Biological responses of cells and organisms to nanoparticle exposure crucially depend on the properties of the protein adsorption layer ("protein corona") forming on nanoparticle surfaces and their characterization is a crucial step toward a deep, mechanistic understanding of their build-up. Previously, adsorption of one type of model protein on nanoparticles was systematically studied in situ by using fluorescence correlation spectroscopy. Here, the first such study of interactions is presented between water-solubilized CdSe/ZnS quantum dots (QDs) and a complex biofluid, human blood serum. Despite the large number of proteins in serum, a protein layer of well-defined (average) thickness forming on QD surfaces is observed. Both the thickness and the apparent binding affinity depend on the type of QD surface ligand. Kinetic experiments reveal that the protein corona formed from serum is irreversibly bound, whereas the one formed from human serum albumin was earlier observed to be reversible. By using sodium dodecyl sulfate-polyacrylamide gel electrophoresis and mass spectrometry, the most abundant serum proteins contributing to the formation of a hard corona on the QDs are identified.
Monolayer doping (MLD) is a relatively new method to incorporate shallow dopants from an adsorbed organic monolayer. To prevent evaporation of the dopantcontaining organic layer during thermal processing, an oxide capping layer has typically been used, without clearly understanding surface mass transport. In this work, we investigate the thermal evolution of a phosphorus-containing organic layer grafted on oxide silicon surfaces, to determine whether phosphorus can diffuse through the oxide into silicon in the absence of a capping oxide layer. Self-assembled monolayers (SAM) of phosphonic acid are grown by tethering by aggregation and growth (T-BAG) on native oxide-terminated silicon wafers, and in situ characterization is performed by infrared spectroscopy and X-ray photoelectron spectroscopy, with complementary ex situ time-of-flight secondary ion mass spectrometry and impedance spectroscopy measurements, supported by ab initio density-functional theory (DFT) calculations. We find that annealing to 700 K initiates a self-decomposition of the chemisorbed phosphonic acid molecules at the SAM/oxide interface. As the temperature is further increased, the P−C bond, which is the weakest link of the adsorbed molecule, breaks and releases the organic ligand, followed by a molecular rearrangement of the bonding configuration. Then, phosphorus transport through the silicon oxide is mediated by PO 3-x species, further driven by the transformation of the native silicon oxide to a thermal silicon oxide phase. At 1000 K, diffusion of phosphorus into the subsurface region of silicon is finally observed, without evidence for P desorption or C contamination. Our DFT results provide a mechanistic understanding of the pathway followed by the phosphorus atoms. Together, these findings provide a fundamental platform for MLD of silicon and other semiconductors in general.
We propose surface acoustic wave (SAW) resonators as a complementary tool for conditioning film monitoring. Conditioning films are formed by adsorption of inorganic and organic substances on a substrate the moment this substrate comes into contact with a liquid phase. In the case of implant insertion, for instance, initial protein adsorption is required to start wound healing, but it will also trigger immune reactions leading to inflammatory responses. The control of the initial protein adsorption would allow to promote the healing process and to suppress adverse immune reactions. Methods to investigate these adsorption processes are available, but it remains difficult to translate measurement results into actual protein binding events. Biosensor transducers allow user-friendly investigation of protein adsorption on different surfaces. The combination of several transduction principles leads to complementary results, allowing a more comprehensive characterization of the adsorbing layer. We introduce SAW resonators as a novel complementary tool for time-resolved conditioning film monitoring. SAW resonators were coated with polymers. The adsorption of the plasma proteins human serum albumin (HSA) and fibrinogen onto the polymer-coated surfaces were monitored. Frequency results were compared with quartz crystal microbalance (QCM) sensor measurements, which confirmed the suitability of the SAW resonators for this application.
A benchtop device that combines segmented flow with magnetic particle separation and active resuspension capabilities for biotechnological applications, e.g. biomolecule purification.
Strontium, calcium, and magnesium silicate hydrate phases are synthesized by the reaction between silica and solution of metal hydroxides. The kinetics of the reaction is recorded using a quartz crystal microbalance (QCM), continuously monitoring the change in frequency and dissipation energy. Based on QCM results, it is shown that properties of solutions like the pH-value or the type of ions play a pivotal function on the rate-determining stage of the reaction, the thickness of the diffuse layer, the formation of carbonates, as well as the kinetics of the formed phases. Further properties of the reaction products are investigated using X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and infrared spectroscopy (IR). With the help of thermogravimetric analysis (TGA) and temperature-dependent X-ray diffraction (XRD), we investigate how our synthesized phases can be turned into MSiO 3 structures. Finally, the Goldschmidt rules for perovskites structures show that this might be an attractive way for new and nontoxic phases in the future.
Conditioning films are an important factor in the initiation and development of microbial biofilms, which are the leading cause of chronic infections associated with medical devices. Here, we analyzed the protein content of conditioning films formed after exposure to supernatants of cultures of the human pathogen Pseudomonas aeruginosa PAO1. Adhesion of substances from the supernatant was monitored using quartz crystal microbalance with dissipation monitoring (QCM-D) sensor chips modified with the commonly used implant material titanium dioxide (TiO). Attached proteins were identified after on-chip digestion using matrix-assisted laser desorption/ionization (MALDI) time of flight (ToF) mass spectrometry (MS), and a new data processing tool consisting of an XML-database with theoretical tryptic peptides of every PAO1 protein and PHP scripts. Sub-databases containing only proteins, that we found in all replicates, were created and used for MS/MS precursor selection. The obtained MS/MS peaklists were then matched against theoretical fragmentations of the expected peptide sequences to verify protein identification. Using this approach we were able to identify 40 surface-associated proteins. In addition to extracellular proteins such as adhesins, a number of intra-cellular proteins were identified which may be involved in conditioning film formation, suggesting an as-yet unidentified role for these proteins, possibly after cell lysis. Graphical Abstract Flowchart of the method.
We have developed an ultrahigh-vacuum (UHV) apparatus which enables reflection high-energy electron diffraction (RHEED), sputtering yield measurement and ion scattering spectroscopy (ISS) to be performed simultaneously, leading to a more comprehensive understanding of the growth mechanism of titanium nitride (TiN) film by post-irradiation processing. The sputtering yield measurement revealed an anomalous sputtering phenomenon in the initial stage of post-irradiation processing, i.e., sputtering hardly took place on a titanium film under 3 keV N2 + ion irradiation for doses below ∼5×1015 ions/cm2. Further N2 + ion irradiation led to a low sputtering yield for doses between ∼5×1015 ions/cm2 to ∼3×1016 ions/cm2, and finally approached a steady-state sputtering for doses above ∼3×1016 ions/cm2. Monitoring of the surface composition was also performed by ISS to examine whether the surface composition follows the change of the sputtering behavior or not.
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