Phantom membrane microfluidic cross-flow filtration device for the direct optical detection of water pollutants

Abstract

The diffusion of autonomous sensing platforms capable of a remote large-scale surveillance of environmental water basins is currently limited by the cost and complexity of standard analytical methods. In order to create a new generation of water analysis systems suitable for continuous monitoring of a large number of sites, novel technical solutions for fluid handling and detection are needed. Here we present a microfluidic device hosting a perfluorinated microporous membrane with refractive index similar to that of water, which enables the combination of filtration and labelfree sensing of molecular pollutants in environmental water samples. The cross-flow design of the microfluidic device avoids the clogging of the membrane due to particulate, whereas molecules with some hydrophobic moiety contained in the crossing flow are partially retained and their adhesion on the inner surface of the membrane yields an increase of light scattering intensity, which can be easily measured using a simple instrument based on Light Emitting Diode illumination. By cycling sample water and pure water as a reference, we demonstrate the detection of 0.5 M of a model cationic surfactant and regeneration of the sensing surface. The optical response of the membrane sensor was characterized using a simple theoretical model that enables to quantify the concentration of target molecules from the amplitude and kinetics of the measured binding curves. The device was tested with real water samples containing large amount of environmental particles, without showing clogging of the membrane, and enabling nonspecific quantification of molecular pollutants in a few minutes.

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

“…In particular, membranes made of Hyflon AD are almost index‐matched with water, hence they can be exploited as optical sensor for water contaminants. [ 38 ] The adsorption strength and kinetics on Hyflon AD depends on both the hydrophobic contact area and the net charge of the compounds. [ 36 ] Among other types of molecules, cationic surfactants spontaneously adsorb on Hyflon AD and fully cover the interface with water at large concentrations.…”

“…[ 37 ] A microfluidic device embedding this membrane sensor in a cross‐flow configuration has been proposed for continuous monitoring of environmental water pollution. [ 38 ]…”

“…[37] A microfluidic device embedding this membrane sensor in a cross-flow configuration has been proposed for continuous monitoring of environmental water pollution. [38] In this work, we present the manufacturing and the characterization of micro-porous membranes made of Hyflon AD 40 suitable for optical sensing. Hyflon AD 40 was used as the sole component of the porous membranes, in order to exploit its amorphous structure and low refractive index.…”

Rapid Manufacturing of Multilayered Microfluidic Devices for Organ on a Chip Applications

“…Only a few works can be found in the microfluidics literature regarding processing COP with cutting plotter [ 41 , 44 ] or laser cutters [ 45 ], and even a Lab-on-Chip (LoC) device fabricated in COP using cutting plotter and PSA with an embedded white polyester membrane [ 46 ]. COP has a relatively low permeability to water vapor compared to other gases such as oxygen, limiting sample evaporation and favoring the culture of respiring cells [ 42 , 44 ].…”

Self-aligned 3D microlenses in a chip fabricated with two-photon stereolithography for highly sensitive absorbance measurement

“…The EOL can also be used as an inspection indicator of stray light. The stray light is a great concern in optimizing optical systems, 20,33,35,36 as it can increase the noise level and reduce the sensitivity of optical analysis. Normally, the EOL value should not be smaller than the GOL value due to light divergence.…”