Rectification of polymer translocation through nanopores by nonchiral and chiral active particles.

We study translocation of a flexible polymer chain through a membrane pore under the influence of active forces and steric exclusion using Langevin dynamics simulations within a minimal two-dimensional model. The active forces on the polymer are imparted by nonchiral and chiral active particles that are introduced on one side or both sides of a rigid membrane positioned across the midline of a confining box. We show that the polymer can translocate through the pore to either side of the dividing membrane in the absence of external forcing. Translocation of the polymer to a given side of the membrane is driven (hindered) by an effective pulling (pushing) exerted by the active particles that are present on that side. The effective pulling results from accumulation of active particles around the polymer. This crowding effect signifies persistent motion of active particles causing prolonged detention times for them close to the confining walls and the polymer. The effective pushing that hinders the translocation, on the other hand, results from steric collisions that occur between the polymer and active particles. As a result of the competition between these effective forces, we find a transition between two rectified cis-to-trans and trans-to-cis translocation regimes. This transition is identified by a sharp peak in the average translocation time. The effects of active particles on the transition is studied by analyzing how the translocation peak is regulated by the activity (self-propulsion) strength of these particles, their area fraction, and chirality strength.

Electrochemically controlled solid-phase microextraction based on conductive molecularly imprinted polymer combined with ion mobility spectrometry for separation and determination of thiopental.

In this work, electrochemically controlled solid-phase microextraction (EC-SPME) based on conductive molecularly imprinted polymer (CMIP) is coupled with ion mobility spectrometry (IMS) for analysis of thiopental (TP) as an anesthesia drug. The CMIP film was synthesized on the modified stainless steel wire surface by electropolymerization of pyrrole in the presence of TP as the template anion. Under the optimal experimental conditions, the developed method offered good linear range from 3.3 to 200 µM with coefficients of determination more than 0.99. Using these conditions, the detection limit of 1.1 µM was obtained. The single-fiber relative standard deviations (RSD %) were 3.7 and the fiber-to-fiber RSDs were 5.6 respectively. The developed EC-SPME-IMS was carried out to confirm the ability of the proposed method for determination of TP in the serum matrices. It was indicated that the proposed EC-SPME-IMS provides effective sample clean-up for the analysis of TP in complex matrices. Additionally, EC-SPME-IMS showed great potential for fast, sensitive, and low-cost detection of TP without spectra interfering of co-administered drugs and similar structural compounds (barbituric acid). Conductive molecularly imprinted polymer (CMIP) fiber based on polypyrrole/TP template for analysis of TP in serum matrices by using IMS without the spectra-interfering effect of co-administered drugs.

Active particles with polar alignment in ring-shaped confinement.

We study steady-state properties of active, nonchiral and chiral Brownian particles with polar alignment and steric interactions confined within a ring-shaped confinement (annulus) in two dimensions. Exploring possible interplays between polar interparticle alignment, geometric confinement and the surface curvature, being incorporated here on minimal levels, we report a surface-population reversal effect, whereby active particles migrate from the outer concave boundary of the annulus to accumulate on its inner convex boundary. This contrasts the conventional picture, implying stronger accumulation of active particles on concave boundaries relative to the convex ones. The population reversal is caused by both particle alignment and surface curvature, disappearing when either of these factors is absent. We explore the ensuing consequences for the chirality-induced current and swim pressure of active particles and analyze possible roles of system parameters, such as the mean number density of particles and particle self-propulsion, chirality, and alignment strengths.

A 2D suspension of active agents: the role of fluid mediated interactions.

Taking into account both the Vicsek short-range ordering and the far-field hydrodynamic interactions mediated by the ambient fluid, we investigate the role of long-range interactions in the ordering phenomena in a quasi 2-dimensional active suspension. By studying the number fluctuations, the velocity correlation functions and cluster size distribution function, we show that depending on the number density of swimmers and the strength of noise, the hydrodynamic interactions can have significant effects in a suspension. For a fixed value of noise, at larger density of particles, long-range interactions enhance the particle pairing and cluster formation in the system.