Open AccessReview
The Use of Hoechst Dyes for DNA Staining and Beyond
Chemosensors 2018, 6(2), 18; doi:10.3390/chemosensors6020018 -
Abstract
Hoechst dyes are among the most popular fluorophores used to stain DNA in living and fixed cells. Moreover, their high affinity and specificity towards DNA make Hoechst dyes excellent targeting moieties, which can be conjugated to various other molecules in order to tether
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Hoechst dyes are among the most popular fluorophores used to stain DNA in living and fixed cells. Moreover, their high affinity and specificity towards DNA make Hoechst dyes excellent targeting moieties, which can be conjugated to various other molecules in order to tether them to DNA. The recent developments in the fields of microscopy and flow cytometry have sparked interest in such composite molecules, whose applications range from investigating nucleus microenvironment to drug delivery into tumours. Here we provide an overview of the properties of Hoechst dyes and discuss recent developments in Hoechst-based composite probes. Full article
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Open AccessFeature PaperArticle
A Rationally Designed, Spiropyran-Based Chemosensor for Magnesium
Chemosensors 2018, 6(2), 17; doi:10.3390/chemosensors6020017 -
Abstract
Magnesium ions (Mg2+) play an important role in mammalian cell function; however, relatively little is known about the mechanisms of Mg2+ regulation in disease states. An advance in this field would come from the development of selective, reversible fluorescent chemosensors,
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Magnesium ions (Mg2+) play an important role in mammalian cell function; however, relatively little is known about the mechanisms of Mg2+ regulation in disease states. An advance in this field would come from the development of selective, reversible fluorescent chemosensors, capable of repeated measurements. To this end, the rational design and fluorescence-based photophysical characterisation of two spiropyran-based chemosensors for Mg2+ are presented. The most promising analogue, chemosensor 1, exhibits 2-fold fluorescence enhancement factor and 3-fold higher binding affinity for Mg2+ (Kd 6.0 µM) over Ca2+ (Kd 18.7 µM). Incorporation of spiropyran-based sensors into optical fibre sensing platforms has been shown to yield significant signal-to-background changes with minimal sample volumes, a real advance in biological sensing that enables measurement on subcellular-scale samples. In order to demonstrate chemosensor compatibility within the light intense microenvironment of an optical fibre, photoswitching and photostability of 1 within a suspended core optical fibre (SCF) was subsequently explored, revealing reversible Mg2+ binding with improved photostability compared to the non-photoswitchable Rhodamine B fluorophore. The spiropyran-based chemosensors reported here highlight untapped opportunities for a new class of photoswitchable Mg2+ probe and present a first step in the development of a light-controlled, reversible dip-sensor for Mg2+. Full article
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Open AccessReview
Metal Oxide Nanostructures in Food Applications: Quality Control and Packaging
Chemosensors 2018, 6(2), 16; doi:10.3390/chemosensors6020016 -
Abstract
Metal oxide materials have been applied in different fields due to their excellent functional properties. Metal oxides nanostructuration, preparation with the various morphologies, and their coupling with other structures enhance the unique properties of the materials and open new perspectives for their application
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Metal oxide materials have been applied in different fields due to their excellent functional properties. Metal oxides nanostructuration, preparation with the various morphologies, and their coupling with other structures enhance the unique properties of the materials and open new perspectives for their application in the food industry. Chemical gas sensors that are based on semiconducting metal oxide materials can detect the presence of toxins and volatile organic compounds that are produced in food products due to their spoilage and hazardous processes that may take place during the food aging and transportation. Metal oxide nanomaterials can be used in food processing, packaging, and the preservation industry as well. Moreover, the metal oxide-based nanocomposite structures can provide many advantageous features to the final food packaging material, such as antimicrobial activity, enzyme immobilization, oxygen scavenging, mechanical strength, increasing the stability and the shelf life of food, and securing the food against humidity, temperature, and other physiological factors. In this paper, we review the most recent achievements on the synthesis of metal oxide-based nanostructures and their applications in food quality monitoring and active and intelligent packaging. Full article
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Open AccessFeature PaperArticle
Simultaneous Analysis of Sensor Data for Breath Control in Respiratory Air
Chemosensors 2018, 6(2), 15; doi:10.3390/chemosensors6020015 -
Abstract
There is a broad field of applications of breath monitoring in human health care, medical applications and alcohol control. In this report, an innovative mobile sensor system for breath control in respiratory air called AGaMon will be introduced. The sensor system is able
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There is a broad field of applications of breath monitoring in human health care, medical applications and alcohol control. In this report, an innovative mobile sensor system for breath control in respiratory air called AGaMon will be introduced. The sensor system is able to recognize a multitude of different gases like ethanol (which is the leading component of alcoholic drinks), H2S (which is the leading component for halitosis), H2 (which is the leading component for dyspepsia and food intolerance), NO (which is the leading component for asthma) or acetone (which is the leading component for diabetes), thus ,covering almost all significant aspects. An innovative calibration and evaluation procedure called SimPlus was developed which is able to evaluate the sensor data simultaneously. That means, SimPlus is able to identify the samples simultaneously; for example, whether the measured sample is ethanol or another substance under consideration. Furthermore, SimPlus is able to determine the concentration of the identified sample. This will be demonstrated in this report for the application of ethanol, H2, acetone and the binary mixture ethanol-H2. It has been shown that SimPlus could identify the investigated gases and volatile organic compounds (VOCs) very well and that the relative analysis errors were smaller than 10% in all considered applications. Full article
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Open AccessFeature PaperReview
Colorimetric Materials for Fire Gas Detection—A Review
Chemosensors 2018, 6(2), 14; doi:10.3390/chemosensors6020014 -
Abstract
The damage caused by outbreaks of fire continues to be enormous despite ongoing improvements in fire detection and fighting. Therefore, the detection of fires at the earliest possible stage is essential. The latest developments in fire detection devices include the addition of carbon
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The damage caused by outbreaks of fire continues to be enormous despite ongoing improvements in fire detection and fighting. Therefore, the detection of fires at the earliest possible stage is essential. The latest developments in fire detection devices include the addition of carbon monoxide (CO) or temperature sensors into the widespread smoke detectors, but also alternative solutions are searched for. Advantageous is the direct detection of the most relevant fire gases CO and nitrogen dioxide (NO2), because they are produced very early in a developing fire. A sensitive, selective, and low-cost method to detect these gases is the use of colorimetric materials combined with a compact optical readout. In this review, we take account of recent developments in this research field and provide a comprehensive overview on suitable materials for CO and NO2 detection in fire gas sensing and first steps towards novel fire gas detectors. Full article
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Open AccessFeature PaperReview
Detection and Digital Resolution Counting of Nanoparticles with Optical Resonators and Applications in Biosensing
Chemosensors 2018, 6(2), 13; doi:10.3390/chemosensors6020013 -
Abstract
The interaction between nanoparticles and the electromagnetic fields associated with optical nanostructures enables sensing with single-nanoparticle limits of detection and digital resolution counting of captured nanoparticles through their intrinsic dielectric permittivity, absorption, and scattering. This paper will review the fundamental sensing methods, device
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The interaction between nanoparticles and the electromagnetic fields associated with optical nanostructures enables sensing with single-nanoparticle limits of detection and digital resolution counting of captured nanoparticles through their intrinsic dielectric permittivity, absorption, and scattering. This paper will review the fundamental sensing methods, device structures, and detection instruments that have demonstrated the capability to observe the binding and interaction of nanoparticles at the single-unit level, where the nanoparticles are comprised of biomaterial (in the case of a virus or liposome), metal (plasmonic and magnetic nanomaterials), or inorganic dielectric material (such as TiO2 or SiN). We classify sensing approaches based upon their ability to observe single-nanoparticle attachment/detachment events that occur in a specific location, versus approaches that are capable of generating images of nanoparticle attachment on a nanostructured surface. We describe applications that include study of biomolecular interactions, viral load monitoring, and enzyme-free detection of biomolecules in a test sample in the context of in vitro diagnostics. Full article
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Open AccessReview
Smart Polymers in Micro and Nano Sensory Devices
Chemosensors 2018, 6(2), 12; doi:10.3390/chemosensors6020012 -
Abstract
The present review presents the most recent developments concerning the application of sensory polymers in the detection and quantification of different target species. We will firstly describe the main polymers that are being employed as sensory polymers, including, for example, conducting or acrylate-based
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The present review presents the most recent developments concerning the application of sensory polymers in the detection and quantification of different target species. We will firstly describe the main polymers that are being employed as sensory polymers, including, for example, conducting or acrylate-based polymers. In the second part of the review, we will briefly describe the different mechanisms of detection and the target species, such as metal cations and anions, explosives, and biological and biomedical substances. To conclude, we will describe the advancements in recent years concerning the fabrication of micro and nano sensory devices based on smart polymers, with a bibliographic revision of the research work published between 2005 and today, with special emphasis on research work presented since 2010. A final section exposing the perspectives and challenges of this interesting research line will end the present review article. Full article
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Open AccessFeature PaperReview
Spectroscopic Chemical Sensing and Imaging: From Plants to Animals and Humans
Chemosensors 2018, 6(1), 11; doi:10.3390/chemosensors6010011 -
Abstract
Chemical sensing and imaging technologies are of great importance in medical diagnostics and environmental sensing due to their ability to detect and localize chemical targets and provide valuable information in real-time. Biophotonic techniques are the most promising for in vivo applications due to
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Chemical sensing and imaging technologies are of great importance in medical diagnostics and environmental sensing due to their ability to detect and localize chemical targets and provide valuable information in real-time. Biophotonic techniques are the most promising for in vivo applications due to their minimal invasivity. Our laboratory has introduced various biophotonics-based technologies for chemical sensing and imaging for biochemical sensing, medical diagnostics, and fundamental research. Over the years, we have developed a wide variety of fluorescence and surface-enhanced Raman scattering (SERS)-based technologies for the detection of biomarkers for cancer and other diseases. This paper provides an overview of the research on chemical and biological sensors developed in our laboratory, highlighting our work on in vivo imaging and sensing, including minimally invasive detection of endogenous fluorophores associated with malignant tissue, SERS-tag localization of cancer cells and tissues, and SERS-based detection of nucleic acid biotargets and its feasibility for in vivo applications. This manuscript also presents new development on the use of Raman imaging of SERS-labeled nanoprobes incubated in leaves for use in biofuel research, laying the foundation for studies on functional imaging of nucleic acid biomarkers in plants. Full article
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Open AccessFeature PaperArticle
Synthesis, Curing Behavior and Swell Tests of pH-Responsive Coatings from Acryl-Terminated Oligo(β-Amino Esters)
Chemosensors 2018, 6(1), 10; doi:10.3390/chemosensors6010010 -
Abstract
The ability of acryl-terminated oligo(β-amino esters) (AOBAE) to be coated on fibers and printed electronics without solvents and to be cross-linked to a pH-responsive coatings, makes AOBAE-based coatings a potential type of pH-sensor coating. However, there are currently no reports of
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The ability of acryl-terminated oligo(β-amino esters) (AOBAE) to be coated on fibers and printed electronics without solvents and to be cross-linked to a pH-responsive coatings, makes AOBAE-based coatings a potential type of pH-sensor coating. However, there are currently no reports of AOBAEs used as a pH-responsive coating material in sensor applications. Here we present an investigation of the synthesis, curing behavior and swell tests of AOBAEs. AOBAEs were synthesized from reacting an excess of asymmetric diacrylates with piperazine without the use of any solvents. They were then cross-linked to an insoluble network by UV-curing. Nuclear magnetic resonance (NMR) and Fourier transform infrared (FTIR) spectroscopy were used to characterize the AOBAEs. NMR was used to clarify the irregular structure of the AOBAE. FTIR was used to monitor the effects of UV-curing dose and air exposure on monomer conversion during curing. An interferometric technique was used to monitor the swelling behavior of the coating in response to pH variations. Swell experiments showed that the AOBAE also responded to pH variations after polymerization. Therefore, AOBAE is an interesting class of material with potential use as a pH responsive coating in optical-and printed electronics pH-sensors applications. Full article
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Open AccessFeature PaperReview
Exploring the Emotion of Disgust: Differences in Smelling and Feeling
Chemosensors 2018, 6(1), 9; doi:10.3390/chemosensors6010009 -
Abstract
Disgust evolved to motivate humans away from disease cues and may heighten discernment of these cues. Disease cues are often best perceived through our sense of smell, however very few studies have examined how eliciting disgust influences smell intensity or valence. In two
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Disgust evolved to motivate humans away from disease cues and may heighten discernment of these cues. Disease cues are often best perceived through our sense of smell, however very few studies have examined how eliciting disgust influences smell intensity or valence. In two novel experiments we investigated how domains of disgust induction influence odor perception. In experiment 1 participants (n = 90) were randomly allocated to one of two kinds of Disgust Induction (DI): Pathogen (DI-P), Moral (DI-M) or a Control (DI-C), followed by an evaluation of three affectively distinct odors (disgust-related, neutral, liked). Using a modified procedure in experiment 2, participants (n = 70) were again randomly assigned to one of the three disgust induction conditions, but here they evaluated one (disgust-related) odor during disgust induction. In experiment 2 we also measured feelings of disgust and anger. In experiment 1, surprisingly, we found overall ratings of odor disgust were lower in the DI-P compared to other groups, whereas in experiment 2, odor disgust was higher in the DI-P versus the DI-M/DI-C conditions, which also differed from each other. We also found that whereas feelings of disgust were higher in DI-P, in contrast, anger was higher for those individuals in the DI-M condition. These findings suggest that compared to a Control condition, inducing state Pathogen and Moral disgust lead to higher perceived odor disgust, whereas feelings of disgust/anger yield divergent effects. The work here also demonstrates that methodologies utilizing odor perception (disgust) can be a useful addition to measuring changes in state disgust. Full article
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Open AccessFeature PaperReview
Nitric Oxide Sensors for Biological Applications
Chemosensors 2018, 6(1), 8; doi:10.3390/chemosensors6010008 -
Abstract
Nitric oxide (NO) is an essential signaling molecule within biological systems and is believed to be involved in numerous diseases. As a result of NO’s high reaction rate, the detection of the concentration of NO, let alone the presence or absence of the
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Nitric oxide (NO) is an essential signaling molecule within biological systems and is believed to be involved in numerous diseases. As a result of NO’s high reaction rate, the detection of the concentration of NO, let alone the presence or absence of the molecule, is extremely difficult. Researchers have developed multiple assays and probes in an attempt to quantify NO within biological solutions, each of which has advantages and disadvantages. This review highlights many of the current NO sensors, from those that are commercially available to the newest sensors being optimized in research labs, to assist in the understanding and utilization of NO sensors in biological fields. Full article
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Open AccessFeature PaperArticle
CO-Sensing Properties of Diode-Type Gas Sensors Employing Anodized Titania and Noble-Metal Electrodes under Hydrogen Atmosphere
Chemosensors 2018, 6(1), 7; doi:10.3390/chemosensors6010007 -
Abstract
CO-sensing properties of diode-type sensors employing an anodized TiO2 film and noble-metal (M) electrodes (M/TiO2 sensor, M: Pd, Pt, and Pd-nPt, n: the amount of Pt (wt %) in the Pd-nPt electrode) were investigated at 50–250
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CO-sensing properties of diode-type sensors employing an anodized TiO2 film and noble-metal (M) electrodes (M/TiO2 sensor, M: Pd, Pt, and Pd-nPt, n: the amount of Pt (wt %) in the Pd-nPt electrode) were investigated at 50–250 °C in dry or wet H2. All the M/TiO2 sensors showed nonlinear IV characteristics as a diode device in air and N2, but the IV characteristics of the sensors were actually linear in H2 because of the negligible small height of Schottky barrier at their M/TiO2 interface. The Pd/TiO2 sensor showed no CO response in H2, but the Pt/TiO2 and Pd-nPt/TiO2 sensors responded to CO in H2. Among them, the Pd-64Pt/TiO2 sensor showed the largest CO response at 100 °C in H2. The reason why the mixing of Pd with Pt was effective in improving the CO response is probably because of a decrease in the amount of dissolved hydrogen species, an increase in the amount of dissociatively adsorbed hydrogen species, and an increase in the amount of adsorbed CO species in CO balanced with H2 by the mixing of Pt into Pd. The interference from moisture in the target gas on the CO response should be largely improved from a practical application perspective. Full article
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Open AccessArticle
Stand-Off Chemical Detection Using Photoacoustic Sensing Techniques—From Single Element to Phase Array
Chemosensors 2018, 6(1), 6; doi:10.3390/chemosensors6010006 -
Abstract
Technologies that can detect harmful chemicals, such as explosive devices, harmful gas leaks, airborne chemicals or/and biological agents, are heavily invested in by the government to prevent any possible catastrophic consequences. Some key features of such technology are, but not limited to, effective
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Technologies that can detect harmful chemicals, such as explosive devices, harmful gas leaks, airborne chemicals or/and biological agents, are heavily invested in by the government to prevent any possible catastrophic consequences. Some key features of such technology are, but not limited to, effective signal-to-noise ratio (SNR) of the detected signal and extended distance between the detector and target. In this work, we describe the development of photoacoustic sensing techniques from simple to more complex systems. These techniques include passive and active noise filters, parabolic sound reflectors, a lock-in amplifier, and beam-forming with an array of microphones; using these techniques, we increased detection distance from a few cm in an indoor setting to over 41 feet in an outdoor setting. We also establish a theoretical mathematical model that explains the underlying principle of how SNR can be improved with an increasing number of microphone elements in the phase array. We validate this model with computational simulations as well as experimental results. Full article
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Open AccessReview
Raman and Surface-Enhanced Raman Scattering for Biofilm Characterization
Chemosensors 2018, 6(1), 5; doi:10.3390/chemosensors6010005 -
Abstract
Biofilms are a communal way of living for microorganisms in which microorganism cells are surrounded by extracellular polymeric substances (EPS). Most microorganisms can live in biofilm form. Since microorganisms are everywhere, understanding biofilm structure and composition is crucial for making the world a
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Biofilms are a communal way of living for microorganisms in which microorganism cells are surrounded by extracellular polymeric substances (EPS). Most microorganisms can live in biofilm form. Since microorganisms are everywhere, understanding biofilm structure and composition is crucial for making the world a better place to live, not only for humans but also for other living creatures. Raman spectroscopy is a nondestructive technique and provides fingerprint information about an analyte of interest. Surface-enhanced Raman spectroscopy is a form of this technique and provides enhanced scattering of the analyte that is in close vicinity of a nanostructured noble metal surface such as silver or gold. In this review, the applications of both techniques and their combination with other biofilm analysis techniques for characterization of composition and structure of biofilms are discussed. Full article
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Open AccessFeature PaperReview
Infra-Red Plasmonic Sensors
Chemosensors 2018, 6(1), 4; doi:10.3390/chemosensors6010004 -
Abstract
Plasmonic sensors exploiting the localized surface plasmon resonance (LSPR) of noble metal nanoparticles are common in the visual spectrum. However, bio-sensors near the infra-red (NIR) windows (600–900 nm and 1000–1400 nm) are of interest, as in these regions the absorption coefficients of water,
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Plasmonic sensors exploiting the localized surface plasmon resonance (LSPR) of noble metal nanoparticles are common in the visual spectrum. However, bio-sensors near the infra-red (NIR) windows (600–900 nm and 1000–1400 nm) are of interest, as in these regions the absorption coefficients of water, melanin deoxyglobin, and hemoglobin are all low. The first part of this paper reviews the work that has been undertaken using gold (Au) and silver (Ag) particles in metal enhanced fluorescence (MEF) in the NIR. Despite this success, there are limitations, as there is only a narrow band in the visual and NIR where losses are low for traditional plasmonic materials. Further, noble metals are not compatible with standard silicon manufacturing processes, making it challenging to produce on-chip integrated plasmonic sensors with Au or Ag. Therefore, it is desirable to use different materials for plasmonic chemical and biological sensing, that are foundry-compatible with silicon (Si) and germanium (Ge). One material that has received significant attention is highly-doped Ge, which starts to exhibit metallic properties at a wavelength as short as 6 μm. This is discussed in the second part of the paper and the results of recent analysis are included. Full article
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Open AccessArticle
Effect of Dangling Bonds on De-Poling Time for Polymeric Electric Field Optical Sensors
Chemosensors 2018, 6(1), 3; doi:10.3390/chemosensors6010003 -
Abstract
This paper investigates the possible chemical changes in polydimethylsiloxane (PDMS) caused by two different techniques of fabrication for ultra-sensitive electric field optical sensors. The sensing element is a micro-sphere made from 60:1 PDMS (60 parts base silicon elastomer to one part polymer curing
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This paper investigates the possible chemical changes in polydimethylsiloxane (PDMS) caused by two different techniques of fabrication for ultra-sensitive electric field optical sensors. The sensing element is a micro-sphere made from 60:1 PDMS (60 parts base silicon elastomer to one part polymer curing agent by volume). The measurement principle is based on the morphology dependent resonances (MDR) shifts of the micro-sphere. We present the effects of curing and poling of polymer micro-spheres used as optical sensors. The degree of curing leads to changes in the de-poling time which results from dangling bonds in the polymeric chains. Consequently, the longevity of the sensitivity of the sensor can extended by two orders of magnitude. An analysis is carried out along with preliminary experiments to investigate that behavior. Full article
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Open AccessEditorial
Acknowledgement to Reviewers of Chemosensors in 2017
Chemosensors 2018, 6(1), 2; doi:10.3390/chemosensors6010002 -
Abstract
Peer review is an essential part in the publication process, ensuring that Chemosensors maintains high quality standards for its published papers. In 2017, a total of 32 papers were published in the journal.[...] Full article
Open AccessFeature PaperReview
Recent Advances in the Detection of Neurotransmitters
Chemosensors 2018, 6(1), 1; doi:10.3390/chemosensors6010001 -
Abstract
Neurotransmitters are chemicals that act as messengers in the synaptic transmission process. They are essential for human health and any imbalance in their activities can cause serious mental disorders such as Parkinson’s disease, schizophrenia, and Alzheimer’s disease. Hence, monitoring the concentrations of various
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Neurotransmitters are chemicals that act as messengers in the synaptic transmission process. They are essential for human health and any imbalance in their activities can cause serious mental disorders such as Parkinson’s disease, schizophrenia, and Alzheimer’s disease. Hence, monitoring the concentrations of various neurotransmitters is of great importance in studying and diagnosing such mental illnesses. Recently, many researchers have explored the use of unique materials for developing biosensors for both in vivo and ex vivo neurotransmitter detection. A combination of nanomaterials, polymers, and biomolecules were incorporated to implement such sensor devices. For in vivo detection, electrochemical sensing has been commonly applied, with fast-scan cyclic voltammetry being the most promising technique to date, due to the advantages such as easy miniaturization, simple device architecture, and high sensitivity. However, the main challenges for in vivo electrochemical neurotransmitter sensors are limited target selectivity, large background signal and noise, and device fouling and degradation over time. Therefore, achieving simultaneous detection of multiple neurotransmitters in real time with long-term stability remains the focus of research. The purpose of this review paper is to summarize the recently developed sensing techniques with the focus on neurotransmitters as the target analyte, and to discuss the outlook of simultaneous detection of multiple neurotransmitter species. This paper is organized as follows: firstly, the common materials used for developing neurotransmitter sensors are discussed. Secondly, several sensor surface modification approaches to enhance sensing performance are reviewed. Finally, we discuss recent developments in the simultaneous detection capability of multiple neurotransmitters. Full article
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Open AccessFeature PaperReview
Luminescent Metal Nanoclusters for Potential Chemosensor Applications
Chemosensors 2017, 5(4), 36; doi:10.3390/chemosensors5040036 -
Abstract
Studies of metal nanocluster (M-NCs)-based sensors for specific analyte detection have achieved significant progress in recent decades. Ultra-small-size (<2 nm) M-NCs consist of several to a few hundred metal atoms and exhibit extraordinary physical and chemical properties. Similar to organic molecules, M-NCs display
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Studies of metal nanocluster (M-NCs)-based sensors for specific analyte detection have achieved significant progress in recent decades. Ultra-small-size (<2 nm) M-NCs consist of several to a few hundred metal atoms and exhibit extraordinary physical and chemical properties. Similar to organic molecules, M-NCs display absorption and emission properties via electronic transitions between energy levels upon interaction with light. As such, researchers tend to apply M-NCs in diverse fields, such as in chemosensors, biological imaging, catalysis, and environmental and electronic devices. Chemo- and bio-sensory uses have been extensively explored with luminescent NCs of Au, Ag, Cu, and Pt as potential sensory materials. Luminescent bi-metallic NCs, such as Au-Ag, Au-Cu, Au-Pd, and Au-Pt have also been used as probes in chemosensory investigations. Both metallic and bi-metallic NCs have been utilized to detect various analytes, such as metal ions, anions, biomolecules, proteins, acidity or alkalinity of a solution (pH), and nucleic acids, at diverse detection ranges and limits. In this review, we have summarized the chemosensory applications of luminescent M-NCs and bi-metallic NCs. Full article
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Open AccessFeature PaperArticle
Biochars as Innovative Humidity Sensing Materials
Chemosensors 2017, 5(4), 35; doi:10.3390/chemosensors5040035 -
Abstract
In this work, biochar-based humidity sensors were prepared by drop-coating technique. Polyvinylpyrrolidone (PVP) was added as an organic binder to improve the adhesion of the sensing material onto ceramic substrates having platinum electrodes. Two biochars obtained from different precursors were used. The sensors
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In this work, biochar-based humidity sensors were prepared by drop-coating technique. Polyvinylpyrrolidone (PVP) was added as an organic binder to improve the adhesion of the sensing material onto ceramic substrates having platinum electrodes. Two biochars obtained from different precursors were used. The sensors were tested toward relative humidity (RH) at room temperature and showed a response starting around 5 RH%, varying the impedance of 2 orders of magnitude after exposure to almost 100% relative humidity. In both cases, biochar materials are behaving as p-type semiconductors under low amounts of humidity. On the contrary, for higher RH values, the impedance decreased due to water molecules adsorption. When PVP is added to SWP700 biochar, n-p heterojunctions are formed between the two semiconductors, leading to a higher sensitivity at low RH values for the sensors SWP700-10% PVP and SWP700-20% PVP with respect to pure SWP700 sensor. Finally, response and recovery times were both reasonably fast (in the order of 1 min). Full article
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