Anharmonic acoustic effects during DNA hybridization on an electrochemical quartz crystal resonator

The paper describes a sensor for single-stranded DNA (ssDNA) biomarker based on anharmonic acoustic signals arising during hybridization with complementary thiolated ssDNA functionalised on the gold electrode of an electrochemical quartz crystal resonator. The steps of sensor preparation and hybridization are carried out in an electrochemical microfluidic flowcell. While the electrochemical impedance spectroscopy does not allow a definitive interpretation, the changes in resonance frequency and third Fourier harmonic current of the resonator on actuation at the fundamental mode indicate formation of a flexibly bound layer. The functionalization and hybridization steps monitored by the anharmonic detection technique (ADT) are described with a simple model based on Duffing nonlinear equation

Characterisation of particle-surface interactions via anharmonic acoustic transduction

Most transduction methods for measuring particle-surface interactions are unable to differentiate the strength of interaction and largely reliant on extensive washing to reduce the ubiquitous non-specific background. Label-based methods, in particular, are limited in wide applicability due to their inherent operational complexity. On the other hand, label-free force-spectroscopic methods that can differentiate particle-surface interaction strength are skill-demanding and time-consuming. Here, we present a label-free anharmonic (nonlinear) acoustic transduction method employing the quartz crystal resonator that reads out ligand-receptor binding based on the interaction strength. We show that while stronger specific interactions are transduced more strongly, and in linear proportionality to the ligand concentration on microparticles, non-specific interactions are significantly attenuated. This allows ligand quantification with high specificity and sensitivity in realtime under flow without separate washing steps. Constructing an analytical model of a quartz resonator, we can relate the number and type (specific vs. non-specific) of ligand-receptor interactions with the change in characteristic nonlinearity coefficient of the resonator. The entirely-electronic and microfluidic-integrable transduction method could potentially allow a simple, fast and reliable way for characterising particle-surface interactions with economy of scale

Measuring and Enhancing the Ionic Conductivity of Chloroaluminate Electrolytes for Al-Ion Batteries

At the core of the aluminum (Al) ion battery is the liquid electrolyte, which governs the underlying chemistry. Optimizing the rheological properties of the electrolyte is critical to advance the state of the art. In the present work, the chloroaluminate electrolyte is made by reacting AlCl3 with a recently reported acetamidinium chloride (Acet-Cl) salt in an effort to make a more performant liquid electrolyte. Using AlCl3:Acet-Cl as a model electrolyte, we build on our previous work, which established a new method for extracting the ionic conductivity from fitting voltammetric data, and in this contribution, we validate the method across a range of measurement parameters in addition to highlighting the model electrolytes' conductivity relative to current chloroaluminate liquids. Specifically, our method allows the extraction of both the ionic conductivity and voltammetric data from a single, simple, and routine measurement. To bring these results in the context of current methods, we compare our results to two independent standard conductivity measurement techniques. Several different measurement parameters (potential scan rate, potential excursion, temperature, and composition) are examined. We find that our novel method can resolve similar trends in conductivity to conventional methods, but typically, the values are a factor of two higher. The values from our method, on the other hand, agree closely with literature values reported elsewhere. Importantly, having now established the approach for our new method, we discuss the conductivity of AlCl3:Acet-Cl-based formulations. These electrolytes provide a significant improvement (5-10× higher) over electrolytes made from similar Lewis base salts (e.g., urea or acetamide). The Lewis base salt precursors have a low economic cost compared to state-of-the-art imidazolium-based salts and are non-toxic, which is advantageous for scale-up. Overall, this is a noteworthy step at designing cost-effective and performant liquid electrolytes for Al-ion battery applications

The Mechanism of Substrate Inhibition in Human Indoleamine 2,3-Dioxygenase

Indoleamine 2,3-dioxygenase catalyzes the O₂-dependent oxidation of l-tryptophan (l-Trp) to <i>N</i>-formylkynurenine (NFK) as part of the kynurenine pathway. Inhibition of enzyme activity at high l-Trp concentrations was first noted more than 30 years ago, but the mechanism of inhibition has not been established. Using a combination of kinetic and reduction potential measurements, we present evidence showing that inhibition of enzyme activity in human indoleamine 2,3-dioxygenase (hIDO) and a number of site-directed variants during turnover with l-tryptophan (l-Trp) can be accounted for by the sequential, ordered binding of O₂ and l-Trp. Analysis of the data shows that at low concentrations of l-Trp, O₂ binds first followed by the binding of l-Trp; at higher concentrations of l-Trp, the order of binding is reversed. In addition, we show that the heme reduction potential (<i>E</i>_m⁰) has a regulatory role in controlling the overall rate of catalysis (and hence the extent of inhibition) because there is a quantifiable correlation between <i>E</i>_m⁰ (that increases in the presence of l-Trp) and the rate constant for O₂ binding. This means that the initial formation of ferric superoxide (Fe³⁺–O₂^•–) from Fe²⁺-O₂ becomes thermodynamically less favorable as substrate binds, and we propose that it is the slowing down of this oxidation step at higher concentrations of substrate that is the origin of the inhibition. In contrast, we show that regeneration of the ferrous enzyme (and formation of NFK) in the final step of the mechanism, which formally requires reduction of the heme, is facilitated by the higher reduction potential in the substrate-bound enzyme and the two constants (<i>k</i>_cat and <i>E</i>_m⁰) are shown also to be correlated. Thus, the overall catalytic activity is balanced between the equal and opposite dependencies of the initial and final steps of the mechanism on the heme reduction potential. This tuning of the reduction potential provides a simple mechanism for regulation of the reactivity, which may be used more widely across this family of enzymes

Amidine-based ionic liquid analogues with AlCl3: a credible new electrolyte for rechargeable Al batteries

Here we demonstrate the generation of novel ionic liquid analogue (ILA) electrolytes for aluminium (Al) electrodeposition that are based on salts of amidine Lewis bases. The electrolytes exhibit reversible voltammetric plating/stripping of Al, good ionic conductivities (10–14 mS cm−1), and relatively low viscosities (50–80 cP). The rheological properties are an improvement on analogous amide-based ILAs and make these liquids credible alternatives to ILAs based on urea or acetamide, or conventional chloroaluminate ionic liquids (IL) for Al battery applications.</div

Direct detection of whole bacteria using a nonlinear acoustic resonator

Direct detection of whole vegetative bacteria was investigated employing a quartz crystal resonator (QCR) in its nonlinear regime. Escherichia coli (E. coli) in buffer solution under flow was captured on a QCR in a microfluidic cell using a whole-cell anti-E.coli aptamer. The nonlinear distortion in QCR response due to the ‘pull’ from surface-bound bacteria was measured in realtime as the change in third Fourier harmonic (3f) current and compared with shifts in the traditional acoustic parameters of resonance frequency and dissipation. The change in 3f current showed superior quantitative correlation with E. coli concentrations (105-108 cfu/mL) and at least an order of magnitude better sensitivity than shifts in the traditional acoustic parameters. Most interestingly, underpinned by the strength of bacteria-QCR pull, the nonlinear acoustic principle demonstrated a unique specificity in transduction, even in a mixed sample with another gram-negative bacteria, that can supplement the specificity of the bioreceptors. An analytical expression was derived to quantitatively relate the competing influence of shifts in dissipation and nonlinearity coefficient of the QCR on the change in 3f current. This study demonstrates the potential for reliable direct readout of bioreceptor-mediated binding of whole vegetative bacteria from complex samples using a nonlinear acoustic resonator.</p

A simple method for the determination of reduction potentials in heme proteins

We describe a simple method for the determination of heme protein reduction potentials. We use the method to determine the reduction potentials for the PAS-A domains of the regulatory heme proteins human NPAS2 (E[subscript m] = ˗115 mV ± 2 mV, pH 7.0) and human CLOCK (E[subscript m] = ˗111 mV ± 2 mV, pH 7.0). We suggest that the method can be easily and routinely applied to the determination of reduction potentials across the family of heme proteins