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

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 label-free sensing of adsorbing substances, mainly 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 \uce\ubcM 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 adsorbing substances in a few minutes

Selective adsorption on fluorinated plastic enables the optical detection of molecular pollutants in water

Amorphous fluorinated plastic can be produced with a refractive index similar to that of water, a condition that makes it essentially invisible when immersed in aqueous solutions. Because of this property, even a small amount of adsorbed molecules on the plastic-water interface provides a detectable optical signal. We investigate two distinct substrates made of this material, characterized by different interface areas: a prism and a microporous membrane. We demonstrate that both substrates enable the label-free detection of molecular compounds in water even without any surface functionalization. The adsorption of molecules on the planar surface of the prism provides an increase of optical reflectivity, whereas the adsorption on the internal surface of the microporous membrane yields an increase of scattered light. Despite the different mechanisms, we find a similar optical response upon adsorption. We confirm this result by a theoretical model accounting for both reflection and scattering. We investigate the spontaneous adsorption process for different kinds of molecules: surfactants with different charges, a protein (lysozyme), and a constituent of gasoline (hexane). The measured equilibrium and kinetic constants for adsorption differ by orders of magnitudes among the different classes of molecules. By suitable analytical models, accounting for the effects of mass limitation and transport, we find a simple and general scaling of the adsorption parameters with the molecular size

Ritornando sulla canzone di Auliver e su altre liriche di et\ue0 caminese

Annotazioni filologiche ed esegetiche su componimenti di Aulvere e di Nicol\uf2 de' Ross

Optical detection of surfactants by means of reflective phantom interface method

Surfactants are among the most relevant organic pollutants of water with threatening potential for the aquatic environment. The most common and widespread techniques to detect surfactants in water samples are typically expensive and time consuming. In this context, we propose a new kind of optical sensor, based on an amorphous fluorinated plastic iso-refractive to water and, therefore, barely visible in aqueous solutions. When a thin molecular layer with a different refractive index adsorbs at the interface, the intensity of reflected or scattered light markedly increases, hence enabling a simple and real-time detection. We investigated the interaction between the plastic iso-refractive to water and a non-ionic surfactant (Tween 20) by measuring the intensity of light reflected by a planar interface as a function of time after the addition of different concentrations of surfactant. This detection scheme has been also tested with natural water samples taken from the Lambro river across the city of Milan