Supramolecular optical sensor arrays for on-site analytical devices

Supramolecular optical chemosensors are useful tools in analytical chemistry for the visualization of molecular recognition information. One advantage is that they can be utilized for array systems to detect multiple analytes. However, chemosensor arrays have been evaluated mainly in the solution phase, which limits a wide range of practical applications. Thus, appropriate solid support materials such as polymer gels and papers are required to broaden the scope of the application of chemosensors as on-site analytical tools. In this review, we summarize the actual approaches for the fabrication of solid-state chemosensor arrays combined with powerful data processing techniques and portable digital recorders for real-world applications.     

New chromogenic and fluorogenic reagents and sensors for neutral and ionic analytes based on covalent bond formation–a review of recent developments

To date, hydrogen bonding and Coulomb, van der Waals and hydrophobic interactions are the major contributors to non-covalent analyte recognition using ionophores, ligands, aptamers and chemosensors. However, this article describes recent developments in the use of (reversible) covalent bond formation to detect analyte molecules, with special focus on optical signal transduction. Several new indicator dyes for analytes such as amines and diamines, amino acids, cyanide, formaldehyde, hydrogen peroxide, organophosphates, nitrogen oxide and nitrite, peptides and proteins, as well as saccharides have become available. New means of converting analyte recognition into optical signals have also been introduced, such as colour changes of chiral nematic layers. This article gives an overview of recent developments and discusses response mechanisms, selectivity and sensitivity.     

Molecular recognition in a supramolecular hydrogel to afford a semi-wet sensor chip

This communication describes a new molecular recognition chip using a semi-wet microenvironment provided by a self-assembled hydrogel. On the basis of the evidence that the molecular recognition capability of artificial chemosensors are practically retained even in the hydrogel compared to those in aqueous solution, we miniaturized the functionalized hydrogel to produce an unprecedented molecular recognition chip. We believe that the present noncovalent immobilization method is generally applicable to many chemosensors, which leads to a unique semi-wet sensor chip suitable to convenient and high-throughput assay to plural analytes.     

Analytical supramolecular chemistry: Colorimetric and fluorimetric chemosensors

Chemical sensing using indicators, or chemosensor, has rapidly developed over the past decades. Its chemistry covers a wide range of scientific fields, in which analytical and supramolecular chemistry are key ideas to create functional and smart chemosensors. The principle of such a chemosensor design consists of three major processes: (1) to separate analytes, (2) to capture a specific analyte from a complex mixture, and (3) to output a signal from a [chemosensor•analyte] complex. In this review, “Analytical Supramolecular Chemistry” as a new scientific area was proposed, enabling us to promote deep insights into the mechanistic understanding of chemosensors. This review describes the interesting and representative chemosensors involving significant photochemical and photophysical processes and recent our advances in analytical supramolecular chemistry.     

Optical colorimetric sensor arrays for chemical and biological analysis

In recent years, the sensor array has attracted much attention in the field of complex system analysis on the basis of its good selectivity and easy operation. Many optical colorimetric sensor arrays are designed to analyze multi-target analytes due to the good sensitivity of optical signal. In this review, we introduce the targeting analytes, sensing mechanisms and data processing methods of the optical colorimetric sensor array based on optical probes (including organic molecular probes, polymer materials and nanomaterials). The research progress in the detection of metal ions, anions, toxic gases, organic compounds, biomolecules and living organisms (such as DNA, amino acids, proteins, microbes and cells) and actual sample mixtures are summarized here. The review illustrates the types, application advantages and development prospects of the optical colorimetric sensor array to help broad readers to understand the research progress in the application of chemical sensor array.     

Chemical sensors based on π-conjugated organic molecules and gold nanoparticles

Scientists have developed techniques for synthesizing and characterizing many new materials including conjugated small molecules, polymers and gold particles protected by conjugated organic chromophores for testing specific sensing properties in the past decade. Still, the design and synthesis or supermolecular systems fabrication of novel materials with controlled sensing properties is a significant and ongoing challenge within nanoscience and nanotechnology. Recently, our group has successfully constructed a series of chemosensors using small organic molecules, conjugated polymers and gold nanoparticles for real-time detection of specific analytes. The chemosensors show high selectivity and sensitivity in the detection of cations and biologic analytes and thus are potentially promising for applications in sensing assay system. In this review, recent sutdies on the design, synthesis and photo-physical properties of novel materials and construct of chemosensors are summarized with an emphasis on the development in our groups in recent years. Supported by the National Natural Science Foundation of China (Grant Nos. 20531060, 20721061 & 20873155), and the National Basic Research 973 Programme of China (Grant No. 2007CB936401)     

Recent progress in fluorescent and colorimetric chemosensors for detection of amino acids

Due to the biological importance of amino acids, the development of optical probes for these molecules has been an active research area in recent years. This tutorial review focuses on recent contributions since the year 2000 concerning the fluorescent or colorimetric sensors for amino acids, and is organized according to their structural classification and reaction types. For reaction based chemosensors, the works are classified according to the mechanisms between sensors and amino acids, including imine formation, Michael addition, thiazinane or thiazolidine formation, cleavage of a sulfonate ester, cleavage of disulfide, metal complexes-displace coordination and others.     

Silica-based optical chemosensors for detection and removal of metal ions

Because some metal ions are highly toxic even at trace level, a constant demand of developing methods for monitoring and removing these metal ions is extremely urgent. Silica-based optical chemosensors are supposed as good alternatives to classical instrumental methods for detecting and adsorbing metal ions, due to their effect and lower price. Silica nanoparticles, silica gel and mesoporous silica are used as supporting platforms to fabricate optical chemosensors. They have certain properties containing high porosity and expectant adsorption capacity. Chromogenic-type and fluorogenic-type optical probes, such as azobenzene, naphthalimide and rhodamine, are grafted to the surface of silica-based materials by sol–gel reaction, the limit of detection, response time and selective properties of optical sensors are improved sequentially. In this paper, the articles of silica-based optical chemosensors are retrospected since 2008, describing silica-based optical sensors used for sensing metal ions. The sensing mechanism, optical phenomenon, detection limit, adsorption capacity and application are also reviewed.     

Thiacalix[4]arene based reconfigurable molecular switches: set-reset memorized sequential device

The fluorescent chemosensors 3, 5 and 7 based on thiacalix[4]arene bearing naphthyl groups have been designed and synthesized. The optical chemosensor 3 based on a thiacalix[4]arene of cone conformation behaves as "turn-on" optical chemosensor for Fe(3+) and F(-) ions. However, chemosensors 5 and 7 based on a thiacalix[4]arene of 1,3-alternate conformation demonstrate "turn-on" optical behaviour for Hg(2+), F(-) ions (with receptor 5 as turn-on for K(+) ions also) and "turn-off" behaviour for Fe(3+) ions. The simultaneous presence of Fe(3+) and Hg(2+) or K(+) or F(-) ions results in formulation of reversible "on-off" switches. Various molecular logic gates developed in response to molecular switching between these chemical inputs have been integrated into sequential logic circuits with memory function in a feedback loop which mimics "set-reset" molecular level information processing device.     

Recent progress on polymer-based fluorescent and colorimetric chemosensors

Recently, fluorescent or colorimetric chemosensors based on polymers have attracted great attention due to several important advantages, such as their simplicity of use, signal amplification, easy fabrication into devices, and combination of different outputs, etc. This tutorial review will cover polymer-based optical chemosensors from 2007 to 2010.     

Excited state intramolecular proton transfer (ESIPT): from principal photophysics to the development of new chromophores and applications in fluorescent molecular probes and luminescent materials

In this perspective we introduce the basic photophysics of the excited-state intramolecular proton transfer (ESIPT) chromophores, then the state-of-the-art development of the ESIPT chromophores and their applications in chemosensors, biological imaging and white-light emitting materials are summarized. Most of the applications of the ESIPT chromophores are based on the photophysics properties, such as design of fluorescent chemosensors by perturbation of the ESIPT process upon interaction with the analytes, their use as biological fluorescent tags to study DNA-protein interaction by probing the variation of the hydration, or design of white-light emitting materials by employing the large Stokes shift of the ESIPT chromophores (to inhibit the F?ster energy transfer of the components). The photophysical mechanism of these applications is discussed. Furthermore, a new research topic concerning the ESIPT chromophores is proposed based on our group's results, that is, to develop organic triplet sensitizers with ESIPT chromophores.     

Direct optical sensors: principles and selected applications

In the field of bio and chemosensors a large number of detection principles has been published within the last decade. These detection principles are based either on the observation of fluorescence-labelled systems or on direct optical detection in the heterogeneous phase. Direct optical detection can be measured by remission (absorption of reflected radiation, opt(r)odes), by measuring micro-refractivity, or measuring interference. In the last case either Mach–Zehnder interferometers or measurement of changes in the physical thickness of the layer (measuring micro-reflectivity) caused, e.g., by swelling effects in polymers (due to interaction with analytes) or in bioassays (due to affinity reactions) also play an important role. Here, an overview of methods of microrefractometric and microreflectometric principles is given and benefits and drawbacks of the various approaches are demonstrated using samples from the chemo and biosensor field. The quality of sensors does not just depend on transduction principles but on the total sensor system defined by this transduction, the sensitive layer, data acquisition electronics, and evaluation software. The intention of this article is, therefore, to demonstrate the essentials of the interaction of these parts within the system, and the focus is on optical sensing using planar transducers, because fibre optical sensors have been reviewed in this journal only recently. Lack of selectivity of chemosensors can be compensated either by the use of sensor arrays or by evaluating time-resolved measurements of analyte/sensitive layer interaction. In both cases chemometrics enables the quantification of analyte mixtures. These data-processing methods have also been successfully applied to antibody/antigen interactions even using cross-reactive antibodies. Because miniaturisation and parallelisation are essential approaches in recent years, some aspects and current trends, especially for bio-applications, will be discussed. Miniaturisation is especially well covered in the literature.     

Pattern‐Based Detection of Toxic Metals in Surface Water with DNA Polyfluorophores

Heavy metal contamination of water can be toxic to humans and wildlife; thus the development of methods to detect this contamination is of high importance. Here we describe the design and application of DNA‐based fluorescent chemosensors on microbeads to differentiate eight toxic metal ions in water. We developed and synthesized four fluorescent 2′‐deoxyribosides of metal‐binding ligands. A tetramer‐length oligodeoxy‐fluoroside (ODF) library of 6561 members was constructed and screened for sequences responsive to metal ions, of which seven sequences were selected. Statistical analysis of the response patterns showed successful differentiation of the analytes at concentrations as low as 100 nM . Sensors were able to classify water samples from 13 varied sites and quantify metal contamination in unknown specimens. The results demonstrate the practical potential of bead‐based ODF chemosensors to analyze heavy metal contamination in water samples by a simple and inexpensive optical method.     

香豆素类荧光传感器

荧光传感器能够将分子识别的信息转换成荧光信号,荧光法在灵敏度、选择性和实时原位检测等方面优势突出。实时检测被分析物的水平已引起包括化学家、生物学家、临床生物化学家和环境学家的极大兴趣。以香豆素为基础的荧光传感器近年来已成为一个新兴的研究热点。本文综述了香豆素类荧光传感器在阳离子、阴离子、中性分子识别检测中的分子设计、作用机理和应用效果,展望了该领域的发展方向。     

Surface modification of natural cellulose substances:toward functional materials and applications

Combining various synthetic chemical processes and biological assemblies provides a promising strategy for the design and fabrication of functional materials with tailored structures and properties.The unique multilevel structures and morphologies of natural cellulose substances such as ordinary commercial laboratory filter paper make them ideal platforms for the self-assemblies of various functional guest molecules that are to be deposited on the surfaces of their fine structures,and the resulting composite matters show significant potentials for various applications.The surface sol-gel process was employed to deposit ultrathin metal-oxide(e.g.,titania and zirconia)gel films to coat the cellulose nanofibers in bulk filter papers;thereafter,monolayers of specific guest substrates were immobilized onto the surfaces of the metal-oxide gel films.Highly selective,sensitive,and reversible chemosensors based on the surface modification of filter paper were obtained toward the fluorescence and colorimetric detection of various analytes such as heavy-metal ions,inorganic anions,amino acids,and gases.Cellulosebased composite materials with superhydrophobic,antibacterial,or luminescent properties were fabricated by self-assembly approaches toward practical applications.     

An indirect approach for anion detection: the displacement strategy and its application

The development of new optical anion chemosensors with high sensitivity and selectivity is very important, since anions possess some fundamental roles in a wide range of biological and chemical processes. The displacement approach is a method using anion binding sites and signaling subunits, which are not covalently attached but forming a coordination complex, in which the presence of anions revives the noncoordinated spectroscopic behavior of the indicator. In the past five years, according to the displacement strategy, many good optical anion chemosensors have been successfully obtained. This paper reviews the recent progress in the field of the fluorescent and colorimetric anion chemosensors designed according to the displacement strategy (mainly from 2008 to 2011), and gives some outlooks for the further exploration of new optical anion chemosensors.     

Fluorescent Chemosensors Based upon Macrocyclic Polyamines Containing Aromatic Sectors

The basicity and the coordination properties of several polyamine macrocycles containing phenanthroline or dipyridine moieties as integral part of the cyclic framework are reported. The ligands behaves as fluorescent chemosensors for both H⁺ and metal ions. The use of such ligands in the preparation of simple molecular machines, of chemosensors for metallo-hexacyanide anions, and of catalysts for photoinduced redoxreactions is also described. The paper is a brief review of recent works performed by the authors.     

Materials‐Based Receptors: Design Principle and Applications

This review focuses on recent developments and growth potential in colorimetric and/or fluorimetric chemosensors based on rationally designed materials and suitable for use in highly selective and sensitive naked‐eye detection of environmental and biological analytes.     

Recent progress in graphene-material-based optical sensors

Graphene material has been widely used for optical sensors owing to its excellent properties, including high-energy transfer efficiency, large surface area, and great biocompatibility. Different analytes such as nucleic acids, proteins, and small molecules can be detected by graphene-material-based optical sensors. This review provides a comprehensive discussion of graphene-material-based optical sensors focusing on detection mechanisms and biosensor designs. Challenges and future perspectives for graphene-material-based optical sensors are also presented.     

Molecular meccano for light-sensitive and light-emitting nanosized systems based on unsaturated and macrocyclic compounds

The review presents the results of the development of an universal approach to the molecular design of light-sensitive and light-emitting nanosized systems with desired properties based on unsaturated and macrocyclic compounds. Within the same class of compounds, various nanosized systems were constructed using a limited number of structural fragments. These nanosized systems are susceptible to all main types of photoprocesses, such as fluorescence, photodissociation, photoisomerization, photocycloaddition, photoelectrocyclization, excimer formation, charge-transfer complex formation, the formation of the twisted intramolecular charge-transfer state (TICT state), and the electron transfer. The use of photostructural transformations for controlling the complexation and mechanical movements in molecular devices and machines is discussed. The prospects of application of the new strategy are exemplified by the design of the previously unknown types of molecular switches, materials for optical chemosensors, optical data recording and storage media, photoswitchable molecular devices, and photocontrolled molecular machines. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1299–1323, July, 2008.