Search

Non-Newtonian fluids analysis in microdevices 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 ( $\mu $ OFD), in which microoptical 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 microchannel at 26 mm far from the T-junction. The optical signal variations, correlated with 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 $\mu $ OFD prototypes were presented. One prototype was entirely made in poly-dimethyl-siloxane (PDMS), while in the second, the microoptical 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 microchannels, without constraints on the localization of the observation point and microchannel height, opens the way to the design of a great variety of lab-on-a-chip (LOC) microdevices for complex fluids investigation.

A versatile and low-cost plasmonic biosensor was designed, realized, and tested by combining a bioreceptor layer with a probe based on two plastic optical fibers (POFs) built-in with a sensing chip carried out via a multilayer on UV-curable optical adhesives. The proposed sensitive multilayer has been developed to excite the surface plasmon resonance (SPR) phenomenon on a gold surface in contact with the monitored bioreceptor layer. More specifically, a binding interaction between a bioreceptor layer and its analyte has been studied for the first time by exploiting SPR platforms based on UV-curable optical adhesives. First, a resin block with a V-shaped channel on its surface was designed and printed using a 3-D printer to locate the source and receiver on the same side. Then, the channel was covered by a silver layer to obtain the mirror effect. After this, it was filled with an UV-curable optical adhesive, with two POFs fixed at the end of the trench, in order to obtain the core of the sensor’s waveguide. Finally, an optical buffer layer and a gold nanofilm were deposited on the core to excite the SPR phenomenon efficiently. The obtained SPR probe was first tested as a refractometer to obtain the bulk sensitivity, and then, following a functionalization process, binding tests were carried out to detect immunoglobulin (IgG) in the buffer. The experimental results show an ultralow detection limit of 1.17 fM, a detection range from 1 to 250 fM, and a sensitivity at low concentrations of 3.42 nm/fM.