Fabrication and Optical Modeling of Micro‐Porous Membranes Index‐Matched with Water for On‐Line Sensing Applications

Abstract

Membranes made of perfluorinated materials having a refractive index close to that of water enable straightforward detection of water solutes at the interface, hence providing a novel sensing tool for fluidic systems. Here it is reported the production by non‐solvent induced phase separation and characterization of microporous membranes made of Hyflon AD, an amorphous copolymer of tetrafluoroethylene. Their optical turbidity when soaked in liquids having different refractive indices is studied and the data are interpreted with an optical model linking scattered light and structural features of the membrane. The average polymer and pore chord lengths obtained in this way scale with the filtering pore size measured by capillary flow porometry. Then, the optical response of the membranes when soaked in aqueous surfactant solutions is investigated and the effects of the molecular adsorption on the internal membrane surface is successfully interpreted by an extension of the model. Overall, the results show that index‐matched membranes can be designed and produced to provide a simple optical detection of the composition of the soaking liquid or to monitor the initial stage of membrane fouling.

Design of a rapid, multiplex, one-pot miRNA assay optimized by label-free analysis

“…In previous works, we have shown the use of Reflective Phantom Interface (RPI), an optical label-free biosensor based on the measurement of the intensity of light reflected by a surface with very low reflectivity, for studying a variety of interactions, including antigen-antibody (Tagliabue et al, 2017), protein-glycan (Zilio et al, 2015), and DNA-DNA (Vanjur et al, 2020). The direct, unamplified RPI signal was exploited to quantify hormones (Salina et al, 2015), biomarkers for viral infections in humans and plants (Salina et al, 2016), single base mismatches in DNA strand , and pollutants in environmental water (Lanfranco et al, 2016) (Lanfranco et al, 2018) (Lanfranco et al, 2020). Among other label-free biosensors, RPI provides the advantage of combining large sensitivity for parallel detection with low-cost disposable cartridges and compact instrumentation (Giavazzi et al, 2014).…”

A microfluidic column of water index–matched packed microspheres for label-free observation of water pollutants

“…The RPI method has been previously exploited to capture molecular targets by immobilized ligands [17][18] [19][20], as well as to characterize the adsorption strength and kinetics on the surface of a prism of perfluorinated material that matches water's refractive index [21]. An analogous strategy, named as Scattering Phantom Interface (SPI) method [14][21] [22], can be exploited to measure the amount of molecules binding on the internal surface of a micro-porous medium with refractive index similar to that of the liquid phase. In this approach, originated from a fundamental principle of optics, a collection of molecules freely diffusing in solution provide a very small light scattering, whereas the same amount of molecules confined in a shell with nmscale thickness but extending on the micron scale yields to a much larger scattering contribution [23].…”