Integration of Microfluidics and Optical Fibers for Real-Time Viscosimetry: Towards a Practical Tool for Biomedical Studies

Optical fiber-based solutions are increasingly prominent in developing compact, reliable, and user-friendly devices, particularly in biomedical applications. This work introduces a novel fiber-assisted optofluidic viscometer designed to determine fluid viscosity by measuring the transit time of a metallic microsphere through a microfluidic channel under constant pressure. A comprehensive theoretical framework guided the device's design and was experimentally validated across a viscosity range of 5 - 1 1 0 c P, encompassing values typical of blood. The system supports a dual-point detection schemes, employing two spaced OFs, demonstrate sensitivities of ∼ 0.2 s/cP (measurement times in the tens of seconds), with resolution in the range of ∼ 1 0 - 1 c P and accuracy pushed down to ∼ 1. 5% Further improvements in resolution and accuracy can be achieved by reducing uncertainty in bead size and bead path length, offering advantages in terms of measurement time and minimum sample volume required. The proposed viscometer offers a cost-effective, fast, and easily integrated solution for microfluidic platforms and can operate with microliter-scale fluid volumes. Its simplicity and performance make it suitable for clinical use, particularly for real-time blood and plasma viscosity monitoring under physiological conditions.