Search Results (271)

Listeria monocytogenes (LM) poses a serious threat to food safety and public health. Current detection methods suffer from drawbacks such as expensive equipment, complex procedures, and time-consuming processes, highlighting the urgent need for a simple, rapid, accurate, and cost-effective detection approach. The bacterial metabolite 3-hydroxy-2-butanone (3H2B), due to its high abundance, can serve as a reliable biomarker for detection. Herein, ordered mesoporous silica nanoparticles (MSNs) were synthesized via a one-pot method and subsequently functionalized with APTES. The NH₂-MSNs-2 exhibits extremely high sensitivity (768 Hz@50 ppm) and selectivity towards 3H2B due to its high specific surface area, abundant mesoporous structure, and weak chemical adsorption between amino groups and the 3H2B. The quartz crystal microbalance (QCM) sensor developed based on this material demonstrated outstanding performance in testing the contamination levels of LM in food. This study provides a solid foundation for further exploring the fundamental mechanisms of QCM sensors in the real-time, non-invasive detection of LM, while also demonstrating significant application potential in the field of food safety assurance. Full article

Neonicotinoids are a novel class of insecticides that exhibit environmental persistence and off-target effects on both humans and ecosystems. Therefore, there is a need for sensitive and selective sensors to monitor concentrations of neonicotinoids in environmental water and soil systems. Molecularly imprinted polymer (MIP)-based sensors are an emerging technology with strong potential for reliable, sensitive, and selective detection of neonicotinoids. Moreover, MIPs are versatile and compatible with a wide range of analytical techniques, which can further enhance measurement capabilities in the development of practical and robust sensors. Despite this promise, many routes remain underexplored for neonicotinoid detection. This review reports on the current state of neonicotinoid chemical sensors and detection methods using MIPs and highlights potential applications of MIP-based approaches as cost-effective and easy-to-operate solutions for monitoring neonicotinoids. Recent sensors incorporating MIPs and electrochemical or optical techniques for neonicotinoid detection are described and compared. Approaches employing magnetic solid-phase extraction and quartz crystal microbalance are also discussed. Additionally, the influence of monomer choice for MIP synthesis, as well as the use of additives and nanomaterials for sensor construction and analyte detection, is reviewed. These methods may promote sustainability, reusability, ratiometric or simultaneous detection of neonicotinoids, and sensor portability for on-site monitoring. Full article

Accurate and early detection of alpha-fetoprotein (AFP) in human serum is essential for the diagnosis and monitoring of hepatocellular carcinoma and related diseases. In this study, we present a highly sensitive and reproducible quartz crystal microbalance (QCM) immunosensor for the quantitative detection of AFP. The detection strategy is based on a sandwich-type immunoassay coupled with a signal amplification method utilizing photocatalytic silver deposition on tungsten(IV) oxide (WO₃) nanoparticles. Since QCM detects resonance frequency shifts induced by mass changes on the sensor surface, the silver-enhanced growth of WO₃ nanoparticles enables significant signal amplification, allowing for precise mass-based quantification. Without amplification, the limit of detection (LOD) for AFP using the QCM immunosensor was 286 pg/mL, which was significantly improved to 43.7 pg/mL with photocatalytic silver staining. This approach markedly improves both sensitivity and reproducibility of the assay, offering a robust and efficient platform for clinical biomarker detection and early cancer diagnostics. Full article

Nanostructured oxide coatings play a critical role in determining molecular adsorption and desorption behavior on solid surfaces. In this study, we propose a rapid and simple method to estimate the apparent vapor pressure of fragrance compounds using a quartz crystal microbalance (QCM) sensor modified with a nanostructured silica surface. Here, the term “apparent vapor pressure” refers to the vapor pressure values predicted from the QCM response characteristics, which correlate quantitatively with reference data obtained from conventional thermodynamic calculations. The QCM responses of various fragrances were analyzed in relation to the adsorption–desorption dynamics occurring at the nanostructured interface. We found a quantitative relationship between the sensor responses and the reference vapor pressure values, with a mean absolute percentage error (MAPE) ranging from 19.3% to 220% depending on the compound. This correlation enables rapid evaluation of vapor pressure-related behavior without relying on conventional vapor pressure measurement methods. The results suggest that the surface nanostructure influences the adsorption–desorption balance governed by vapor pressure. This approach provides a practical and efficient means of evaluating the apparent vapor pressure of volatile compounds on nanostructured materials, offering insights into interfacial phenomena relevant to materials science and applied nanosciences. Full article

This review critically evaluates the performance of approximately 80 commercially available mobile detectors for explosive identification. The majority of devices utilize Ion Mobility Spectrometry (IMS), Fourier Transform Infrared Spectroscopy (FTIR), or Raman Spectroscopy (RS). IMS-based instruments, such as the M-ION (Inward Detection), typically achieve sensitivities at the ppt level, while other IMS implementations demonstrate detection ranges from low ppb to ppm. Gas Chromatography–Mass Spectrometry (GC–MS) systems, represented by the Griffin™ G510 (Teledyne FLIR Detection), provide detection limits in the ppb range. Transportable Mass Spectrometers (Bay Spec) operate at ppb to ppt levels, whereas Laser-Induced Fluorescence (LIF) devices, such as the Fido X4 (Teledyne FLIR Detection), achieve detection at the nanogram level. Quartz Crystal Microbalance (QCM) sensors, exemplified by the EXPLOSCAN (MS Technologies Inc. 8609 Westwood Center Drive Suite 110, Tysons Corner, VA, USA), typically reach the ppb range. Only four devices employ two orthogonal analytical techniques, enhancing detection reliability and reducing false alarms. Traditional colorimetric tests based on reagent–analyte reactions remain in use, demonstrating the continued relevance of simple yet effective methods. By analyzing the capabilities, limitations, and technological trends of current detection systems, this study underscores the importance of multi-technique approaches to improve accuracy, efficiency, and operational effectiveness in real-world applications. The findings provide guidance for the development and selection of mobile detection technologies for security, defense, and emergency response. Full article

The prevalence of food allergies has been steadily increasing in recent years. β-lactoglobulin (β-LG), the main allergenic protein of milk and dairy allergies, is more commonly observed in infants and children. In this study, a β-LG-specific aptamer was selected using the combinatorial chemistry process known as systematic evolution of ligands by exponential enrichment (SELEX), and a quartz crystal microbalance with dissipation monitoring (QCM-D)-based aptasensor was developed using a novel surface functionalization technique, which mimics an artificial cell membrane on the QCM-D sensor surface, creating a physiologically relevant environment for the binding of the target to the sensor. Through SELEX combined with next-generation sequencing (NGS), the aptamer Apt 356 was identified. Its binding to β-LG was confirmed via dot blot analysis. The selected Apt 356 was then used for the development of a QCM-D-based sensor. To fabricate the sensor, the quartz surface was functionalized with a supported lipid bilayer (SLB). The β-LG-specific aptamer was immobilized onto this SLB. The results demonstrated that the QCM-D system allows real-time observation and evaluation of the binding of β-LG. While there have been some studies on aptasensors for the β-LG protein, to the best of our knowledge, this is the first QCM-D-based aptasensor developed specifically for β-LG protein detection. Full article

In this study, a hybrid sensor-based electronic nose circuit was developed using eight metal-oxide semiconductors and 14 quartz crystal microbalance gas sensors. This study included 100 participants: 60 individuals diagnosed with lung cancer, 20 healthy nonsmokers, and 20 healthy smokers. A total of 338 experiments were performed using breath samples throughout this study. In the classification phase of the obtained data, in addition to traditional classification algorithms, such as decision trees, support vector machines, k-nearest neighbors, and random forests, the fuzzy logic method supported by the optimization algorithm was also used. While the data were classified using the fuzzy logic method, the parameters of the membership functions were optimized using a nature-inspired optimization algorithm. In addition, principal component analysis and linear discriminant analysis were used to determine the effects of dimension-reduction algorithms. As a result of all the operations performed, the highest classification accuracy of 94.58% was achieved using traditional classification algorithms, whereas the data were classified with 97.93% accuracy using the fuzzy logic method optimized with optimization algorithms inspired by nature. Full article

Mercury (Hg) is a globally recognized toxic element, and the Minamata Convention on Mercury entered into force in 2017 to address its associated risks. Under the United Nations Environment Programme, international efforts to reduce Hg emissions and monitor its environmental presence are ongoing. In support of these initiatives, we developed a simple and rapid mercury detection device based on a quartz crystal microbalance (QCM-Hg sensor), which utilizes the direct amalgamation reaction between Hg and a gold (Au) electrode. The experimental results demonstrated a proportional relationship between Hg concentration and the resulting oscillation frequency shift. Increased flow rates and prolonged measurement durations enhanced detection sensitivity. The system achieved a detection limit of approximately 1 µg/m³, comparable to that of commercially available analyzers. Furthermore, a measurement configuration integrating the reduction-vaporization method with the QCM-Hg sensor enabled the detection of mercury in aqueous samples. Based on the experimental results and the gas-phase detection sensitivity achieved to date, concentrations as low as approximately 0.05 µg/L appear to be detectable. These findings highlight the potential of the QCM-Hg system for on-site mercury monitoring. This review aims to provide a comprehensive yet concise overview of QCM-Hg sensor development and its potential as a next-generation tool for environmental and occupational mercury monitoring. Full article

Protein adsorption on dental zirconia (ZrO₂) surfaces plays a crucial role in plaque formation, tissue healing, and bone osseointegration. This study investigated and compared the adsorption behavior of three salivary antimicrobial proteins—peroxidase, lactoferrin, and lysozyme—on a ZrO₂ sensor and an Au sensor using a quartz crystal microbalance (QCM) operating at 27 MHz. Protein adsorption was determined from frequency decreases, and the apparent reaction rate constant (k_obs) was calculated by fitting frequency–time curves to a kinetic model. The amount of lactoferrin adsorbed on the ZrO₂ sensor was significantly higher than that of peroxidase and lysozyme (p < 0.05). Significantly smaller amounts of peroxidase and lysozyme were adsorbed onto the ZrO₂ sensor than the Au sensor (p < 0.05). The k_obs for lysozyme on the Au sensor was significantly higher than those for lactoferrin on sensors and for peroxidase on the Au sensor (p < 0.05). Differences in salivary antimicrobial protein adsorption between Au and ZrO₂ surfaces were influenced, in part, by electrostatic interactions between the proteins and the material surface. Full article

Newly developed hygrosensitive poly(vinyl alcohol) derivatives comprising grafted poly(N,N-dimethylacrylamide) chains of varied length and graft density are presented. The optical, sensing, and hydration properties of these copolymer thin films prepared by spin-coating were systematically studied. Refractive indices (n), absorption coefficients (k), and thicknesses (d) were calculated via curve fitting of the reflection spectra. Reflectance measurements across a relative humidity range of 5% to 95% were used to evaluate the humidity sensing behavior. Coating swelling exceeding 100% was observed. Hydration levels under high humidity conditions were studied using a quartz crystal microbalance method. This revealed approximately 24% water content in the polymer with the higher grafting density and shorter PDMA chains compared to around 31% in the copolymer with longer PDMA brushes that were loosely grafted The potential application of these copolymers as responsive materials for advanced humidity sensing is discussed. A combined optical and gravimetric approach for characterizing the humidity sensing properties of thin nanosized coatings is demonstrated, providing opportunities for advanced characterization of new functional materials, thus broadly contributing to the state of the art of sensor technologies. Full article

We present a dual biosensing strategy integrating Quartz Crystal Microbalance (QCM) and Surface-Enhanced Raman Spectroscopy (SERS) for the quantitative and molecular-specific detection of FKBP12. Silver nanodendritic arrays were electrodeposited onto QCM sensors, optimized for SERS enhancement using Rhodamine 6G, and functionalized with a custom-designed receptor to selectively capture FKBP12. QCM measurements revealed a two-step Langmuir adsorption behavior, enabling sensitive mass quantification with a low limit of detection. Concurrently, in situ SERS analysis on the same sensor provided vibrational fingerprints of FKBP12, resolved through comparative studies of the free protein, surface-bound receptor, and surface-bound receptor–protein complex. Ethanol-induced denaturation confirmed protein-specific peaks, while shifts in receptor vibrational modes—linked to FKBP12 binding—demonstrated dynamic molecular interactions. A ratiometric parameter, derived from key peak intensities, served as a robust, concentration-dependent signature of complex formation. This platform bridges quantitative (QCM) and structural (SERS) biosensing, offering real-time mass tracking and conformational insights. The nanodendritic substrate’s dual functionality, combined with the receptor’s selectivity, advances label-free protein detection for applications in drug diagnostics, with potential adaptability to other target analytes. Full article

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

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

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

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