Influence of microphone characteristics on demodulated sound measurement in near field of parametric loudspeaker

This study evaluates the accuracy of demodulated sound measurements using a condenser microphone in the near field of a parametric loudspeaker system. Microphones with different sensitivities placed at incidence angles of 0° and 90° were used to measure demodulation frequency components without special acoustic filters. The measured components were compared with theoretical predictions. The results show that the measured sound pressure using microphones placed at 0° was up to several tens of decibels larger than the theoretical predictions and significantly inaccurate in the near field. This was due to the nonlinear response of the microphone, which had high sensitivity at primary sound frequencies, inducing spurious signals. This result suggests that using a microphone with low sensitivity at primary sound frequencies placed at an appropriate angle that reduces sensitivity improves parametric sound measurement accuracy.

Electrochemical aptasensors: unravelling the critical interactions between aptamers, ligands, and electrodes

<p><b>Aptamers are synthetic nucleic acid single-stranded oligonucleotides that bind to a wide range of ligands, including cells, proteins, DNA strands, metal ions, and small molecules, with high specificity and affinity. Aptamers have also proven to be highly stable, readily adaptable to chemical modifications, and exhibit reversible binding. As a result, aptamer-based biosensors (aptasensors) are promising replacements for antibody-based biosensors in many applications, particularly for small molecule ligands. This thesis explores an aptamer that binds the drug methamphetamine, and its prospects when incorporated in an electrochemical (e-chem) signal transduction platform. Specifically, we examine the range of interactions between the aptamer and ligand, and with electrodes, and identify a number of challenges in generating robust e-chem aptasensors.</b></p> <p>Due to their size and limited number of functional groups, further understanding of the aptamer-small molecule ligand interactions is required for the design of future aptasensors – particularly the thermodynamics and structural information about the aptamer-ligand interaction. In fact, detecting small molecules with aptasensors can become challenging because target addition may induce little structural change, and therefore numerous nonspecific interactions may emerge as transduced signals from the biosensor. In this thesis, the combination of spectroscopic and calorimetric analytical techniques reveals a conformational selection binding model, in which binding is entropically driven, and the meth binds via hydrophobic and electrostatic interactions and only induces a modest structural change. This first-of-its-kind study is important for the selection and the design of the aptasensor transduction system.</p> <p>Electrochemical (e-chem) aptasensors offer high inherent sensitivity and practicality as a signal transduction platform. Indeed, different e-chem aptasensor formats have been published before, including labelled and label-free sensors. In screening the viability of three commonly used methods – including labelled and label-free, as well voltammetric and impedance-based methods – we find that each of them suffers from instability of the aptamer-functionalised electrode. This instability compromises our ability to resolve real signals and prompted us to develop ways to understand – and suppress – this baseline drift.</p> <p>The functionalization of the electrode is the critical step in terms of self-assembled monolayer (SAM) stability and SAM aptamer density. Consequently, different protocols of SAMformation were explored and evaluated with respect to stability. We find that instability arises from the uncontrolled arrangement of thiolated aptamers on gold electrodes (including aptamers lying down on the electrode), which is in turn affected by the density of aptamers that can be coupled to the surface. As a consequence, a new protocol is developed using disulfide aptamer pairs to increase the density of correctly tethered aptamers, and generate a stable SAM.</p> <p>Because of the high sensitivity of electrochemical platforms, numerous spurious electrochemical signals may be produced, and controlled for in order to confirm a positive ligand-binding signal. The specificity of the aptamer-target interaction can be checked by testing the response with an interferent molecule, or by substituting the aptamer with a non-binding nucleotide sequence. In this work, these control experiments reveal that target and interferent molecules interact directly (and in different ways) with the bare gold surface, as well as perturbing signals from the aptamer in ways that cannot be linked to a specific aptamer-ligand complex formation. Ultimately, these spurious signals compromise our ability to confirm a real binding signal.</p> <p>The results from this work provide the first clear picture of how an aptamer binds to its small molecule target – which we find is entropically driven, and with only minor structural change induced in the aptamer stem. In addition, the label-free EIS measurements on aptamer SAM electrodes reveal the nature of instabilities, and reveal spurious signals that cannot be sufficiently suppressed at this stage. This knowledge highlights the difficulty in fabricating e-chem aptasensors, and will assist in overcoming challenges faced during research and commercialization of aptasensors area, as well as contributing new insights into troubleshooting, data acquisition, and data validation.</p>

Electrochemical aptasensors: unravelling the critical interactions between aptamers, ligands, and electrodes

<p><b>Aptamers are synthetic nucleic acid single-stranded oligonucleotides that bind to a wide range of ligands, including cells, proteins, DNA strands, metal ions, and small molecules, with high specificity and affinity. Aptamers have also proven to be highly stable, readily adaptable to chemical modifications, and exhibit reversible binding. As a result, aptamer-based biosensors (aptasensors) are promising replacements for antibody-based biosensors in many applications, particularly for small molecule ligands. This thesis explores an aptamer that binds the drug methamphetamine, and its prospects when incorporated in an electrochemical (e-chem) signal transduction platform. Specifically, we examine the range of interactions between the aptamer and ligand, and with electrodes, and identify a number of challenges in generating robust e-chem aptasensors.</b></p> <p>Due to their size and limited number of functional groups, further understanding of the aptamer-small molecule ligand interactions is required for the design of future aptasensors – particularly the thermodynamics and structural information about the aptamer-ligand interaction. In fact, detecting small molecules with aptasensors can become challenging because target addition may induce little structural change, and therefore numerous nonspecific interactions may emerge as transduced signals from the biosensor. In this thesis, the combination of spectroscopic and calorimetric analytical techniques reveals a conformational selection binding model, in which binding is entropically driven, and the meth binds via hydrophobic and electrostatic interactions and only induces a modest structural change. This first-of-its-kind study is important for the selection and the design of the aptasensor transduction system.</p> <p>Electrochemical (e-chem) aptasensors offer high inherent sensitivity and practicality as a signal transduction platform. Indeed, different e-chem aptasensor formats have been published before, including labelled and label-free sensors. In screening the viability of three commonly used methods – including labelled and label-free, as well voltammetric and impedance-based methods – we find that each of them suffers from instability of the aptamer-functionalised electrode. This instability compromises our ability to resolve real signals and prompted us to develop ways to understand – and suppress – this baseline drift.</p> <p>The functionalization of the electrode is the critical step in terms of self-assembled monolayer (SAM) stability and SAM aptamer density. Consequently, different protocols of SAMformation were explored and evaluated with respect to stability. We find that instability arises from the uncontrolled arrangement of thiolated aptamers on gold electrodes (including aptamers lying down on the electrode), which is in turn affected by the density of aptamers that can be coupled to the surface. As a consequence, a new protocol is developed using disulfide aptamer pairs to increase the density of correctly tethered aptamers, and generate a stable SAM.</p> <p>Because of the high sensitivity of electrochemical platforms, numerous spurious electrochemical signals may be produced, and controlled for in order to confirm a positive ligand-binding signal. The specificity of the aptamer-target interaction can be checked by testing the response with an interferent molecule, or by substituting the aptamer with a non-binding nucleotide sequence. In this work, these control experiments reveal that target and interferent molecules interact directly (and in different ways) with the bare gold surface, as well as perturbing signals from the aptamer in ways that cannot be linked to a specific aptamer-ligand complex formation. Ultimately, these spurious signals compromise our ability to confirm a real binding signal.</p> <p>The results from this work provide the first clear picture of how an aptamer binds to its small molecule target – which we find is entropically driven, and with only minor structural change induced in the aptamer stem. In addition, the label-free EIS measurements on aptamer SAM electrodes reveal the nature of instabilities, and reveal spurious signals that cannot be sufficiently suppressed at this stage. This knowledge highlights the difficulty in fabricating e-chem aptasensors, and will assist in overcoming challenges faced during research and commercialization of aptasensors area, as well as contributing new insights into troubleshooting, data acquisition, and data validation.</p>

Functioning of EPR Automatic Frequency Control in the Presence of the Circulator’s Spurious Leakage

This article presents an analysis of spurious signals’ influence on automatic frequency control (AFC) in EPR spectrometers. The primary source of spurious signals is leakage across the circulator in the microwave bridge. Additionally, the signals reflected from connectors in the line between the circulator and the resonator modify that signal. Spurious signals may degrade the performance of AFC, significantly offsetting lock points from the center frequency of the resonator. The offset’s size depends on the parameters of the resonator and the amount of the circulator isolation. It can be minimized by the appropriate use of a phase shifter located in the line between the circulator and the resonator. Another way to avoid these problems is to introduce a leakage compensation arm to the microwave bridge.

Sample preparation and imaging procedures for super-resolution microscopy using Repeat DNA-PAINT.

The performance of DNA-PAINT in biological samples is often constrained by strong background signals and non-specific binding events, both of which are exacerbated by high imager concentrations. Here we describe the procedure for conducting Repeat Domain DNA-PAINT, a method that substantially reduces imager concentration and thus suppresses spurious signals.

Experimental Characterization of Spurious Signals in Magnetic Nanoparticles Enhanced Microwave Imaging of Cancer

Magnetic nanoparticles enhanced microwave imaging relies on the capability of modulating the response of such nanocomponents at microwaves by means of a (low frequency) polarizing magnetic field. In medical imaging, this capability allows for the detection and imaging of tumors loaded with nanoparticles. As the useful signal is the one which arises from nanoparticles, it is crucial to remove sources of undesired disturbance to enable the diagnosis of early-stage tumors. In particular, spurious signals arise from instrumental drift, as well as from the unavoidable interaction between the polarizing field and the imaging system. In this paper, we experimentally assess and characterize such spurious effects in order to set the optimal working conditions for magnetic nanoparticles enhanced microwave imaging of cancer. To this end, simple test devices, which include all components typically comprised in a microwave imaging system, have been realized and exploited. The experiment’s results allow us to derive design formulas and guidelines useful for limiting the impact of unwanted magnetic effects, as well as that relative to the instrumental drift on the signal generated by the magnetic nanoparticles-loaded tumor.

Repeat DNA-PAINT suppresses background and non-specific signals in optical nanoscopy

DNA-PAINT is a versatile optical super-resolution technique relying on the transient binding of fluorescent DNA ‘imagers’ to target epitopes. Its performance in biological samples is often constrained by strong background signals and non-specific binding events, both exacerbated by high imager concentrations. Here we describe Repeat DNA-PAINT, a method that enables a substantial reduction in imager concentration, thus suppressing spurious signals. Additionally, Repeat DNA-PAINT reduces photoinduced target-site loss and can accelerate sampling, all without affecting spatial resolution.

Assessing telluric correction methods for Na detections with high-resolution exoplanet transmission spectroscopy

ABSTRACT Using high-resolution ground-based transmission spectroscopy to probe exoplanetary atmospheres is difficult due to the inherent telluric contamination from absorption in Earth’s atmosphere. A variety of methods have previously been used to remove telluric features in the optical regime and calculate the planetary transmission spectrum. In this paper we present and compare two such methods, specifically focusing on Na detections using high-resolution optical transmission spectra: (1) calculating the telluric absorption empirically based on the airmass and (2) using a model of the Earth’s transmission spectrum. We test these methods on the transmission spectrum of the hot Jupiter HD 189733 b using archival data obtained with the HARPS spectrograph during three transits. Using models for Centre-to-Limb Variation and the Rossiter–McLaughlin effect, spurious signals which are imprinted within the transmission spectrum are reduced. We find that correcting tellurics with an atmospheric model of the Earth is more robust and produces consistent results when applied to data from different nights with changing atmospheric conditions. We confirm the detection of sodium in the atmosphere of HD 189733 b, with doublet line contrasts of $-0.64 \pm 0.07~{{\ \rm per\ cent}}$ (D2) and $-0.53 \pm 0.07~{{\ \rm per\ cent}}$ (D1). The average line contrast corresponds to an effective photosphere in the Na line located around 1.13 Rp. We also confirm an overall blueshift of the line centroids corresponding to net atmospheric eastward winds with a speed of 1.8 ± 1.2 km s−1. Our study highlights the importance of accurate telluric removal for consistent and reliable characterization of exoplanetary atmospheres using high-resolution transmission spectroscopy.