Magnetite-doped polydimethylsiloxane (PDMS) for phosphopeptide enrichment

Reversible phosphorylation plays a key role in numerous biological processes. Mass spectrometry-based approaches are commonly used to analyze protein phosphorylation, but such analysis is challenging, largely due to the low phosphorylation stoichiometry. Hence, a number of phosphopeptide enrichment strategies have been developed, including metal oxide affinity chromatography (MOAC). Here, we describe a new material for performing MOAC that employs a magnetite-doped polydimethylsiloxane (PDMS), that is suitable for the creation of microwell array and microfluidic systems to enable low volume, high throughput analysis. Incubation time and sample loading were explored and optimized and demonstrate that the embedded magnetite is able to enrich phosphopeptides. This substrate-based approach is rapid, straightforward and suitable for simultaneously performing multiple, low volume enrichments

Wettability-independent bouncing on flat surfaces mediated by thin air films

The impingement of drops onto solid surfaces1, 2 plays a crucial role in a variety of processes, including inkjet printing, fog harvesting, anti-icing, dropwise condensation and spray coating3, 4, 5, 6. Recent efforts in understanding and controlling drop impact behaviour focused on superhydrophobic surfaces with specific surface structures enabling drop bouncing with reduced contact time7, 8. Here, we report a different universal bouncing mechanism that occurs on both wetting and non-wetting flat surfaces for both high and low surface tension liquids. Using high-speed multiple-wavelength interferometry9, we show that this bouncing mechanism is based on the continuous presence of an air film for moderate drop impact velocities. This submicrometre ‘air cushion’ slows down the incoming drop and reverses its momentum. Viscous forces in the air film play a key role in this process: they provide transient stability of the air cushion against squeeze-out, mediate momentum transfer, and contribute a substantial part of the energy dissipation during bouncing

Wetting theory for small droplets on textured solid surfaces

This work is supported by the National Research Foundation of Korea (NRF) funded by the Ministry of Science, ICT & Future Planning (2016M3D1A1900038). N.M.P. is supported by the European Research Council (ERC StG Ideas 2011 BIHSNAM n. 279985, ERC PoC 2015 SILKENE nr. 693670), by the European Commission under the Graphene Flagship (WP14 Polymer Composites, no. 696656). N.M.P. thanks Profs. Della Volpe and Siboni for useful comments on the paper

A microfabricated cyclo-olefin polymer microcolumn used for reversed-phase chromatography

The fabrication of a deep (28 μm, aspect ratio 3:1) cyclo-olefin polymer (COP) microcolumn and separation of varying polarity chemicals is described. A silicon master is first fabricated and utilized to hot-emboss the COP foil, which is subsequently sealed with thermal bonding. The microcolumn material (COP) is used unmodified, taking advantage of the hydrophobic properties of the COP which simplify the fabrication process of the microcolumn. Then, evaluation of the COP microcolumn ability for reversed phase chromatographic separations is performed and finally a successful separation of a mixture of four chemicals is demonstrated using a portable microfluidic set up and large injection volumes (100 nl) without an on-chip injector. © 2015 IOP Publishing Ltd

Binding kinetics of bacteria cells on immobilized antibodies in microfluidic channels: Modeling and experiments

Many separation or detection techniques, such as chromatography or detection on a sensor, are based upon the interaction between analyte molecules and immobilized ligand molecules on the surface of a microfluidic channel. Typically, the aim is to capture an analyte with the maximum possible binding to the ligands. Here, we elaborate a mathematical model for the binding kinetics of analyte molecules passing through a microchannel with simultaneous association to ligand molecules on its surface to provide deeper understanding and prediction of experimental behavior. The focus and contribution of this work is on analytes that are not discrete units, but are grouped as binding sites (e.g. antigens on the outer cell membrane), while our results can also find application for functionalized micro particles. We apply and validate the model for the case where analytes are grouped on Salmonella cells, and ligands are anti-Salmonella antibodies. A simple equation is developed with variables the flow rate, microchannel dimensions, concentrations, and the active area-ratio increase when a rough microchannel is used. The model is used to fit the association rate constants with spatially varying experimental data of number densities (cells/mm2) of Green Fluorescent Protein (GFP)-Salmonella cell binding in a microfluidic device. The model is also used to predict cell binding in various microchannels with different geometries, and to design microfluidics for specific operations. © 2017 Elsevier B.V

Mechanisms of Oxygen Plasma Nanotexturing of Organic Polymer Surfaces: From Stable Super Hydrophilic to Super Hydrophobic Surfaces

International audiencePlasma processing is used to fabricate super hydrophilic or super hydrophobic polymeric surfaces by means of O-2 plasma etching of two organic polymers, namely, poly(methyl methacrylate) (PMMA) and poly(ether ether ketone) (PEEK); a C4F8 plasma deposition follows O-2 plasma etching, if surface hydrophobization is desired. We demonstrate high aspect ratio pillars with height ranging from 16 nm to several micrometers depending oil the processing time, and contact angle (CA) close to 0 degrees after O-2-Plasma treatment or CA of 153 degrees (with CA hysteresis lower than 5 degrees) after fluorocarbon deposition. Super hydrophobic surfaces are robust and stable in time; in addition, aging of super hydrophilic surfaces is significantly retarded because of the beneficial effect of the nanotextured topography. The mechanisms responsible for the plasma-induced PMMA and PEEK surface nanotexturing are unveiled through intelligent experiments involving intentional modification of the reactor wall material and X-ray photoelectron spectroscopy, which is also used to study the surface chemical modification in the plasma. We prove that control of plasma nanotexture call be achieved by carefully choosing the reactor wall material

Gradient-temperature hot-embossing for dense micropillar array fabrication on thick cyclo-olefin polymeric plates: An example of a microfluidic chromatography column fabrication

The fabrication of dense and high aspect ratio pillar arrays is important for several applications. In particular polymeric microfluidic chromatography columns are of high importance for various biological, pharmaceutical and chemical separations. Here, a cyclo‐olefin polymeric (COP) microcolumn fabrication process is developed using hot embossing with a temperature gradient for replication of a fine and highly dense array of micropillars on the surface of a 2 mm thick polymer plate without chip deformation. The design consists of an array of ordered cylindrical pillars with 15 μm diameter, 4 μm interpillar, and 2 μm pillar-wall distance with 20 μm height. The produced microcolumn is subsequently sealed with thermal bonding in a laminator and tested for liquid pressure operation up to 20 bar. Since COPs are hydrophobic by nature and have been used for reversed-phase liquid chromatographic (RPLC) separations in the past, preliminary separation experiments are also demonstrated in the fabricated column. © 201

Direct covalent biomolecule immobilization on plasma-nanotextured chemically stable substrates

A new method for direct covalent immobilization of protein molecules (including antibodies) on organic polymers with plasma-induced random micronanoscale topography and stable-in-time chemical functionality is presented. This is achieved using a short (1–5 min) plasma etching and simultaneous micronanotexturing process, followed by a fast thermal annealing step, which induces accelerated hydrophobic recovery while preserving important chemical functionality created by the plasma. Surface-bound biomolecules resist harsh washing with sodium dodecyl sulfate and other detergents even at elevated temperatures, losing less than 40% of the biomolecules bound even at the harshest washing conditions. X-ray photoelectron spectroscopy, secondary-ion mass spectrometry, and electron paramagnetic resonance are used to unveil the chemical modification of the plasma-treated and stabilized surfaces. The nanotextured and chemically stabilized surfaces are used as substrates for the development of immunochemical assays for the sensitive detection of C-reactive protein and salmonella lipopolysaccharides through immobilization of the respective analyte-specific antibodies onto them. Such substrates are stable for a period of 1 year with ambient storage