Specific Versus Non-specific Response in Exponential Molecular Amplification from Cross-Catalysis: Modeling the Influence of Background Amplifications on the Analytical Performances

Molecule based signal amplifications relying on an autocatalytic process may represent an ideal strategy for the development of ultrasensitive analytical or bioanalytical assays, the main reason being the exponential nature of the amplification. However, to take full advantage of such amplification rates, high stability of the starting co-reactants is required in order to avoid any undesirable background amplification. Here, on the basis of a simple kinetic model of cross-catalysis including a certain degree of intrinsic instability of co-reactants, we highlight the key parameters governing the analytical response of the system and discuss the analytical performances that are expected from a given kinetic set. In particular, we show how the detection limit is directly related to the relative instability of reactants within each catalytic loop. The model is validated with an experimental dataset and is intended to serve as a guide in the design and optimization of autocatalytic molecular-based amplification systems with improved analytical performances.     

An easily-prepared impedance matched Josephson parametric amplifier

An impedance matched parametric amplifier (IMPA) with Josephson junctions is fabricated and characterized. A hybrid structure containing coplanar and strip structures is implemented to realize an impedance taper line and a plate capacitor in an LC nonlinear resonator based on Josephson junctions. The upper plate of the capacitor is isolated with SiN_x without grounding as well as the strips. Such easily-prepared designs greatly reduce the requirements for lithography alignment and precision, which makes the fabrication process more reliable. The experimental results show that in such IMPA a gain higher than 25 dB with a bandwidth of about 100 MHz can be obtained. This broadband amplifier operates close to the quantum limit. By adjusting the working point, a higher bandwidth of about 400 MHz can be obtained with a gain of about 17 dB.     

Energetics of Competing Chiral Supramolecular Polymers

Chirality can have unexpected consequences including on properties other than spectroscopic. We show herein that a racemic mixture of bis-urea stereoisomers forms thermodynamically stable supramolecular polymers that result in a more viscous solution than for the pure stereoisomer. The origin of this macroscopic property was probed by characterizing the structure and stability of the assemblies. Both racemic and non-racemic bis-urea stereoisomers form two competing helical supramolecular polymers in solution: a double and a single helical structure at low and high temperature, respectively. The transition temperature between these assemblies, as probed by spectroscopic and calorimetric analyses, is strongly influenced by the composition (by up to 70 °C). A simple model that accounts for the thermodynamics of this system, indicates that the stereochemical defects (chiral mismatches and helix reversals) affect much more the stability of single helices. Therefore, the heterochiral double helical structure predominates over the single helical structure (whilst the opposite holds for the homochiral structures), which explains the aforementioned higher viscosity of the racemic bis-urea solution. This rationale constitutes a new basis to tune the macroscopic properties of the increasing number of supramolecular polymers reported to exhibit competing chiral nanostructures.     

Recent trends in thermoelectrochemical cells and thermally regenerative batteries

Given the ever-growing awareness on global warming, much interest has focused on new and effective ways to manage energy, especially by harvesting and exploiting low-temperature heat sources, ubiquitous in the modern environment. Here, the holy grail is the direct conversion of heat into electricity especially using thermoelectric devices, and in this contribution, we focus on thermoelectrochemical systems.We give a brief overview of the most common thermally regenerative electrochemical cells developed nowadays with a short overview of their thermodynamic derivation, and we collect some of the most recent results in terms of their thermoelectrochemical properties, in particular, their temperature coefficients. We see that although the most used redox couples are based on Fe³⁺/Fe²⁺ and their derivates, thermodiffusion effects and other entropy-related phenomena are attracting the attention of the scientific community and boosting astonishing results. On the other hand, thermally regenerative batteries are emerging, showing modest performance.     

Nanophotonic Device in Combination with Bacteriophages for Enhancing Detection Sensitivity of Escherichia coli in Simulated Wash Water

Among various approaches to control and monitor cross-contamination of fresh produce, a biosensor that can rapidly detect the presence of a specific bacterium in wash water or on fresh produce can be effective. This research demonstrates the development of a rapid biosensor based on a combination of a nanophotonic device and the bacteriophage T7 for the detection of Escherichia coli without the need for culturing or nucleic acid extraction. This biosensor platform is based on bacteriophage mediated specific lysis of target bacteria and release of β-galactosidase. The enzyme could be further detected by a nanophotonic device that amplifies the fluorescent signal, therefore allowing better sensitivity. Production of β-galactosidase is induced by isopropyl β-D-1-thiogalactopyranoside (IPTG) and the enzyme is then released by bacteriophage lysis, which is detected by the nanophotonic device using a fluorescent enzyme substrate resorufin β-D-galactopyranoside. Using this approach, the results demonstrated successful detection of 10 CFU mL^?1 of E. coli BL21 in simulated spinach wash water within 8?hours. Specificity of the assay was demonstrated with negative controls including Pseudomonas fluorescens and Listeria innocua.     

Different Regimes of Ultrashort Pulse Propagation in Disordered Layered Media with Resonant Loss and Gain

Different optical nanostructures containing both loss and gain components attract ever‐increasing attention as novel advanced materials and building blocks for a variety of nanophotonic and plasmonic applications. Unique tunable optical signatures of the so‐called active metamaterials support their utilization for sensing, imaging, and signal processing on micro‐ and nanoscales. However, this tunability requires flexible control over the metamaterial parameters, which could be provided by involving a set of nonlinear interactions. In this paper, a method of governing ultrashort pulses is proposed by varying the level of a population difference disorder in a random active metamaterial. This enables us to deliver three different interaction regimes: self‐induced transparency (low disorder), localization regime (moderate disorder), and light amplification (strong disorder) corresponding to strongly different light pulse speeds. Since this control could be realized via rather plain tools, like simple pump tuning, the proposed disordered medium opens a room of opportunities for designing a peculiar active component for a whole set of highly demanded optical applications.     

Target-Dependent Protection of DNA Aptamers against Nucleolytic Digestion Enables Signal-On Biosensing with Toehold-Mediated Rolling Circle Amplification

We report a generalizable strategy for biosensing that takes advantage of the resistance of DNA aptamers against nuclease digestion when bound with their targets, coupled with toehold mediated strand displacement (TMSD) and rolling circle amplification (RCA). A DNA aptamer containing a toehold extension at its 5′-end protects it from 3′-exonuclease digestion by phi29 DNA polymerase (phi29 DP) in a concentration-dependent manner. The protected aptamer can participate in RCA in the presence of a circular template that is designed to free the aptamer from its target via TMSD. The absence of the target leads to aptamer digestion, and thus no RCA product is produced, resulting in a turn-on sensor. Using two different DNA aptamers, we demonstrate rapid and quantitative real-time fluorescence detection of two human proteins: platelet-derived growth factor (PDGF) and thrombin. Sensitive detection of PDGF was also achieved in human serum and human plasma, demonstrating the selectivity of the assay.     

Biosensor for multiplex detection of two DNA target sequences using enzyme-functionalized Au nanoparticles as signal amplification

Multiplex electrochemical detection of two DNA target sequences in one sample using enzyme-functionalized Au nanoparticles (AuNPs) as catalytic labels for was proposed. This DNA sensor was fabricated using a “sandwich” detection strategy, involving two kinds of capture probes DNA immobilized on glassy carbon electrode (GCE), and hybridization with target DNA sequences, which further hybridized with the reporter DNA loaded on the AuNPs. The AuNP contained two kinds of DNA sequences, one was complementary to the target DNA, while the other was noncomplementary to the target. The noncomplementary sequences were linked with horseradish peroxidase (HRP) and alkaline phosphatase (ALP), respectively. Enhanced detection sensitivity was obtained where the AuNPs carriers increased the amount of enzyme molecules per hybridization. Electrochemical signals were generated from the enzymatic products produced from the substrates catalyzed by HRP and ALP. Under optimal conditions, a 33-mer sequence could be quantified over the ranges from 1.5 × 10⁻¹³ to 5.0 × 10⁻¹² M with a detection limit of 1.0 × 10⁻¹³ M using HRP-AuNP as labels, and a 33-mer sequence could be quantified over the ranges from 4.5 × 10⁻¹¹ M to 1.0 × 10⁻⁹ M with a detection limit of 1.2 × 10⁻¹¹ M using ALP-AuNP as labels.     

Autocatalytic Enantiomerisation at the Crystal Surface in Deracemisation of Scalemic Conglomerates

Deracemisation of racemic or scalemic conglomerates of intrinsically chiral compounds appears to be a promising method of chiral resolution. By combining the established methods of asymmetric synthesis and the physical process of crystal growth, we were able to achieve a complete deracemisation (with 100 % ee) of an asymmetric Mannich product conglomerate—vigorously stirred in its saturated solution—from a starting enantiomeric excess value of 15.8 % in the presence of pyrrolidine (8 mol %) as an achiral catalyst for the CC bond‐forming reaction. Strong activation of this deracemisation process was observed on mild isothermal heating to only 40 °C, resulting in dramatic acceleration by a factor of about 20 with respect to the results obtained at room temperature. Despite the fact that the racemisation half‐life time of the nearly enantiopure Mannich product (with 99 % ee) in the homogenous solution at the reaction temperature is eight days, the deracemisation process took only hours in a small‐scale experiment. This apparent paradox is explained by a proposed rapid enantiomerisation at the crystal/solution interface, which was corroborated by a ¹³C labelling experiment that confirmed the involvement of rapid enantiomerisation. Frequent monitoring of the solution‐phase ee of the slowly racemising compound further revealed that the minor enantiomer dominated in solution, supporting an explanation based on a kinetic model. A generalisation of the process of “aymmetric autocatalysis” (resulting in automultiplication of chiral products in homogenous media) to encompass heterogeneous systems is also suggested.