Nanometer-Scale Distribution of a Lubricant Modifier on Iron Films: A Frequency-Modulation Atomic Force Microscopy Study Combined with a Friction Test.

Liquid lubricants used in mechanical applications are low-vapor-pressure hydrocarbons modified with a small quantity of polar compounds. The polar modifiers adsorbed on the surface of sliding solids dominate the friction properties when the sliding surfaces are in close proximity. However, a few methods are available for the characterization of the adsorbed modifiers of a nanometer-scale thickness. In this study, we applied frequency-modulation atomic force microscopy to evaluate the vertical and lateral density distributions of the adsorbed modifier in a real lubricant, namely, poly-α-olefin (PAO) modified with an orthophosphoric acid oleyl ester. The liquid-induced force on the probing tip was mapped on a plane that was perpendicular to the lubricant-iron interface with a force sensitivity on the order of 10 pN. The PAO in the absence of the ester modifier was directly exposed to the film, which produced a few liquid layers parallel to the film surface with layer-to-layer distances of 0.6-0.7 nm. A monomolecular layer of the modifier was intermittently adsorbed with increasing ester concentration in the bulk lubricant, with complete coverage seen at 20 ppm. The C18H35 chains of the oleyl esters fluctuating in the lubricant produced a repulsive force on the tip, which monotonically decayed with the tip-to-surface distance. The dynamic friction coefficient of sliding steel-lubricant-steel interfaces, which was separately determined using a friction tester, was compared with the force map determined on the iron film immersed in the corresponding lubricant. The complete monomolecular layer of the ester modifier on the static lubricant-iron boundary is a requirement for achieving smooth and stable friction at the sliding interface.

Photoinduced Ligand Release from a Silicon Phthalocyanine Dye Conjugated with Monoclonal Antibodies: A Mechanism of Cancer Cell Cytotoxicity after Near-Infrared Photoimmunotherapy.

Photochemical reactions can dramatically alter physical characteristics of reacted molecules. In this study, we demonstrate that near-infrared (NIR) light induces an axial ligand-releasing reaction, which dramatically alters hydrophilicity of a silicon phthalocyanine derivative (IR700) dye leading to a change in the shape of the conjugate and its propensity to aggregate in aqueous solution. This photochemical reaction is proposed as a major mechanism of cell death induced by NIR photoimmunotherapy (NIR-PIT), which was recently developed as a molecularly targeted cancer therapy. Once the antibody-IR700 conjugate is bound to its target, activation by NIR light causes physical changes in the shape of antibody antigen complexes that are thought to induce physical stress within the cellular membrane leading to increases in transmembrane water flow that eventually lead to cell bursting and necrotic cell death.

Variability in Microplate Surface Properties and Its Impact on ELISA.

BACKGROUND: Microplate-based immunoassays are widely used in clinical and research settings to measure a broad range of biomarkers present in complex matrices. Assay variability within and between microplates can give rise to false-negative and false-positive results leading to incorrect conclusions. To date, the contribution of microplates to this variability remains poorly characterized and described. This study provides new insights into variability in immunoassays attributable to surface characteristics of commercial microplates. METHODS: Well-to-well assay variation in γ-treated and nontreated 96-well opaque microplates suitable for chemiluminescence assays was determined by use of a validated sandwich ELISA. Microplate surface characteristics were assessed by sessile drop contact angle measurements, scanning electron microscopy, energy dispersive x-ray spectroscopy, and atomic force microscopy. RESULTS: All microplate types tested exhibited vendor-specific assay response profiles; and "rogue" plates with very high intraassay variation and deviant mean assay responses were found. Within-plate, location-dependent bias in assay responses and variability in well contact angle were also observed. We demonstrate substantial differences in well-surface properties with putative effects on protein-coating reproducibility and hence consistency in immunoassay responses. A surface "cleaning" effect on manufacturing residues was attributed to γ-irradiation, and treated microplates manifest increased polar functionalities, surface roughness, and assay responses. CONCLUSIONS: Our data suggest that tighter control of variability in surface roughness, wettability, chemistry, and level of residual contaminants during microplate preparation is warranted to improve consistency of ELISA assay read out.