Search Results (15)

Nucleic acid amplification reactions such as polymerase chain reaction (PCR), which uses a DNA polymerase to amplify individual double-stranded DNA fragments, are a useful technique for visualizing the presence of specific genomes. Although the fluorescent labeling method is mainly used with DNA amplification, other detection methods should be considered for further improvements, such as miniaturization and cost reduction, of reaction-monitoring devices. In this study, the quartz-crystal microbalance (QCM) method, which can measure nanogram-order masses, was applied for the real-time detection of DNA fragments in a solution with nucleic acids. This was combined with an isothermal nucleic acid amplification reaction based on the recombinase polymerase amplification (RPA) method, which allowed DNA amplification at a constant temperature. When the DNA amplification reaction was initiated on a QCM sensor plate with an immobilized primer DNA strand, a significant increase in mass was observed compared to when the primer DNA was not immobilized. QCM was shown to be sufficiently sensitive for the in situ detection of amplified DNA fragments. Combining a portable QCM device and RPA offers a sensitive point-of-care method for detecting nucleic acids. Full article

The Amperometric Gas Sensor (AGS) uses an electrode as the transducer element which converts its signal into a current from the electrochemical reaction of analytes taking place at the electrode surface. Many attempts to improve AGS performance, such as modifying the working electrode, applying a particular gas-permeable membrane, and selecting the proper electrolyte, etc., have been reported in the scientific literature. On the other hand, in the materials community, atomic gold has gained much attention because its physicochemical properties dramatically differ from those of gold nanoparticles. This paper provides an overview of the use of atomic gold in AGSs, both in a bulky AGS and a miniaturized AGS. In the miniaturized AGS, the system must be redesigned; for example, the aqueous electrolyte commonly used in a bulky AGS cannot be used due to volatility and fluidity issues. A Room Temperature Ionic Liquid (RTIL) can be used to replace the aqueous electrolyte since it has negligible vapor pressure; thus, a thin film of RTIL can be realized in a miniaturized AGS. In this paper, we also explain the possibility of using RTIL for a miniaturized AGS by incorporating a quartz crystal microbalance sensor. Several RTILs coated onto modified electrodes used for isomeric gas measurement are presented. Based on the results, the bulky and miniaturized AGS with atomic gold exhibited a higher sensor response than the AGS without atomic gold. Full article

R-(+)-limonene, one of the major constituents of citrus oils, is a monoterpene that is widely used as a fragrance additive in cosmetics, foods, and industrial solvents. Nowadays, its detection mainly relies on bulky and expensive analytical methods and only a few research works proved its revelation through affordable and portable sensors, such as electrochemical and quartz crystal microbalance sensors. In response to the demand for effective miniaturized sensing devices to be integrated into Internet of Things systems, this study represents a pioneering investigation of chemoresistive gas sensor capabilities addressed to R-(+)-limonene detection. An array of seven metal-oxide sensors was exploited to perform a complete electrical characterization of the target analyte. The experimental evidence allowed us to identify the WO₃-based sensor as the most promising candidate for R-(+)-limonene detection. The material was highly sensitive already at sub-ppm concentrations (response of 2.5 at 100 ppb), consistent with applicative parameters, and it resulted in selective vs. different gases at a lower operating temperature (200 °C) than the other sensors tested. Furthermore, it exhibited a humidity-independent behavior under real-life conditions (relative humidity > 20%). Finally, the WO₃ sensor also demonstrated a remarkable cross-selectivity, thus enabling its exploitation in cutting-edge applications. Full article

Suspended particulate matter (PMx) is one of the most important environmental pollutants. Miniaturized sensors capable of measuring and analyzing PMx are crucial in environmental research fields. The quartz crystal microbalance (QCM) is one of the most well-known sensors that could be used to monitor PMx. In general, in environmental pollution science, PMx is divided into two main categories correlated to particle diameter (e.g., PM < 2.5 µm and PM < 10 µm). QCM-based systems are capable of measuring this range of particles, but there is an important issue that limits the application. In fact, if particles with different diameters are collected on QCM electrodes, the response will be a result of the total mass of particles; there are no simple methods to discriminate the mass of the two categories without the use of a filter or manipulation during sampling. The QCM response depends on particle dimensions, fundamental resonant frequency, the amplitude of oscillation, and system dissipation properties. In this paper, we study the effects of oscillation amplitude variations and fundamental frequency (10, 5, and 2.5 MHz) values on the response, when particle matter with different sizes (2 µm and 10 µm) is deposited on the electrodes. The results showed that the 10 MHz QCM was not capable of detecting the 10 µm particles, and its response was not influenced by oscillation amplitude. On the other hand, the 2.5 MHz QCM detected the diameters of both particles, but only if a low amplitude value was used. Full article

Quartz-crystal microbalance (QCM) is a technique that can measure nanogram-order masses. When a receptor is immobilized on the sensor surface of a QCM device, the device can detect chemical molecules captured by the mass change. Although QCM devices have been applied to biosensors that detect biomolecules without labels for biomolecular interaction analysis, most highly sensitive QCM devices are benchtop devices. We considered the fabrication of an IC card-sized QCM device that is both portable and battery-powered. Its miniaturization was achieved by repurposing electronic components and film batteries from smartphones and wearable devices. To demonstrate the applicability of the card-sized QCM device as a biosensor, DNA-detection experiments were performed. The card-sized QCM device could detect specific 10-mer DNA chains while discerning single-base differences with a sensitivity similar to that of a conventional benchtop device. The card-sized QCM device can be used in laboratories and in various other fields as a mass sensor. Full article

Currently, several biosensors are reported to confirm the absence/presence of an abnormal level of specific human biomarkers in research laboratories. Unfortunately, public marketing and/or pharmacy accessibility are not yet possible for many bodily fluid biomarkers. The questions are numerous, starting from the preparation of the substrates, the wet/dry form of recognizing the (bio)ligands, the exposure time, and the choice of the running buffers. In this context, for the first time, the present overview summarizes the pre-functionalization of standard and nanostructured solid/flexible supports with cysteamine (Cys) and glutaraldehyde (GA) chemicals for robust protein immobilization and detection of biomarkers in body fluids (serum, saliva, and urine) using three transductions: piezoelectrical, electrochemical, and optical, respectively. Thus, the reader can easily access and compare step-by-step conjugate protocols published over the past 10 years. In conclusion, Cys/GA chemistry seems widely used for electrochemical sensing applications with different types of recorded signals, either current, potential, or impedance. On the other hand, piezoelectric detection via quartz crystal microbalance (QCM) and optical detection by surface plasmon resonance (LSPR)/surface-enhanced Raman spectroscopy (SERS) are ultrasensitive platforms and very good candidates for the miniaturization of medical devices in the near future. Full article

The quartz crystal microbalance (QCM) has been widely used in laboratory settings as an analytical tool for recognizing and discriminating biological and chemical molecules of interest. As a result, recent studies have shown there to be considerable attention in practical applications of the QCM technique beyond the laboratory. However, most commercial QCM instruments are not suitable for off-laboratory usage. For field-deployable applications and in situ detection, the development of a portable QCM measurement system achieving comparable performance to benchtop instruments is highly desired. In this paper, we describe the development of a fully customizable, miniaturized, battery-powered, and cost-efficient QCM system employing a phase-locked loop (PLL) electronic circuit-based QCM measurement system. The performance of this developed system showed a minimum frequency resolution of approximately 0.22 Hz at 0.1 s measurement time. This novel, miniaturized system successfully demonstrated an ability to detect two common volatile organic compounds (VOCs), methanol and dichloromethane (DCM), and the obtained results were comparable to responses from a commercially available benchtop instrument. Full article

Monolithic quartz crystal microbalance (MQCM) has recently emerged as a very promising technology suitable for biosensing applications. These devices consist of an array of miniaturized QCM sensors integrated within the same quartz substrate capable of detecting multiple target analytes simultaneously. Their relevant benefits include high throughput, low cost per sensor unit, low sample/reagent consumption and fast sensing response. Despite the great potential of MQCM, unwanted environmental factors (e.g., temperature, humidity, vibrations, or pressure) and perturbations intrinsic to the sensor setup (e.g., mechanical stress exerted by the measurement cell or electronic noise of the characterization system) can affect sensor stability, masking the signal of interest and degrading the limit of detection (LoD). Here, we present a method based on the discrete wavelet transform (DWT) to improve the stability of the resonance frequency and dissipation signals in real time. The method takes advantage of the similarity among the noise patterns of the resonators integrated in an MQCM device to mitigate disturbing factors that impact on sensor response. Performance of the method is validated by studying the adsorption of proteins (neutravidin and biotinylated albumin) under external controlled factors (temperature and pressure/flow rate) that simulate unwanted disturbances. Full article

A miniaturized quartz crystal microbalance (QCM) genosensor is proposed for sensitive and real-time detection of short ssDNA sequences (53 bp) or DNA extracted from Brettanomyces bruxellensis (Brett) yeast cells. The presence of Brett yeast causes a depreciation of the quality of aged fine wines, producing molecules of unpleasant odors and biogenic amines that are harmful to human health. More specifically, standard quartz crystal (S-QCM) and homemade 4 nm gold transmission electron microscopy (TEM)-grid patterned quartz (multi-TEM QCM) are herein proposed for biofunctionalization steps with different ssDNA sequences. By employing a rapid and efficient drop and collect protocol, the specific detection of 1 pg/µL ssDNA Brett of a short sequence and 100 ng/μL DNA of B. bruxellensis extracted from a wine sample (VR2008) is reported. Full article

Acoustic devices have found wide applications in chemical and biosensing fields owing to their high sensitivity, ruggedness, miniaturized design and integration ability with on-field electronic systems. One of the potential advantages of using these devices are their label-free detection mechanism since mass is the fundamental property of any target analyte which is monitored by these devices. Herein, we provide a concise overview of high frequency acoustic transducers such as quartz crystal microbalance (QCM), surface acoustic wave (SAW) and film bulk acoustic resonators (FBARs) to compare their working principles, resonance frequencies, selection of piezoelectric materials for their fabrication, temperature-frequency dependency and operation in the liquid phase. The selected sensor applications of these high frequency acoustic transducers are discussed primarily focusing on the two main sensing domains, i.e., biosensing for working in liquids and gas/vapor phase sensing. Furthermore, the sensor performance of high frequency acoustic transducers in selected cases is compared with well-established analytical tools such as liquid chromatography mass spectrometry (LC-MS), gas chromatographic (GC) analysis and enzyme-linked immunosorbent assay (ELISA) methods. Finally, a general comparison of these acoustic devices is conducted to discuss their strengths, limitations, and commercial adaptability thus, to select the most suitable transducer for a particular chemical/biochemical sensing domain. Full article

When the quartz crystal microbalance (QCM) is used in liquid for adsorption or desorption monitoring based bio- or chemical sensing applications, the frequency shift is not only determined by the surface mass change, but also by the change of liquid characteristics, such as density and viscosity, which are greatly affected by the liquid environmental temperature. A monolithic dual-channel QCM is designed and fabricated by arranging two QCM resonators on one single chip for cancelling the fluctuation induced by environmental factors. In actual applications, one QCM works as a specific sensor by modifying with functional membranes and the other acts as a reference, only measuring the liquid property. The dual-channel QCM is designed with an inverted-mesa structure, aiming to realize a high frequency miniaturized chip and suppress the frequency interference between the neighbored QCM resonators. The key problem of dual-channel QCMs is the interference between two channels, which is influenced by the distance of adjacent resonators. The diameter of the reference electrode has been designed into several values in order to find the optimal parameter. Experimental results demonstrated that the two QCMs could vibrate individually and the output frequency stability and drift can be greatly improved with the aid of the reference QCM. Full article

We developed a highly sensitive humidity sensor based on the combination of ultrahigh-frequency film bulk acoustic resonator (FBAR) and nano-assembled polyelectrolyte (PET) thin films. The water molecule absorption efficiency was optimized by forming loosely-packed PET nanostructures. Then, the humidity sensing characteristics were analyzed in terms of sensitivity, linearity, reversibility, stability and detection limit. As a result, PET-coated FBAR exhibits excellent humidity sensitivity of 2202.20 Hz/ppm, which is five orders of magnitude higher than quartz crystal microbalance (QCM). Additionally, temperature dependence was investigated with the result that PET-coated FBAR possessed a higher sensitivity at low temperature. Furthermore, we realized the selective detection of water vapor from volatile organic compounds (VOCs) with respect to the polarity property. Owing to the high sensitivity, miniaturized size and ultrahigh operating frequency, PET-coated FBAR is uniquely favorable as a wireless humidity sensor node to integrate into wireless sensor networks (WSNs). Full article

Viruses are pathogenic microorganisms that can inhabit and replicate in human bodies causing a number of widespread infectious diseases such as influenza, gastroenteritis, hepatitis, meningitis, pneumonia, acquired immune deficiency syndrome (AIDS) etc. A majority of these viral diseases are contagious and can spread from infected to healthy human beings. The most important step in the treatment of these contagious diseases and to prevent their unwanted spread is to timely detect the disease-causing viruses. Gravimetric viral diagnostics based on quartz crystal microbalance (QCM) transducers and natural or synthetic receptors are miniaturized sensing platforms that can selectively recognize and quantify harmful virus species. Herein, a review of the label-free QCM virus sensors for clinical diagnostics and point of care (POC) applications is presented with major emphasis on the nature and performance of different receptors ranging from the natural or synthetic antibodies to selective macromolecular materials such as DNA and aptamers. A performance comparison of different receptors is provided and their limitations are discussed. Full article

A miniature quartz crystal microbalance (mQCM) was integrated with a polydimethylsiloxane (PDMS) microfluidic device for on-chip determination of amyloid polypeptide–Aβ₄₂. The integration techniques included photolithography and plasma coupling. Aβ₄₂ antibody was immobilized on the mQCM surface using a cross-linker method, and the resonance frequency of mQCM shifted negatively due to antibody-antigen binding. A linear range from 0.1 µM to 3.2 µM was achieved. By using matrix elimination buffer, i.e., matrix phosphate buffer containing 500 µg/mL dextran and 0.5% Tween 20, Aβ₄₂ could be successfully detected in the presence of 75% human serum. Additionally, high temperature treatments at 150 °C provided a valid method to recover mQCM, and PDMS-mQCM microfluidic device could be reused to some extent. Since the detectable Aβ₄₂ concentration could be as low as 0.1 µM, which is close to cut-off value for Alzheimer patients, the PDMS-mQCM device could be applied in early Alzheimer’s disease diagnosis. Full article

In this study, a miniaturized high fundamental frequency quartz crystal microbalance (QCM) is fabricated for sensor applications using a wet etching technique. The vibration area is reduced in the fabrication of the high frequency QCM with an inverted mesa structure. To reduce the complexity of the side wall profile that results from anisotropic quartz etching, a rectangular vibration area is used instead of the conventional circular structure. QCMs with high Q values exceeding 25,000 at 47 MHz, 27,000 at 60 MHz, 24,000 at 73 MHz and 25,000 at 84 MHz are fabricated on 4 × 4 mm² chips with small vibration areas of 1.2 × 1.4 mm². A PMMA-based flow cell is designed and manufactured to characterize the behavior of the fabricated QCM chip in a liquid. Q values as high as 1,006 at 47 MHz, 904 at 62 MHz, 867 at 71 MHz and 747 at 84 MHz are obtained when one side of the chip is exposed to pure water. These results show that fabricated QCM chips can be used for bio- and chemical sensor applications in liquids. Full article