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Chemosensors, Volume 6, Issue 2 (June 2018)

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Open AccessReview Advances and Perspectives in Chemical Imaging in Cellular Environments Using Electrochemical Methods
Chemosensors 2018, 6(2), 24; https://doi.org/10.3390/chemosensors6020024
Received: 23 April 2018 / Revised: 22 May 2018 / Accepted: 23 May 2018 / Published: 29 May 2018
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Abstract
This review discusses a broad range of recent advances (2013–2017) in chemical imaging using electrochemical methods, with a particular focus on techniques that have been applied to study cellular processes, or techniques that show promise for use in this field in the future.
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This review discusses a broad range of recent advances (2013–2017) in chemical imaging using electrochemical methods, with a particular focus on techniques that have been applied to study cellular processes, or techniques that show promise for use in this field in the future. Non-scanning techniques such as microelectrode arrays (MEAs) offer high time-resolution (<10 ms) imaging; however, at reduced spatial resolution. In contrast, scanning electrochemical probe microscopies (SEPMs) offer higher spatial resolution (as low as a few nm per pixel) imaging, with images collected typically over many minutes. Recent significant research efforts to improve the spatial resolution of SEPMs using nanoscale probes and to improve the temporal resolution using fast scanning have resulted in movie (multiple frame) imaging with frame rates as low as a few seconds per image. Many SEPM techniques lack chemical specificity or have poor selectivity (defined by the choice of applied potential for redox-active species). This can be improved using multifunctional probes, ion-selective electrodes and tip-integrated biosensors, although additional effort may be required to preserve sensor performance after miniaturization of these probes. We discuss advances to the field of electrochemical imaging, and technological developments which are anticipated to extend the range of processes that can be studied. This includes imaging cellular processes with increased sensor selectivity and at much improved spatiotemporal resolution than has been previously customary. Full article
(This article belongs to the Special Issue Advances in Chemical Imaging and its Applications)
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Open AccessFeature PaperReview Label-Free Sensing in Microdroplet-Based Microfluidic Systems
Chemosensors 2018, 6(2), 23; https://doi.org/10.3390/chemosensors6020023
Received: 31 March 2018 / Revised: 14 May 2018 / Accepted: 17 May 2018 / Published: 24 May 2018
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Abstract
Droplet microfluidic systems have evolved as fluidic platforms that use much less sample volume and provide high throughput for biochemical analysis compared to conventional microfluidic devices. The variety of droplet fluidic applications triggered several detection techniques to be applied for analysis of droplets.
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Droplet microfluidic systems have evolved as fluidic platforms that use much less sample volume and provide high throughput for biochemical analysis compared to conventional microfluidic devices. The variety of droplet fluidic applications triggered several detection techniques to be applied for analysis of droplets. In this review, we focus on label-free droplet detection techniques that were adapted to various droplet microfluidic platforms. We provide a classification of most commonly used droplet platform technologies. Then we discuss the examples of various label-free droplet detection schemes implemented for these platforms. While providing the research landscape for label-free droplet detection methods, we aim to highlight the strengths and shortcomings of each droplet platform so that a more targeted approach can be taken by researchers when selecting a droplet platform and a detection scheme for any given application. Full article
(This article belongs to the Special Issue Label-Free Biosensors and Chemical Sensors)
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Open AccessFeature PaperArticle Miniaturized Single Chip Arrangement of a Wheatstone Bridge Based Calorimetric Gas Sensor
Chemosensors 2018, 6(2), 22; https://doi.org/10.3390/chemosensors6020022
Received: 2 April 2018 / Revised: 14 May 2018 / Accepted: 16 May 2018 / Published: 19 May 2018
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Abstract
The design and fabrication of a miniaturized calorimetric-type gas sensor in a single chip arrangement is presented. Active and passive thin-film Pt meanders are integrated in a single platform (7 × 7 mm2) together with a temperature sensor and a thin-film
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The design and fabrication of a miniaturized calorimetric-type gas sensor in a single chip arrangement is presented. Active and passive thin-film Pt meanders are integrated in a single platform (7 × 7 mm2) together with a temperature sensor and a thin-film microheater at the reverse side. Active meanders are covered by a porous Al2O3/2 wt % Pt thick-film layer. The selection of substrate, position of meanders, and active catalysts (especially their concentration) play a crucial role in directing sensor performance. The presented results show that the sensor signal (Wheatstone bridge voltage) is generated by diffusion-limited exothermic reactions which point towards catalytically enhanced combustion reactions mainly inside the active porous layer. By extrapolation of the linear sensitivity curves, the sensitivity limit was estimated to be 4 ppm for propene and to be 18 ppm for CO. In general, the one-chip-sensing concept has high potential to be used as a gas sensor for analysis of combustible gases; however, further optimization of the meander design and the catalyst material as well as investigations of the sensing behavior under varying ambient temperatures are necessary before such applications shall be considered. Full article
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Open AccessFeature PaperArticle Using Fluorescence Intensity of Enhanced Green Fluorescent Protein to Quantify Pseudomonas aeruginosa
Chemosensors 2018, 6(2), 21; https://doi.org/10.3390/chemosensors6020021
Received: 30 March 2018 / Revised: 25 April 2018 / Accepted: 27 April 2018 / Published: 3 May 2018
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Abstract
A variety of direct and indirect methods have been used to quantify planktonic and biofilm bacterial cells. Direct counting methods to determine the total number of cells include plate counts, microscopic cell counts, Coulter cell counting, flow cytometry, and fluorescence microscopy. However, indirect
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A variety of direct and indirect methods have been used to quantify planktonic and biofilm bacterial cells. Direct counting methods to determine the total number of cells include plate counts, microscopic cell counts, Coulter cell counting, flow cytometry, and fluorescence microscopy. However, indirect methods are often used to supplement direct cell counting, as they are often more convenient, less time-consuming, and require less material, while providing a number that can be related to the direct cell count. Herein, an indirect method is presented that uses fluorescence emission intensity as a proxy marker for studying bacterial accumulation. A clinical strain of Pseudomonas aeruginosa was genetically modified to express a green fluorescent protein (PA14/EGFP). The fluorescence intensity of EGFP in live cells was used as an indirect measure of live cell density, and was compared with the traditional cell counting methods of optical density (OD600) and plate counting (colony-forming units (CFUs)). While both OD600 and CFUs are well-established methods, the use of fluorescence spectroscopy to quantify bacteria is less common. This study demonstrates that EGFP intensity is a convenient reporter for bacterial quantification. In addition, we demonstrate the potential for fluorescence spectroscopy to be used to measure the quantity of PA14/EGFP biofilms, which have important human health implications due to their antimicrobial resistance. Therefore, fluorescence spectroscopy could serve as an alternative or complementary quick assay to quantify bacteria in planktonic cultures and biofilms. Full article
(This article belongs to the Special Issue Fluorescent Probes for Live Cell Imaging)
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Open AccessFeature PaperReview Modelling and Development of Electrical Aptasensors: A Short Review
Chemosensors 2018, 6(2), 20; https://doi.org/10.3390/chemosensors6020020
Received: 14 March 2018 / Revised: 14 April 2018 / Accepted: 25 April 2018 / Published: 27 April 2018
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Abstract
Aptamers are strands of DNA or RNA molecules, chemically synthetized and able to bind a wide range of targets, from small molecules to live cells, and even tissues, with high affinity and specificity. Due to their efficient targeting ability, they have many different
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Aptamers are strands of DNA or RNA molecules, chemically synthetized and able to bind a wide range of targets, from small molecules to live cells, and even tissues, with high affinity and specificity. Due to their efficient targeting ability, they have many different kinds of applications. Particularly attractive is their use in biotechnology and disease therapy, in substitution of antibodies. They represent a promising way for early diagnosis (aptasensors), but also for delivering imaging agents and drugs and for inhibiting specific proteins (therapeutic aptamers). Starting by briefly reviewing the most recent literature concerning advances in biomedical applications of aptamers and aptasensors, the focus is on the issues of a theoretical/computational framework (proteotronics) for modelling the electrical properties of biomolecules. Some recent results of proteotronics concerning the electrical, topological and affinity properties of aptamers are reviewed. Full article
(This article belongs to the Special Issue Aptamer Technologies)
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Open AccessFeature PaperReview Dissection of Protein Kinase Pathways in Live Cells Using Photoluminescent Probes: Surveillance or Interrogation?
Chemosensors 2018, 6(2), 19; https://doi.org/10.3390/chemosensors6020019
Received: 31 March 2018 / Revised: 22 April 2018 / Accepted: 23 April 2018 / Published: 25 April 2018
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Abstract
Protein kinases catalyze phosphorylation, a small yet crucial modification that affects participation of the substrate proteins in the intracellular signaling pathways. The activity of 538 protein kinases encoded in human genome relies upon spatiotemporally controlled mechanisms, ensuring correct progression of virtually all physiological
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Protein kinases catalyze phosphorylation, a small yet crucial modification that affects participation of the substrate proteins in the intracellular signaling pathways. The activity of 538 protein kinases encoded in human genome relies upon spatiotemporally controlled mechanisms, ensuring correct progression of virtually all physiological processes on the cellular level—from cell division to cell death. The aberrant functioning of protein kinases is linked to a wide spectrum of major health issues including cancer, cardiovascular diseases, neurodegenerative diseases, inflammatory diseases, etc. Hence, significant effort of scientific community has been dedicated to the dissection of protein kinase pathways in their natural milieu. The combination of recent advances in the field of light microscopy, the wide variety of genetically encoded or synthetic photoluminescent scaffolds, and the techniques for intracellular delivery of cargoes has enabled design of a plethora of probes that can report activation of target protein kinases in human live cells. The question remains: how much do we bias intracellular signaling of protein kinases by monitoring it? This review seeks answers to this question by analyzing different classes of probes according to their general structure, mechanism of recognition of biological target, and optical properties necessary for the reporting of intracellular events. Full article
(This article belongs to the Special Issue Fluorescent Probes for Live Cell Imaging)
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Open AccessReview The Use of Hoechst Dyes for DNA Staining and Beyond
Chemosensors 2018, 6(2), 18; https://doi.org/10.3390/chemosensors6020018
Received: 20 March 2018 / Revised: 15 April 2018 / Accepted: 17 April 2018 / Published: 18 April 2018
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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
(This article belongs to the Special Issue Fluorescent Probes for Live Cell Imaging)
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Open AccessFeature PaperArticle A Rationally Designed, Spiropyran-Based Chemosensor for Magnesium
Chemosensors 2018, 6(2), 17; https://doi.org/10.3390/chemosensors6020017
Received: 8 March 2018 / Revised: 14 April 2018 / Accepted: 16 April 2018 / Published: 17 April 2018
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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
(This article belongs to the Special Issue Fluorescent Probes for Live Cell Imaging)
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Open AccessReview Metal Oxide Nanostructures in Food Applications: Quality Control and Packaging
Chemosensors 2018, 6(2), 16; https://doi.org/10.3390/chemosensors6020016
Received: 26 February 2018 / Revised: 7 April 2018 / Accepted: 12 April 2018 / Published: 14 April 2018
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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; https://doi.org/10.3390/chemosensors6020015
Received: 12 February 2018 / Revised: 20 March 2018 / Accepted: 29 March 2018 / Published: 3 April 2018
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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; https://doi.org/10.3390/chemosensors6020014
Received: 28 February 2018 / Revised: 23 March 2018 / Accepted: 27 March 2018 / Published: 29 March 2018
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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; https://doi.org/10.3390/chemosensors6020013
Received: 4 December 2017 / Revised: 16 March 2018 / Accepted: 23 March 2018 / Published: 29 March 2018
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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
(This article belongs to the Special Issue Label-Free Biosensors and Chemical Sensors)
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Open AccessReview Smart Polymers in Micro and Nano Sensory Devices
Chemosensors 2018, 6(2), 12; https://doi.org/10.3390/chemosensors6020012
Received: 25 February 2018 / Revised: 16 March 2018 / Accepted: 19 March 2018 / Published: 21 March 2018
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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
(This article belongs to the Special Issue Polymers Based Chemical Sensors)
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