Nanoparticle-based electrochemical detection in conventional and miniaturized systems and their bioanalytical applications: a review

With recent advances in nanotechnology making more easily available the novel chemical and physical properties of metal nanoparticles (NPs), these have become extremely suitable for creating new sensing assays. Many kinds of NPs, including metal, metal-oxide, semiconductor and even composite-metal NPs, have been used for constructing electrochemical sensors. This article reviews the progress of NP-based electrochemical detection in recent applications, especially in bioanalysis, and summarizes the main functions of NPs in conventional and miniaturized systems. All references cited here generally show one or more of the following characteristics: a low detection limit, good signal amplification and simultaneous-detection capabilities.     

Recent advancement on chromo-fluorogenic sensing of aluminum(III) with Schiff bases

The consumption of non-essential aluminum ion (Al³⁺) at higher concentration from biotic and abiotic sources can cause serious adverse effects to the human body. Therefore, there is bourgeoning need of developing facile analytical methods for the on-site and real-time monitoring of Al³⁺ concentration in various environmental and biological samples. The chromo-fluorogenic based sensors have been widely developed in the recent years to detect and monitor Al³⁺ ion. Among the various types of developed chemical sensors, the Schiff bases proved to have several advantages due to their facile synthesis with high yield, fascinating coordination behavior and easy structural modification. This review was narrated to compile the Schiff bases introduced recently for the sensing of Al³⁺ in various environmental and biological samples. The designing of sensor, sensing mechanisms and other analytical novelties of the developed sensors are discussed.     

Advances in nitric oxide-releasing hydrogels for biomedical applications

Hydrogels provide a plethora of advantages to biomedical treatments due to their highly hydrophilic nature and tissue-like mechanical properties. Additionally, the numerous and widespread endogenous roles of nitric oxide have led to an eruption in research developing biomimetic solutions to the many challenges the biomedical world faces. Though many design factors and fabrication details must be considered, utilizing hydrogels as nitric oxide delivery vehicles provides promising materials in several applications. Such applications include cardiovascular therapy, vasodilation and angiogenesis, antimicrobial treatments, wound dressings, and stem cell research. Herein, a recent update on the progress of NO-releasing hydrogels is presented in depth. In addition, considerations for the design and fabrication of hydrogels and specific biomedical applications of nitric oxide-releasing hydrogels are discussed.     

Green fluorescent protein based pH indicators for in vivo use: a review

Green fluorescent protein (GFP) and its variants have been used as fluorescent reporters in a variety of applications for monitoring dynamic processes in cells and organisms, including gene expression, protein localization, and intracellular dynamics. GFP fluorescence is stable, species-independent, and can be monitored noninvasively in living cells by fluorescence microscopy, flow cytometry, or macroscopic imaging techniques. Owing to the presence of a phenol group on the chromophore, most GFP variants display pH-sensitive absorption and fluorescence bands. Such behavior has been exploited to genetically engineer encodable pH indicators for studies of pH regulation within specific intracellular compartments that cannot be probed using conventional pH-sensitive dyes. These pH indicators contributed to shedding light on a number of cell functions for which intracellular pH is an important modulator. In this review we discuss the photophysical properties that make GFPs so special as pH indicators for in vivo use and we describe the probes that are utilized most by the scientific community.     

Patterned surfaces for biological applications: A new platform using two dimensional structures as biomaterials

With the highly interdisciplinary of research and great development of microfabrication techniques, patterned surfaces have attracted great attention of researchers since they possess specific regularity and orderness of structures.In recent years,series of two dimensional patterned structures have been successfully fabricated,and widely used in anti-reflection,anti-fogging,self-cleaning,and sensing,etc.In the meantime,patterned structures have been gradually used in biologically relative fields such as biomaterials,aiming to deepen the perception of organism and understand the vital movements of human body.In this review,we provide a brief introduction on current status of techniques for two dimensional patterns fabrication,the applications of patterned surfaces in biologically related fields,and give out a prospective on the development of these patterned surfaces in the future.     

Challenges in the electrochemical (bio)sensing of nonelectroactive food and environmental contaminants

Electrochemical detection of nonelectroactive contaminants can be successfully faced via the use of indirect detection strategies. These strategies can provide sensitive and selective responses often coupled with portable and user-friendly analytical tools. Indirect detection strategies are usually based on the change in the signal of an electroactive probe, induced by the presence of the target molecule at a modified electrode. This critical review aims at addressing the developments in indirect electrosensing strategies for nonelectroactive contaminants in food and environmental analysis in the last few years. Emphasis is given to the strategy design, the electrode modifiers used and the feasibility of technological transfer.     

Diazonium salts: Stable monolayers on gold electrodes for sensing applications

The modification of gold electrodes with 4-carboxyphenyl diazonium salts to form stable layers for sensing applications is reported. Electrochemical reduction of 4-carboxyphenyl diazonium salts on gold electrodes yielded more stable layers than alkanethiol self-assembled monolayers in terms of extremes of electrode potential, sonication and with time. The application of the 4-carboxyphenyl modified electrodes for electrochemical sensing, which typically requires short chain alkanethiols on gold electrodes, is demonstrated via the covalent attachment of oligopeptides for the selective detection of Cu²⁺, Cd²⁺ and Pb²⁺. The diazonium salt/peptide modified gold electrodes not only had greater stability but also performed with lowest detected concentration to alkanethiol/peptide modified electrodes and with far greater sensitivity than the metal ion sensors when diazonium salt/peptide modified similar glassy carbon electrodes were employed.     

Responsive polymers for analytical applications: A review

Stimuli-responsive polymers are capable of translating changes in their local environment to changes in their chemical and/or physical properties. This ability allows stimuli-responsive polymers to be used for a wide range of applications. In this review, we highlight the analytical applications of stimuli-responsive polymers that have been published over the past few years with a focus on their applications in sensing/biosensing and separations. From this review, we hope to make clear that while the history of using stimuli-responsive polymers for analytical applications is rich, there are still a number of directions to explore and exciting advancements to be made in this flourishing field of research.     

Thin film composite optical waveguides for sensor applications: a review

We review the design and fabrication of thin-film composite optical waveguides (OWG) with high refractive index for sensor applications. A highly sensitive optical sensor device has been developed on the basis of thin-film, composite OWG. The thin-film OWG was deposited onto the surface of a potassium-ion-exchanged (K⁺) glass OWG by sputtering or spin coating (5–9 mm wide, and with tapers at both ends). By allowing an adiabatic transition of the guided light from the secondary OWG to the thin-film OWG, the electric field of the evanescent wave at the thin film was enhanced. The attenuation of the guided light in the thin film layer was small, and the guided light intensity changed sensitively with the refractive index of the cladding layer. Our experimental results demonstrate that thin-film, composite OWG gas sensors or immunosensors are much more sensitive than sensors based on other technologies.     

Polymer-supported calix[4]arenes for sensing and conversion of NO2/N2O4

The use of simple calix[4]arenes 1a,b for NO₂/N₂O₄ sensing and conversion is demonstrated, both in solution and in the solid state. Upon reacting with these gases, compounds 1a,b encapsulate reactive NO⁺ cations within their cavities with the formation of deeply colored (λ_max∼570 nm) charge-transfer complexes 2a,b. Further functionalization of the calix[4]arene platform is reported for attachment to solid supports. Polymer-supported calixarene material 3 was prepared, which reversibly traps NO₂/N₂O₄ with the formation of nitrosonium storing polymer 4. Material 4 was effectively used for nitrosation of amides.     

Recent advances of injectable hydrogels for drug delivery and tissue engineering applications

Injectable hydrogel is a kind of in situ gelling system but has its specificity on the process procedure, which requires a better control of gelation kinetics. Hydrogels with injectability under mild condition are preferred in the field of biomedicine, especially for drug delivery and tissue engineering, because of the favorable carrier property in three-dimension, biocompatibility, low invasive and adaptable shape for administration. Despite the advantages, the development of injectable hydrogels may also face some challenges to meet the various clinical requirements. In this review, we provide a brief summary on the recent progresses on the design, synthesis and evaluation of injectable hydrogels towards biomedical applications.     

Molecularly imprinted polymer based enantioselective sensing devices: A review

Chiral recognition is the fundamental property of many biological molecules and is a quite important field in pharmaceutical analysis because of the pharmacologically different activities of enantiomers in living systems. Enantio-differentiating signal of the sensor requires specific interaction between the chiral compounds (one or a mixture of enantiomers) in question and the selector. This type of interaction is controlled normally by at least three binding centers, whose mutual arrangement and interacting characteristics with one of the enantiomers effectively control the selectivity of recognition. Molecular imprinting technology provides a unique opportunity for the creation of three-dimensional cavities with tailored recognition properties. Over the past decade, this field has expanded considerably across the variety of disciplines, leading to novel transduction approaches and many potential applications. The state-of-art of molecularly imprinted polymer-based chiral recognition might set an exotic trend toward the development of chiral sensors. The objective of this review is to provide comprehensive knowledge and information to all researchers who are interested in exploiting molecular imprinting technology toward the rational design of chiral sensors operating on different transduction principles, ranging from electrochemical to piezoelectric, being used for the detection of chiral compounds as they pose significant impact on the understanding of the origin of life and all processes that occur in living organisms.     

Recent developments in the field of screen-printed electrodes and their related applications

The development of analytical methods that respond to the growing need to perform rapid ‘in situ’ analyses shows disposable screen-printed electrodes (SPEs) as an alternative to the traditional electrodes. This review presents recent developments in the electrochemical application of disposable screen-printed sensors, according to the types of materials used to modify the working electrode. Therefore, unmodified SPE, film-modified SPE, enzyme-modified SPE and antigen/antibody-modified SPE are described. Applications are included where available.     

Electrochemical Sensors,a Bright Future in the Fabrication of Portable Kits in Analytical Systems

Analysis of food, pharmaceutical, and environmental compounds is an inevitable issue to evaluate quality of the compounds used in human life. Quality of drinking water, food products, and pharmaceutical compounds is directly associated with human health. Presence of forbidden additives in food products, toxic compounds in water samples and drugs with low quality lead to important problems for human health. Therefore, attention to analytical strategy for investigation of quality of food, pharmaceutical, and environmental compounds and monitoring presence of forbidden compounds in materials used by humans has increased in recent years. Analytical methods help to identify and quantify both permissible and unauthorized compounds present in the materials used in human daily life. Among analytical methods, electrochemical methods have been shown to have more advantages compared to other analytical methods due to their portability and low cost. Most of big companies have applied this type of analytical methods because of their fast and selective analysis. Due to simple operation and high diversity of electroanalytical sensors, these types of sensors are expected to be the future generation of analytical systems. Therefore, many scientists and researchers have focused on designing and fabrication of electroanalytical sensors with good selectivity and high sensitivity for different types of compounds such as drugs, food, and environmental pollutants. In this paper, we described the mechanism and different examples of DNA, enzymatic and electro‐catalytic methods for electroanalytical determination of drug, food and environmental compounds.     

Ion-selective potentiometric sensors with silicone sensing membranes: A review

Ion-selective electrodes (ISEs) are used widely in mainframe analyzers for clinical chemistry, but there is also an increasing interest in the development of paper-based devices, wearable and implantable sensors, and other miniaturized ISEs. This trend is spurring much research in developing solid contact materials that enable miniaturization. The development of suitable polymeric matrixes for such sensors has only received less attention. In particular, in spite of lifetime limitations and toxicity concerns, polymeric matrixes comprising plasticizers are still commonly used. To that end, we note the benefits of silicone materials as alternative polymeric matrixes and, in particular, their promise for enhanced biocompatibility. While there has been steady progress in the development of ISEs with silicone membranes, this topic has not been reviewed for many years. This review critically discusses key fundamental characteristics of ISEs with silicone sensing and reference membranes, including their biocompatibility, adhesion to device substrates, water uptake, polarity, common impurities, and commercial availabilities. This is followed by a discussion of specific types of silicones and their use in ISEs, with the goal to inform and stimulate future research efforts into such devices.     

Chiral recognition applications of molecularly imprinted polymers: a critical review

Molecular imprinting technology offers the unique opportunity to tailor chiral stationary phases with predefined chiral recognition properties by employing the enantiomers of interest as binding-site-forming templates. Added advantages, such as ease of preparation, chemical robustness, low-cost production, and the possibility of shaping molecularly imprinted polymers (MIPs) in various self-supporting formats, render them attractive materials for a broad range of chiral recognition applications. In this review a critical overview on recent developments in the field of MIP-based chiral recognition applications is given, focusing on separation techniques and molecular sensing. Inherent limitations associated with the use of enantioselective MIP materials in high-performance separation techniques are outlined, including binding site heterogeneity and slow mass transfer characteristics. The prospects of MIP materials as versatile recognition elements for the design of enantioselective sensor systems are highlighted.     

Molecularly engineered graphene surfaces for sensing applications: A review

Graphene is scientifically and commercially important because of its unique molecular structure which is monoatomic in thickness, rigorously two-dimensional and highly conjugated. Consequently, graphene exhibits exceptional electrical, optical, thermal and mechanical properties. Herein, we critically discuss the surface modification of graphene, the specific advantages that graphene-based materials can provide over other materials in sensor research and their related chemical and electrochemical properties. Furthermore, we describe the latest developments in the use of these materials for sensing technology, including chemical sensors and biosensors and their applications in security, environmental safety and diseases detection and diagnosis.     

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.