Gate Electrodes Enable Tunable Nanofluidic Particle Traps.

The ability to control the location of nanoscale objects in liquids is essential for fundamental and applied research from nanofluidics to molecular biology. To overcome their random Brownian motion, the electrostatic fluid trap creates local minima in potential energy by shaping electrostatic interactions with a tailored wall topography. However, this strategy is inherently static; once fabricated, the potential wells cannot be modulated. Here, we propose and experimentally demonstrate that such a trap can be controlled through a buried gate electrode. We measure changes in the average escape times of nanoparticles from the traps to quantify the induced modulations of 0.7 kBT in potential energy and 50 mV in surface potential. Finally, we summarize the mechanism in a parameter-free predictive model, including surface chemistry and electrostatic fringing, that reproduces the experimental results. Our findings open a route toward real-time controllable nanoparticle traps.

Assessment and pain management during the triage phase of children with extremity trauma. A retrospective analysis in a Pediatric Emergency Room after the introduction of the PIPER recommendations.

BACKGROUND AND AIM OF THE WORK: Pain is one of the most common symptoms in children who access the Pediatric Emergency Room (PER). However, many studies show that it is poorly evaluated and treated during the triage phase and that in many cases algometric scales aren't used for its evaluation. Faced with this, the Piacenza PER (Italy) implemented the Pain in Pediatric Emergency Room (PIPER) recommendations for the assessment and management of pain from the 1st July 2017. The aim of this study was to detect the possible differences in the trend of the outcomes for the detection and treatment of pain in July-October 2016, 2017, 2018. METHODS: A retrospective observational study was chosen. 811 discharge letters of extremity traumatized children aged 0-9 years were analyzed, of which 309 referred to the 2016 quarter, 243 to the 2017 quarter and 259 to the 2018 quarter. RESULTS: In 2016, the pain of 12 patients was assessed out of a total of 309, in 2017 of 227 out of 243 and in 2018 of 245 out of 259. The Chi Square test about assessed and not assessed pain, gave statistically significant value (p = 1.36E-98), comparing 2016vs2017 and gave not significant value comparing 2017vs2018 (p = 0.58). 4 patients were treated during the triage phase in 2016, 68 in 2017 and 70 in 2018. CONCLUSIONS: Recommendations introduction has increased the frequency of pain algometric measurements during the triage phase by leading to an improvement in the nursing care outcomes in terms of pediatric pain management.

Entropic Trapping of a Singly Charged Molecule in Solution.

We demonstrate the ability to confine a single molecule in solution by spatial modulation of its local configurational entropy. Previously we established electrostatic trapping of a charged macromolecule by geometric tailoring of a repulsive electrical interaction potential in a parallel plate system. However, since the lifetime of the trapped state depends exponentially on the electrical charge of the molecule, the electrostatic interaction alone is often insufficient in magnitude to stably confine molecules carrying a net charge of magnitude ≤5 e. Here we show that the configurational entropy of a thermally fluctuating molecule in a geometrically modulated system can be exploited to spatially confine weakly charged molecules in solution. Measurement of the configurational entropy contribution reveals good agreement with theoretical expectations. This additional translational contribution to the total free energy facilitates direct optical imaging and measurement of the effective charge of molecules on the size scale of ∼1 nm and a charge as low as 1 e, physical properties comparable with those of a monovalent ion in solution.

Single-molecule electrometry.

Mass and electrical charge are fundamental properties of biological macromolecules. Although molecular mass has long been determined with atomic precision, a direct and precise determination of molecular charge remains an outstanding challenge. Here we report high-precision (<1e) measurements of the electrical charge of molecules such as nucleic acids, and globular and disordered proteins in solution. The measurement is based on parallel external field-free trapping of single macromolecules, permits the estimation of a dielectric coefficient of the molecular interior and can be performed in real time. Further, we demonstrate the direct detection of single amino acid substitution and chemical modifications in proteins. As the electrical charge of a macromolecule strongly depends on its three-dimensional conformation, this kind of high-precision electrometry offers an approach to probe the structure, fluctuations and interactions of a single molecule in solution.

Lattice diffusion of a single molecule in solution.

The ability to trap a single molecule in an electrostatic potential well in solution has opened up new possibilities for the use of molecular electrical charge to study macromolecular conformation and dynamics at the level of the single entity. Here we study the diffusion of a single macromolecule in a two-dimensional lattice of electrostatic traps in solution. We report the ability to measure both the size and effective electrical charge of a macromolecule by observing single-molecule transport trajectories, typically a few seconds in length, using fluorescence microscopy. While, as shown previously, the time spent by the molecule in a trap is a strong function of its effective charge, we demonstrate here that the average travel time between traps in the landscape yields its hydrodynamic radius. Tailoring the pitch of the lattice thus yields two different experimentally measurable time scales that together uniquely determine both the size and charge of the molecule. Since no information is required on the location of the molecule between consecutive departure and arrival events at lattice sites, the technique is ideally suited to measurements on weakly emitting entities such as single molecules.

Non-specific interactions between soluble and induce irreversible changes in the properties of bilayers.

Soluble in the extracellular matrix experience a crowded environment. However, most of the biophysical studies performed to date have focused on concentrations within the dilute regime (well below the mM range). Here, we systematically studied the interaction of model cell membrane systems (giant unilamellar vesicles and supported bilayers) with soluble globular , bovine serum albumin, and lysozyme at physiologically relevant concentrations. To mimic the extracellular environment more closely, we also used fetal bovine serum as a good representative of a biomimetic mixture. We found that regardless of the used (and thus of their biological function), the interactions between a model cell membrane and these are determined by their physico-chemical characteristics, mainly their dipolar character (or charged patches). In this paper we discuss the specificity and reversibility of these interactions and their potential implications on the living cells. In particular, we report initial evidence for an additional role of in cell membranes: that of reducing the effects of non-specific of soluble on the cell membrane.

The dendrimer impact on vesicles can be tuned based on the bilayer charge and the presence of albumin.

PAMAM (polyamidoamine) dendrimers are promising in biomedical applications that can interact with both the bilayer and . Here we employed giant unilamellar vesicles (GUVs) of two different charge densities to study the effect of albumin, one of the major in blood plasma, on the interactions between PAMAM dendrimers and membranes. The results show that albumin exacerbates the effect of dendrimers on the destabilization of the vesicles in terms of leakage, aggregation and collapse in particular for negatively charged vesicles while neutrally charged membranes are not affected. We conclude that the higher affinity of both albumin and PAMAM G6 towards negatively charged membranes explains their synergistic behavior in this case. In the case of neutral vesicles, the affinity between PAMAM G6 and albumin is stronger than that between PAMAM G6 (or albumin) and neutral vesicles, and thus no synergism is observed for the mixture during the interaction with neutral membranes.