Weak-cooperative binding of a long single-stranded DNA chain on a surface.

Binding gene-wide single-stranded nucleic acids to surface-immobilized complementary probes is an important but challenging process for biophysical studies and diagnostic applications. The challenge comes from the conformational dynamics of the long chain that affects its accessibility and weakens its hybridization to the probes. We investigated the binding of bacteriophage genome M13mp18 on several different 20-mer probes immobilized on the surface of a multi-spot, label-free biosensor, and observed that only a few of them display strong binding capability with dissociation constant as low as 10 pM.

Serum antibody fingerprinting of SARS-CoV-2 variants in infected and vaccinated subjects by label-free microarray biosensor.

Both viral infection and vaccination affect the antibody repertoire of a person. Here, we demonstrate that the analysis of serum antibodies generates information not only on the virus type that caused the infection but also on the specific virus variant. We developed a rapid multiplex assay providing a fingerprint of serum antibodies against five different SARS-CoV-2 variants based on a microarray of virus antigens immobilized on the surface of a label-free reflectometric biosensor.

Digital Detection of Single Virus Particles by Multi-Spot, Label-Free Imaging Biosensor on Anti-Reflective Glass.

Rapid detection of whole virus particles in biological or environmental samples represents an unmet need for the containment of infectious diseases. Here, an optical device enabling the enumeration of single virion particles binding on antibody or aptamers immobilized on a surface with anti-reflective coating is described. In this regime, nanoparticles adhering to the sensor surface provide localized contributions to the reflected field that become detectable because of their mixing with the interfering waves in the reflection direction.

Walking Ferroelectric Liquid Droplets with Light.

The motion of ferroelectric liquid sessile droplets deposited on a ferroelectric lithium niobate substrate can be controlled by a light beam of moderate intensity irradiating the substrate at a distance of several droplet diameters from the droplet itself. The ferroelectric liquid is a nematic liquid crystal, in which almost complete polar ordering of the molecular dipoles generates an internal macroscopic polarization locally collinear to the mean molecular long axis. Upon entering the ferroelectric phase, droplets are either attracted toward the center of the beam or repelled, depending on the side of the lithium niobate exposed to light irradiation.

Label-free optical biosensors in the pandemic era.

The research in the field of optical biosensors is continuously expanding, thanks both to the introduction of brand new technologies and the ingenious use of established methods. A new awareness on the potential societal impact of this research has arisen as a consequence of the Covid-19 pandemic. The availability of a new generation of analytical tools enabling a more accurate understanding of bio-molecular processes or the development of distributed diagnostic devices with improved performance is now in greater demand and more clearly envisioned, but not yet achieved.

Explosive electrostatic instability of ferroelectric liquid droplets on ferroelectric solid surfaces.

We investigated the electrostatic behavior of ferroelectric liquid droplets exposed to the pyroelectric field of a lithium niobate ferroelectric crystal substrate. The ferroelectric liquid is a nematic liquid crystal, in which almost complete polar ordering of the molecular dipoles generates an internal macroscopic polarization locally collinear to the mean molecular long axis. Upon entering the ferroelectric phase by reducing the temperature from the nematic phase, the liquid crystal droplets become electromechanically unstable and disintegrate by the explosive emission of fluid jets.

Correction: Surface alignment of ferroelectric nematic liquid crystals.

Correction for 'Surface alignment of ferroelectric nematic liquid crystals' by Federico Caimi , , 2021, , 8130-8139, https://doi.org/10.1039/D1SM00734C.

Surface alignment of ferroelectric nematic liquid crystals.

The success of nematic liquid crystals in displays and optical applications is due to the combination of their optical uniaxiality, fluidity, elasticity, responsiveness to electric fields and controllable coupling of the molecular orientation at the interface with solid surfaces. The discovery of a polar nematic phase opens new possibilities for liquid crystal-based applications, but also requires a new study of how this phase couples with surfaces. Here we explore the surface alignment of the ferroelectric nematic phase by testing different rubbed and unrubbed substrates that differ in coupling strength and anchoring orientation and find a variety of behaviors - in terms of nematic orientation, topological defects and electric field response - that are specific to the ferroelectric nematic phase and can be understood as a consequence of the polar symmetry breaking.

A Bit Stickier, a Bit Slower, a Lot Stiffer: Specific vs. Nonspecific Binding of Gal4 to DNA.

Transcription factors regulate gene activity by binding specific regions of genomic DNA thanks to a subtle interplay of specific and nonspecific interactions that is challenging to quantify. Here, we exploit Reflective Phantom Interface (RPI), a label-free biosensor based on optical reflectivity, to investigate the binding of the N-terminal domain of Gal4, a well-known gene regulator, to double-stranded DNA fragments containing or not its consensus sequence. The analysis of RPI-binding curves provides interaction strength and kinetics and their dependence on temperature and ionic strength.

Yield stress "in a flash": investigation of nonlinearity and yielding in soft materials with an optofluidic microrheometer.

Yield stress materials deform as elastic solids or flow as viscous liquids, depending on the applied stress, which also allows them to trap particles below a certain size or density threshold. To investigate the conditions for such a transition at the microscale, we use an optofluidic microrheometer, based on the scattering of an infrared beam onto a microbead, which reaches forces in the nN scale. We perform creep experiments on a model soft material composed of swollen microgels, determining the limits of linear response and yield stress values, and observe quantitative agreement with bulk measurements.

Poor concordance between definitions of type III arch and implications for risk prediction and assessment for carotid artery stenting.

Objective: The type III arch configuration has been inconsistently reported as a stroke risk factor during carotid artery stenting. However, at least three different methods for the definition of type III arch can be identified in the literature, related to the level of the origin of the innominate artery (IA). According to Casserly's definition, a type III arch presents with an origin of the IA below the horizontal plane of the inner curvature.

Gelling without Structuring: A SAXS Study of the Interactions among DNA Nanostars.

We evaluate, by means of synchrotron small-angle X-ray scattering, the shape and mutual interactions of DNA tetravalent nanostars as a function of temperature in both the gas-like state and across the gel transition. To this end, we calculate the form factor from coarse-grained molecular dynamics simulations with a novel method that includes hydration effects; we approximate the radial interaction of DNA nanostars as a hard-sphere potential complemented by a repulsive and an attractive Yukawa term; and we predict the structure factors by exploiting the perturbative random phase approximation of the Percus-Yevick equation. Our approach enables us to fit all the data by selecting the particle radius and the width and amplitude of the attractive potential as free parameters.

Elasticity and Viscosity of DNA Liquid Crystals.

Concentrated solutions of blunt-ended DNA oligomer duplexes self-assemble in living polymers and order into lyotropic nematic liquid crystal phase. Using the optical torque provided by three distinct illumination geometries, we induce independent splay, twist, and bend deformations of the DNA nematic and measure the corresponding elastic coefficients , , and , and viscosities η, η, and η. We find the viscoelasticity of the system to be remarkably soft, as the viscoelastic coefficients are smaller than in other lyotropic liquid crystals.

Type III Arch Configuration as a Risk Factor for Carotid Artery Stenting: A Systematic Review of Contemporary Guidelines on Management of Carotid Artery Stenosis.

Background: Type III arch configuration is frequently reported as a stroke risk factor for carotid angioplasty and stenting (CAS). We reviewed contemporary guidelines on management of carotid artery stenosis to assess the clinical relevance attributed to this anatomic feature in current clinical practice.

Methods: The study was conducted according to the Preferred Reporting Items for Systematic Reviews and Meta-analyses guidelines.

Integrated Optofluidic Chip for Oscillatory Microrheology.

We propose and demonstrate an on-chip optofluidic device allowing active oscillatory microrheological measurements with sub-μL sample volume, low cost and high flexibility. Thanks to the use of this optofluidic microrheometer it is possible to measure the viscoelastic properties of complex fluids in the frequency range 0.01-10 Hz at different temperatures.

Quadruplex knots as network nodes: nano-partitioning of guanosine derivates in supramolecular hydrogels.

Aqueous solutions of guanosine-5'-monophosphates (GMP) - known to form G-quadruplexes and liquid crystal phases - can be induced to turn into high water content gels by the addition of guanosine (Gua). By a combination of Light Scattering (LS) and AFM we show that Gua/GMP hydrogels are microscopically heterogeneous, formed by Gua-rich disordered microcoils of intertwined filaments ("knots") connected by GMP-rich long linear threads. The different thermal stability of knots and threads controls the gel transition.

Fluctuating Elasticity Mode in Transient Molecular Networks.

Transient molecular networks, a class of adaptive soft materials with remarkable application potential, display complex, and intriguing dynamic behavior. By performing dynamic light scattering on a wide angular range, we study the relaxation dynamics of a reversible network formed by DNA tetravalent nanoparticles, finding a slow relaxation mode that is wave vector independent at large q and crosses over to a standard q^{-2} viscoelastic relaxation at low q. Exploiting the controlled properties of our DNA network, we attribute this mode to fluctuations in local elasticity induced by connectivity rearrangement.

Liquid Crystal Ordering and Isotropic Gelation in Solutions of Four-Base-Long DNA Oligomers.

Liquid crystal ordering is reported in aqueous solutions of the oligomer 5'-ATTAp-3' and of the oligomer 5'-GCCGp-3'. In both systems, we quantitatively interpret ordering as stemming from the chaining of molecules via a "running-bond" type of pairing, a self-assembly process distinct from the duplex aggregation previously reported for longer oligonucleotides. While concentrated solutions of 5'-ATTAp-3' show only a columnar liquid crystal phase, solutions of 5'-GCCGp-3' display a rich phase diagram, featuring a chiral nematic phase analogous to those observed in solutions of longer oligonucleotides and two unconventional phases, a columnar crystal and, at high concentration, an isotropic amorphous gel.

Nonlinear diffusion model for annealed proton-exchanged waveguides in zirconium-doped lithium niobate.

Photorefractive-damage- (PRD) resistant zirconium-oxide-doped lithium niobate is investigated as a substrate for the realization of annealed proton-exchanged (APE) waveguides. Its advantages are a favorable distribution coefficient, PRD resistance comparable to magnesium-oxide-doped lithium niobate, and a proton-diffusion behavior resembling congruent lithium niobate. A 1D model for APE waveguides was developed based on a previous model for congruently melting lithium niobate.

A comprehensive strategy for the analysis of acoustic compressibility and optical deformability on single cells.

We realized an integrated microfluidic chip that allows measuring both optical deformability and acoustic compressibility on single cells, by optical stretching and acoustophoresis experiments respectively. Additionally, we propose a measurement protocol that allows evaluating the experimental apparatus parameters before performing the cell-characterization experiments, including a non-destructive method to characterize the optical force distribution inside the microchannel. The chip was used to study important cell-mechanics parameters in two human breast cancer cell lines, MCF7 and MDA-MB231.

Investigation of temperature effect on cell mechanics by optofluidic microchips.

Here we present the results of a study concerning the effect of temperature on cell mechanical properties. Two different optofluidic microchips with external temperature control are used to investigate the temperature-induced changes of highly metastatic human melanoma cells (A375MC2) in the range of ~0 - 35 °C. By means of an integrated optical stretcher, we observe that cells' optical deformability is strongly enhanced by increasing cell and buffer-fluid temperature.