Biosensors for phenolic compounds: The catechol as a substrate model

The behaviour of three different laccase-based graphite biosensors was studied in view of their use in agricultural or industrial waters polluted by phenolic compounds. Catechol was used as a substrate model. Laccase from Trametes versicolor was immobilized on one biosensor (type A electrode) by adsorption while, on the other two biosensor types, laccase was covalently bound through the carboxylic groups created on the graphite by means of treatment with an electric potential difference (type B electrode) or with nitric acid (type C electrode). In the latter two cases, hexamethylenediamine and glutaraldehyde were used as the spacer and the coupling agent, respectively. The extension of linear response range and the sensitivity and time stability of each biosensor type were investigated. The type C biosensor gave the best results and its electrochemical properties proved comparable to those reported by other authors.     

Insight of smart biosensors for COVID-19: A review

The review discusses the diagnostic application of biosensors as point-of-care devices in the COVID-19 pandemic. Biosensors are important analytical tools that can be used for the robust and effective detection of infectious diseases in real-time. In this current scenario, the utilization of smart, efficient biosensors for COVID-19 detection is increasing and we have included a few smart biosensors such as smart and intelligent based biosensors, plasmonic biosensors, field effect transistor (FET) biosensors, smart optical biosensors, surface enhanced Raman scattering (SERS) biosensor, screen printed electrode (SPE)-based biosensor, molecular imprinted polymer (MIP)-based biosensor, MXene-based biosensor and metal–organic frame smart sensor. Their significance as well as the benefits and drawbacks of each kind of smart sensor are mentioned in depth. Furthermore, we have compiled a list of various biosensors which have been developed across the globe for COVID-19 and have shown promise as commercial detection devices. Significant challenges in the development of effective diagnostic methods are discussed and recommendations have been made for better diagnostic outcomes to manage the ongoing pandemic effectively.     

Genetic Programming as a tool for identification of analyte-specificity from complex response patterns using a non-specific whole-cell biosensor

Whole-cell biosensors are mostly non-specific with respect to their detection capabilities for toxicants, and therefore offering an interesting perspective in environmental monitoring. However, to fully employ this feature, a robust classification method needs to be implemented into these sensor systems to allow further identification of detected substances. Substance-specific information can be extracted from signals derived from biosensors harbouring one or multiple biological components. Here, a major task is the identification of substance-specific information among considerable amounts of biosensor data. For this purpose, several approaches make use of statistical methods or machine learning algorithms. Genetic Programming (GP), a heuristic machine learning technique offers several advantages compared to other machine learning approaches and consequently may be a promising tool for biosensor data classification. In the present study, we have evaluated the use of GP for the classification of herbicides and herbicide classes (chemical classes) by analysis of substance-specific patterns derived from a whole-cell multi-species biosensor. We re-analysed data from a previously described array-based biosensor system employing diverse microalgae (Podola and Melkonian, 2005), aiming on the identification of five individual herbicides as well as two herbicide classes. GP analyses were performed using the commercially available GP software 'Discipulus', resulting in classifiers (computer programs) for the binary classification of each individual herbicide or herbicide class. GP-generated classifiers both for individual herbicides and herbicide classes were able to perform a statistically significant identification of herbicides or herbicide classes, respectively. The majority of classifiers were able to perform correct classifications (sensitivity) of about 80-95% of test data sets, whereas the false positive rate (specificity) was lower than 20% for most classifiers. Results suggest that a higher number of data sets may lead to a better classification performance. In the present paper, GP-based classification was combined with a biosensor for the first time. Our results demonstrate GP was able to identify substance-specific information within complex biosensor response patterns and furthermore use this information for successful toxicant classification in unknown samples. This suggests further research to assess perspectives and limitations of this approach in the field of biosensors.     

Comparative study of semi-specific Aeromonas hydrophila and universal Pseudomonas fluorescens biosensors for BOD measurements in meat industry wastewaters

Aeromonas hydrophila P69.1 (A. hydrophila) was used to construct a semi-specific biosensor to estimate biochemical oxygen demand (BOD) in high fat and grease content wastewaters. A. hydrophila cells were grown in fat containing medium to induce necessary enzymes for transport and degradation of fatty substances. Universal biosensor based on non-specific Pseudomonas fluorescens P75 (P. fluorescens) was used to conduct comparison experiments. Biosensors were calibrated using OECD synthetic wastewater and steady-state method, subsequently several experiments with synthetic and industrial wastewaters were conducted. A linear range up to 45 mg l(-1) BOD(7) was gained using A. hydrophila biosensor, in comparison to 40 mg l(-1) BOD(7) obtained using P. fluorescens biosensors. The lower limit of detection was 5 mg l(-1) BOD(7). Service life of A. hydrophila and P. fluorescens biosensors were 110 and 115 days, respectively. The response time of the biosensors depended on the BOD(7) of measuring solution and was up to 20 min when analyzing different wastewaters. Both biosensors underestimated BOD in meat industry wastewater from 43% up to 71%, but more accurate results could be obtained with A. hydrophila biosensor. Semi-specific A. hydrophila biosensor was able to measure proportion of fat found in wastewater sample, while other refractory compounds remained undetectable to both biosensors.     

A novel amperometric bienzymatic biosensor based on alcohol oxidase coupled PVC reaction cell and nanomaterials modified working electrode for rapid quantification of alcohol

Abstract

A new amperometric sensor has been fabricated for sensitive and rapid quantification of ethanol. The biosensor assembly was prepared by covalently immobilizing alcohol oxidase (AOX) from Pichia pastoris onto chemically modified surface of polyvinylchloride (PVC) beaker with glutaraldehyde as a coupling agent followed by immobilization of horseradish peroxidase (HRP), silver nanoparticles (AgNPs), chitosan (CHIT), carboxylated multi-walled carbon nanotubes (c-MWCNTs) and nafion (Nf) nanocomposite onto the surface of Au electrode (working electrode). Owing to properties such as chemical inertness, light weight, weather resistance, corrosion resistance, toughness and cost-effectiveness, PVC membrane has attracted a growing interest as a support for enzyme immobilization in the development of biosensors. The amperometric biosensor displayed optimum response within 8?s at pH 7.5 and 35°C temperature. A linear response to alcohol in the range of 0.01mM–50?mM and 0.0001?µM as a minimum limit of detection was displayed by the proposed biosensor with excellent storage stability (190?days) at 4°C. The sensitivity of the sensor was found to be 155?µA mM^?1?cm^?2. A good correlation (R²?=?0.99) was found between alcohol level in commercial samples as evaluated by standard ethanol assay kit and the current biosensor which validates its performance.     

Overview of vaccines and vaccination

Of the 80-plus known infectious agents pathogenic for humans, there are now more than 30 vaccines against 26 mainly viral and bacterial infections and these greatly minimize subsequent disease and prevent death after exposure to those agents. This article describes the nature of the vaccines, from live attenuated agents to subunits, their efficacy and safety, and the kind of the immune responses generated by those vaccines, which are so effective. To date, all licensed vaccines generate especially specific antibodies, which attach to the infectious agent and therefore can very largely prevent infection. These vaccines have been so effective in developed countries in preventing mortality after a subsequent infection that attempts are being made to develop vaccines against many of the remaining infectious agents. Many of the latter are difficult to manipulate; they can cause persisting infections or show great antigenic variation. A range of new approaches to improve selected immune responses, such as immunization with DNA or chimeric live vectors, viral or bacterial, are under intense scrutiny, as well as genomic analysis of the agent.     

What risks should be permissible in controlled human infection model studies?

Controlled human infection model (CHIM) studies involve the intentional exposure of healthy research volunteers to infectious agents. These studies contribute to knowledge about the cause or development of disease and to the advancement of vaccine research. But they also raise ethical questions about the kinds of risks that should be permissible and whether limits should be imposed on research risks in CHIM studies. Two possible risk thresholds have been considered for CHIM studies. The first suggests constraining ethically permissible risks according to a minimal risk threshold and the second endorses a higher risk threshold that excludes irreversible or fatal infections. I argue that neither of these thresholds is persuasive and situate questions about risk thresholds in CHIM studies within a broader debate about permissible risks in research. I argue that risks in CHIM studies should be constrained according to limits on research risks that do not offer corresponding benefits in all studies rather than developing a unique risk threshold for CHIM studies. I then propose five recommendations for the ethical assessment of risk in CHIM studies.     

The use of multiple-strain algal sensor chips for the detection and identification of volatile organic compounds

Although biosensors detecting a great variety of toxicants have been developed during the last decades, the simultaneous detection and identification of several targets by one biosensor is not possible in the majority of the biosensor systems. In our study we proved the concept of the detection and identification of two different volatile toxic compounds with a non-selective biochip-based algal biosensor. For that purpose we produced array plate biochips to utilise three membrane-immobilised algal strains of genus Klebsormidium and Chlorella in one biosensor system. A novel IMAGING-PAM chlorophyll fluorometer was applied to measure the impact of volatile organic compounds (VOC) on photosynthesis of chip-immobilized algae in terms of quantum efficiency of electron transport (DeltaF/F'm). Formaldehyde (FA) vapour was detectable with statistical significance in concentrations relevant to human health from 10 ppb to 10 ppm. The biosensor response recorded within minutes was concentration-dependent and reversible. Moreover, vapours of formaldehyde (0.05-1 ppm) and methanol (MeOH) (200-1000 ppm) were significantly identified by the compound-specific response rate as a quotient of the biosensor responses of the respective algal strains. Using the IMAGING-PAM chlorophyll fluorometer, data sampling proved to be highly efficient. Based on our results we conclude that the principle of the algal sensor chip (ASC) suggests further research on the detection and identification of VOCs and other toxic substances in gaseous environment with that biochip system.     

基于荧光检测的新型细胞传感器

主要介绍了一类基于荧光检测的新型细胞传感器,这类传感器利用免疫细胞表面分子特异性识别、结合抗原的特性和生物(或化学)发光技术,通过检测荧光信号在数分钟内达到检测病原体或其他抗原的目的.这类传感器的发光原理主要是利用钙离子敏感型化学荧光探针发光,如Fluo-4等,或钙离子敏感型发光蛋白发光,如水母发光蛋白、绿色荧光蛋白等.现在已经应用的主要是B细胞传感器和肥大细胞传感器.这类传感器具有灵敏度高、检测准确、反应速度快的优点.同时又存在交叉反应、细胞不易保存等不足之处.这类传感器在疾病诊断、环境监测、生物战剂检测等领域具有较大的应用前景.     

常见生物传感芯片及其应用进展

生物传感芯片是一类综合了生物芯片和生物传感器的优点的新型生物芯片,在保持传统生物芯片的高通量、可寻址、并行处理等特点的基础上,与生物传感器技术相结合,进一步提高了芯片检测的灵敏度和特异性。常见的生物传感芯片主要有光纤传感芯片、表面等离子体共振传感芯片、热生物传感芯片、压电晶体传感芯片等,可用于各种生物大分子,如蛋白质、核酸等的检测,金属离子的测定,病原体的检测,药物筛选等。     

Models of epidemics and endemicity in genetically variable host populations

A discrete time genetics model is developed for populations that are undergoing selection due to infectious disease. It is assumed that the generation time of the host and infectious agent are non-synchronous and that only the host population is evolving. Two classes of epidemic processes are considered. The first class is for infectious agents that confer immunity following infection, while the second class is for those that do not confer immunity. The necessary and sufficient conditions are found in order for the disease to persist in a stable polymorphic host population. These conditions are shown to depend on the density of susceptibles, the selection coefficients, and the severity and class of the disease process.     

Biosensors for the evaluation of lipase activity

In the review a comprehensive analysis is given of instrumental analytical approaches to control the activity of lipolytic enzymes and their substrates. A special attention is attached to the methods based on the biosensor technology. A number of electrochemical, optical and mechanical biosensors that were developed in several laboratories are analyzed in detail. In addition, perspectives are evaluated for the development of these biosensors and their practical application. It was concluded that biosensors may provide all practical demands which are in enzymology field at the express determination of lipase activity and triacylglycerol levels in biological objects.     

One-step construction of biosensor based on chitosan-ionic liquid-horseradish peroxidase biocomposite formed by electrodeposition

A simple and controllable electrodeposition approach was established for one-step construction of hydrogen peroxide (H(2)O(2)) biosensors by in situ formation of chitosan-ionic liquid-horseradish peroxidase (CS-IL-HRP) biocomposite film on electrode surface. A highly porous surface with orderly three-dimensional network was revealed by scanning electron microscopy (SEM) investigation. The biocomposite provided improved conductivity and biocompatible microenvironment. The developed biosensor exhibited a fast amperometric response for the determination of H(2)O(2) and 95% of the steady-state current was obtained within 2s. The linear response of the developed biosensor for the determination of H(2)O(2) ranged from 6.0x10(-7) to 1.6x10(-4)M with a detection limit of 1.5x10(-7)M. Performance of the biosensor was evaluated with respect to possible interferences and a good selectivity was revealed. The fabricated biosensor exhibited high reproducibility and long-time storage stability. The ease of the one-step non-manual technique and the promising feature of biocomposite could serve as a versatile platform for the fabrication of electrochemical biosensors.     

Disposable superoxide anion biosensor based on superoxide dismutase entrapped in silica sol–gel matrix at gold nanoparticles modified ITO electrode

A novel disposable biosensor based on direct electron transfer of superoxide dismutase (SOD) was fabricated for the determination of superoxide anion. The biosensor was constructed by electrodeposition of gold nanoparticles (GNPs) on the indium tin oxide (ITO) electrode and then immobilization of SOD in silica sol–gel (SG) network in the presence of cysteine on GNPs/ITO modified electrode surface. The distribution of GNPs on ITO electrode surface was examined by scanning electron microscopy (SEM). The immobilized SOD exhibited high catalytical activity towards superoxide anion. Parameters affecting the performance of the biosensor were also investigated. A linear calibration curve was obtained over the range from 0.08 to 0.64 μM with a correlation coefficient of 0.9937. The resulted biosensors were demonstrated to possess striking analytical properties for superoxide anion determination, such as high sensitivity, good accuracy, and long-term stability. It provides a promising platform for the fabrication of disposable biosensors.     

A dual biosensor for 2-alkyl-4-quinolone quorum-sensing signal molecules

Pseudomonas, Burkholderia and Alteromonas species produce diverse 2-alkyl-4-quinolones (AHQs) which inhibit the growth of bacteria, algae and phytoplankton, chelate iron, modulate mammalian host immune defences and act as quorum-sensing (QS) signal molecules. To facilitate the detection, identification and quantification of the major Pseudomonas aeruginosa AHQs 2-heptyl-3-hydroxy-4-quinolone (PQS) and 2-heptyl-4-quinolone (HHQ) we developed two different AHQ biosensors. These were constructed by introducing either a lecA::luxCDABE or a pqsA::luxCDABE reporter gene fusion into a P. aeruginosa pqsA mutant which cannot synthesize AHQs. While both biosensors responded similarly to PQS (EC(50) 18 +/- 4 microM), the pqsA::luxCDABE biosensor was most sensitively activated by HHQ (EC(50) 0.44 +/- 0.1 microM). This biosensor was also activated albeit less sensitively by (i) PQS analogues with alkyl chains varying from C1 to C11, (ii) HHQ analogues with C9 and C11 alkyl chains and (iii) 2-heptyl-4-hydroxyquinoline-N-oxide (HHQNO). The AHQ biosensor also responded differentially to the AHQs present in cell free culture supernatants prepared from PAO1 and isogenic strains carrying mutations in genes (pqsA, pqsH, lasR, lasI, rhlR, rhlI) known to influence AHQ production. The AHQ profiles of P. aeruginosa strains was also evaluated by overlaying thin layer chromatogram (TLC) plates with the pqsA::luxCDABE biosensor. In PAO1, three major bioluminescent spots were observed which correspond to PQS, HHQ and a mixture of 2 nonyl-4-quinolone and HHQNO. We also noted that on TLC plates the biosensor not only produced bioluminescence in response to AHQs but also the green pigment, pyocyanin which offers an alternative visual indicator for AHQ production.     

A versatile biosensor device for continuous biomedical monitoring

Although biosensors are by means suitable for continuous biomedical monitoring, due to fouling and blood clotting, in vivo performance is far from optimal. For this reason, ultrafiltration, microdialysis or open tubular flow is frequently used as interface. To secure quantitative recoveries of the analyte of interest, sampling at submicrolitre level will be necessary which in turn necessitates the development of small and versatile biosensor devices. Here, a miniaturised biosensor device, which directly can be connected to various interfaces will be presented. The biosensor device consists of a pulsefree pump and a biosensor with an internal volume of 10–20 nl. In this article, the production as well as the construction of the flow-through cell of the biosensor will be discussed. The advantages and disadvantages of several production processes will be demonstrated and a detailed protocol for the production of such a nanoliter flow-through cell will be presented. With respect to the bio-selector, several permselective membranes have been tested on their performance characteristics. Results obtained with these biosensors will be presented and discussed. Finally, a protocol based upon in situ electropolymerisation for the immobilisation of the biological component was defined and several biosensors based upon this principle have been produced and tested for the monitoring of glucose respectively lactate. To demonstrate, data obtained during a variety of in vivo studies at different clinical relevant applications will be presented.     

A further insight into the biosorption mechanism of Au(III) by infrared spectrometry

Background

Fluorescent protein (FP)-based biosensors based on the principle of intramolecular Förster resonance energy transfer (FRET) enable the visualization of a variety of biochemical events in living cells. The construction of these biosensors requires the genetic insertion of a judiciously chosen molecular recognition element between two distinct hues of FP. When the molecular recognition element interacts with the analyte of interest and undergoes a conformational change, the ratiometric emission of the construct is altered due to a change in the FRET efficiency. The sensitivity of such biosensors is proportional to the change in ratiometric emission, and so there is a pressing need for methods to maximize the ratiometric change of existing biosensor constructs in order to increase the breadth of their utility.

Results

To accelerate the development and optimization of improved FRET-based biosensors, we have developed a method for function-based high-throughput screening of biosensor variants in colonies of Escherichia coli. We have demonstrated this technology by undertaking the optimization of a biosensor for detection of methylation of lysine 27 of histone H3 (H3K27). This effort involved the construction and screening of 3 distinct libraries: a domain library that included several engineered binding domains isolated by phage-display; a lower-resolution linker library; and a higher-resolution linker library.

Conclusion

Application of this library screening methodology led to the identification of an optimized H3K27-trimethylation biosensor that exhibited an emission ratio change (66%) that was 2.3 × improved relative to that of the initially constructed biosensor (29%).     

A reagentless optical biosensor based on the intrinsic absorption properties of peroxidase

During the reversible reaction between peroxidase (HRP) and H(2)O(2), several peroxidase intermediate species, showing different molecular absorption spectra, are formed which can be used for H(2)O(2) determination; when H(2)O(2) is generated in a previous enzymatic reaction, the substrate involved in this reaction can also be determined. On this basis, a new family of fully reversible reagentless optical biosensors containing HRP is presented; glucose determination is used as a model. The biosensor (which can be used for at least 6 months and/or more than 750 measurements) is prepared by HRP and glucose oxidase entrapment in a polyacrylamide gel matrix. A mathematical model (in which optical, kinetic and transport aspects are considered) relating the measured absorbance with the substrate concentration is also presented together with a simple methodology for characterization of this kind of biosensor. Regarding the optical model, the Kubelka-Mulk theory of reflectance does not give good results and the biosensors are better described by the Rayleigh theory of polymer solutions. Under working conditions, linear response ranges from 1.5x10(-6) to 3.0x10(-4)M glucose and CV was about 4%. This biosensor has been applied for glucose determination in fruit juices and synthetic serum samples without sample pretreatment.     

Methyl parathion hydrolase based nanocomposite biosensors for highly sensitive and selective determination of methyl parathion

This article reports the fabrication of a nanocomposite biosensor for the sensitive and specific detection of methyl parathion. The nanocomposite sensing film was prepared via the formation of gold nanoparticles on silica particles, mixing with multiwall carbon nanotubes and subsequent covalent immobilization of methyl parathion hydrolase. The composite of the individual materials was finely tuned to offer the sensing film with high specific surface area and high conductivity. A significant synergistic effect of nanocomposites on the biosensor performance was observed in biosensing methyl parathion. The square wave voltammetric responses displayed well defined peaks, linearly proportional to the concentrations of methyl parathion in the range from 0.001 μg mL?1 to 5.0 μg mL?1 with a detection limit of 0.3 ng mL?1. The application of this biosensor in the analysis of spiked garlic samples was also evaluated. The proposed protocol can be used as a platform for the simple and fast construction of biosensors with good performance for the determination of enzyme-specific electroactive species.