Organic fluorophores-based molecular probes with dual-fluorescence ratiometric responses to in-vitro/in-vivo pH for biosensing, bioimaging and biotherapeutics applications

In recent years, organic fluorophores-based molecular probes with dual-fluorescence ratiometric responses to in-vitro/in-vivo pH (DFR-MPs-pH) have been attracting much interest in fundamental application research fields. More and more scientific publications have reported the exploration of various DFR-MPs-pH systems that have unique dual-fluorescence ratiometry as the signal output, in-built and signal self-calibration functions to improve precise detection of targets. DFR-MPs-pH systems possess high-performance applications in biosensing, bioimaging and biomedicine fields. This review has comprehensively summarized recent advances of DFR-MPs-pH for the first time. First of all, the compositions and types of DFR-MPs-pH are introduced by summarizing different organic fluorophores-based molecule systems. Then, construction strategies are analyzed based on specific components, structures, properties and functions of DFR-MPs-pH. Afterward, biosensing and bioimaging applications are discussed in detail, primarily referring to pH sensing and imaging detection at the levels of living cells and small animals. Finally, biomedicine applications are fully summarized, majorly involving bio-toxicity evaluation, bio-distribution, biomedical diagnosis and therapeutics. Meanwhile, the current status, challenges and perspectives are rationally commented after detailed discussions of representative and state-of-the-art studies. Overall, this present review is comprehensive, in-time and in-depth, and can facilitate the following further exploration of new and versatile DFR-MPs-pH systems toward rational design, facile preparation, superior properties, adjustable functions and highly efficient applications in promising fields.

Dual Optical Nanosensor Based on Ormosil Nanoparticles for Monitoring O2 and pH

Monitoring O₂ and pH has excellent potential in different sensing applications, especially in biological and clinical applications. This report presents a protocol for synthesizing an optical dual nanosensor for those two parameters. The organically modified silica (ormosil) nanoparticles were prepared based on phenytrimethoxysilane in an aqueous solution using an acid-base one-pot strategy. Ormosil was selected as a lipophilic matrix for loading fluorescent O₂-sensitive dye platinum(II)-tetrakis-(pentafluorophenyl) porphyrin (Pt-TPFPP), which was quenched in the presence of O₂ gas and exhibited a considerable detection proficiency within a percentage range of (0-100%) O₂. Commercially available drug ingredient salicylamide was labeled on the surface of the nanoparticles using a coupling agent (3-glycidoxypropyl) trimethoxysilane (GPTMS). For measuring pH, salicylamide acted for the first time as a pH-sensitive probe based on a turn-on process with increasing pH. The nanosensor displayed a significant pH detection efficiency in the range of (pH = 6-10). Salicylamide turn-on fluorescence was attributed to the excited state intramolecular transfer (ESIPT) process followed by the inter charge transfer (ICT). The presented dual nanosensor opens new opportunities as a promising candidate material for industrial systems and medical applications.

Uniquely sized nanogels via crosslinking polymerization

Nanogels are very promising carriers for nanomedicine, as they can be prepared in the favorable nanometer size regime, can be functionalized with targeting agents and are responsive to stimuli, i.e. temperature and pH. This induces shrinking or swelling, resulting in controlled release of a therapeutic cargo. Our interest lies in the controlled synthesis of functional nanogels, such as those containing epoxide moieties, that can be subsequently functionalized. Co-polymerization of glycidyl methacrylate and a bifunctional methacrylate crosslinker under dilute conditions gives rise to well-defined epoxide-functional nanogels, of which the sizes are controlled by the degree of polymerization. Nanogels with well-defined sizes (polydispersity of 0.2) ranging from 38 nm to 95 nm were prepared by means of controlled radical polymerization. The nanogels were characterized in detail by FT-IR, DLS, size exclusion chromatography, NMR spectroscopy, AFM and TEM. Nucleophilic attack with functional thiols or amines on the least hindered carbon of the epoxide provides water-soluble nanogels, without altering the backbone structure, while reaction with sodium azide provides handles for further functionalization via click chemistry.

Overview of nanoparticulate strategies for solubility enhancement of poorly soluble drugs

Poor aqueous solubility and poor bioavailability are major issues with many pharmaceutical industries. By some estimation, 70-90% drug candidates in development stage while up-to 40% of the marketed products are poorly soluble which leads to low bioavailability, reduced therapeutic effects and dosage escalation. That's why solubility is an important factor to consider during design and manufacturing of the pharmaceutical products. To-date, various strategies have been explored to tackle the issue of poor solubility. This review article focuses the updated overview of commonly used macro and nano drug delivery systems and techniques such as micronization, solid dispersion (SD), supercritical fluid (SCF), hydrotropy, co-solvency, micellar solubilization, cryogenic technique, inclusion complex formation-based techniques, nanosuspension, solid lipid nanoparticles, and nanogels/nanomatrices explored for solubility enhancement of poorly soluble drugs. Among various techniques, nanomatrices were found a promising and impeccable strategy for solubility enhancement of poorly soluble drugs. This article also describes the mechanism of action of each technique used in solubilization enhancement.

Modulating the Excited State Chirality of Dynamic Chemical Reactions in Chiral Micelles

Chirality generation and transfer is not only of critical importance in resolving the origin of biological homochirality, but also is of great significance for exploring the chirality-related functionalities in nanomaterials and supramolecular systems. Although modulating the ground state chirality in chiral nanomaterials has been widely demonstrated, it remains a big challenge to steer the excited state chirality (circularly polarized luminescence, CPL). Herein, we present a kind of chiral spherical micelles constructed by chiral cationic gemini surfactants, whose surfaces and cavities could co-assemble with hydrophilic and hydrophobic emitters concurrently. Subsequently, the hydrophilic and hydrophobic emitters could be endowed with CPL activity in the aqueous phase. Additionally, the cavities of such micelles can be regarded as the powerful chiral confined space, which could effectively modulate the excited state chirality of dynamic chemical reactions, enabling color-adjustable CPL emission.

Recent Advances in Small Molecule-Based Intracellular pH Probes

Intracellular pH plays an important role in many biological and pathological processes. Small-molecule based pH probes are found to be the most effective for pH sensing because of ease of preparation, high sensitivity, and quick response. They have many advantages such as small perturbation to the functions of the target, functional adaptability, cellular component-specific localization, etc. The present review highlights the flurry of recent activity in the development of such probes. The probes are categorized based on the type of fluorophore used like quinoline, coumarin, BODIPY, rhodamine, indolium, naphthalimide, etc., and their analytical performance is discussed.

Spatial Confinement Tunes Cleavage and Re-Formation of C=N Bonds in Fluorescent Molecules

Molecules in confined spaces exhibit unusual behaviors that are not typically observed in bulk systems. Such behavior can provide alternative strategies for exploring new reaction pathways. Cleavage of the C=N bond of Nile red (NR) in solution is an irreversible reaction. Here, we used spatial confinement within a cationic micelle-confined system to convert this reaction to a reversible process. The fluorescence of NR shifted between red and green for nine cycles. The new chemical pathway based on spatial confinement can be attributed to two factors: increasing the local concentration of reactants and reducing the reaction energy barrier. This effect is supported by both experimental evidence and theoretical calculations. The cross-linked silica shell comprising the confinement chamber stabilizes the enclosed molecules. This reduces fluorophore leakage and maintains fluorescence intensity in most environments, including in solution, on paper, and in hydrogel films, and expands practical applications in encrypted information and multi-informational displays.

Ratiometric fluorescent nanoprobes for visual detection: Design principles and recent advances - A review

Signal generation techniques for visual detection of analytes have received a great deal of attention in various sensing fields. These approaches are considered to be advantageous when instrumentation cannot be employed, such as for on-site assays, point-of-care tests, and he althcare diagnostics in resource-constrained areas. Amongst various visual detection approaches explored for non-invasive quantitative measurements, ratiometric fluorescence sensing has received particular attention as a potential method to overcome the limitations of intensity-based probes. This technique relies on changes in the intensity of two or more emission bands (induced by an analyte), resulting in an effective internal referencing which improves the sensitivity of the detection. The self-calibration, together with the unique optophysical properties of nanoparticles (NPs) have made the ratiometric fluorescent nanoprobes more sensitive and reliable, which in turn, can result in more precise visual detection of the analytes. Over the past few years, a vast number of ratiometric sensing probes using nanostructured fluorophores have been designed and reported for a wide variety of sensing, imaging, and biomedical applications. In this work, a review on the NP-based ratiometric fluorescent sensors has been presented to meticulously elucidate their development, advances and challenges. With a special emphasis on visual detection, the most important steps in the design of fluorescent ratiometric nanoprobes have been given and based on different classes of analytes, recent applications of fluorescent ratiometric nanoprobes have been summarized. The challenges for the future use of the technique investigated in this review have been also discussed.

Application of radiation for the synthesis of poly(n-vinyl pyrrolidone) nanogels with controlled sizes from aqueous solutions

Controlling of sizes of nanogels is very important for any biomedical application. In the present study we report a facile and reproducible method of preparing biocompatible nanogels of poly(N-vinyl pyrrolidone) (PVP) which were synthesized by using either electron beam (e-beam) (NGEB) or gamma irradiation (NGG) of dilute aqueous solutions. Nanogels with different hydrodynamic sizes were obtained at the variance of the polymer molecular weight, concentration, type of radiation source hence dose rate and total absorbed dose. For the first time a comparative study of gamma and e-beam irradiation was made on the same polymer with the aim of controlling sizes of nanogels in the range of 30-250 nm. Moreover the stability of radiation-synthesized nanogels was followed up to 2 years in refrigerated solution and found to retain their original sizes and distributions enabling their long-term storage and use. The synthesized nanogels were characterized by using dynamic light scattering (DLS), gel permeation chromatography (GPC), scanning electron microscopy (SEM) and atomic force microscopy (AFM) techniques. This work provides a clue to the fundamental question of how to control sizes of nanogels without using any additives which are indispensable with the other techniques. The technique is applicable to any water soluble polymer.

Ratiometric optical nanoprobes enable accurate molecular detection and imaging

Exploring and understanding biological and pathological changes are of great significance for early diagnosis and therapy of diseases. Optical sensing and imaging approaches have experienced major progress in this field. Particularly, an emergence of various functional optical nanoprobes has provided enhanced sensitivity, specificity, targeting ability, as well as multiplexing and multimodal capabilities due to improvements in their intrinsic physicochemical and optical properties. However, one of the biggest challenges of conventional optical nanoprobes is their absolute intensity-dependent signal readout, which causes inaccurate sensing and imaging results due to the presence of various analyte-independent factors that can cause fluctuations in their absolute signal intensity. Ratiometric measurements provide built-in self-calibration for signal correction, enabling more sensitive and reliable detection. Optimizing nanoprobe designs with ratiometric strategies can surmount many of the limitations encountered by traditional optical nanoprobes. This review first elaborates upon existing optical nanoprobes that exploit ratiometric measurements for improved sensing and imaging, including fluorescence, surface enhanced Raman scattering (SERS), and photoacoustic nanoprobes. Next, a thorough discussion is provided on design strategies for these nanoprobes, and their potential biomedical applications for targeting specific biomolecule populations (e.g. cancer biomarkers and small molecules with physiological relevance), for imaging the tumor microenvironment (e.g. pH, reactive oxygen species, hypoxia, enzyme and metal ions), as well as for intraoperative image guidance of tumor-resection procedures.

Controlled drug delivery vehicles for cancer treatment and their performance

Although conventional chemotherapy has been successful to some extent, the main drawbacks of chemotherapy are its poor bioavailability, high-dose requirements, adverse side effects, low therapeutic indices, development of multiple drug resistance, and non-specific targeting. The main aim in the development of drug delivery vehicles is to successfully address these delivery-related problems and carry drugs to the desired sites of therapeutic action while reducing adverse side effects. In this review, we will discuss the different types of materials used as delivery vehicles for chemotherapeutic agents and their structural characteristics that improve the therapeutic efficacy of their drugs and will describe recent scientific advances in the area of chemotherapy, emphasizing challenges in cancer treatments.

Improving the delivery of cancer therapies to tumor sites is crucial to reduce unwanted side effects and patient mortality rates. Pralay Maiti and colleagues at the Indian Institute of Technology in Varanasi, India, review the latest developments in drug delivery vehicles and treatment approaches designed to enhance the effectiveness of current cancer therapies. New nanoparticle-based carriers, hydrogels and hybrid materials that offer controlled and sustained drug release are showing great promise in animal models. Furthermore, materials that respond to stimuli such as heat, light, magnetic or electric fields are also being tested to aid target-specific drug delivery and, thus, avoid damage to healthy tissues. Although there are some challenges in translating these findings to the clinic, there is no doubt that technological advances are shaping better and safer treatment options.

Photoactivation of Ligands for Extrinsically and Intrinsically Triggered Disassembly of Amphiphilic Nanoassemblies

Specific response to the concurrent presence of two different inputs is one of the hallmarks of incorporating specificities in nature. Artificial nanoassemblies that concurrently respond to two very different inputs are of great interest in a variety of applications, especially in biomedicine. Here, we present a design strategy for amphiphilic nanoassemblies with such capabilities, enabled by photocaging a ligand moiety that is capable of binding to a specific protein. New molecular designs that offer nanoassemblies that respond to either of two inputs or only to the concurrent presence of two inputs are outlined. Such biomimetic nanoassemblies could find use in many applications, including drug delivery and diagnostics.

Conjugated Polymer Nanoparticles for Bioimaging

During the last decade, conjugated polymers have emerged as an interesting class of fluorescence imaging probes since they generally show high fluorescence brightness, high photostability, fast emission rates, non-blinking behavior and low cytotoxicity. The main concern related to most conjugated polymers is their lack of hydrophilicity and thereby poor bio-availability. This can, however, be overcome by the formulation of conjugated polymer nanoparticles in aqueous medium. This review provides an overview of the different techniques employed for the preparation of conjugated polymer nanoparticles, together with methods to improve their photoluminescence quantum yields. For selective targeting of specific cells, dedicated surface functionalization protocols have been developed, using different functional groups for ligand immobilization. Finally, conjugated polymer nanoparticles have recently also been employed for theranostic applications, wherein the particles are simultaneously used as fluorescent probes and carriers for anti-tumor drugs.

Imaging Lysosomal pH Alteration in Stressed Cells with a Sensitive Ratiometric Fluorescence Sensor

The organelle-specific pH is crucial for cell homeostasis. Aberrant pH of lysosomes has been manifested in myriad diseases. To probe lysosome responses to cell stress, we herein report the detection of lysosomal pH changes with a dual colored probe (CM-ROX), featuring a coumarin domain with "always-on" blue fluorescence and a rhodamine-lactam domain activatable to lysosomal acidity to give red fluorescence. With sensitive ratiometric signals upon subtle pH changes, CM-ROX enables discernment of lysosomal pH changes in cells undergoing autophagy, cell death, and viral infection.

A G-quadruplex based fluorescent oligonucleotide turn-on probe towards iodides detection in real samples

A basket-type G-quadruplex (GQ) fluorescent oligonucleotide (OND) probe is designed to detect iodides dependent on thymine-Hg(II)-thymine (T-Hg(II)-T) base pairs and the intrinsic fluorescence quenching capacity of GQ. In the presence of Hg(II) ions (Hg²⁺), the two hexachloro-fluorescein-labeled ONDs form a hairpin structure and the fluorophores are dragged close to the GQ, leading to fluorescence quenching of the probe due to photoinduced electron transfer. Upon addition of iodide anions, Hg²⁺ are extracted from T-Hg(II)-T complexes which attributes to the stronger binding with iodide anions, resulting in the fluorescence recovery. Through performing the fluorescence quenching and recovery processes, this probe developed a fluorescence turn-on sensor for iodide anions determination over a linear range of 20-200nmol/L with a limit of detection of 5nmol/L. The practical use of the turn-on technology was demonstrated by its application in determination of iodides in water, food, pharmaceutical products and biological samples.

Accurate Quantitative Sensing of Intracellular pH based on Self-ratiometric Upconversion Luminescent Nanoprobe

Accurate quantitation of intracellular pH (pH_i) is of great importance in revealing the cellular activities and early warning of diseases. A series of fluorescence-based nano-bioprobes composed of different nanoparticles or/and dye pairs have already been developed for pH_i sensing. Till now, biological auto-fluorescence background upon UV-Vis excitation and severe photo-bleaching of dyes are the two main factors impeding the accurate quantitative detection of pH_i. Herein, we have developed a self-ratiometric luminescence nanoprobe based on förster resonant energy transfer (FRET) for probing pH_i, in which pH-sensitive fluorescein isothiocyanate (FITC) and upconversion nanoparticles (UCNPs) were served as energy acceptor and donor, respectively. Under 980 nm excitation, upconversion emission bands at 475 nm and 645 nm of NaYF₄:Yb³⁺, Tm³⁺ UCNPs were used as pH_i response and self-ratiometric reference signal, respectively. This direct quantitative sensing approach has circumvented the traditional software-based subsequent processing of images which may lead to relatively large uncertainty of the results. Due to efficient FRET and fluorescence background free, a highly-sensitive and accurate sensing has been achieved, featured by 3.56 per unit change in pH_i value 3.0-7.0 with deviation less than 0.43. This approach shall facilitate the researches in pH_i related areas and development of the intracellular drug delivery systems.

An efficient core-shell fluorescent silica nanoprobe for ratiometric fluorescence detection of pH in living cells

Intracellular pH plays a vital role in cell biology, including signal transduction, ion transport and homeostasis. Herein, a ratiometric fluorescent silica probe was developed to detect intracellular pH values. The pH sensitive dye fluorescein isothiocyanate isomer I (FITC), emitting green fluorescence, was hybridized with reference dye rhodamine B (RB), emitting red fluorescence, as a dual-emission fluorophore, in which RB was embedded in a silica core of ∼40 nm diameter. Moreover, to prevent fluorescence resonance energy transfer between FITC and RB, FITC was grafted onto the surface of core-shell silica colloidal particles with a shell thickness of 10-12 nm. The nanoprobe exhibited dual emission bands centered at 517 and 570 nm, under single wavelength excitation of 488 nm. RB encapsulated in silica was inert to pH change and only served as reference signals for providing built-in correction to avoid environmental effects. Moreover, FITC (λem = 517 nm) showed high selectivity toward H(+) against metal ions and amino acids, leading to fluorescence variation upon pH change. Consequently, variations of the two fluorescence intensities (Fgreen/Fred) resulted in a ratiometric pH fluorescent sensor. The specific nanoprobe showed good linearity with pH variation in the range of 6.0-7.8. It can be noted that the fluorescent silica probe demonstrated good water dispersibility, high stability and low cytotoxicity. Accordingly, imaging and biosensing of pH variation was successfully achieved in HeLa cells.

Intracellular pH sensing using polymeric micelle containing tetraphenylethylene-oxazolidine

The self-assembled polymeric micelle can be used as an effective probe for intracellular pH detection by switching its luminescence from cyan to red with high selectivity and contrast.

Intracellular FRET-based probes: a review

Probes that exploit Förster resonance energy transfer (FRET) in their feedback mechanism are touted for their sensitivity, robustness, and low background, and thanks to the exceptional distance dependence of the energy transfer process, they provide a means of probing lengthscales well below the resolution of light. These attributes make FRET-based probes superbly suited to an intracellular environment, and recent developments in biofunctionalization and expansion of imaging capabilities have put them at the forefront of intracellular studies. Here, we present an overview of the engineering and execution of a variety of recent intracellular FRET probes, highlighting the diversity of this class of materials and the breadth of application they have found in the intracellular environment.

Nanoparticle-based luminescent probes for intracellular sensing and imaging of pH

Fluorescence imaging microscopy is an essential tool in biomedical research. Meanwhile, various fluorescent probes are available for the staining of cells, cell membranes, and organelles. Though, to monitor intracellular processes and dysfunctions, probes that respond to ubiquitous chemical parameters determining the cellular function such as pH, pO2 , and Ca(2+) are required. This review is focused on the progress in the design, fabrication, and application of photoluminescent nanoprobes for sensing and imaging of pH in living cells. The advantages of using nanoprobes carrying fluorescent pH indicators compared to single molecule probes are discussed as well as their limitations due to the mostly lysosomal uptake by cells. Particular attention is paid to ratiometric dual wavelength nanosensors that enable intrinsic referenced measurements. Referencing and proper calibration procedures are basic prerequisites to carry out reliable quantitative pH determinations in complex samples such as living cells. A variety of examples will be presented that highlight the diverseness of nanocarrier materials (polymers, micelles, silica, quantum dots, carbon dots, gold, photon upconversion nanocrystals, or bacteriophages), fluorescent pH indicators for the weak acidic range, and referenced sensing mechanisms, that have been applied intracellularly up to now. WIREs Nanomed Nanobiotechnol 2016, 8:378-413. doi: 10.1002/wnan.1366 For further resources related to this article, please visit the WIREs website.

Single-cell intracellular nano-pH probes

Within a large clonal population, such as cancerous tumor entities, cells are not identical, and the differences between intracellular pH levels of individual cells may be important indicators of heterogeneity that could be relevant in clinical practice, especially in personalized medicine. Therefore, the detection of the intracellular pH at the single-cell level is of great importance to identify and study outlier cells. However, quantitative and real-time measurements of the intracellular pH of individual cells within a cell population is challenging with existing technologies, and there is a need to engineer new methodologies. In this paper, we discuss the use of nanopipette technology to overcome the limitations of intracellular pH measurements at the single-cell level. We have developed a nano-pH probe through physisorption of chitosan onto hydroxylated quartz nanopipettes with extremely small pore sizes (~100 nm). The dynamic pH range of the nano-pH probe was from 2.6 to 10.7 with a sensitivity of 0.09 units. We have performed single-cell intracellular pH measurements using non-cancerous and cancerous cell lines, including human fibroblasts, HeLa, MDA-MB-231 and MCF-7, with the pH nanoprobe. We have further demonstrated the real-time continuous single-cell pH measurement capability of the sensor, showing the cellular pH response to pharmaceutical manipulations. These findings suggest that the chitosan-functionalized nanopore is a powerful nano-tool for pH sensing at the single-cell level with high temporal and spatial resolution.

A pH-responsive molecular switch with tricolor luminescence

We developed a new ratiometric pH sensor based on poly(N-phenylmaleimide) (PPMI)-containing block copolymer that emits three different fluorescent colors depending on the pH. The strong solvatochromism and tautomerism of the PPMI derivatives enabled precise pH sensing for almost the entire range of the pH scale. Theoretical calculations have predicted largely dissimilar band gaps for the keto, enol, and enolate tautomers of PPMI owing to low-dimensional conjugation effects. The tunable emission wavelength and intensity of our sensors, as well as the reversible color switching with high-luminescent contrast, were achieved using rational molecular design of PPMI analogues as an innovative platform for accurate H(+) detection. The self-assembly of block copolymers on the nanometer length scale was particularly highlighted as a novel prospective means of regulating fluorescence properties while avoiding the self-quenching phenomenon, and this system can be used as a fast responsive pH sensor in versatile device forms.

Fluorescence ratiometric sensor for trace vapor detection of hydrogen peroxide

Trace vapor detection of hydrogen peroxide (H2O2) represents a practical approach to nondestructive detection of peroxide-based explosives, including liquid mixtures of H2O2 and fuels and energetic peroxide derivatives, such as triacetone triperoxide (TATP), diacetone diperoxide (DADP), and hexamethylene triperoxide diamine (HMTD). Development of a simple chemical sensor system that responds to H2O2 vapor with high reliability and sufficient sensitivity (reactivity) remains a challenge. We report a fluorescence ratiometric sensor molecule, diethyl 2,5-bis((((4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)benzyl)oxy)carbonyl)amino)terephthalate (DAT-B), for H2O2 that can be fabricated into an expedient, reliable, and sensitive sensor system suitable for trace vapor detection of H2O2. DAT-B is fluorescent in the blue region, with an emission maximum at 500 nm in the solid state. Upon reaction with H2O2, DAT-B is converted to an electronic "push-pull" structure, diethyl 2,5-diaminoterephthalate (DAT-N), which has an emission peak at a longer wavelength centered at 574 nm. Such H2O2-mediated oxidation of aryl boronates can be accelerated through the addition of an organic base such as tetrabutylammonium hydroxide (TBAH), resulting in a response time of less than 0.5 s under 1 ppm of H2O2 vapor. The strong overlap between the absorption band of DAT-N and the emission band of DAT-B enables efficient Förster resonance energy transfer (FRET), thus allowing further enhancement of the sensing efficiency of H2O2 vapor. The detection limit of a drop-cast DAT-B/TBAH film was projected to be 7.7 ppb. By combining high sensitivity and selectivity, the reported sensor system may find broad application in vapor detection of peroxide-based explosives and relevant chemical reagents through its fabrication into easy-to-use, cost-effective kits.

Optical sensor arrays for chemical sensing: the optoelectronic nose

A comprehensive review is presented on the development and state of the art of colorimetric and fluorometric sensor arrays. Optical arrays based on chemoresponsive colorants (dyes and nanoporous pigments) probe the chemical reactivity of analytes, rather than their physical properties. This provides a high dimensionality to chemical sensing that permits high sensitivity (often down to ppb levels), impressive discrimination among very similar analytes and exquisite fingerprinting of extremely similar mixtures over a wide range of analyte types, both in the gas and liquid phases.

Low cost referenced luminescent imaging of oxygen and pH with a 2-CCD colour near infrared camera

A low cost imaging set-up for NIR-emitting optical chemical sensors for pH and oxygen based on a 2-CCD camera is presented.

Reaction-based and single fluorescent emitter decorated ratiometric nanoprobe to detect hydrogen peroxide

A novel reaction-based cross-linked polymeric nanoprobe with a self-calibrating ratiometric fluorescence readout to selectively detect H2O2 is reported. The polymeric nanoprobe is fabricated by using hydrophobic H2O2-reactive boronic ester groups, crosslinker units, and environmentally sensitive 3-hydroxyflavone fluorophores through a miniemulsion polymerization. On treatment with H2O2, the boronic esters in the polymer are cleaved to form hydrophilic alcohols and subsequently lead to a hydrophobic-hydrophilic transition. Covalently linked 3-hydroxyflavones manifest the change in polarity as a ratiometric transition from green to blue, accompanied by a 500-fold increase in volume. Furthermore, this nanoprobe has been used for ratiometric sensing of glucose by monitoring the H2O2 generated during the oxidation of glucose by glucose oxidase, and thus successfully distinguished between normal and pathological levels of glucose.