3D-Printed Micro-Optofluidic Slug Flow Detector

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.