Chemosensors — Open Access Journal

The thermal degradation related to stability in long-term storage of a carbon nanotube-based biosensor has been investigated. The effect of storage temperature on detachment and denaturation of glucose oxidase (GOx) biocatalyst has been proved. The carbon nanotubes (CNTs) coated with polyethyleneimine (PEI) as entrapping polymer to attract more GOx to form a durable and layered CNT/PEI/GOx structure is used for long-term storage to minimize GOx detachment from the structure and minimize the possibility of enzyme and protein denaturation. After 120 days, the glucose response of the CNT/PEI/GOx biosensor stored under 4°C is preserved up to 66.7% of its initial value, while under a 25 °C storage the response is maintained up to 41.7%. The enzyme coverage activity of CNT/PEI/GOx stored at 4 °C and 25 °C has decreased by 31.1% and 51.4%, respectively. Denaturation and detachment of GOx are the common causes of thermal degradation in biosensors under improper storage temperatures, but the presence of PEI in the structure can slow-down these phenomena. Moreover, the electrons transfer constant of CNT/PEI/GOx biocatalyst stored at 4 °C and 25 °C were 7.5 ± 0.5 s⁻¹ and 6.6 ± 0.3 s⁻¹, respectively, indicating that also electrons mobility is damaged by detachment and denaturation of enzyme protein and the detection of glucose from the glucose oxidation reaction (GOR) is compromised. Full article

The article reviews the current status of label-free integrated optical biosensors focusing on the evolution over the years of their analytical performance. At first, a short introduction to the evanescent wave optics is provided followed by detailed description of the main categories of label-free optical biosensors, including sensors based on surface plasmon resonance (SPR), grating couplers, photonic crystals, ring resonators, and interferometric transducers. For each type of biosensor, the detection principle is first provided followed by description of the different transducer configurations so far developed and their performance as biosensors. Finally, a short discussion about the current limitations and future perspectives of integrated label-free optical biosensors is provided. Full article

Drinking water contamination of lead from various environmental sources, leaching consumer products, and intrinsic water-pipe infrastructure is still today a matter of great concern. Therefore, new highly sensitive and convenient Pb²⁺ measurement schemes are necessary, especially for in-situ measurements at a low cost. Within this work dye/ionophore/Pb²⁺ co-extraction and effective water phase de-colorization was utilized for highly sensitive lead measurements and sub-ppb naked-eye detection. A low-cost ionophore Benzo-18-Crown-6-ether was used, and a simple test-tube mix and separate procedure was developed. Instrumental detection limits were in the low ppt region (LOD = 3, LOQ = 10), and naked-eye detection was 500 ppt. Note, however, that this sensing scheme still has improvement potential as concentrations of fluorophore and ionophore were not optimized. Artificial tap-water samples, leached by a standardized method, demonstrated drinking water application. Implications for this method are convenient in-situ lead ion measurements. Full article

The electro-reduction of nitrate ions in artificial sea water was investigated at a gold substrate (E_Au) functionalized by silver nanoparticles (AgNPs). These AgNPs were generated in situ on the gold substrate by the direct decomposition of the metalorganic N,N′-diisopropylacetamidinate silver precursor [Ag(Amd)] in the liquid phase. Very small and well dispersed AgNPs were deposited on the gold electrode and then used as working electrode (E_Au/AgNPs). Square wave voltammetry (SWV) was successfully employed to detect nitrate ions (NO₃⁻) with a detection limit (LOD) of 0.9 nmol∙L⁻¹ in artificial sea water (pH = 6.0) without pre-concentration or pH adjustment. Full article

We report on studies of new gas sensing devices to be used in high humidity environments. Highly thermal-stable, super hydrophobic 2-dimensional (2D) boron nitride nanosheets (BNNSs) functionalized with Pt nanoparticles were prepared and used as an active layer for the prototype. The morphologic surface, crystallographic structures and chemical compositions of the synthesized 2D materials were characterized by using optical microscope, scanning electron microscope (SEM), transmission electron microscope (TEM) and atomic force microscope (AFM) and Raman scattering, respectively. The experimental data reveals that high-quality BNNSs were prepared. A pair of Au electrodes were combined with a basic electrical circuit and the 2D sensing material to form high-performance gas sensors for the detection of pollution gases. The present structure is simple and the fabrication is easy and fast, which ensures the creation of a low-cost prototype with harsh (high humidity, high temperature) environment resistance and potential for miniaturization. The responses of the prototype to different target gases with different concentrations were characterized. The influences of the operating temperature and bias voltage effect on sensing performances were also investigated. The fabricated sensors appear to have high selectivity, high sensitivity and fast response to target gases. The sensing mechanism in the present case is attributed to the electron donation from the target gas molecules to the active layer, leading to the change of electrical properties on the surface of BNNS layer. Full article

Recent progress in the area of molecular logic, in particular molecules capable of sensing for acidity and oxidizability, are gathered together in this short review. Originally proposed as AND logic gates that provide a high fluorescence output when simultaneously protonated and oxidized, the concept has been extended from two-input to three-input variants and to include molecules that function as INHIBIT logic gates. Photochemical concepts such as photoinduced electron transfer (PET) and internal charge transfer (ICT) are exploited as favorite design concepts. This review highlights the evolution of Pourbaix sensors with anthracene, pyrazoline, and naphthalimide fluorophores. Future applications abound in various disciplines from corrosion science, material science, geochemistry to cell imaging. Full article

In this study, we examine a means for developing near-IR fluorescent sensors through streamlined, site-specific coupling with peptide-based receptors. As the penultimate step of solid-phase synthesis of a peptide-based receptor, we show a simple means of labeling the N’ terminus with the near IR fluorophore IR-783 to afford a viable fluorescent sensor after cleavage from the resin. The proof-of-concept probe utilized a biotin mimetic peptide sequence as the receptive moiety. Here we revealed a “turn-on” fluorescence enhancement upon binding of the biotin mimetic probe to its intended streptavidin target. Not all peptide-receptive moieties tested were able to generate such an enhancement upon target binding, and as such, the rationale for the observed fluorescence response properties is discussed. Full article

A micro-level technique so-called “microfluidic technology or simply microfluidic” has gained a special place as a powerful tool in bioengineering and biomedical engineering research due to its core advantages in modern science and engineering. Microfluidic technology has played a substantial role in numerous applications with special reference to bioscience, biomedical and biotechnological research. It has facilitated noteworthy development in various sectors of bio-research and upsurges the efficacy of research at the molecular level, in recent years. Microfluidic technology can manipulate sample volumes with precise control outside cellular microenvironment, at micro-level. Thus, enable the reduction of discrepancies between in vivo and in vitro environments and reduce the overall reaction time and cost. In this review, we discuss various integrations of microfluidic technologies into biotechnology and its paradigmatic significance in bio-research, supporting mechanical and chemical in vitro cellular microenvironment. Furthermore, specific innovations related to the application of microfluidics to advance microbial life, solitary and co-cultures along with a multiple-type cell culturing, cellular communications, cellular interactions, and population dynamics are also discussed. Full article

The development of electronic-nose (e-nose) technologies for disease diagnostics was initiated in the biomedical field for detection of biotic (microbial) causes of human diseases during the mid-1980s. The use of e-nose devices for disease-diagnostic applications subsequently was extended to plant and animal hosts through the invention of new gas-sensing instrument types and disease-detection methods with sensor arrays developed and adapted for additional host types and chemical classes of volatile organic compounds (VOCs) closely associated with individual diseases. Considerable progress in animal disease detection using e-noses in combination with metabolomics has been accomplished in the field of veterinary medicine with new important discoveries of biomarker metabolites and aroma profiles for major infectious diseases of livestock, wildlife, and fish from both terrestrial and aquaculture pathology research. Progress in the discovery of new e-nose technologies developed for biomedical applications has exploded with new information and methods for diagnostic sampling and disease detection, identification of key chemical disease biomarkers, improvements in sensor designs, algorithms for discriminant analysis, and greater, more widespread testing of efficacy in clinical trials. This review summarizes progressive advancements in utilizing these specialized gas-sensing devices for numerous diagnostic applications involving noninvasive early detections of plant, animal, and human diseases. Full article

Olfactory systems typically process signals produced by mixtures composed of very many natural odors, some that can be elicited by single compounds. The several hundred different olfactory receptors aided by several dozen different taste receptors are sufficient to define our complex chemosensory world. However, sensory processing by selective adaptation and mixture suppression leaves only a few perceptual components recognized at any time. Thresholds determined by stochastic processes are described by functions relating stimulus detection to concentration. Relative saliences of mixture components are established by relating component recognition to concentration in the presence of background components. Mathematically distinct stochastic models of perceptual component dominance in binary mixtures were developed that accommodate prediction of an appropriate range of probabilities from 0 to 1, and include errors in identifications. Prior short-term selective adaptation to some components allows temporally emergent recognition of non-adapted mixture-suppressed components. Thus, broadly tuned receptors are neutralized or suppressed by activation of other more efficacious receptors. This ‘combinatorial’ coding is more a process of subtraction than addition, with the more intense components dominating the perception. It is in this way that complex chemosensory mixtures are reduced to manageable numbers of odor notes and taste qualities. Full article

Sensitive and specific DNA biomarker detection is critical for accurately diagnosing a broad range of clinical conditions. However, the incorporation of such biosensing structures in integrated microfluidic devices is often complicated by the need for an additional labelling step to be implemented on the device. In this review we focused on presenting recent advances in label-free DNA biosensor technology, with a particular focus on microfluidic integrated devices. The key biosensing approaches miniaturized in flow-cell structures were presented, followed by more sophisticated microfluidic devices and higher integration examples in the literature. The option of full DNA sequencing on microfluidic chips via nanopore technology was highlighted, along with current developments in the commercialization of microfluidic, label-free DNA detection devices. Full article

Cell Imaging Platforms (CIPs) are research infrastructures offering support to a number of scientific projects including the choice of adapted fluorescent probes for live cell imaging. What to detect in what type of sample and for how long is a major issue with fluorescent probes and, for this, the “hat-trick” “Probe–Sample–Instrument” (PSI) has to be considered. We propose here to deal with key points usually discussed in CIPs including the properties of fluorescent organic probes, the modality of cell labeling, and the best equipment to obtain appropriate spectral, spatial, and temporal resolution. New strategies in organic synthesis and click chemistry for accessing probes with enhanced photophysical characteristics and targeting abilities will also be addressed. Finally, methods for image processing will be described to optimize exploitation of fluorescence signals. Full article

This work presents theoretical studies of the interaction of molecules of several gaseous pollutants with polyacrylonitrile (PAN) surface in the presence of a water and/or oxygen molecule. For this purpose, a PAN cluster model has been proposed by the methods of quantum chemical calculations and molecular modeling. The energy-favorable positions, in which the gas molecules are located relative to the surface of the PAN cluster, are determined and the thermodynamic and the following geometric parameters of the systems are calculated: “PAN cluster − oxygen molecule”, “PAN cluster − oxygen molecule − gas molecule”, “PAN cluster − water molecule − molecule of oxygen”, and “PAN cluster − a molecule of water − an oxygen molecule − a gas molecule”. It is concluded that PAN in atmospheric air in the presence of oxygen molecules is sensitive to carbon oxide (IV), sulfur (IV) oxide, chlorine, hydrogen sulfide and carbon oxide (II). In an anoxic environment, PAN films will show selective sensitivity to chlorine. The presence of water molecules in the investigated air should not affect the gas sensitivity of PAN films. Full article

Five types of new solid-state oxygen sensors, four based on microporous polypropylene fabric materials and one on polyphenylene sulphide films impregnated with phosphorescent platinum(II)-benzoporphyrin dye, were tested for their stability and safety in food packaging applications. All these sensors exhibit useful optical signals (phosphorescence lifetime readout) and working characteristics and are simpler and cheaper to produce and integrate into standard packaging materials than existing commercial sensors. When exposed to a panel of standard food simulants and upon direct contact with raw beef and chicken meat and cheddar cheese samples packaged under modified atmosphere, the sensors based on ungrafted polypropylene fabric, impregnated with PtBP dye by the swelling method, outperformed the other sensors. The sensors are also stable upon storage under normal atmospheric conditions for at least 12 months, without any significant changes in calibration. Full article

Decentralization of on-site and in-site trace metal analysis has been a key topic over the last 30 years, owing to the increasing need for environmental protection as well as industrial and health-based field applications. In trace (and ultratrace) metal analysis, electrochemical stripping analysis with mercury (or bismuth) screen-printed film electrodes has shown a fast growth in popularity thanks to the good limits of detection, the ease of application in the field, and the low cost. Moreover, the availability of new wall-jet flow cells has opened the opportunity for their use in in situ industrial monitoring. The analytical figures of merit in stripping voltammetry with screen-printed electrodes (SPEs) under decentralized conditions and/or with sensor arrays are heavily affected by some analytical factors, primarily the presence of a pseudo-reference electrode, the efficiency of mass transport during the preconcentration step, and the need for external calibration. A careful model investigation of the analytical parameters for an efficient use of SPEs in decentralized conditions has been undertaken and discussed. Different instrumental approaches were investigated, comparing optimized batch conditions and flow cell operation under either continuous flow or stopped-flow sample injection. The stripping efficiency under wall-jet flow conditions was found to be high and comparable to that in batch conditions, leading to sub-ppb (μg/L) limit of detection (LOD) figures. Finally, external calibration in stripping voltammetry was studied as a viable alternative to conventional standard addition quantitation. Results showed, indeed, that external calibration was demonstrated to be reliable for quantitation of Pb and Cd in real water samples. Full article

The poor solubility and dispersibility of carbon nanotubes in both aqueous and organic solvents restrict their applications in biological science. Herein, a simple and cheap method for synthesizing and purification of water soluble multiwall carbon nanotubes from coal combustion fly ash and characterization of this water soluble multiwall carbon nanotubes after conjugation with gold nanoparticles has been described. Full article

Development of oxidative and reductive flavors in wine can be influenced by the concentration and form of Cu within the wine. Electrochemical techniques have been devised to quantitate electrochemically active Cu (labile) in wine, as opposed to inactive Cu (non-labile). However, the electrochemical methods to measure labile Cu may be biased by the wine matrix, require lengthy calibration processes and/or unduly perturb the wine matrix during measurement. In this study, medium exchange stripping potentiometry was utilized with a thin mercury film on a screen-printed carbon electrode to provide a quantitation method that could largely overcome these limitations. The best average recoveries for 0.040 mg/L of labile Cu of 101 ± 15% (n = 12) were observed using composite calibration graphs prepared in oxidized wines and on multiple electrodes and using Pb as an internal standard. Composite calibration curves performed on different electrodes to the sample analysis were as effective in quantifying labile Cu as calibration curves performed on the same electrode as the sample. The results allow selection of a quantitation procedure that will suit the required speed and accuracy of labile Cu determination. Full article