Biosensors for environmental monitoring of endocrine disruptors: a review article

This article provides an overview of the applications of biosensors in analysis and monitoring of endocrine-disrupting compounds (EDCs) in the environment. Special attention is devoted to the various types of physical-chemical signal transduction elements, biological mechanisms employed as sensing elements and techniques used for immobilisation of the bioreceptor molecules on the transducer surface. Two different classes of biosensors for EDCs are considered: biosensors that measure endocrine-disrupting effects, and biosensors that respond to the presence of a specific substance (or group of substances) based on the specific recognition of a biomolecule. Several examples of them are presented to illustrate the power of the biosensor technology for environmental applications. Future trends in the development of new, more advanced devices are also outlined.     

pH-Induced Difference Spectrophotometry in the Analysis of Binary Mixtures.

Abstract

A concise overview of selected literature concerning biosensors based on surface plasmon resonance and acoustic wave technologies is presented. A comparison in terms of their performance and potential advances in the bioanalytical field is discussed. This Mini-Review highlights the generally underrecognized potential of acoustic wave technology, in the field of biosensors relative to plasmon resonance, and focuses on stimulating not only the development of acoustic wave biosensors but also a broader and increased use of them. These sensors are anticipated to play a central role in biodetection in the near future.     

Towards Maintenance‐Free Biosensors for Hundreds of Bind/Release Cycles

A single aptamer bioreceptor layer was formed using a common streptavidin–biotin immobilization strategy and employed for 100–365 bind/release cycles. Chemically induced aptamer unfolding and release of its bound target was accomplished using alkaline solutions with high salt concentrations or deionized (DI) water. The use of DI water scavenged from the ambient atmosphere represents a first step towards maintenance‐free biosensors that do not require the storage of liquid reagents. The aptamer binding affinity was determined by surface plasmon resonance and found to be almost constant over 100–365 bind/release cycles with a variation of less than 5 % relative standard deviation. This reversible operation of biosensors based on immobilized aptamers without storage of liquid reagents introduces a conceptually new perspective in biosensing. Such new biosensing capability will be important for distributed sensor networks, sensors in resource‐limited settings, and wearable sensor applications.     

Atomic force microscopy for the characterization of immobilized enzyme molecules on biosensor surfaces

The development of biosensors has been one of the key areas in biotechnology and biomedical studies. Often it is difficult to investigate the immobilized biomolecules on the surfaces for biosensor optimization. Atomic force microscopy (AFM) should provide an ideal means for the visualization of biosensor surface and for the investigation of biomolecule activities. Therefore, AFM has been employed to study the surface topography of immobilized glutamate dehydrogenase (GDH) on two-dimensional glutamate biosensor surfaces. Correlation between the surface topography and the activity of the biosensor was investigated. Surface analysis has revealed that the enzymatic activity of the immobilized GDH molecules on the biosensor surface is linked to surface roughness, as measured by the peak-to-valley distance. Fractal dimension of the immobilization sensor surface was found to be a good parameter for judging the quality of the immobilized biosensors. As enzyme immobilization time increases, the biosensor has its maximum activity with around 18 h of immobilization in 10(-6) M GDH solution. Various biosensors prepared under different experimental conditions have been studied by AFM. This technique is shown to be an effective tool to characterize biosensor surfaces.     

Atomic force microscopy for the characterization of immobilized enzyme molecules on biosensor surfaces

The development of biosensors has been one of the key areas in biotechnology and biomedical studies. Often it is difficult to investigate the immobilized biomolecules on the surfaces for biosensor optimization. Atomic force microscopy (AFM) should provide an ideal means for the visualization of biosensor surface and for the investigation of biomolecule activities. Therefore, AFM has been employed to study the surface topography of immobilized glutamate dehydrogenase (GDH) on two-dimensional glutamate biosensor surfaces. Correlation between the surface topography and the activity of the biosensor was investigated. Surface analysis has revealed that the enzymatic activity of the immobilized GDH molecules on the biosensor surface is linked to surface roughness, as measured by the peak-to-valley distance. Fractal dimension of the immobilization sensor surface was found to be a good parameter for judging the quality of the immobilized biosensors. As enzyme immobilization time increases, the biosensor has its maximum activity with around 18 h of immobilization in 10^–6 M GDH solution. Various biosensors prepared under different experimental conditions have been studied by AFM. This technique is shown to be an effective tool to characterize biosensor surfaces.     

Chemical surface modifications for the development of silicon-based label-free integrated optical (IO) biosensors: A review

Increasing interest has been paid to label-free biosensors in recent years. Among them, refractive index (RI) optical biosensors enable high density and the chip-scale integration of optical components. This makes them more appealing to help develop lab-on-a-chip devices. Today, many RI integrated optical (IO) devices are made using silicon-based materials. A key issue in their development is the biofunctionalization of sensing surfaces because they provide a specific, sensitive response to the analyte of interest. This review critically discusses the biofunctionalization procedures, assay formats and characterization techniques employed in setting up IO biosensors. In addition, it provides the most relevant results obtained from using these devices for real sample biosensing. Finally, an overview of the most promising future developments in the fields of chemical surface modification and capture agent attachment for IO biosensors follows.     

Label-Free Impedance Biosensors: Opportunities and Challenges

Impedance biosensors are a class of electrical biosensors that show promise for point-of-care and other applications due to low cost, ease of miniaturization, and label-free operation. Unlabeled DNA and protein targets can be detected by monitoring changes in surface impedance when a target molecule binds to an immobilized probe. The affinity capture step leads to challenges shared by all label-free affinity biosensors; these challenges are discussed along with others unique to impedance readout. Various possible mechanisms for impedance change upon target binding are discussed. We critically summarize accomplishments of past label-free impedance biosensors and identify areas for future research.     

Optical chemical biosensors for high-throughput screening of drugs

Optical biosensors have been commercially available since the early 1990s, and have been used extensively in many areas of research in the life sciences. Optical biosensors developed for drug analysis generally exploit the high selectivity of the antigen-antibody and drug-protein interaction. Optical biosensors can be made based on optical diffraction or electro-chemiluminescence. High-throughput screening, (HTS) which includes automated preparation of a large number of samples and then screening of their properties in multi-well plates, improves the efficiency of research in many scientific areas, e.g., catalyst screening, food processing, chemical synthesis, drug discovery, absorption, distribution, metabolism, and excretion and toxicological and cell based screening. The three most common detection techniques used in HTS are UV-VIS absorbance, fluorescence and luminescence. In this review, we summarize some recent trends and developments in the construction of optical chemical biosensors used in high-throughput screening of drugs. Also, we have included environmental, biological and other medical applications of biosensors.     

A Review on Synthesis and Characterization of Nanostructured Conducting Polymers (NSCP) and Application in Biosensors

The development of nanostructured conducting polymers has opened up novel fundamental and applied frontiers. The present article reviews recent works dealing with synthesis, characterization of nanostructured conducting polymers, and their applications related to biosensors. Various synthesis strategies, mechanism and process parameters, along with their characterization techniques are discussed. Some potential areas for biosensor related applications of nanostructured conducting polymers are highlighted, including catalytic biosensors and bioaffinity biosensors.     

Nanoanalytical measurement of protein orientation on conductive sensor surfaces

The control of protein immobilisation and orientation at surfaces is of increasing relevance in biotechnological devices. These devices include reproducible biosensors, biofuel cells, and protein arrays, all of which require the immobilisation of protein/enzymatic sensing elements with retention of their activity. The control of protein orientation upon immobilisation is of importance in (1) facilitating equal access of analyte molecules to the protein that acts as a sensing element and (2) creating favourable interactions to stabilise the protein on the surface for long-term storage and usage of bio-devices. This review presents a comparison of a number of surface analysis techniques that have been widely used in the chemical analysis of surfaces that offer the potential to discriminate different orientations of the same protein on a conductive surface.     

Application of surface plasmon resonance for the detection of carbohydrates,glycoconjugates, and measurement of the carbohydrate-specific interactions: A comparison with conventional analytical techniques. A critical review

Carbohydrates (glycans) and their conjugates with proteins and lipids contribute significantly to many biological processes. That makes these compounds important targets to be detected, monitored and identified. The identification of the carbohydrate content in their conjugates with proteins and lipids (glycoforms) is often a challenging task. Most of the conventional instrumental analytical techniques are time-consuming and require tedious sample pretreatment and utilising various labeling agents. Surface plasmon resonance (SPR) has been intensively developed during last two decades and has received the increasing attention for different applications, from the real-time monitoring of affinity bindings to biosensors. SPR does not require any labels and is capable of direct measurement of biospecific interaction occurring on the sensing surface. This review provides a critical comparison of modern analytical instrumental techniques with SPR in terms of their analytical capabilities to detect carbohydrates, their conjugates with proteins and lipids and to study the carbohydrate-specific bindings. A few selected examples of the SPR approaches developed during 2004–2011 for the biosensing of glycoforms and for glycan–protein affinity studies are comprehensively discussed.     

Piezoelectric crystal/surface acoustic wave biosensors based on fullerene C60 and enzymes/antibodies/proteins

The development of piezoelectric (PZ) quartz crystal and surface acoustic wave (SAW) biosensors based on fullerene C60 and immobilized C60-enzymes/antibodies/proteins for the detection of various biological species are reported. The C60 coated piezoelectric crystal sensors can be applied to the study of interactions between fullerene C60 and some biological species, such as enzymes, antibodies, proteins and heparin. The partial irreversible responses for some biospecies from C60 molecules were observed by the desorption study which implied that C60 could chemically react with these biological species. Thus, immobilized biological species, e.g. C60-GOD, C60-catalase, C60-urease, C60-lipase, C60-anti IgG, C60-heparin, C60-Hb, C60-Mb and C60-anti-Hb were successfully prepared. The immobilized C60-GOD, C60-catalase, C60-urease, C60-anti-IgG and C60-anti-Hb were employed as adsorbents onto quartz crystal of various piezoelectric biosensors to detect glucose, H₂O₂, urea, IgG, and hemoglobin respectively. The immobilized C60-lipase was applied to distinguishably catalyze the hydrolysis of some optical isomers such as L- and D-phenyalanine methyl ester and to determine these optical isomers. The immobilized C60-heparin was employed as a good inhibitor for blood clotting like solvated heparin. The H₂O₂ bio-sensor was set up with the immobilized C60-catalase to detect oxygen, the product of the hydrolysis of H₂O₂ by C60-catalase. The immobilized C60-GOD enzyme piezoelectric glucose sensor exhibited a good sensitivity and a good lower limit for glucose. A piezoelectric crystal urea biosensor based on immobilized C60-urease was also prepared to detect urea. Comparison between solvated and immobilized enzymes used for biosensors was also made. The C60-anti IgG or C60-anti-Hb coated IgG piezoelectric crystal sensors exhibited good sensitivity, selectivity and repeatability for IgG or hemoglobin. Fullerene C60-Hb and C60-myoglobin (C60-Mb) coated surface acoustic wave (SAW) immunosensors were prepared to detect the anti-hemoglobin (anti-Hb) and anti-myoglobin (anti-Mb) antibody, respectively. An electrochemical SAW (ESAW) detection system was also developed to detect glucose in aqueous solutions.     

Progress in Enzyme-Based Biosensors Using Optical Transducers

Enzyme-based biosensors are well developed and relatively mature technique in the biosensing field. Biosensors that utilise enzymes as the recognition elements represent the most extensively studied area. The organisation of an enzyme-based biosensor requires the integration of the biocatalyst with the support or immobilised materials to the extent that the biocatalytic transformation is either optically or electronically transduced. Any optical or electrical changes at the support material as a result of the biocatalytic process, that is, depletion of the reactant or formation of the product, provide routes for the opto/electronic transduction of the biological process occurring at the sensing surface. This review focuses on the discussion of some enzyme immobilisation techniques including physical and chemical immobilisation. Enzyme-based biosensors using various optical detection methods such as absorptiometry, luminometry, chemiluminescence, evanescent wave, and surface plasmon resonance are also included. Finally, different types of enzyme-based optical biosensors for ascorbic acid, bilirubin, cholesterol, choline, ethanol, glucose, glutamate/glutamine, lactate, penicillin, urea, and uric acid determinations are presented.On sabbatical leave at The University of North Carolina at Chapel Hill in July 2004–July 2005     

Akustische Rastermikroskopie als Methode zur Oberfl?chenuntersuchung

Summary Techniques of scanning acoustic microscopy generally rely on local variations of such solid state parameters influencing generation or propagation of acoustic waves. Depending on the manner of impressing acoustic waves into the sample various methods are distinguished. In conventional scanning acoustic microscopy ultrasound is generated by a lens-transducer arrangement outside the sample and focussed onto or below its surface. Changes in the propagation of this ultrasound wave, like absorption and reflexion or temporal propagation delays, enable analysis of the mechanical or elastic response. At very high frequencies and with additional time-resolving detection techniques applications of this technique to surface analysis become possible. Other scanning acoustic microscopes imply the generation of sound or ultrasound directly within the sample itself due to the impact of temporarily modulated particle or photon beams. These are presently laser, electron, or ion beams. With these methods the acoustic signal as detected by a transducer attached to the sample is on principle affected by propagation properties, too, but it is dominated by local changes of the generation process for the acoustic wave, mainly because the frequency ranges used presently are associated with very long acoustic wavelengths. Depending on the physical nature of the primary probe used many sound generation mechanisms are given resulting in a large amount of different applications. By adjusting the probe parameters in a suitable manner the sound generation process can be confined to the direct vicinity of the specimen surface, which makes this technique feasible for surface characterization. The principles of the various techniques are described, and their usability for surface analysis is discussed.     

Enzyme stabilization strategies based on electrolytes and polyelectrolytes for biosensor applications

The achievements in the area of enzyme stabilization based on electrolytes, polyelectrolytes and polyols is reviewed, in the context of biosensor applications. Both the storage and operational stabilities of the biosensors can be improved using these stabilizers. The deactivation of the enzymes used for the development of biosensors from thermal shock, proteolytic degradation, and non-specific metal-catalyzed oxidation can be drastically reduced with the use of one or more of these stabilizers. It is attempted to deconvolute the effect of these additives on (a) the storage stability or shelf life, and (b) the operational stabilities of the biosensors. Even though there are a large number of techniques and reports dealing with enzyme stabilization, their application to biosensor technology is still very limited. It is thus concluded that the use of the existing enzyme stabilization techniques will have a drastic effect on the storage and operational stabilities of biosensors in the near future.     

Amperometric biosensors based on electrosynthesised polymeric films

The most significant goals achieved in the course of the last decade in the design of amperometric biosensors based on redox enzymes entrapped in electrosynthesised polymeric films are reviewed. Particular emphasis is devoted to non-conducting polymers with built-in permselectivity that revealed very promising materials for designing fast-response and interference-free, H2O2 detecting, amperometric biosensors. The role of surface analytical techniques to provide structural information allowing a better understanding of polymers properties and their relationship with the ultimate performance of the final device is also outlined. The most relevant applications of amperometric biosensors based on electropolymerised films to real samples analysis are also reviewed and some possible future trends highlighted.     

Recent developments, characteristics, and potential applications of electrochemical biosensors.

The objective of this study is to analyze the technical importance, performance, techniques, advantages, and disadvantages of the biosensors in general and of the electrochemical biosensors in particular. A product of reaction diffuses to the transducer in the first generation biosensors (based on Clark biosensors). The mediated biosensors or second generation biosensors use specific mediators between the reaction and the transducer to improve sensitivity. The second generation biosensors involve two steps: first, there is a redox reaction between enzyme and substrate that is reoxidized by the mediator, and eventually the mediator is oxidized by the electrode. No normal product or mediator diffusion is directly involved in the third generation biosensors, direct biosensors. Based on the type of transducer, current biosensors are divided into optical, mass, thermal, and electrochemical sensors. They are used in medical diagnostics, food quality controls, environmental monitoring, and other applications. These biosensors are also grouped under two broad categories of sensors: direct and indirect detection systems. Moreover, these systems could be further grouped into continuous or batch operation. Therefore, amperometric biosensors and their current applications are focused on more in detail since they are the most commonly used biosensors in monitoring and diagnosing tests in clinical analysis. Problems related to the commercialization of medical, environmental, and industrial biosensors as well as their performance characteristics, their competitiveness in comparison to the conventional analytical tools, and their costs determine the future development of these biosensors.     

电化学DNA生物传感器*

对特异DNA序列的检测在基因相关疾病的诊断、军事反恐和环境监测等方面均具有非常重要的意义,DNA传感器的研究就是为了满足对特异DNA序列的快速、便捷、高灵敏度和高选择性检测的需要。近年来涌现出了多种传感策略,根据检测方法的不同可以大致分为光学传感器、电化学传感器、声学传感器等。由于电化学检测方法本身所具有的灵敏、快速、低成本和低能耗等特点,电化学DNA传感器已成为一个非常活跃的研究领域并在近几年中得到了快速发展。本文概括了近年来在DNA传感器的重要分支——电化学DNA传感器领域内的一些重要进展,主要包括DNA探针在传感界面上的固定方法和各种电化学DNA杂交信号的检测方法。     

Present and future of surface plasmon resonance biosensors

Surface plasmon resonance (SPR) biosensors are optical sensors exploiting special electromagnetic waves—surface plasmon-polaritons—to probe interactions between an analyte in solution and a biomolecular recognition element immobilized on the SPR sensor surface. Major application areas include detection of biological analytes and analysis of biomolecular interactions where SPR biosensors provide benefits of label-free real-time analytical technology. This paper reviews fundamentals of SPR affinity biosensors and discusses recent advances in development and applications of SPR biosensors.