Hydrogel-Based Sensors for Ethanol Detection in Alcoholic Beverages

Applications of Functional Polymeric Eutectogels

Over the past two decades, deep eutectic solvents (DESs) have captured significant attention as an emergent class of solvents that have unique properties and applications in differing fields of chemistry. One area where DES systems find utility is the design of polymeric gels, often referred to as "eutectogels," which can be prepared either using a DES to replace a traditional solvent, or where monomers form part of the DES themselves. Due to the extensive network of intramolecular interactions (e.g., hydrogen bonding) and ionic species that exist in DES systems, polymeric eutectogels often possess appealing material properties-high adhesive strength, tuneable viscosity, rapid polymerization kinetics, good conductivity, as well as high strength and flexibility. In addition, non-covalent crosslinking approaches are possible due to the inherent interactions that exist in these materials. This review considers several key applications of polymeric eutectogels, including organic electronics, wearable sensor technologies, 3D printing resins, adhesives, and a range of various biomedical applications. The design, synthesis, and properties of these eutectogels are discussed, in addition to the advantages of this synthetic approach in comparison to traditional gel design. Perspectives on the future directions of this field are also highlighted.

Smart Hydrogel Swelling State Detection Based on a Power-Transfer Transduction Principle

Stimulus-responsive (smart) hydrogels are a promising sensing material for biomedical contexts due to their reversible swelling change in response to target analytes. The design of application-specific sensors that utilize this behavior requires the development of suitable transduction concepts. The presented study investigates a power-transfer-based readout approach that is sensitive to small volumetric changes of the smart hydrogel. The concept employs two thin film polyimide substrates with embedded conductive strip lines, which are shielded from each other except at the tip region, where the smart hydrogel is sandwiched in between. The hydrogel's volume change in response to a target analyte alters the distance and orientation of the thin films, affecting the amount of transferred power between the two transducer parts and, consequently, the measured sensor output voltage. With proper calibration, the output signal can be used to determine the swelling change of the hydrogel and, consequently, to quantify the stimulus. In proof-of-principle experiments with glucose- and pH-sensitive smart hydrogels, high sensitivity to small analyte concentration changes was found along with very good reproducibility and stability. The concept was tested with two exemplary hydrogels, but the transduction principle in general is independent of the specific hydrogel material, as long as it exhibits a stimulus-dependent volume change. The application vision of the presented research is to integrate in situ blood analyte monitoring capabilities into standard (micro)catheters. The developed sensor is designed to fit into a catheter without obstructing its normal use and, therefore, offers great potential for providing a universally applicable transducer platform for smart catheter-based sensing.

Development of Pd/In2O3 hybrid nanoclusters to optimize ethanol vapor sensing

In this study, we successfully synthesize palladium-decorated indium trioxide (Pd/In2O3) hybrid nanoclusters (NCs) using an advanced dual-target cluster beam deposition (CBD) method, a significant stride in developing high-performance ethanol sensors. The prepared Pd/In2O3 hybrid NCs exhibit exceptional sensitivity, stability, and selectivity to low concentrations of ethanol vapor, with a maximum response value of 101.2 at an optimal operating temperature of 260 °C for 6 at% Pd loading. The dynamic response of the Pd/In2O3-based sensor shows an increase in response with increasing ethanol vapor concentrations within the range of 50 to 1000 ppm. The limit of detection is as low as 24 ppb. The sensor exhibits a high sensitivity of 28.24 ppm-1/2, with response and recovery times of 2.7 and 4.4 seconds, respectively, for 100 ppm ethanol vapor. Additionally, the sensor demonstrates excellent repeatability and stability, with only a minor decrease in response observed over 30 days and notable selectivity for ethanol compared to other common volatile organic compounds. The study highlights the potential of Pd/In2O3 NCs as promising materials for ethanol gas sensors, leveraging the unique capabilities of CBD for controlled synthesis and the catalytic properties of Pd for enhanced gas-sensing performance.

Study on the modulating effect of halogen atom substitution on the detection range of water content detection probes in organic solvents

Fluorescence probes based on the variations of aggregation state (Aggregation-Induced Emission (AIE) and Aggregation-Caused Quenching (ACQ)) have received widespread attention due to their simplicity, efficiency and intuitiveness. However, typical probes are highly sensitive to changes in polarity and slight variations in the external environment can cause a complete change in the aggregation state. With the aim of expanding the detection range of the molecular probe, this work adopts a different design strategy from adjusting the molecular backbone but regulates the fluorescence behavior of the Schiff base molecular backbone by introducing different halogen atoms. Systematic studies show that when chlorine serves as substitutional atoms (3,5-Cl Salen), the probe can achieve full-range detection of water content (0-100 vol%) in ethanol and DMF. To our knowledge, the 3,5-Cl Salen represents the best water content probe in organic molecules. Experimental and theoretical studies have shown that the adjustment of halogen atoms can linearly change the charge distribution on the benzene ring and precisely control the strength of intermolecular interactions. At the same time, we developed a fluorescent filter paper based on 3,5-Cl Salen and used smartphones for rapid, sensitive and precise on-site measurement of water content in organic solvents.

Biocompatible, Antibacterial, and Stable Deep Eutectic Solvent-Based Ionic Gel Multimodal Sensors for Healthcare Applications

In this study, we investigated a novel approach to fabricate multifunctional ionic gel sensors by using deep eutectic solvents (DESs) as replacements for water. When two distinct DESs were combined, customizable mechanical and conductive properties were created, resulting in improved performance compared with traditional hydrogel-based strain sensors. DES ionic gels possess superior mechanical properties, transparency, biocompatibility, and antimicrobial properties, making them suitable for a wide range of applications such as flexible electronics, soft robotics, and healthcare. We conducted a comprehensive evaluation of the DES ionic gels, evaluating their performance under extreme temperature conditions (-70 to 80 °C), impressive optical transparency (94%), and biocompatibility. Furthermore, a series of tests were conducted to evaluate the antibacterial performance (Escherichia coli) of the DES ionic gels. Their wide strain (1-400%) and temperature (15-50 °C)-sensing ranges demonstrate the versatility and adaptability of DES ionic gels for diverse sensing requirements. The resulting DES ionic gels were successfully applied in human activity and vital sign monitoring, demonstrating their potential for biointegrated sensing devices and healthcare applications. This study offers valuable insights into the development and optimization of hydrogel sensors, particularly for applications that require environmental stability, biocompatibility, and antibacterial performance, thereby paving the way for future advancements in this field.

Metal-Phenolic Film Coated Quartz Crystal Microbalance as a Selective Sensor for Methanol Detection in Alcoholic Beverages

The facile real-time monitoring of methyl content in fermented beverages is of fundamental significance in the alcohol and restaurant industry, since as little as 4 mL of methanol entering the blood may cause intoxication or blindness. So far, the practical applicability of available methanol sensors, including the piezoresonance analogs, is somewhat limited to laboratory use due to the complexity and bulkiness of the measuring equipment involving multistep procedures. This article introduces a hydrophobic metal-phenolic film-coated quartz crystal microbalance (MPF-QCM) as a novel streamlined detector of methanol in alcoholic drinks. Unlike other QCM-based alcohol sensors, our device operates under saturated vapor pressure conditions, permitting rapid detection of methyl fractions up to seven times below the tolerable levels in spirits (e.g., whisky) while effectively suppressing the cross-sensitivity to interfering chemical compounds such as water, petroleum ether or ammonium hydroxide. Furthermore, the good surface adhesion of metal-phenolic complexes endows the MPF-QCM with superior long-term stability, contributing to the repeatable and reversible physical sorption of the target analytes. These features, combined with the lack of mass flow controllers, valves and connecting pipes delivering the gas mixture, outline the likelihood for future design of a portable MPF-QCM prototype suitable to point-of-use analysis in drinking establishments.

Metal-Filled Polyvinylpyrrolidone Copolymers: Promising Platforms for Creating Sensors

This paper presents research results on the properties of composite materials based on cross-linked grafted copolymers of 2-hydroxyethylmethacrylate (HEMA) with polyvinylpyrrolidone (PVP) and their hydrogels filled with finely dispersed metal powders (Zn, Co, Cu). Metal-filled pHEMA-gr-PVP copolymers in the dry state were studied for surface hardness and swelling ability, which was characterized by swelling kinetics curves and water content. Copolymers swollen in water to an equilibrium state were studied for hardness, elasticity, and plasticity. The heat resistance of dry composites was evaluated by the Vicat softening temperature. As a result, materials with a wide range of predetermined properties were obtained, including physico-mechanical properties (surface hardness 240 ÷ 330 MPa, hardness number 0.06 ÷ 2.8 MPa, elasticity number 75 ÷ 90%), electrical properties (specific volume resistance 10² ÷ 10⁸ Ω⋅m), thermophysical properties (Vicat heat resistance 87 ÷ 122 °C), and sorption (swelling degree 0.7 ÷ 1.6 g (H₂O)/g (polymer)) at room temperature. Resistance to the destruction of the polymer matrix was confirmed by the results concerning its behavior in aggressive media such as solutions of alkalis and acids (HCl, H₂SO₄, NaOH), as well as some solvents (ethanol, acetone, benzene, toluene). The obtained composites are characterized by electrical conductivity, which can be adjusted within wide limits depending on the nature and content of the metal filler. The specific electrical resistance of metal-filled pHEMA-gr-PVP copolymers is sensitive to changes in moisture (with a moisture increase from 0 to 50%, ρ_V decreases from 10⁸ to 10² Ω⋅m), temperature (with a temperature change from 20 °C to 175 °C, ρ_V of dry samples decreases by 4.5 times), pH medium (within pH from 2 to 9, the range of ρ_V change is from 2 to 170 kΩ⋅m), load (with a change in compressive stress from 0 kPa to 140 kPa, ρ_V of swollen composites decreases by 2-4 times), and the presence of low molecular weight substances, which is proven by the example involving ethanol and ammonium hydroxide. The established dependencies of the electrical conductivity of metal-filled pHEMA-gr-PVP copolymers and their hydrogels on various factors, in combination with high strength, elastic properties, sorption capacity, and resistance to aggressive media, suggest the potential for further research as a platform for the manufacture of sensors for various purposes.

Physics-Based Circuit Modeling of the Impedance Characteristics of a Smart Hydrogel-Actuated Bending Sensor

Smart hydrogels are stimuli-responsive polymers which exhibit a volume-phase transition in response to external influences. This makes them promising candidates for sensing elements, especially in a biomedical context due to their easily achievable biocompatibility. The main challenge in harnessing the smart polymer's potential for sensor applications lies in a reliable transduction of the swelling change into an electrical signal. A novel platform approach is based on a bending sensor where the smart hydrogel acts as an actuator on a thin film with embedded metal traces. Mechanical deformation due to the hydrogel volume change alters the traces' electric impedance. However, besides deformation, the medium surrounding the sensor structure will also affect the impedance. For sensor design it is therefore crucial to understand the complex interdependencies between electric sensor properties, influences of the surrounding medium and mechanical deformation. Here, an electric circuit model is presented which considers all these contributions through a minimum number of lumped elements and is strictly based on physical considerations. By employing measured impedance spectra from an experimental sensor implementation subjected to different surrounding media and mechanical deformation, the validity of the simplified model is demonstrated. A detailed analysis and discussion give insights into the determination of the different model parameters and how external influences can clearly be attributed to specific circuit elements. This work provides a general approach for deducing minimalistic but strictly physics-based circuit models which can still adequately replicate the actual behavior of such types of impedance-based bending sensors.

A Smart Alcoholmeter Sensor Based on Deep Learning Visual Perception

Process automation, in general, enables the enhancement of productivity, product quality, and consistency alongside other production metrics. Liquor production on an industrial scale also follows the automation trend. However, small and medium producers lag with equipment modernization due to the high costs of industrial equipment. One of the important sensors in automation equipment for distilleries is the alcohol concentration sensor used for fraction separation, process automation, and supervision. This paper proposes a novel low-cost approach to alcohol concentration sensing by employing deep learning on the visual perception of traditional alcoholmeter. For purposes of the training model, dataset acquisition apparatus is developed and a large dataset of labeled images of alcoholmeter readings is acquired. The problem of reading alcohol concentration from an alcoholometer image is treated as a regression and classification problem. Performances of both regression and classification models were investigated with Resnet18 as an architecture of choice. Both models achieved satisfying performance metrics demonstrating the feasibility of the proposed approaches. The proposed system implemented on Raspberry Pi with a camera can be integrated into new distillation equipment. Additionally, it can be used for retrofitting existing equipment due to its non-invasive nature of reading. The scope of use can be further expanded to the reading of other types of analog instruments simply by retraining the model.

Multiresonant analysis improves the limit of detection of tilted fiber Bragg grating refractometers

A multiresonant approach based on tracking 27 cladding mode resonances of tilted fiber Bragg grating refractometers is shown to improve the limit of detection by a factor of 3 to 4 relative to the conventional approach of tracking the single-most sensitive resonance. Limits of detection below 2 × 10^-5 in index change are achieved for dilutions of ethanol in water in repeated experiments. In all cases, wavelengths are referenced to the core mode resonance which eliminates the effect of small temperature changes during and between experiments.

Functional Thermoresponsive Hydrogel Molecule to Material Design for Biomedical Applications

Temperature-induced, rapid changes in the viscosity and reproducible 3-D structure formation makes thermos-sensitive hydrogels an ideal delivery system to act as a cell scaffold or a drug reservoir. Moreover, the hydrogels’ minimum invasiveness, high biocompatibility, and facile elimination from the body have gathered a lot of attention from researchers. This review article attempts to present a complete picture of the exhaustive arena, including the synthesis, mechanism, and biomedical applications of thermosensitive hydrogels. A special section on intellectual property and marketed products tries to shed some light on the commercial potential of thermosensitive hydrogels.

Home-Made Membraneless Vaporization Gas-Liquid Separator for Colorimetric Determination of Ethanol in Alcoholic Beverages

This work utilized the simplicity of a so-called membraneless vaporization (MBL-VP) unit as a gas separator for the colorimetric determination of ethanol in alcoholic beverages. A beverage sample with a volume of 1 mL was directly injected into a small container which was hung from a lid inside a closed 40 mL reused glass bottle without pretreatment such as distillation. An acidified potassium dichromate (Cr₂O₇ ^2-) acceptor solution, preadded to the glass bottle, was reduced to Chromium (III) ion by the diffusion of vaporized ethanol from the sample. After 5 min, the absorbing solution was collected for colorimetric detection at 590 nm. The unit manually quantifies ethanol in the range 1.0-90% (v/v) with satisfactory interday precision but without matrix effect (recovery 89-109%). The method was validated with the conventional distillation/pycnometer method which showed no significant difference of ethanol contents between those two methods and the declared values of 12 alcoholic beverages, indicating sufficient accuracy. Analyses of alcoholic beverages using this method were successful with benefits of simplicity, cheapness, and less energy consumption.

A Review of Optical Fibre Ethanol Sensors: Current State and Future Prospects

A range of optical fibre-based sensors for the measurement of ethanol, primarily in aqueous solution, have been developed and are reviewed here. The sensing approaches can be classified into four groups according to the measurement techniques used, namely absorption (or absorbance), external interferometric, internal fibre grating and plasmonic sensing. The sensors within these groupings can be compared in terms of their characteristic performance indicators, which include sensitivity, resolution and measurement range. Here, particular attention is paid to the potential application areas of these sensors as ethanol production is globally viewed as an important industrial activity. Potential industrial applications are highlighted in the context of the emergence of the internet of things (IoT), which is driving widespread utilization of these sensors in the commercially significant industrial and medical sectors. The review concludes with a summary of the current status and future prospects of optical fibre ethanol sensors for industrial use.

Strong nanozymatic activity of thiocyanate capped gold nanoparticles: an enzyme–nanozyme cascade reaction based dual mode ethanol detection in saliva

This article reports on the strong nanozymatic activity of thiocyanide capped gold nanoparticles (TC-AuNPs) in the presence of 3,3′,5,5′-tetramethylbenzidine (TMB) and H2O2.

NiO Grained-Flowers and Nanoparticles for Ethanol Sensing

Grained-flower and nanoparticles NiO samples were synthesized with a straightforward, surfactant-free hydrothermal procedure, and probed with respect to ethanol gas-sensing. Both morphologies displayed excellent performances in terms of gas response vs. temperature and concentration and are very reproducible. The grained-flower, however, performed better than the nanoparticles NiO, probably due to the shorter travelling distance of the electrons and/or adsorbates during the detection process. Both sensors displayed high stability over three weeks. The grained-flower NiO sensor also has a good selectivity.

Enzyme-Functionalized Piezoresistive Hydrogel Biosensors for the Detection of Urea

Urea is used in a wide variety of industrial applications such as the production of fertilizers. Furthermore, urea as a metabolic product is an important indicator in biomedical diagnostics. For these applications, reliable urea sensors are essential. In this work, we present a novel hydrogel-based biosensor for the detection of urea. The hydrolysis of urea by the enzyme urease leads to an alkaline pH change, which is detected with a pH-sensitive poly(acrylic acid-co-dimethylaminoethyl methacrylate) hydrogel. For this purpose, the enzyme is physically entrapped during polymerization. This enzyme-hydrogel system shows a large sensitivity in the range from 1 mmol/L up to 20 mmol/L urea with a high long-term stability over at least eight weeks. Furthermore, this urea-sensitive hydrogel is highly selective to urea in comparison to similar species like thiourea or N-methylurea. For sensory applications, the swelling pressure of this hydrogel system is transformed via a piezoresistive pressure sensor into a measurable output voltage. In this way, the basic principle of hydrogel-based piezoresistive urea biosensors was demonstrated.

Real-time optical fiber sensors based on light diffusing microlens arrays

The applications of optical fibers are impeded in implantable medical diagnostics due to incompatibility with biological tissues, and immune reaction in vivo. The utilization of biocompatible materials to construct a photonic sensing platform can reduce the immune response in in vivo medical diagnostics. Here, we developed real-time optical fiber sensors to determine the volumetric modulation of stimuli-responsive polymers. Asymmetric microlens structures were replicated on stimuli-sensitive hydrogels as stand-alone sensors and were chemically attached to the tips of silica and biocompatible optical fibers. Quantitative measurements were carried out using a smartphone to demonstrate the ease, simplicity, and practicality of the readout methodology. To demonstrate the utility in real-time sensing, the fiber probe was investigated in various concentrations of ethanol, propan-2-ol, and dimethyl sulfoxide. Also, the fiber probe showed a rapid response to pH in the acidic region with a sensitivity of 40 nW pH-1. To develop biocompatible probes for physiological applications, a microlens array-imprinted polymer was attached to the tip of a hydrogel optical fiber. The optical fiber probe in the refection configuration showed a sensitivity of 7 nW pH-1. The developed hydrogel fiber probes may have application in point-of-care diagnostics, continuous biomarker monitoring, and critical care sensing devices.