Adhesion forces controlled by chemical self-assembly and pH. Application to robotic microhandling.

International audienceRobotic microhandling is a promising way to assemble microcomponents in order to manufacture new generation of Hybrid Micro ElectroMechanical Systems (HMEMS). However, at the scale of several micrometers, adhesion phenomenon highly perturbs the micro-objects release and the positioning. This phenomenon is directly linked to both the object and the gripper surface chemical composition. We propose to control adhesion by using chemical selfassembly monolayer (SAM) on both surfaces. Different types of chemical functionalisation have been tested and this paper focuses on the presentation of aminosilane grafted (3 (ethoxydimethylsilyl) propyl amine (APTES) and (3 aminopropyl) triethoxysilane (APDMES)). We show that the liquid pH can be used to modify the adhesion and to switch from an attractive behaviour to a repulsive behaviour. The pH control can thus be used to increase adhesion during handling and cancel adhesion during release. Experiments have shown that the pH control is able to control the release of a micro-object. This paper shows the relevance of a new type of reliable submerged robotic microhandling principle, which is based on adjusting chemical properties of liquid

Reduction of a micro-object's adhesion using chemical functionalisation.

International audienceThe adhesion and interaction properties of functionalised surfaces (substrate or cantilever) were investigated by means of atomic force microscope (AFM) related force measurements. The surfaces were functionalised with a polyelectrolyte: Poly(Allylamine Hydrochloride) (PAH), or with silanes: 3 (ethoxydimethylsilyl) propyl amine (APTES) or (3 aminopropyl) triethoxysilane (APDMES). Measurements of forces acting between a bare glass sphere (functionalised or not) and a functionalised surface indicated repulsive or attractive forces, depending on functionnalisation and medium (wet or dry). Adhesion forces (pull-off) can be observed in dry medium while in wet medium, this phenomenon can be cancelled. Now, the pull-off forces is an important problem in the automation of micro-object manipulations. The cancellation of this force by chemical functionnalisation is thus a promising way to improve micro-assembly in the future

Immunologically Modified FETs for Protein Detection in Biological Fluids

Engineering: 3rd Place (The Ohio State University Denman Undergraduate Research Forum)Field effect transistors (FETs) are solid-state electrical devices with semiconductor channels through which charge carriers migrate and generate current. The application of an electric field proximal to the conductive channel causes a change in current depending on the sign and magnitude of the field. FETs can be modified for protein sensing by deployment of antibodies as receptors on the channel surface to create an immunologically modified FET (immunoFET). Binding of analytes brings a layer of charge proximal to the channel surface, causing modulation of current that is easily detectable, allowing for quantitative detection of unlabeled analytes. We present the successful detection of​ inflammatory chemokine CXCL9 in both murine serum and human urine from transplant patients using immunoFETs modified with anti-CXCL9 IgG. CXCL9 was detected in renal transplant urine at biologically relevant levels and correlated with rejection by renal biopsy. The presented work demonstrates the feasibility of immunoFET sensor operation in physiologic buffers, and shows the potential to provide real-time quantification and monitoring of inflammatory mediators, allowing for minimally invasive interrogation of graft status. The FET design may be scalable to allow for real-time, label-free, point-of-care diagnostic use.Academic Major: Biomedical EngineeringAcademic Major: Electrical and Computer Engineerin

Mesoporous Coatings with Simultaneous Light‐Triggered Transition of Water Imbibition and Droplet Coalescence

A systematic study of gating water infiltration and condensation into ceramic nanopores by carefully adjusting the wetting properties of mesoporous films using photoactive spiropyran is presented. Contact angle measurements from the side reveal significant changes in wettability after irradiation due to spiropyran/merocyanine-isomerization, which induce a wetting transition from dry to wet pores. The change in wettability allows the control of water imbibition in the nanopores and is reflected by the formation of an imbibition ring around a droplet. Furthermore, the photoresponsive wettability is able to overcome pinning effects and cause a movement of a droplet contact line, facilitating droplet coalescence, as recorded by high-speed imaging. The absorbed light not only effectuates droplet merging but also causes flows inside the drop due to heat absorption by the spiropyran, which results in gradients in the surface tension. IR imaging and particle tracking is used to investigate the heat absorption and temperature-induced flows, respectively. These flows can be used to manipulate, for example, molecular movement inside water and deposition inside solid mesoporous materials and are therefore of great importance for nanofluidic devices as well as for future water management concepts, which include filtering by imbibition and collection by droplet coalescence. © 2021 The Authors. Advanced Materials Interfaces published by Wiley-VCH Gmb

A Molecular Investigation of Absorption onto Mineral Pigments

Pigment suspensions are important in several processes such as ceramics, paints, inks, and coatings. In the wet state, pigments are combined with a variety of chemical species such as polymers, surfactants, and polyelectrolytes which produce a complex colloidal system. The adsorption, desorption, and redistribution of these species at the pigment - aqueous solution interface can have an impact on the behavior in both the wet state or its final dried state. The goal of this work is to establish a molecular picture of the adsorption properties of these pigmented systems. A novel in situ infrared technique has been developed which allows the detection of adsorbed surface species on pigment particles in an aqueous environment. The technique involves the use of a polymeric binder to anchor the colloidal pigment particles to the surface of an internal reflection element (IRE). The binder only weakly perturbs about 25% of the reactive surface sites (hydroxyl groups) on silica. The reaction of succinic anhydride with an aminosilanized silica surface has been quantified using this technique. The adsorption dynamics of the cationic surfactant cetyltrimethylamrnonium bromide (C16TAB) at the Ti02 - aqueous solution interface has been investigated using Fourier transform infrared - attenuated total reflection spectroscopy (FTIR-ATR) and electrokinetic analysis. At low bulk concentrations, C16TAB is shown to adsorb as isolated islands with a defective bilayer structure. Anionic probe molecules are shown to effectively tune the adsorbed surfactant microstructure. The results indicate that the structure of the adsorbed surfactant layer, and not the amount of adsorbed surfactant, dictates the subsequent adsorption behavior of the system. Atomic Layer Deposition is used to deposit a TiO2 layer onto the surfaces of silica and kaolin pigments. The process involves the cyclic reaction sequence of the vapors of TiC14 and H2O. Three complete deposition cycles are needed before the surfaces of the modified pigments are dominated by the presence of TiO2. The modified kaolin pigments display increased dispersion stability as compared to the parent kaolin. The electrokinetic behavior of the modified kaolin is shown to be identical to that of pure TiO2 pigments

Determination of Nano-sized Adsorbate Mass in Solution using Mechanical Resonators: Elimination of the so far Inseparable Liquid Contribution

Assumption-free mass quantification of nanofilms, nanoparticles, and (supra)molecular adsorbates in liquid environment remains a key challenge in many branches of science. Mechanical resonators can uniquely determine the mass of essentially any adsorbate; yet, when operating in liquid environment, the liquid dynamically coupled to the adsorbate contributes significantly to the measured response, which complicates data interpretation and impairs quantitative adsorbate mass determination. Employing the Navier-Stokes equation for liquid velocity in contact with an oscillating surface, we show that the liquid contribution can be eliminated by measuring the response in solutions with identical kinematic viscosity but different densities. Guided by this insight, we used quartz crystal microbalance (QCM), one of the most widely-employed mechanical resonator, to demonstrate that kinematic-viscosity matching can be utilized to accurately quantify the dry mass of systems such as adsorbed rigid nanoparticles, tethered biological nanoparticles (lipid vesicles), as well as highly hydrated polymeric films. The same approach applied to the simultaneously measured energy dissipation made it possible to quantify the mechanical properties of the adsorbate and its attachment to the surface, as demonstrated by, for example, probing the hydrodynamic stablization induced by nanoparticles crowding. Finally, we envision that the possibility to simultaneously determine the dry mass and mechanical properties of adsorbates as well as the liquid contributions will provide the experimental tools to use mechanical resonators for applications beyond mass determination, as for example to directly interrogate the orientation, spatial distribution, and binding strength of adsorbates without the need for complementary techniques.Comment: 22 pages, 7 figure

Investigation of reagent storage and electrochemical testing on filter paper

Thesis (Ph.D.)--Boston UniversityDiagnosis and detection is one of the most effective means of controlling matters that adversely affect public health and safety. Yet, in the developing world with a high burden of disease, most gold standard diagnostics remain widely inaccessible due to cost and lack of infrastructure. In recent years, one strategy to increase access to health and safety devices has been through the development of point-of-care diagnostics that are low-cost, portable, and easy-to-use for on-site analysis. In particular, paper has recently been in the spotlight as such a point-of-care (POC) platform. Compared to conventional POC tests made of glass or plastic substrates, paper itself is even thinner, light-weight, portable, disposable, and can store biological and chemical molecules for analytical measurement within its fibrous network. Several paper-based tests have demonstrated high sensitivity and specificity to detect proteins, bacteria, and metals for applications in disease diagnosis, health monitoring, and food and water safety. However, several gaps still remain in order to fully develop these paper-based analytical devices for point-of-care use in low-resource settings. First, reagent stability on filter paper is poorly understood, as well as its influence on quantitative, long-term testing. Second, the need for specialized instrumentation to perform the analytical methods on the paper devices can be a logistical and financial burden to end users in resource-limited settings. This dissertation addressed these questions through the development of quantitative paper assays for robust and point-of-care testing in low-resource settings. First, we fabricated micro-paper electrochemical devices, or µPEDs, for the amperometric detection of ethanol. This target analyte has direct applications in the global issue of road safety, which claims thousands of lives due to driving under the influence of alcohol. Also, we demonstrate that ethanol detection can provide the basis for the novel detection of substandard misoprostol, a high impact drug to save mothers from post-partum bleeding that is often the reason for maternal mortality. Second, we developed an independent method to study reagent stability on filter paper under conditions likely encountered in low-resource settings. Methods that enhanced stability were also used in the development of the µPEDs. Finally, we demonstrate that the ethanol measurements on our µPEDs could be performed with a commercial glucose meter, which operate by the same principles required to measure analyte concentrations. This integration of device and reader presents a cheap, reliable, low-power, and portable platform that can be adapted for the detection of other analytes relevant to health and safety

Quantification and Reduction of the Residual Chemical Reactivity of Passivated Biodegradable Porous Silicon for Drug Delivery Applications

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