DNA Carrier-Assisted Molecular Ping-Pong in an Asymmetric Nanopore.

Nanopore analysis relies on ensemble averaging of translocation signals obtained from numerous molecules, requiring a relatively high sample concentration and a long turnaround time from the sample to results. The recapture and subsequent re-reading of the same molecule is a promising alternative that enriches the signal information from a single molecule. Here, we describe how an asymmetric nanopore improves molecular ping-pong by promoting the recapture of the molecule in the trans reservoir. We also demonstrate that the molecular recapture could be improved by linking the target molecule to a long DNA carrier to reduce the diffusion, thereby achieving over 100 recapture events. Using this ping-pong methodology, we demonstrate its use in accurately resolving nanostructure motifs along a DNA scaffold through repeated detection. Our method offers novel insights into the control of DNA polymer dynamics within nanopore confinement and opens avenues for the development of a high-fidelity DNA detection platform.

DNA-Based Optical Quantification of Ion Transport across Giant Vesicles.

Accurate measurements of ion permeability through cellular membranes remains challenging due to the lack of suitable ion-selective probes. Here we use giant unilamellar vesicles (GUVs) as membrane models for the direct visualization of mass translocation at the single-vesicle level. Ion transport is indicated with a fluorescently adjustable DNA-based sensor that accurately detects sub-millimolar variations in K+ concentration. In combination with microfluidics, we employed our DNA-based K+ sensor for extraction of the permeation coefficient of potassium ions. We measured K+ permeability coefficients at least 1 order of magnitude larger than previously reported values from bulk experiments and show that permeation rates across the lipid bilayer increase in the presence of octanol. In addition, an analysis of the K+ flux in different concentration gradients allows us to estimate the complementary H+ flux that dissipates the charge imbalance across the GUV membrane. Subsequently, we show that our sensor can quantify the K+ transport across prototypical cation-selective ion channels, gramicidin A and OmpF, revealing their relative H+/K+ selectivity. Our results show that gramicidin A is much more selective to protons than OmpF with a H+/K+ permeability ratio of ∼104.

Bifunctional polyaniline electroconductive hydrogels with applications in supercapacitor and wearable strain sensors.

In this article, bifunctional polyaniline/polyacrylamide (PANI/PAAm) hydrogel is fabricated. The hydrogel has capacitive performance and can be used for monitoring human motions. The effect of PANI doped with two different acids on the properties of hydrogels was researched. The first type of PANI hydrogel is doped with hydrochloric (HCl) and the second one with p-toluenesulfonic acid (PTSA). One application of these two kinds of hydrogels was prepared to serve as solid electrolytes in supercapacitors with sandwich structure. The sandwich structure was constructed by introducing two PANI film parts reinforced on both sides of the PANI hydrogel. Supercapacitors with sandwich structure possess areal capacitance of 635 mF/cm2 (HCl-PANI hydrogel) and 1022 mF/cm2 (PTSA-PANI hydrogel). In this structure, PANI hydrogel provides channels for ion transport as a solid electrolyte. In addition, the PANI hydrogel can be utilized as the sensitive sensors as well. By employing I-v curve and I-t curve to characterize the performance of the sensor, the hydrogel material can be used as a wearable sensor with sensitivity to slight deformation. This is a sensitive sensor that it can respond to the speed and amplitude of the bending movement of the arm. The effective bifunctional property results indicate that the hydrogel, capacitive and conductive PANI hydrogel has great piezoelectric sensitivity as the sensors, which has become promising materials for wearable sensors and solid electrolytes.

Indole Pulse Signalling Regulates the Cytoplasmic pH of E. coli in a Memory-Like Manner.

Bacterial cells are critically dependent upon pH regulation. Here we demonstrate that indole plays a critical role in the regulation of the cytoplasmic pH of Escherichia coli. Indole is an aromatic molecule with diverse signalling roles. Two modes of indole signalling have been described: persistent and pulse signalling. The latter is illustrated by the brief but intense elevation of intracellular indole during stationary phase entry. We show that under conditions permitting indole production, cells maintain their cytoplasmic pH at 7.2. In contrast, under conditions where no indole is produced, the cytoplasmic pH is near 7.8. We demonstrate that pH regulation results from pulse, rather than persistent, indole signalling. Furthermore, we illustrate that the relevant property of indole in this context is its ability to conduct protons across the cytoplasmic membrane. Additionally, we show that the effect of the indole pulse that occurs normally during stationary phase entry in rich medium remains as a "memory" to maintain the cytoplasmic pH until entry into the next stationary phase. The indole-mediated reduction in cytoplasmic pH may explain why indole provides E. coli with a degree of protection against stresses, including some bactericidal antibiotics.

A nanochannel based on-line universal logic ion sensing platform.

In this work, a novel ion sensing platform was constructed in a microfluidic chip based on a very easy nano-fabrication technique, with which the nanoscale channel generated along the junction of the PDMS and metal strip could serve as a salt bridge for electrochemical measurements. More importantly, we have proposed a flexible and universal ion sensing strategy based on Boolean logic, which can rapidly report the concentration of analyte by the approach method. Firstly, the performance of the nanochannel based salt bridge was characterized, and the results showed that the nanoscale salt bridge behaved comparably to the traditional ones. To illustrate the promising applications of this wonderful design, an IrOx electrode was employed to construct the on-line pH sensing device as an example, and a wide linearity range (pH 2-12) was obtained with a really high sensitivity of 74.15 mV per pH unit. Owing to the use of the logic sensing strategy, we achieved rapid identification of the sample pH on-line, and demonstrated the broad potential of our system in designing sensing devices with extremely high integration, automation and throughput.