A Simple Graphene NH₃ Gas Sensor via Laser Direct Writing.

Ammonia gas sensors are very essential in many industries and everyday life. However, their complicated fabrication process, severe environmental fabrication requirements and desorption of residual ammonia molecules result in high cost and hinder their market acceptance. Here, laser direct writing is used to fabricate three parallel porous 3D graphene lines on a polyimide (PI) tape to simply construct an ammonia gas sensor. The middle one works as an ammonia sensing element and the other two on both sides work as heaters to improve the desorption performance of the sensing element to ammonia gas molecules. The graphene lines were characterized by scanning electron microscopy and Raman spectroscopy. The response and recovery time of the sensor without heating are 214 s and 222 s with a sensitivity of 0.087% ppm-1 for sensing 75 ppm ammonia gas, respectively. The experimental results prove that under the optimized heating temperature of about 70 °C the heaters successfully help implement complete desorption of residual NH₃ showing a good sensitivity and cyclic stability

Review—Non-Invasive Monitoring of Human Health by Exhaled Breath Analysis: A Comprehensive Review

Exhaled human breath analysis is a very promisingfield of research work having great potential for diagnosis of diseases in non-invasive way. Breath analysis has attracted huge attention in thefield of medical diagnosis and disease monitoring in the last twodecades. VOCs/gases (Volatile Organic Compounds) in exhaled breath bear thefinger-prints of metabolic and biophysicalprocesses going on in human body. It’s a non-invasive, fast, non-hazardous, cost effective, and point of care process for diseasestate monitoring and environmental exposure assessment in human beings. Some VOCs/gases in exhaled breath are bio-markers ofdifferent diseases and their presence in excess amount is indicative of un-healthiness. Breath analysis has the potential for earlydetection of diseases. However, it is still underused and commercial device is yet not available owing to multiferrious challenges.This review is intended to provide an overview of major biomarkers (VOCs/gases) present in exhaled breath, importance of theiranalysis towards disease monitoring, analytical techniques involved, promising materials for breath analysis etc. Finally, relatedchallenges and limitations along with future scope will be touched upon.will be touched upon

Micro-/Nano-Fiber Sensors and Optical Integration Devices

The development of micro/nanofiber sensors and associated integrated systems is a major project spanning photonics, engineering, and materials science, and has become a key academic research trend. During the development of miniature optical sensors, different materials and micro/nanostructures have been reasonably designed and functionalized on the ordinary single-mode optical fibers. The combination of various special optical fibers and new micro/nanomaterials has greatly improved the performance of the sensors. In terms of optical integration, micro/nanofibers play roles in independent and movable optical waveguide devices, and can be conveniently integrated into two-dimensional chips to realize the efficient transmission and information exchange of optical signals based on optical evanescent field coupling technology. In terms of systematic integration, the unique optical transmission mode of optical fiber has shown great potential in the array and networking of multiple sensor units.In this book, more than ten research papers were collected and studied, presenting research on optical micro/nanofiber devices and related integrated systems, covering high-performance optical micro/nanofiber sensors, fine characterization technologies for optical micro/nanostructures, weak signal detection technologies in photonic structures, as well as fiber-assisted highly integrated optical detection systems

The 1st International Electronic Conference on Chemical Sensors and Analytical Chemistry

The 1st International Electronic Conference on Chemical Sensors and Analytical Chemistry was held on 1–15 July 2021. The scope of this online conference was to gather experts that are well-known worldwide who are currently working in chemical sensor technologies and to provide an online forum for the presention and discussion of new results. Throughout this event, topics of interest included, but were not limited to, the following: electrochemical devices and sensors; optical chemical sensors; mass-sensitive sensors; materials for chemical sensing; nano- and micro-technologies for sensing; chemical assays and validation; chemical sensor applications; analytical methods; gas sensors and apparatuses; electronic noses; electronic tongues; microfluidic devices; lab-on-a-chip; single-molecule sensing; nanosensors; and medico-diagnostic testing

Polymer Processing and Surfaces

This book focuses on fundamental and applied research on polymer processing and its effect on the final surface as the optimization of polymer surface properties results in the unique applicability of these over other materials. The development and testing of the next generation of polymeric and composite materials is of particular interest. Special attention is given to polymer surface modification, external stimuli-responsive surfaces, coatings, adhesion, polymer and composites fatigue analysis, evaluation of the surface quality and microhardness, processing parameter optimization, characterization techniques, among others

Graphene-Polymer Composites II

Graphene-polymer nanocomposites continue to gain interest in diverse scientific and technological fields. Graphene-based nanomaterials present the advantages of other carbon nanofillers, like electrical and thermal conductivity, while having significantly lower production costs when compared to materials such as carbon nanotubes, for instance. In addition, in the oxidized forms of graphene, the large specific area combined with a large quantity of functionalizable chemical groups available for physical or chemical interaction with polymers, allow for good dispersion and tunable binding with the surrounding matrix. Other features are noteworthy in graphene-based nanomaterials, like their generally good biocompatibility and the ability to absorb near-infrared radiation, allowing for the use in biomedical applications, such as drug delivery and photothermal therapy.This Special Issue provides an encompassing view on the state of the art of graphene-polymer composites, showing how current research is dealing with new and exciting challenges. The published papers cover topics ranging from novel production methods and insights on mechanisms of mechanical reinforcement of composites, to applications as diverse as automotive and aeronautics, cancer treatment, anticorrosive coatings, thermally conductive fabrics and foams, and oil-adsorbent aerogels

Selection and characterization of DNA aptamers for estradiol and ethynylestradiol for aptasensor development

Small organic contaminants have been widely detected in the surface and ground waters of this nation. A sub-class of these contaminants called endocrine disrupting compounds (EDCs) are known to have adverse effects on aquatic and human health. Among the EDCs, natural hormone 17β-estradiol (E2) and synthetic hormone 17α-ethynylestradiol (EE) possess high estrogenic potency and hence are contaminants of interest. Conventional methods to detect these compounds are expensive, time consuming and need implementation by an expert. By contrast, antibody-based assays are relatively inexpensive and commercially available but suffer from poor selectivity. A promising alternative makes use of DNA aptamers as molecular recognition elements. In order to evaluate the potential of DNA aptamers and aptasensors to detect small organics in natural waters, the following objectives were pursued: (1) critically review DNA aptamers and aptasensors developed for small organic molecules and assess their use for monitoring environmentally relevant organics, (2) select and characterize DNA aptamers that bind to E2 and EE and, (3) study the effect of immobilization on the binding affinity of the selected E2 and EE aptamers. A review of ~80 aptamers and ~200 aptasensors for small organics was conducted to identify factors that affect binding affinity of the aptamer and limits of detection (LODs) of the aptasensor. Based on regression analyses, aptamer binding affinities are found to have a weak relationship with hydrophobicity of the target and length of the aptamer (p-values<0.05). Independent t-tests comparing aptasensor LODs suggest that the electrochemical platform is significantly more sensitive than colorimetric and fluorescence-based platforms. The inherent binding affinity of the aptamer was found to have a significant effect on the LOD of the aptasensor. While some fabricated aptasensors are sufficiently sensitive to detect contaminants at environmentally relevant concentrations, they are often associated with complex fabrication steps, and/or interference from structurally similar analogs. As a result, aptasensor commercialization faces many challenges including reusability, reproducibility and robustness. In vitro selections were conducted with different selection pressures to isolate sensitive and selective DNA aptamers for E2 and EE. An equilibrium-filtration assay was used to determine dissociation constants (Kd) of the aptamer towards its parent target and its analogues. The E2 aptamers, E2Apt1 and E2Apt2 were found to have Kd values of 0.6 µM. They bound to analogue estrone (E1) with a similar affinity but were at least 74-fold more selective over EE. The EE aptamers Kd values are 0.5-1 µM. While one EE aptamer (EEApt1) was 53-fold more selective for EE over E2 and E1, the second EE aptamer (EEApt2) bound to all three EDCs (E1, E2 and EE) with similar affinities. The aptamers maintained their binding affinities in natural waters samples (tap water and lake water). DMS probing of the structure of the DNA aptamer revealed that the binding regions were mostly located in the single-stranded loop regions of the aptamer. Aptasensors typically employ immobilized aptamers though the aptamers are selected and characterized while free or unattached in solution. The Kd values of immobilized selective aptamers were evaluated using magnetic microbeads surface for attachment. E2Apt1 immobilized at either end (5′ or 3′) and E2Apt2 immobilized at the 3′ end retain their binding affinity. The binding affinity is inversely correlated to the average linear distance of the binding pocket from the immobilized end. This result suggests that unwanted interactions between the aptamer and other moieties are more likely when the binding pocket is further away from the surface. Binding curve of E2Apt2 immobilized at the 5′ end indicates potential dimerization at high loadings of aptamer on the beads due to increased proximity between aptamer strands. EEApt1 loses its binding affinity upon immobilization potentially due to disruption in its tertiary structure upon attachment to the surface. Despite no loss in binding affinity upon immobilization, E2Apt1 (5′) shows no significant change in electrochemical current on binding to E2 when incorporated into an electrochemical sensor. This result implies an insufficient conformational change of the aptamer on binding to the target. Overall, this work identifies the first aptamers for EE and selective aptamers for E2, while also highlighting the issues with development of aptamers and their eventual incorporation into aptasensors to detect small organics. Two major concerns are (1) immobilizing aptamers in sensor platforms while selections of aptamers are conducted with free/unattached aptamers, resulting in loss of binding affinity and (2) insufficient conformational change of the aptamer on binding to small molecule targets, resulting in a lack of change in the sensor signal. The findings from this dissertation support additional research directions regarding employing free aptamers in sensors and/or conducting new selections for aptamers using a DNA pool that is attached to a surface

A Dibutyl Phthalate Sensor Based on a Nanofiber Polyaniline Coated Quartz Crystal Monitor

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A Dibutyl Phthalate Sensor Based on a Nanofiber Polyaniline Coated Quartz Crystal Monitor

Dibutyl phthalate (DBP) is a commonly used plasticizer and additive to adhesives, printing inks and nail polishes. Because it has been found to be a powerful reproductive and developmental toxicant, a sensor to monitor DBP in some working spaces and the environment is required. In this work polyaniline nanofibers were deposited on the electrode of a quartz crystal oscillator to form a Quartz Crystal Microbalance gas sensor. The coated quartz crystal and a non-coated quartz crystal were mounted in a sealed chamber, and their frequency difference was monitored. When DBP vapor was injected into the chamber, gas adsorption decreased the frequency of the coated quartz crystal oscillator and thereby caused an increase in the frequency difference between the two crystals. The change of the frequency difference was recorded as the sensor response. The sensor was extremely sensitive to DBP and could be easily recovered by N2 purging. A low measurement limit of 20 ppb was achieved. The morphologies of the polyaniline films prepared by different approaches have been studied by SEM and BET. How the nanofiber-structure can improve the sensitivity and stability is discussed, while its selectivity and long-term stability were investigated