The Density and Refractive Index of Adsorbing Protein Layers

AbstractThe structure of the adsorbing layers of native and denatured proteins (fibrinogen, γ-immunoglobulin, albumin, and lysozyme) was studied on hydrophilic TiO2 and hydrophobic Teflon-AF surfaces using the quartz crystal microbalance with dissipation and optical waveguide lightmode spectroscopy techniques. The density and the refractive index of the adsorbing protein layers could be determined from the complementary information provided by the two in situ instruments. The observed density and refractive index changes during the protein-adsorption process indicated the presence of conformational changes (e.g., partial unfolding) in general, especially upon contact with the hydrophobic surface. The structure of the formed layers was found to depend on the size of the proteins and on the experimental conditions. On the TiO2 surface smaller proteins formed a denser layer than larger ones and the layer of unfolded proteins was less dense than that adsorbed from the native conformation. The hydrophobic surface induced denaturation and resulted in the formation of thin compact protein films of albumin and lysozyme. A linear correlation was found between the quartz crystal microbalance measured dissipation factor and the total water content of the layer, suggesting the existence of a dissipative process that is related to the solvent molecules present inside the adsorbed protein layer. Our measurements indicated that water and solvent molecules not only influence the 3D structure of proteins in solution but also play a crucial role in their adsorption onto surfaces

Trends in Epidermal Stretchable Electronics for Noninvasive Long-term Healthcare Applications

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Electrochemically switchable platform for the micro-patterning and release of heterotypic cell sheets

This article describes a dynamic platform in which the biointerfacial properties of micro-patterned domains can be switched electrochemically through the spatio-temporally controlled dissolution and adsorption of polyelectrolyte coatings. Insulating SU-8 micro-patterns created on a transparent indium tin oxide electrode by photolithography allowed for the local control over the electrochemical dissolution of polyelectrolyte mono- and multilayers, with polyelectrolytes shielded from the electrochemical treatment by the underlying photoresist stencil. The platform allowed for the creation of micro-patterned cell co-cultures through the electrochemical removal of a non-fouling polyelectrolyte coating and the localized adsorption of a cell adhesive one after attachment of the first cell population. In addition, the use of weak adhesive polyelectrolyte coatings on the photoresist domains allowed for the detachment of a contiguous heterotypic cell sheet upon electrochemical trigger. Cells grown on the ITO domains peeled off upon electrochemical dissolution of the sacrificial polyelectrolyte substrate, whereas adjacent cell areas on the insulated weakly adhesive substrate easily detached through the contractile force generated by neighboring cells. This electrochemical strategy for the micro-patterning and detachment of heterotypic cell sheets combines simplicity, precision and versatility, and presents great prospects for the creation of cellular constructs which mimic the cellular complexity of native tissue

Electrical microcurrent to prevent conditioning film and bacterial adhesion to urological stents

Long-term catheters remain a significant clinical problem in urology due to the high rate of bacterial colonization, infection, and encrustation. Minutes after insertion of a catheter, depositions of host urinary components onto the catheter surface form a conditioning film actively supporting the bacterial adhesion process. We investigated the possibility of reducing or avoiding the buildup of these naturally forming conditioning films and of preventing bacterial adhesion by applying different current densities to platinum electrodes as a possible catheter coating material. In this model we employed a defined environment using artificial urine and Proteus mirabilis. The film formation and desorption was analyzed by highly mass sensitive quartz crystal microbalance and surface sensitive atomic force microscopy. Further, we performed bacterial staining to assess adherence, growth, and survival on the electrodes with different current densities. By applying alternating microcurrent densities on platinum electrodes, we could produce a self regenerative surface which actively removed the conditioning film and significantly reduced bacterial adherence, growth, and survival. The results of this study could easily be adapted to a catheter design for clinical us

Cell Adhesion on Dynamic Supramolecular Surfaces Probed by Fluid Force Microscopy-Based Single-Cell Force Spectroscopy

Biomimetic and stimuli-responsive cell-material interfaces are actively being developed to study and control various cell-dynamics phenomena. Since cells naturally reside in the highly dynamic and complex environment of the extracellular matrix, attempts are being made to replicate these conditions in synthetic biomaterials. Supramolecular chemistry, dealing with noncovalent interactions, has recently provided possibilities to incorporate such dynamicity and responsiveness in various types of architectures. Using a cucurbit[8]uril-based host−guest system, we have successfully established a dynamic and electrochemically responsive interface for the display of the integrin-specific ligand, Arg-Gly-Asp (RGD), to promote cell adhesion. Due to the weak nature of the noncovalent forces by which the components at the interface are held together, we expected that cell adhesion would also be weaker in comparison to traditional interfaces where ligands are usually immobilized by covalent linkages. To assess the stability and limitations of our noncovalent interfaces, we performed single-cell force spectroscopy studies using fluid force microscopy. This technique enabled us to measure rupture forces of multiple cells that were allowed to adhere for several hours on individual substrates. We found that the rupture forces of cells adhered to both the noncovalent and covalent interfaces were nearly identical for up to several hours. We have analyzed and elucidated the reasons behind this result as a combination of factors including the weak rupture force between linear Arg-Gly-Asp and integrin, high surface density of the ligand, and increase in effective concentration of the supramolecular components under spread cells. These characteristics enable the construction of highly dynamic biointerfaces without compromising cell-adhesive properties

Boundary Lubrication of Oxide Surfaces by Poly(L-lysine)- g -poly(ethylene glycol) (PLL- g -PEG) in Aqueous Media

In this work, we have explored the application of poly(L-lysine)-g-poly(ethylene glycol) (PLL-g-PEG) as an additive to improve the lubricating properties of water for metal-oxide-based tribo-systems. The adsorption behavior of the polymer onto both silicon oxide and iron oxide has been characterized by optical waveguide lightmode spectroscopy (OWLS). Several tribological approaches, including ultra-thin-film interferometry, the mini traction machine (MTM), and pin-on-disk tribometry, have been employed to characterize the frictional properties of the oxide tribo-systems in various contact regimes. The polymer appears to form a protective layer on the tribological interface in aqueous buffer solution and improves both the load-carrying and boundary-layer-lubrication properties of wate

Local surface modification via confined electrochemical deposition with FluidFM †

International audienceWe show how the association of AFM with microfluidics, namely FluidFM, is a valuable approach for the versatile electrochemical creation of patterns having diverse shapes and topologies. Localization of the electrochemical reactions was obtained by confining the electroactive species in the microchannel and dispensing them at a precise position through the aperture of FluidFM probes. The force feedback enabled a gentle approach onto the electrode as well as a gentle contact during both the lithography procedure as well as in situ topographical AFM imaging just before or after deposition. As model systems, we demonstrate electroplating of copper and electrografting of organic moieties by reduction of aryldiazonium salts

Optical sensing and determination of complex reflection coefficients of plasmonic structures using transmission interferometric plasmonic sensor

The combination of interferometry and plasmonic structure, which consists of gold nanoparticle layer, sputter coated silicon oxide spacer layer, and aluminum mirror layer, was studied in transmission mode for biosensing and refractive index sensing applications. Because of the interferometric nature of the system, the information of the reflection amplitude and phase of the plasmonic layer can be deduced from one spectrum. The modulation amplitude in the transmission spectrum, caused by the interference between the plasmonic particle layer and the mirror layer, increases upon the refractive index increase around the plasmonic particles due to their coherent backscattering property. Our proposed evaluation method requires only two light sources with different wavelengths for a stable self-referenced signal, which can be easily and precisely tuned by a transparent spacer layer thickness. Unlike the standard localized surface plasmon sensors, where a sharp resonance peak is essential, a broad band plasmon resonance is accepted in this method. This leads to large fabrication tolerance of the plasmonic structures. We investigated bulk and adsorption layer sensitivities both experimentally and by simulation. The highest sensitivity wavelength corresponded to the resonance of the plasmonic particles, but useful signals are produced in a much broader spectral range. Analysis of a single transmission spectrum allowed us to access the wavelength-dependent complex reflection coefficient of the plasmonic particle layer, which confirmed the reflection amplitude increase in the plasmonic particle layer upon molecular adsorption