Luminescence-Based Optical Sensors Fabricated by Means of the Layer-by-Layer Nano-Assembly Technique

Covalent Organic Polymers and Frameworks for Fluorescence-Based Sensors

Following the advancements and diversification in synthetic strategies for porous covalent materials in the literature, the materials science community started to investigate the performance of covalent organic polymers (COPs) and covalent organic frameworks (COFs) in applications that require large surface areas for interaction with other molecules, chemical stability, and insolubility. Sensorics is an area where COPs and COFs have demonstrated immense potential and achieved high levels of sensitivity and selectivity on account of their tunable structures. In this review, we focus on those covalent polymeric systems that use fluorescence spectroscopy as a method of detection. After briefly reviewing the physical basis of fluorescence-based sensors, we delve into various kinds of analytes that have been explored with COPs and COFs, namely, heavy metal ions, explosives, biological molecules, amines, pH, volatile organic compounds and solvents, iodine, enantiomers, gases, and anions. Throughout this work, we discuss the mechanisms involved in each sensing application and aim to quantify the potency of the discussed sensors by providing limits of detection and quenching constants when available. This review concludes with a summary of the surveyed literature and raises a few concerns that should be addressed in the future development of COP and COF fluorescence-based sensors.

Classification of analytics, sensorics, and bioanalytics with polyelectrolyte multilayer capsules

Polyelectrolyte multilayer (PEM) capsules, constructed by LbL (layer-by-layer)-adsorbing polymers on sacrificial templates, have become important carriers due to multifunctionality of materials adsorbed on their surface or encapsulated into their interior. They have been also been used broadly used as analytical tools. Chronologically and traditionally, chemical analytics has been developed first, which has long been synonymous with all analytics. But it is not the only development. To the best of our knowledge, a summary of all advances including their classification is not available to date. Here, we classify analytics, sensorics, and biosensorics functionalities implemented with polyelectrolyte multilayer capsules and coated particles according to the respective stimuli and application areas. In this classification, three distinct categories are identified: (I) chemical analytics (pH; K⁺, Na⁺, and Pb²⁺ ion; oxygen; and hydrogen peroxide sensors and chemical sensing with surface-enhanced Raman scattering (SERS)); (II) physical sensorics (temperature, mechanical properties and forces, and osmotic pressure); and (III) biosensorics and bioanalytics (fluorescence, glucose, urea, and protease biosensing and theranostics). In addition to this classification, we discuss also principles of detection using the above-mentioned stimuli. These application areas are expected to grow further, but the classification provided here should help (a) to realize the wealth of already available analytical and bioanalytical tools developed with capsules using inputs of chemical, physical, and biological stimuli and (b) to position future developments in their respective fields according to employed stimuli and application areas. Graphical abstract.

Are plasmonic optical biosensors ready for use in point-of-need applications?

Plasmonics has drawn significant attention in the area of biosensors for decades due to the unique optical properties of plasmonic resonant nanostructures. While the sensitivity and specificity of molecular detection relies significantly on the resonance conditions, significant attention has been dedicated to the design, fabrication, and optimization of plasmonic substrates. The adequate choice of materials, structures, and functionality goes hand in hand with a fundamental understanding of plasmonics to enable the development of practical biosensors that can be deployed in real life situations. Here we provide a brief review of plasmonic biosensors detailing most recent developments and applications. Besides metals, novel plasmonic materials such as graphene are highlighted. Sensors based on Surface Plasmon Resonance (SPR), Localized Surface Plasmon Resonance (LSPR), and Surface Enhanced Raman Spectroscopy (SERS) are presented and classified based on their materials and structure. In addition, most recent applications to environment monitoring, health diagnosis, and food safety are presented. Potential problems related to the implementation in such applications are discussed and an outlook is presented.

Optical and electrochemical-based nano-aptasensing approaches for the detection of circulating tumor cells (CTCs)

More recently, detection of circulating tumor cells (CTCs) has been considered as an appealing prognostic and diagnostic approach for cancer patients. CTCs as a type of tumor-derived cells are secreted by the tumor and released into the blood circulation. Since the migration of CTCs is an early event in cancer progression, patients who still have tumor-free lymph nodes have to be well examined for the CTCs presence in their blood circulation. Nowadays, there is a broad range of detection methods available to identify CTCs. As artificial RNA oligonucleotides or single-stranded DNA with receptor and catalytic characteristics, aptamers have been standing out, owing to their target-induced conformational modifications, elevated stability, and target specificity to be implemented in biosensing techniques. To date, several sensitivity-enhancement methods alongside smart nanomaterials have been used for the creation of new aptasensors to address the limit of detection (LOD), and improve the sensitivity of numerous analyte identification methods. The present review article supports a focused overview of the recent studies in the identification and quantitative determination of CTCs by aptamer-based biosensors and nanobiosensors.

Review on Nanomaterial-Based Melamine Detection

Illegal adulteration of milk products by melamine and its analogs has become a threat to the world. In 2008, the misuse of melamine with infant formula caused serious effects on babies of China. Thereafter, the government of China and the US Food and Drug Administration (FDA) limited the use of melamine of 1 mg/kg for infant formula and 2.5 mg/kg for other dairy products. Similarly, the World Health Organization (WHO) has also limited the daily intake of melamine of 0.2 mg/kg body weight per day. Many sensory schemes have been proposed by the scientists for carrying out screening on melamine poisoning. Among them, nanomaterial-based sensing techniques are very promising in terms of real-time applicability. These materials uncover and quantify the melamine by means of diverse mechanisms, such as fluorescence resonance energy transfer (FRET), aggregation, inner filter effect, surface-enhanced Raman scattering (SERS), and self-assembly, etc. Nanomaterials used for the melamine determination include carbon dots, quantum dots, nanocomposites, nanocrystals, nanoclusters, nanoparticles, nanorods, nanowires, and nanotubes. In this review, we summarize and comment on the melamine sensing abilities of these nanomaterials for their suitability and future research directions.

Nanoarchitectonic-Based Material Platforms for Environmental and Bioprocessing Applications

The challenges of pollution, environmental science, and energy consumption have become global issues of broad societal importance. In order to address these challenges, novel functional systems and advanced materials are needed to achieve high efficiency, low emission, and environmentally friendly performance. A promising approach involves nanostructure-level controls of functional material design through a novel concept, nanoarchitectonics. In this account article, we summarize nanoarchitectonic approaches to create nanoscale platform structures that are potentially useful for environmentally green and bioprocessing applications. The introduced platforms are roughly classified into (i) membrane platforms and (ii) nanostructured platforms. The examples are discussed together with the relevant chemical processes, environmental sensing, bio-related interaction analyses, materials for environmental remediation, non-precious metal catalysts, and facile separation for biomedical uses.

Optical Fiber Sensors Based on Polymeric Sensitive Coatings

Polymer technology is one of the fastest growing fields of contemporary research due to the possibility of using a wide variety of synthetic chemical routes for obtaining a polymeric network with a well-defined structure, resulting in materials with outstanding macroscopic properties. Surface engineering techniques based on the implementation of polymeric structures can be used as an interesting tool for the design of materials with functional properties. In this sense, the use of fabrication techniques for the design of nanostructured polymeric coatings is showing an important growth due to the intrinsic advantages of controlling the structure at a nanoscale level because physical, chemical, or optical properties can be considerably improved in comparison with the bulk materials. In addition, the presence of these sensitive polymeric coatings on optical fiber is a hot topic in the scientific community for its implementation in different market niches because a wide variety of parameters can be perfectly measured with a high selectivity, sensitivity, and fast response time. In this work, the two main roles that a polymeric sensitive matrix can play on an optical fiber for sensing applications are evaluated. In a first section, the polymers are used as a solid support for the immobilization of specific sensitive element, whereas in the second section the polymeric matrix is used as the chemical transducer itself. Additionally, potential applications of the optical fiber sensors in fields as diverse as biology, chemistry, engineering, environmental, industry or medicine will be presented in concordance with these two main roles of the polymeric sensitive matrices.