A split aptamer (SPA)-based sandwich-type biosensor for facile and rapid detection of streptomycin.

T-matrix methods for electromagnetic structured beams mainly encompass Generalized Lorenz-Mie Theories (GLMTs) which form a set of analytical approaches dealing with the interaction between electromagnetic structured beams and a class of particles possessing enough symmetries to allow one to use the method of separation of variables, and Extended Boundary Condition Method (EBCM) which is a semi-analytical method dealing in principle with arbitrary shaped particles. Both approaches, when dealing with structured beams (in principle in the case of GLMTs and occasionally in the case of EBCM) rely on the description of the illuminating beam in terms of Beam Shape Coefficients (BSCs). The present paper provides a commented reference database concerning GLMTs and EBCM for structured beams, and related topics for the period 2014–2018.

T-matrix methods for electromagnetic structured beams: A commented reference database for the period 2014–2018

Among the many works of Arthur Ashkin, many have been devoted to optical tweezers, optical levitation and optical manipulation of macroscopic particles (“macroscopic” being here to beunderstood as opposed to atoms or molecules). From a theoretical point of view, these experiments have been studied in the framework of two limiting regimes, namely Rayleigh regime for small size parameter and ray optics for large size parameter. The generalized Lorenz-Mie theory (GLMT, and more generally GLMTs) bridges the gap between these two regimes. The present paper therefore reviews GLMTs and mechanical effects of laser light, in Rouen where the GLMT had originally been built, but also worldwide. A story in the review concerns the first experimental validations of GLMT using optical levitation experiments.

Generalized Lorenz--Mie theories and mechanical effects of laser light, on the occasion of Arthur Ashkin’s receipt of the 2018 Nobel prize in physics for his pioneering work in optical levitation and manipulation: A review

Once materials come into contact with a biological fluid containing proteins, proteins are generally-whether desired or not-attracted by the material's surface and adsorb onto it. The aim of this Review is to give an overview of the most commonly used characterization methods employed to gain a better understanding of the adsorption processes on either planar or curved surfaces. We continue to illustrate the benefit of combining different methods to different surface geometries of the material. The thus obtained insight ideally paves the way for engineering functional materials that interact with proteins in a predetermined manner.

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Engineering Proteins at Interfaces: From Complementary Characterization to Material Surfaces with Designed Functions.

The contact between a sphere and a planar half space, one being rigid and the other elastic (or between two elastic spheres), can be described by the JKR theory of Johnson, Kendall and Roberts (Proc. R. Soc. Lond. A 1971, 324, 301). One assumption of JKR theory is that the characteristic length scale L ≈ w/E is much smaller than the radius R of the sphere; where w is the work of adhesion and E is the Young's modulus of the soft, elastic body. Relative deformations for a mechanical contact increase with increasing L and decreasing particle size R. Experiments show that up to at least L/R = 0.2, JKR theory predicts the correct dependencies between the contact radius, the indentation and the load. However, when R ≫ L is no longer satisfied, the change in total free surface area due to deformation needs to be considered. Then, elastocapillary effects start playing a significant role. In addition to discussing theory and experiments of pure solid contacts, the effect of elastic deformation on capillary and hydrodynamic forces is discussed. Finally, we consider the interaction of hollow capsules as one example of a deformable body that is still formed from a stiff material.

Forces between a stiff and a soft surface

Here we investigated the stability of an aptamer, which is formed by two RNA strands and binds the antibiotic streptomycin. Molecular dynamics simulations in aqueous solution confirmed the geometry and the pattern of hydrogen bond interactions that was derived from the crystal structure (1NTB). The result of umbrella sampling simulations indicated a favored streptomycin binding with a free energy of ΔGbind° = −101.7 kJ mol–1. Experimentally, the increase in oligonucleotide stability upon binding of streptomycin was probed by single-molecule force spectroscopy. Rate dependent force spectroscopy measurements revealed a decrease in the natural off-rate (koff-COMPLEX = 0.22 ± 0.16 s–1) for the aptamer–streptomycin complex compared to the aptamer having an empty binding pocket (koff-APTAMER = 0.49 ± 0.11 s–1). This decrease in the natural off-rate corresponds to a decrease in the Gibbs free energy of ΔΔGsheer ≈ −3.4 kJ mol–1. The simulated binding pattern and the experimental results led to the conclusion that...

Stability of a Split Streptomycin Binding Aptamer.

It was recently suggested that the electrostatic double-layer force between colloidal particles might weaken at high hydrostatic pressure encountered, for example, in deep seas or during oil recovery. We have addressed this issue by means of a specially designed optical trapping setup that allowed us to explore the interaction of a micrometer-sized glass bead and a solid glass wall in water at hydrostatic pressures of up to 1 kbar. The setup allowed us to measure the distance between bead and wall with a subnanometer resolution. We have determined the Debye lengths in water for salt concentrations of 0.1 and 1 mM. We found that in the pressure range from 1 bar to 1 kbar the maximum variation of the Debye lengths was <1 nm for both salt concentrations. Furthermore, the magnitude of the zeta potentials of the glass surfaces in water showed no dependency on pressure.

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Thomas A. Nick

Papers

Stability of a Split Streptomycin Binding Aptamer.

Surface forces between colloidal particles at high hydrostatic pressure