) were clarified.

Objective: This work presents ROT-QSG, a compact, automated, and user-friendly electrorotation system for label-free dielectric characterization of biological cells, enabling applications in disease diagnosis, drug discovery, and personalized medicine. Methods: The ROT-QSG system consists of three main components: (1) a custom electronic device—Quadrature Signal Generator (QSG); (2) a specifically designed electrorotation chip—ROT-chip; and (3) a dedicated image processing algorithm—Pixel Intensity (PxI)—which enables automatic, operator-independent extraction of cell rotation data. Electrorotation allows the dielectric characterization of cells by analyzing their rotational response to varying electric field frequencies, generating the rotation–frequency spectrum (ROT-spectrum). To ensure high consistency and repeatability, the entire experimental workflow—from signal generation to spectrum extraction—has been fully automated through a dedicated experimental control algorithm. Results: The system was validated by analyzing three immortalized cell lines (CaCo-2, CCD-841, and OPM2), from which ROT spectra and corresponding cell membrane capacitance values were successfully extracted. Conclusion: The comparative study revealed clear differences in membrane capacitance among the three cell types, confirming the system's capability to detect meaningful dielectric variations. The repeatability of measurements within each cell line and the observed distinct spectral differences between the cell lines demonstrate its sensitivity to variations in membrane morphology and structural organization. Significance: The system, designed with a strong focus on integration, automation, and ease of use in biological settings, has the potential to enhance dielectric characterization across a wide range of cell types, contributing to a deeper understanding of cellular functions and disease mechanisms.