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.     

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.     

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.