Search Results (568)

In this study, we systematically investigated the adsorption behavior of a titanium-based metal–organic framework (MOF) sensing layer on five primary alcohol homologs using the quartz crystal microbalance (QCM) technique. Unexpectedly, response signals were significantly enhanced for molecules exceeding the framework’s pore dimensions, contradicting conventional molecular sieving models. Further investigations revealed that the adsorption time constant (${\tau }_a$) is linearly proportional to the molecular diameter ($R^2=0.952$) and the integral response (AUC) increases almost exponentially with the molecular weight ($R^2=0.891$). Although the effective diffusion coefficient ($D_{\mathrm{eff}}$) decreases with increasing molecular size ($D_{\mathrm{eff}}\propto d^{-5.96}$, $R^2=0.981$), the normalized diffusion hindrance ratio ($D_{\mathrm{eff}}/D_{\mathrm{gas}}$) decreases logarithmically with an increasing diameter. Larger responses result from stronger host–guest interactions with the framework despite significant diffusion limitations for larger molecules. These findings demonstrate the synergistic regulation of adsorption and diffusion in MOF-QCM systems. Our investigation experimentally elucidates the ’size-selectivity paradox’ in microporous sensing interfaces and establishes a quantitative framework for optimizing sensor performance through balanced control of diffusion kinetics and interfacial interactions in similar materials. Full article

The solid electrolyte interphase (SEI) on the anode of lithium-ion batteries (LIBs) has been studied thoroughly due to its crucial importance to the battery’s long-term performance. At the same time, most studies of the SEI apply ex situ characterization methods, which may introduce artifacts or misinterpretations as they do not investigate the SEI in its unaltered state immersed in liquid battery electrolyte. Thus, in this work, we focus on using the non-destructive combination of electrochemical quartz crystal microbalance with dissipation monitoring (EQCM-D) and impedance spectroscopy (EIS) in the same electrochemical cell. EQCM-D can not only probe the solidified products of the SEI but also allows for the monitoring of viscoelastic layers and viscosity changes of the electrolyte at the interphase during the SEI formation. EIS complements those results by providing electrochemical properties of the formed interphase. Our results highlight substantial differences in the physical and electrochemical properties between the SEI formed on copper and on amorphous carbon and show how formation parameters and the additive vinylene carbonate (VC) influence their growth. The EQCM-D results show consistently that much thicker SEIs are formed on carbon substrates in comparison to copper substrates. Full article

This study investigates the development and sensing profile of synthetic melanin nanoparticle-coated electrodes for the electrochemical detection of heavy metals, including lead (Pb), cadmium (Cd), cobalt (Co), zinc (Zn), nickel (Ni), and iron (Fe). Synthetic melanin films were prepared in situ by the deacetylation of diacetoxy indole (DAI) to dihydroxy indole (DHI), followed by the deposition of DHI monomers onto indium tin oxide (ITO) and glassy carbon electrodes (GCE) using cyclic voltammetry (CV), forming a thin layer of synthetic melanin film. The deposition process was characterized by electrochemical quartz crystal microbalance (EQCM) in combination with linear sweep voltammetry (LSV) and amperometry to determine the mass and thickness of the deposited film. Surface morphology and elemental composition were examined using scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX). In contrast, Fourier-transform infrared (FTIR) and UV–Vis spectroscopy confirmed the melanin’s chemical structure and its polyphenolic functional groups. Differential pulse voltammetry (DPV) and amperometry were employed to evaluate the melanin films’ electrochemical activity and sensitivity for detecting heavy metal ions. Reproducibility and repeatability were rigorously assessed, showing consistent electrochemical performance across multiple electrodes and trials. A comparative analysis of ITO, GCE, and graphite electrodes was conducted to identify the most suitable substrate for melanin film preparation, focusing on stability, electrochemical response, and metal ion sensing efficiency. Finally, the applicability of melanin-coated electrodes was tested on in-house heavy metal water samples, exploring their potential for practical environmental monitoring of toxic heavy metals. The findings highlight synthetic melanin-coated electrodes as a promising platform for sensitive and reliable detection of iron with a sensitivity of 106 nA/ppm and a limit of quantification as low as 1 ppm. Full article

In the field of enhanced oil recovery (EOR), particularly for water control in high-temperature reservoirs, there is a critical need for effective in-depth water shutoff and conformance control technologies. Polymer-based in situ-cross-linked gels are extensively employed for enhanced oil recovery (EOR), yet their short gelation time under high-temperature reservoir conditions (e.g., >120 °C) limits effective in-depth water shutoff and conformance control. To address this, we developed a hydrogel system via the in situ cross-linking of polyacrylamide (PAM) with phenolic resin (PR), reinforced by silica sol (SS) nanoparticles. We employed a variety of research methods, including bottle tests, viscosity and rheology measurements, scanning electron microscopy (SEM) scanning, density functional theory (DFT) calculations, differential scanning calorimetry (DSC) measurements, quartz crystal microbalance with dissipation (QCM-D) measurement, contact angle (CA) measurement, injectivity and temporary plugging performance evaluations, etc. The composite gel exhibits an exceptional gelation period of 72 h at 130 °C, surpassing conventional systems by more than 4.5 times in terms of duration. The gelation rate remains almost unchanged with the introduction of SS, due to the highly pre-dispersed silica nanoparticles that provide exceptional colloidal stability and the system’s pH changing slightly throughout the gelation process. DFT and SEM results reveal that synergistic interactions between organic (PAM-PR networks) and inorganic (SS) components create a stacked hybrid network, enhancing both mechanical strength and thermal stability. A core flooding experiment demonstrates that the gel system achieves 92.4% plugging efficiency. The tailored nanocomposite allows for the precise management of gelation kinetics and microstructure formation, effectively addressing water control and enhancing the plugging effect in high-temperature reservoirs. These findings advance the mechanistic understanding of organic–inorganic hybrid gel systems and provide a framework for developing next-generation EOR technologies under extreme reservoir conditions. Full article

Two recombinant cutinases, AfCutA and AfCutB, derived from Aspergillus fumigatus, were heterologously expressed in Pichia pastoris and systematically characterized for their biochemical properties and polyester-degrading capabilities. AfCutA demonstrated superior catalytic performance compared with AfCutB, displaying higher optimal pH (8.0–9.0 vs. 7.0–8.0), higher optimal temperature (60 °C vs. 50 °C), and greater thermostability. AfCutA exhibited increased hydrolytic activity toward p-nitrophenyl esters (C4–C16) and synthetic polyesters. Additionally, AfCutA released approximately 3.2-fold more acetic acid from polyvinyl acetate (PVAc) hydrolysis than AfCutB. Quartz crystal microbalance with dissipation monitoring (QCM-D) revealed rapid adsorption of both enzymes onto polyester films. However, their adsorption capacity on poly (ε-caprolactone) (PCL) films was significantly higher than on polybutylene succinate (PBS) films, and was influenced by pH. Comparative modeling of catalytic domains identified distinct structural differences between the two cutinases. AfCutA possesses a shallower substrate-binding cleft, fewer acidic residues, and more extensive hydrophobic regions around the active site, potentially explaining its enhanced interfacial activation and catalytic efficiency toward synthetic polyester substrates. The notably superior performance of AfCutA suggests its potential as a biocatalyst in industrial applications, particularly in polyester waste bioremediation and sustainable polymer processing. Full article

Many odorants fall outside the sensing scope of the human olfactory system, yet they play quite important roles in our daily lives. Thus, numerous devices have been invented for qualitative or quantitative odor detection issues. Some analytical instruments, e.g., gas chromatography–mass spectrometry, are precise and reliable, but also expensive and bulky. Odor sensors with a smaller size and a lower cost play an important role in on-site rapid odor detection. The sensitivity and selectivity of these sensors are mainly determined by their sensing materials. Inspired by the powerful animal olfactory system, researchers extract diverse biological materials and combine them with transducers to form odor biosensors. In this paper, we introduce odor biosensors based on transducer types such as microelectrodes, fluorescence, surface plasmon resonance, field-effect transistor, quartz crystal micro-balance, etc. Then, we list several applications of odor biosensors, such as environmental monitoring, disease diagnosis, food quality control, and security. In addition, we analyze the future development of odor biosensors. Full article

Direct current (DC) reactive magnetron discharge in Ar + O₂ mixtures with an aluminum (Al) target was investigated. Electrical measurements of the discharge voltage and current along with the deposition rate trends observed with varying the oxygen flow rate indicated the presence of hysteresis, typical to when using a DC power supply. The transition between metallic and oxide (compound) modes was analyzed in more detail by measuring the mass-resolved fluxes of positively and negatively charged ions together with the optical emission spectra of plasma. The dependence of constituent ion fluxes (Ar⁺, Ar²⁺, Al⁺, O⁺, O₂⁺, O⁻, and O₂⁻) on the reactive oxygen gas flow rate was revealed, indicating the transition (in 1.2–1.8 sccm O₂ flow range) from a metallic regime to a poisoned regime. The optical diagnostics indicated a nonlinear hysteresis loop pattern of dependence for various constituents (ions and neutrals) of the magnetron discharge plasma. The comparison between the particle and optical measurements, though exhibiting a pronounced correlation, demonstrated individual features of both methods, which need to be taken into account when interpreting the results. The hysteresis patterns were further discussed by comparing the experimental data with the calculation results from the Berg model. An approach of adapting the model results to the case of a power-regulated magnetron power supply is expressed. Full article

Polypyrrole (PPy) is cationic in its conducting form, requiring a charge-balancing counterion, or dopant. The release of bioactive dopants, driven by the reduction of PPy films, offers a route to controlled drug delivery. Thiol-terminated long chain poly (ethylene glycol) (PEG) reacts with a dodecylbenzene sulfonate (DBSA)-doped PPy, forming a dense overlayer and partially liberating DBSA via the chemical reduction of the film. The resulting PEG brush acts as a barrier to dopant diffusion from the film, but proteins have been shown to disrupt this layer, releasing the DBSA. The mechanism by which this disruption occurs has not been thoroughly investigated. In this study, dopant release from PEG-PPy composites was examined via systematic exposure to a variety of chemical stimuli, including macromolecules such as poly (ethylene imine), polyethylene glycol, and poloxamers, as well as small-molecular-weight alcohols, carboxylic acids, and amines. Dopant release was quantified by quartz crystal microbalance. Poly (ethylene imine) efficiently released DBSA, while anionic and uncharged macromolecules did not. All classes of small molecules triggered dopant release, with longer homologues magnifying the response. The mechanisms of dopant removal are dependent on the functional groups of the stimulating agent and include ion exchange and nucleophilic reduction of the polycationic backbone. Tosylate, salicylate, and penicillin dopants showed release behaviors similar to DBSA, demonstrating the generality of the PEG barrier. Full article

Pt catalysts are investigated for methanol oxidation in direct methanol fuel cells, utilizing the electrochemical quartz microbalance method (EQCM) with exceptional resolution and sensitivity. Pt catalysts were deposited onto the gas-diffusion layer of carbon using stationary potential electrodeposition. Physical characterization and electrochemical tests were performed. SEM results showed that Pt presented dendrite crystals with nanoscale facets. Cyclic voltammetry (CV) demonstrated that the current density for the methanol oxidation reaction highly reached 1020 mA·cm⁻² for the deposited Pt catalyst by EQCM. The dendrite crystal structures of deposited Pt provide much area for high catalytic activity. It found that the peak density of the Pt catalysts for the methanol oxidation reaction decreased after five cycles. Furthermore, the response frequency for the adsorption of the deposited Pt catalysts was investigated using EQCM and compared with commercial PtRu catalysts. The results showed that the response frequency of the Pt catalysts decreased more rapidly than that of the PtRu catalysts. It is possible for the adsorption of small organic molecules on Pt catalysts to occur during the methanol electro-oxidation with CO_ad intermediates. The reaction mechanism is preliminarily discussed by the electrochemical measurement combined with EQCM. Full article

Aethina tumida, commonly known as the small hive beetle, poses a threat to honeybee populations, particularly Apis mellifera, across several European regions. Originating in sub-Saharan Africa, there is a risk of the infestation spreading from Calabria, a region in the south of Italy. The essential role played by Apis spp. in pollination biodiversity preservation, agricultural productivity, and the overall economy is related to the dangers posed by the invasion of Aethina tumida. Current detection methods often fail to identify infestations early, leading to significant colony losses. We focused on creating a biosensor to improve the detection of Kodamaea ohmeri, a recently identified yeast that coexists symbiotically with Aethina tumida. The biosensor was designed to exploit the highly sensitive quartz crystal microbalance to identify a specific peptide linked to Kodamaea ohmeri in honey specimens. Its gold-plated surface over quartz was functionalized with an antibody effective in recognizing the peptide associated with Kodamaea ohmeri, a potential warning for detecting Aethina tumida. Preliminary results support the possibility of using such biosensor technology to detect infestation and enhance colony management techniques for honeybees, enabling beekeepers to implement prompt and focused treatments. In addition, reducing the size and cost of these biosensors and offering user training would be very helpful in having them used in beekeeping. Full article

This study presents an efficient method for detecting oxytetracycline, which is critical in environmental monitoring and food safety. A highly sensitive detection platform was developed by combining molecularly imprinted polymers (MIPs) with silica as a carrier, modified with deep eutectic solvents (DES), and a quartz crystal microbalance (QCM) sensor. The MIPs were specifically designed to target oxytetracycline hydrochloride, using SiO₂ as the carrier, DES as the functional monomer, N, N-methylenebisacrylamide as the crosslinker, and ammonium persulfate as the initiator. The MIPs exhibited an adsorption capacity of 27.23 mg/g for oxytetracycline hydrochloride. After modification of the MIPs onto a gold electrode surface, a QCM-based sensor platform was constructed. The sensor demonstrated an exceptionally low detection limit of 0.019 ng/mL for oxytetracycline and exhibited excellent sensitivity in tap water. Furthermore, the sensor maintained over 90% detection performance after two weeks of room-temperature storage, indicating its stability. This method provides a rapid, highly sensitive approach for oxytetracycline detection, with potential for future improvements and widespread application in antibiotic testing. Full article

Its crucial importance to the long-term operation of lithium-ion batteries has made the solid electrolyte interphase (SEI) the subject of intensive research efforts. These investigations are challenging, however, due to the very complex and fragile nature of this layer. With its typical thickness being in the range of some 10 nm and its chemical make-up being highly sensitive to even the smallest amounts of impurities, it becomes clear that artifacts are easily introduced in investigations of the SEI, especially if the measurements are performed ex situ. To help ameliorate these issues, we herein report a combination of non-destructive operando techniques that can be employed simultaneously in the same electrochemical cell to provide a plethora of physical, morphological, and electrochemical data on the macroscopic and microscopic scale. These techniques encompass atomic force microscopy (AFM), electrochemical quartz crystal microbalance with dissipation monitoring (EQCM-D), and impedance spectroscopy (EIS). This work focuses on how to combine these techniques in a single electrochemical cell, which is suitable to study SEI formation while avoiding noise, crosstalk, inhomogeneous SEI formation, and other pitfalls. Full article

This article explores the development and application of innovative piezoelectric sensors in point-of-care diagnostics. It highlights the significance of bedside tests, such as lateral flow and electrochemical tests, in providing rapid and accurate results directly at the patient’s location. This paper delves into the principles of piezoelectric assays, emphasizing their ability to detect disease-related biomarkers through mechanical stress-induced electrical signals. Various applications of piezoelectric chemosensors and biosensors are discussed, including their use in the detection of cancer biomarkers, pathogens, and other health-related analytes. This article also addresses the integration of piezoelectric materials with advanced sensing technologies to improve diagnostic accuracy and efficiency, offering a comprehensive overview of current advances and future directions in medical diagnostics. Full article

This work demonstrates the preliminary results of rapid and direct detection of severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) using the quartz crystal microbalance (QCM) method. Coronavirus Disease 2019 (COVID-19)-specific RNA-dependent RNA polymerase (RdRP) gene-dependent probe DNA was used as a selective agent toward target DNA, the inactivated SARS-CoV-2 virus, and RNAs extracted from clinical samples. This study developed and utilised a unique dry-QCM approach with a mitigated experimental procedure. Contact angle measurements, Atomic Force Microscopy (AFM) and X-ray Photoelectron Spectroscopy (XPS) measurements were employed to investigate the surface during probe immobilisation and target hybridisation. This study also investigates the effect of temperature on probe immobilisation and target hybridisation. The estimated probe density was 0.51 × 10¹² probes/cm², which is below the critical limit. The estimated hybridisation efficiency was about 58.9%. The linear detection range with a Limit of Detection (LoD) was about ~1.22 nM with high selectivity toward SARS-CoV-2 target DNA. The sensor shelf-life was found to be extended to 25 days. The novelty of using a new dry-QCM approach for SARS-CoV-2 detection was proven with the results. Full article

By monitoring the solidification of droplets of plant latices with a fast quartz crystal microbalance with dissipation monitoring (QCM-D), droplets from Campanula glomerata were found to solidify much faster than droplets from Euphorbia characias and also faster than droplets from all technical latices tested. A similar conclusion was drawn from optical videos, where the plants were injured and the milky fluid was stretched (sometimes forming fibers) after the cut. Rapid solidification cannot be explained with physical drying because physical drying is transport-limited and therefore is inherently slow. It can, however, be explained with coagulation being triggered by a sudden decrease in hydrostatic pressure. A mechanism based on a pressure drop is corroborated by optical videos of both plants being injured under water. While the liquid exuded by E. characias keeps streaming away, the liquid exuded by C. glomerata quickly forms a plug even under water. Presumably, the pressure drop causes an influx of serum into the laticifers. The serum, in turn, triggers a transition from a liquid–liquid phase separated state (an LLPS state) of a resin and hardener to a single-phase state. QCM measurements, optical videos, and cryo-SEM images suggest that LLPS plays a role in the solidification of C. glomerata. Full article