Open AccessFeature PaperArticle
Low-Frequency Electrochemical Impedance Spectroscopy as a Monitoring Tool for Yeast Growth in Industrial Brewing Processes
Chemosensors 2017, 5(3), 24; doi:10.3390/chemosensors5030024 -
Abstract
Today’s yeast total biomass and viability measurements during the brewing process are dependent on offline methods such as methylene blue or florescence dye-based staining, and/or the usage of flow cytometric measurements. Additionally, microscopic cell counting methods decelerate an easy and quick prediction of
[...] Read more.
Today’s yeast total biomass and viability measurements during the brewing process are dependent on offline methods such as methylene blue or florescence dye-based staining, and/or the usage of flow cytometric measurements. Additionally, microscopic cell counting methods decelerate an easy and quick prediction of yeast viability. These processes are time consuming and result in a time-delayed response signal, which not only reduces the knowledge of the performance of the yeast itself, but also impacts the quality of the final product. Novel approaches in process monitoring during the aerobic and anaerobic fermentation of Saccharomyces cerevisiae are not only limited to classical pH, dO2 and off-gas analysis, but they also use different in situ and online sensors based on different physical principles to determine the biomass, product quality and cell death. Within this contribution, electrochemical impedance spectroscopy (EIS) was used to monitor the biomass produced in aerobic and anaerobic batch cultivation approaches, simulating the propagation and fermentation unit operation of industrial brewing processes. Increases in the double-layer capacitance (CDL), determined at frequencies below 1 kHz, were proportional to the increase of biomass in the batch, which was monitored in the online and inline mode. A good correlation of CDL with the cell density was found. In order to prove the robustness and flexibility of this novel method, different state-of-the-art biomass measurements (dry cell weight—DCW and optical density—OD) were performed for comparison. Because measurements in this frequency range are largely determined by the double-layer region between the electrode and media, rather minor interferences with process parameters (aeration and stirring) were to be expected. It is shown that impedance spectroscopy at low frequencies is not only a powerful tool for the monitoring of viable yeast cell concentrations during operation, but it is also perfectly suited to determining physiological states of the cells, and may facilitate biomass monitoring in the brewing and yeast-propagating industry drastically. Full article
Figures

Figure 1

Open AccessFeature PaperReview
Thin 2D: The New Dimensionality in Gas Sensing
Chemosensors 2017, 5(3), 21; doi:10.3390/chemosensors5030021 -
Abstract
Since the first report of graphene, thin two-dimensional (2D) nanomaterials with atomic or molecular thicknesses have attracted great research interest for gas sensing applications. This was due to the distinctive physical, chemical, and electronic properties related to their ultrathin thickness, which positively affect
[...] Read more.
Since the first report of graphene, thin two-dimensional (2D) nanomaterials with atomic or molecular thicknesses have attracted great research interest for gas sensing applications. This was due to the distinctive physical, chemical, and electronic properties related to their ultrathin thickness, which positively affect the gas sensing performances. This feature article discusses the latest developments in this field, focusing on the properties, preparation, and sensing applications of thin 2D inorganic nanomaterials such as single- or few-layer layered double hydroxides/transition metal oxides/transition metal dichalcogenides. Recent studies have shown that thin 2D inorganic nanomaterials could provide monitoring of harmful/toxic gases with high sensitivity and a low concentration detection limit by means of conductometric sensors operating at relatively low working temperatures. Promisingly, by using these thin 2D inorganic nanomaterials, it may open a simple way of improving the sensing capabilities of conductometric gas sensors. Full article
Figures

Figure 1

Open AccessReview
Electrochemical Biosensors for the Determination of Toxic Substances Related to Food Safety Developed in South America: Mycotoxins and Herbicides
Chemosensors 2017, 5(3), 23; doi:10.3390/chemosensors5030023 -
Abstract
The goal of achieving food safety and quality has become increasingly important in relevant areas. The achievement of this objective includes a significant effort in different areas related to the production of raw materials, storage, transportation, etc. One of the central areas in
[...] Read more.
The goal of achieving food safety and quality has become increasingly important in relevant areas. The achievement of this objective includes a significant effort in different areas related to the production of raw materials, storage, transportation, etc. One of the central areas in the verification of food safety and food quality control is related to the analysis of food components and, in particular, possible toxic substances that they may contain. Therefore, the demand for appropriate methods for the determination of these substances is increasingly demanding. Thus, not only is accuracy and precision sought in the results of the analysis, but also the speed, simplicity and lowering of costs. In this way, electrochemical techniques and, particularly, electrochemical biosensors have emerged in recent times as good candidates to satisfy such requirements. This review summarizes the advances made in research and development centers located in South American countries related to the development of electrochemical biosensors for the determination of toxic substances present in foods, particularly mycotoxins and herbicides. Full article
Figures

Figure 1

Open AccessFeature PaperArticle
vQRS Based on Hybrids of CNT with PMMA-POSS and PS-POSS Copolymers to Reach the Sub-PPM Detection of Ammonia and Formaldehyde at Room Temperature Despite Moisture
Chemosensors 2017, 5(3), 22; doi:10.3390/chemosensors5030022 -
Abstract
Nanocomposite-based quantum resistive vapour sensors (vQRS) have been developed from the assembly of hybrid copolymers of polyhedral oligomeric silsesquioxane (POSS) and poly(methyl methacrylate) (PMMA) or poly(styrene) (PS) with carbon nanotubes (CNT). The originality of the resulting conducting architecture is expected to be responsible
[...] Read more.
Nanocomposite-based quantum resistive vapour sensors (vQRS) have been developed from the assembly of hybrid copolymers of polyhedral oligomeric silsesquioxane (POSS) and poly(methyl methacrylate) (PMMA) or poly(styrene) (PS) with carbon nanotubes (CNT). The originality of the resulting conducting architecture is expected to be responsible for the ability of the transducer to detect sub-ppm concentrations of ammonia and formaldehyde at room temperature despite the presence of humidity. In particular, the boosting effect of POSS is evidenced in CNT-based nanocomposite vQRS. The additive fabrication by spraying layer-by-layer provides (sLbL) is an effective method to control the reproducibility of the transducers’ chemo-resistive responses. In dry atmosphere, the two types of sensors showed a high sensitivity towards both hazardous gases, as they were able to detect 300 ppb of formaldehyde and 500 ppb of ammonia with a sufficiently good signal to noise ratio (SNR > 10). They also exhibited a quick response times less than 5 s for both vapours and, even in the presence of 100 ppm of water, they were able to detect small amounts of gases (1.5 ppm of NH3 and 9 ppm of CH2O). The results suggest promising applications of POSS-based vQRS for air quality or volatolome monitoring. Full article
Figures

Figure 1

Open AccessFeature PaperArticle
Comparison of the Sensing Properties of ZnO Nanowalls-Based Sensors toward Low Concentrations of CO and NO2
Chemosensors 2017, 5(3), 20; doi:10.3390/chemosensors5030020 -
Abstract
This work focuses on the synthesis and gas sensing properties of ZnO nanowalls (ZnO NWLs) grown by a simple cheap chemical bath deposition method on a thin layer of aluminum (about 20 nm thick) printed on the Pt interdigitated electrodes area of conductometric
[...] Read more.
This work focuses on the synthesis and gas sensing properties of ZnO nanowalls (ZnO NWLs) grown by a simple cheap chemical bath deposition method on a thin layer of aluminum (about 20 nm thick) printed on the Pt interdigitated electrodes area of conductometric alumina platforms. Post-deposition annealing in nitrogen atmosphere at 300 °C enabled the formation of a ZnO intertwined 2D foils network. A wide characterization was carried out to investigate the composition, morphology and microstructure of the nanowalls layer formed. The gas sensing properties of the films were studied by measuring the changes of electrical resistance upon exposure to low concentrations of carbon monoxide (CO) and nitrogen dioxide (NO2) in air. The sensor response to CO or NO2 was found to be strongly dependent on the operating temperature, providing a means to tailor the sensitivity and selectivity toward these selected target gases. Full article
Figures

Figure 1

Open AccessArticle
Ultra-Sensitive Optical Resonator for Organic Solvents Detection Based on Whispering Gallery Modes
Chemosensors 2017, 5(2), 19; doi:10.3390/chemosensors5020019 -
Abstract
In this paper, a novel technique using an ultra-sensitive optical resonator based on whispering gallery modes (WGM) is proposed to detect the diffusion of organic solvents. The sensor configuration is a micro-cavity made of polymeric material. When the solvent starts to diffuse, the
[...] Read more.
In this paper, a novel technique using an ultra-sensitive optical resonator based on whispering gallery modes (WGM) is proposed to detect the diffusion of organic solvents. The sensor configuration is a micro-cavity made of polymeric material. When the solvent starts to diffuse, the polymer of the cavity starts to swallow that solvent. A swollen elastomer is in fact a solution, except that its mechanical response is now elastic rather than viscous. As solvents fill the network, chains are extended. In turn, that leads to the change of the morphology and mechanical properties of the sensing element. These changes could be measured by tracking the WGM shifts. Several experiments were carried out to measure that swelling force. Ethanol and methanol are used in this paper as candidates to study their driving force of diffusion (concentration gradient) on the cavity. Additionally, this sensing design can be used for biological sensing application. Breath diagnosis can use this configuration in diabetes diagnosis since a solvent like acetone concentration in human breath leads to a quick, convenient, accurate, and painless breath diagnosis of diabetes. The optical resonator results are verified through two different analyses: theoretical and experimental modeling. These micro-optical cavities have been examined using preliminary experiments to fully investigate their response and to verify the numerical analysis. Results show that the proposed sensor yields sensitivity for the driving force of diffusion (concentration gradient) (9.405 × 1013 pm/N) with a measurement precision of ~3.6 fN. Full article
Figures

Figure 1

Open AccessFeature PaperArticle
Highly Sensitive ZnO(Ga, In) for Sub-ppm Level NO2 Detection: Effect of Indium Content
Chemosensors 2017, 5(2), 18; doi:10.3390/chemosensors5020018 -
Abstract
Nanocrystalline ZnO, ZnO(Ga), and ZnO(Ga, In) samples with different indium contents were prepared by wet-chemical method and characterized in detail by ICP-MS and XRD methods. Gas sensing properties toward NO2 were studied at 150–450 °C by DC conductance measurements. The optimal temperature
[...] Read more.
Nanocrystalline ZnO, ZnO(Ga), and ZnO(Ga, In) samples with different indium contents were prepared by wet-chemical method and characterized in detail by ICP-MS and XRD methods. Gas sensing properties toward NO2 were studied at 150–450 °C by DC conductance measurements. The optimal temperature for gas sensing experiments was determined. The dependence of the ZnO(Ga, In) sensor signal to NO2 at 250 °C correlates with the change of conductivity of the samples. The introduction of indium into the system leads to an increase in the values of the sensor signal in the temperature range T < 250 °C. The investigation of the local sample conductivity by scanning spreading resistance microscopy demonstrates that, at high indium content, the sensor properties are determined by the In–Ga–Zn–O layer that forms on the ZnO surface. Full article
Figures

Figure 1

Open AccessReview
Two-Dimensional Zinc Oxide Nanostructures for Gas Sensor Applications
Chemosensors 2017, 5(2), 17; doi:10.3390/chemosensors5020017 -
Abstract
Two-dimensional (2D) nanomaterials, due to their unique physical and chemical properties, are showing great potential in catalysis and electronic/optoelectronic devices. Moreover, thanks to the high surface to volume ratio, 2D materials provide a large specific surface area for the adsorption of molecules, making
[...] Read more.
Two-dimensional (2D) nanomaterials, due to their unique physical and chemical properties, are showing great potential in catalysis and electronic/optoelectronic devices. Moreover, thanks to the high surface to volume ratio, 2D materials provide a large specific surface area for the adsorption of molecules, making them efficient in chemical sensing applications. ZnO, owing to its many advantages such as high sensitivity, stability, and low cost, has been one of the most investigated materials for gas sensing. Many ZnO nanostructures have been used to fabricate efficient gas sensors for the detection of various hazardous and toxic gases. This review summarizes most of the research articles focused on the investigation of 2D ZnO structures including nanosheets, nanowalls, nanoflakes, nanoplates, nanodisks, and hierarchically assembled nanostructures as a sensitive material for conductometric gas sensors. The synthesis of the materials and the sensing performances such as sensitivity, selectivity, response, and recovery times as well as the main influencing factors are summarized for each work. Moreover, the effect of mainly exposed crystal facets of the nanostructures on sensitivity towards different gases is also discussed. Full article
Figures

Figure 1

Open AccessArticle
Surface Plasmon Resonance Immunosensor for the Detection of Campylobacter jejuni
Chemosensors 2017, 5(2), 16; doi:10.3390/chemosensors5020016 -
Abstract
Campylobacteriosis is an internationally important foodborne disease caused by Campylobacter jejuni. The bacterium is prevalent in chicken meat and it is estimated that as much as 90% of chicken meat on the market may be contaminated with the bacterium. The current gold
[...] Read more.
Campylobacteriosis is an internationally important foodborne disease caused by Campylobacter jejuni. The bacterium is prevalent in chicken meat and it is estimated that as much as 90% of chicken meat on the market may be contaminated with the bacterium. The current gold standard for the detection of C. jejuni is the culturing method, which takes at least 48 h to confirm the presence of the bacterium. Hence, the aim of this work was to investigate the development of a Surface Plasmon Resonance (SPR) sensor platform for C. jejuni detection. Bacterial strains were cultivated in-house and used in the development of the sensor. SPR sensor chips were first functionalized with polyclonal antibodies raised against C. jejuni using covalent attachment. The gold chips were then applied for the direct detection of C. jejuni. The assay conditions were then optimized and the sensor used for C. jejuni detection, achieving a detection limit of 8 × 106 CFU·mL−1. The sensitivity of the assay was further enhanced to 4 × 104 CFU·mL−1 through the deployment of a sandwich assay format using the same polyclonal antibody. The LOD obtained in the sandwich assay was higher than that achieved using commercial enzyme-linked immunosorbent assay (ELISA) (106–107 CFU·mL−1). This indicate that the SPR-based sandwich sensor method has an excellent potential to replace ELISA tests for C. jejuni detection. Specificity studies performed with Gram-positive and Gram-negative bacteria, demonstrated the high specific of the sensor for C. jejuni. Full article
Figures

Figure 1

Open AccessReview
Two-Dimensional Transition Metal Disulfides for Chemoresistive Gas Sensing: Perspective and Challenges
Chemosensors 2017, 5(2), 15; doi:10.3390/chemosensors5020015 -
Abstract
Transition metal disulfides have been attracting significant attentions in recent years. There are extensive applications of transition metal disulfides, especially on gas sensing applications, due to their large specific surface-to-volume ratios, high sensitivity to adsorption of gas molecules and tunable surface functionality depending
[...] Read more.
Transition metal disulfides have been attracting significant attentions in recent years. There are extensive applications of transition metal disulfides, especially on gas sensing applications, due to their large specific surface-to-volume ratios, high sensitivity to adsorption of gas molecules and tunable surface functionality depending on the decoration species or functional groups. However, there are several drawbacks such as poor gas selectivity, sluggish recovery characteristics and difficulty in the fabrication of large-scale devices. Here, we provide a review of recent progress on the chemoresistive gas sensing properties of two-dimensional transition metal disulfides. This review also provides various methods to enhance the gas sensing performance of two-dimensional disulfides, such as surface functionalization, decoration receptor functions and developing nanostructures. Full article
Figures

Figure 1

Open AccessArticle
Microfluidic Electronic Tongue Applied to Soil Analysis
Chemosensors 2017, 5(2), 14; doi:10.3390/chemosensors5020014 -
Abstract
Precision agriculture is crucial for increasing food output without expanding the cultivable area, which requires sensors to be deployed for controlling the level of nutrients in the soil. In this paper, we report on a microfluidic electronic tongue (e-tongue) based on impedance measurements
[...] Read more.
Precision agriculture is crucial for increasing food output without expanding the cultivable area, which requires sensors to be deployed for controlling the level of nutrients in the soil. In this paper, we report on a microfluidic electronic tongue (e-tongue) based on impedance measurements which is capable of distinguishing soil samples enriched with plant macronutrients. The e-tongue setup consisted of an array of sensing units made with layer-by-layer films deposited onto gold interdigitated electrodes. Significantly, the sensing units could be reused with adequate reproducibility after a simple washing procedure, thus indicating that there is no cross-contamination in three independent sets of measurements. A high performance was achieved by treating the capacitance data with the multidimensional projection techniques Principal Component Analysis (PCA), Interactive Document Map (IDMAP), and Sammon’s Mapping. While an optimized performance was demonstrated with IDMAP and feature selection, during which data of a limited frequency range were used, the distinction of all soil samples was also possible with the well-established PCA analysis for measurements at a single frequency. The successful use of a simple microfluidic e-tongue for soil analysis paves the way for enhanced tools to support precision agriculture. Full article
Figures

Figure 1

Open AccessArticle
A Chemically-Bound Glutathione Sensor Bioinspired by the Defense of Organisms against Heavy Metal Contamination: Optimization of the Immobilization Conditions
Chemosensors 2017, 5(2), 12; doi:10.3390/chemosensors5020012 -
Abstract
The influence of the experimental conditions (glutathione concentration and incubation time and temperature) concerning the covalent immobilization of glutathione via carbodiimide coupling on the behavior of a glutathione modified screen-printed carbon electrode obtained by electrografting is evaluated. The optimized parameters fasten the modification
[...] Read more.
The influence of the experimental conditions (glutathione concentration and incubation time and temperature) concerning the covalent immobilization of glutathione via carbodiimide coupling on the behavior of a glutathione modified screen-printed carbon electrode obtained by electrografting is evaluated. The optimized parameters fasten the modification process and improve the performance of the sensor as compared to the usual procedure. This suggests the convenience of a tailored preparation of metal sensors based on metal-binding biomolecules such as glutathione. Full article
Figures

Figure 1

Open AccessEditorial
Electrochemical Immunosensors and Aptasensors
Chemosensors 2017, 5(2), 13; doi:10.3390/chemosensors5020013 -
Abstract
Since the first electrochemical biosensor for glucose detection, pioneered in 1962 by Clark and Lyons [1], research and application in the field has grown at an impressive rate and we are still witnessing a continuing evolution of research on this topic [2].[...] Full article
Open AccessReview
Enzymes as Tools in MIP-Sensors
Chemosensors 2017, 5(2), 11; doi:10.3390/chemosensors5020011 -
Abstract
Molecularly imprinted polymers (MIPs) have the potential to complement antibodies in bioanalysis, are more stable under harsh conditions, and are potentially cheaper to produce. However, the affinity and especially the selectivity of MIPs are in general lower than those of their biological pendants.
[...] Read more.
Molecularly imprinted polymers (MIPs) have the potential to complement antibodies in bioanalysis, are more stable under harsh conditions, and are potentially cheaper to produce. However, the affinity and especially the selectivity of MIPs are in general lower than those of their biological pendants. Enzymes are useful tools for the preparation of MIPs for both low and high-molecular weight targets: As a green alternative to the well-established methods of chemical polymerization, enzyme-initiated polymerization has been introduced and the removal of protein templates by proteases has been successfully applied. Furthermore, MIPs have been coupled with enzymes in order to enhance the analytical performance of biomimetic sensors: Enzymes have been used in MIP-sensors as “tracers” for the generation and amplification of the measuring signal. In addition, enzymatic pretreatment of an analyte can extend the analyte spectrum and eliminate interferences. Full article
Figures

Scheme 1

Open AccessArticle
Electrochemical Immunosensor for Detection of IgY in Food and Food Supplements
Chemosensors 2017, 5(1), 10; doi:10.3390/chemosensors5010010 -
Abstract
Immunoglobulin Y is a water-soluble protein present in high concentration in hen serum and egg yolk. IgY has applications in many fields, e.g., from food stuff to the mass production of antibodies. In this work, we have implemented an electrochemical immunosensor for IgY
[...] Read more.
Immunoglobulin Y is a water-soluble protein present in high concentration in hen serum and egg yolk. IgY has applications in many fields, e.g., from food stuff to the mass production of antibodies. In this work, we have implemented an electrochemical immunosensor for IgY based on templated nanoelectrodes ensembles. IgY is captured by the templating polycarbonate and reacted with anti-IgY labeled with horseradish peroxidase. In the presence of H2O2 and methylene blue as the redox mediator, an electrocatalytic current is generated which scales with IgY concentration in the sample. After optimizing the extracting procedure, the immunosensor was applied for analysis of fresh eggs and food integrators. The data obtained with the biosensor were validated by SDS-PAGE and Western blot measurements. Full article
Figures

Figure 1

Open AccessArticle
Electrochemical Study of Trametes Versicolor Laccase Compatibility to Different Polyphenolic Substrates
Chemosensors 2017, 5(1), 9; doi:10.3390/chemosensors5010009 -
Abstract
The aim of this electrochemical study was to ascertain which position of hydroxy groups on a benzene ring provides electroactive products after enzymatic oxidation by laccase originating from the Trametes versicolor mushroom, exhibiting intense redox signals that are exploitable for their amperometric determination.
[...] Read more.
The aim of this electrochemical study was to ascertain which position of hydroxy groups on a benzene ring provides electroactive products after enzymatic oxidation by laccase originating from the Trametes versicolor mushroom, exhibiting intense redox signals that are exploitable for their amperometric determination. The electrochemical properties of phenol together with all isomers of benzenediol and cresol at the bare carbon paste electrode (CPE) and CPE modified with enzyme laccase (CPE/Laccase) were investigated using cyclic voltammetry at various scan rates. Comparison of resulting redox signals and their differences confirmed the suitability of classes of polyphenolic compounds as substrates for Trametes versicolor laccase and their potential use as suitable biological components in the development of amperometric enzyme biosensors for the determination of such species. The feasibility of the proposed approach was verified by electrochemical assays of the enzymatic oxidation of polyphenolic analogues of simple phenols, e.g., gentisic acid, caffeic acid, resveratrol, and others. Full article
Figures

Figure 1

Open AccessReview
Electrochemical Affinity Biosensors in Food Safety
Chemosensors 2017, 5(1), 8; doi:10.3390/chemosensors5010008 -
Abstract
Safety and quality are key issues of today’s food industry. Since the food chain is becoming more and more complex, powerful analytical methods are required to verify the performance of food safety and quality systems. Indeed, such methods require high sensitivity, selectivity, ability
[...] Read more.
Safety and quality are key issues of today’s food industry. Since the food chain is becoming more and more complex, powerful analytical methods are required to verify the performance of food safety and quality systems. Indeed, such methods require high sensitivity, selectivity, ability for rapid implementation and capability of automatic screening. Electroanalytical chemistry has, for decades, played a relevant role in food safety and quality assessment, taking more and more significance over time in the solution of analytical problems. At present, the implementation of electrochemical methods in the food is evident. This is in a large part due to the relevant results obtained by combining the attractive advantages of electrochemical transduction strategies (in terms of relatively simple hardware, versatility, interface with automatic logging and feasibility of application outside the laboratory environment) with those from biosensors technology. Important examples of enzyme electrochemical biosensors are those dedicated to the determination of glucose, alcohol or cholesterol are important examples. In addition, other types of different electrochemical biosensing approaches have emerged strongly in the last years. Among these, the strategies involving affinity interactions have been shown to possess a large number of applications. Therefore, electrochemical immunosensors and DNA-based biosensors have been widely used to determine major and minor components in foodstuffs, providing sufficient data to evaluate food freshness, the quality of raw materials, or the origin of samples, as well as to determine a variety of compounds at trace levels related to food safety such as micotoxins, allergens, drugs residues or pathogen microorganisms. This review discusses some critical examples of the latest advances in this area, pointing out relevant methodologies related to the measurement techniques, including the use of nanostructured electrodes and strategies for signal amplification. Full article
Figures

Figure 1

Open AccessReview
Gravimetric Viral Diagnostics: QCM Based Biosensors for Early Detection of Viruses
Chemosensors 2017, 5(1), 7; doi:10.3390/chemosensors5010007 -
Abstract
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
[...] Read more.
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
Figures

Figure 1

Open AccessArticle
Hierarchical Self-Assembly of Amino Acid Derivatives into Enzyme-Responsive Luminescent Gel
Chemosensors 2017, 5(1), 6; doi:10.3390/chemosensors5010006 -
Abstract
In this study, a novel three-component hydrogel has been designed and fabricated via hierarchical self-assembly by amino acid derivative (NPPD), riboflavin (RF) and α-cyclodextrin (α-CD). These molecules were aggregated to form some fibrous structures based on hydrogen bond and π–π stacking. The results
[...] Read more.
In this study, a novel three-component hydrogel has been designed and fabricated via hierarchical self-assembly by amino acid derivative (NPPD), riboflavin (RF) and α-cyclodextrin (α-CD). These molecules were aggregated to form some fibrous structures based on hydrogen bond and π–π stacking. The results show that the hydrogel has a specific response to α-amylase and the fluorescence disappears once hydrolyzed. Therefore, this multi-component hydrogel has potential application in the field of drug delivery. Full article
Figures

Figure 1

Open AccessArticle
Selectivity and Efficiency of Conductive Molecularly Imprinted Polymer (c-MIP) Based on 5-Phenyl-Dipyrromethane and 5-Phenol-Dipyrromethane for Quorum Sensing Precursors Detection
Chemosensors 2017, 5(1), 5; doi:10.3390/chemosensors5010005 -
Abstract
Functional polymers that selectively recognize target compounds are developed by imprinting polymerization. In the present paper, two different dipyrromethanes, 5-phenol-dipyrromethane (5-pOH-DP) and 5-phenyl-dipyrromethane (5-ph-DP), are synthetized and investigated to develop conductive molecularly imprinted polymer (cMIP) sensors. As target molecules, two homoserine lactone derivatives
[...] Read more.
Functional polymers that selectively recognize target compounds are developed by imprinting polymerization. In the present paper, two different dipyrromethanes, 5-phenol-dipyrromethane (5-pOH-DP) and 5-phenyl-dipyrromethane (5-ph-DP), are synthetized and investigated to develop conductive molecularly imprinted polymer (cMIP) sensors. As target molecules, two homoserine lactone derivatives were templated by an electrochemically driven polymerization process. Acyl-homoserine lactones (AHLs), also called homoserine lactones (HS), are a class of signaling molecules involved in bacterial quorum sensing (QS), which is a strategy of coordination among bacteria mediated by population density. The preparation of cMIP from 5-pOH-DP and 5-ph-DP in the presence of acetyl-homoserine lactone (Acetyl-HS) or carboxybenzyl-homoserine lactone (Cbz-HS) was performed by cyclic voltammetry (CV). The cMIP selectivity and sensitivity were assessed by microgravimetry (QCM). Both series of measurements were performed with the aid of an Electrochemical Quartz Crystal Microbalance (EQCM/QCM). The experimental evidences are discussed with respect to NMR measurements that were conducted to gain insight into the interactions established between monomers and templates. The NMR data interpretation offers preliminary information about the most probable positions involved in interaction development for both molecules and highlights the role of the hydration shell. The QCM-cMIP sensor was able to detect the analyte in the linear range from 10−8 mol·L−1 to 10−6 mol·L−1 and a limit of detection (LOD) of 22.3 ng (3σ of the blank signal) were evaluated. QCM rebinding tests demonstrated that cMIP selectivity was driven by the pendant group of dipyrromethane, which was also confirmed by the NMR data. Full article
Figures

Figure 1