The role of "disaggregation" in optical probe development

A new approach to developing diagnostics and therapeutics: Aggregation-induced emission-based fluorescence turn-on

Fluorescence imaging is a promising visualization tool and possesses the advantages of in situ response and facile operation; thus, it is widely exploited for bioassays. However, traditional fluorophores suffer from concentration limits because they are always quenched when they aggregate, which impedes applications, especially for trace analysis and real-time monitoring. Recently, novel molecules with aggregation-induced emission (AIE) characteristics were developed to solve the problems encountered when using traditional organic dyes, because these new molecules exhibit weak or even no fluorescence when they are in free movement states but emit intensely upon the restriction of intramolecular motions. Inspired by the excellent performances of AIE molecules, a substantial number of AIE-based probes have been designed, synthesized, and applied to various fields to fulfill diverse detection tasks. According to numerous experiments, AIE probes are more practical than traditional fluorescent probes, especially when used in bioassays. To bridge bioimaging and materials engineering, this review provides a comprehensive understanding of the development of AIE bioprobes. It begins with a summary of mechanisms of the AIE phenomenon. Then, the strategies to realize accurate detection using AIE probes are discussed. In addition, typical examples of AIE-active materials applied in diagnosis, treatment, and nanocarrier tracking are presented. In addition, some challenges are put forward to inspire more ideas in the promising field of AIE-active materials.

Towards more accurate bioimaging of drug nanocarriers: turning aggregation-caused quenching into a useful tool

One of the current challenges in the monitoring of drug nanocarriers lies in the difficulties in discriminating the carrier-bound signals from the bulk signals of probes. Environment-responsive probes that enable signal switching are making steps towards a solution to this problem. Aggregation-caused quenching (ACQ), a phenomenon generally regarded as unfavorable in bioimaging, has turned out to be a promising characteristic for achieving environment-responsiveness and eliminating free-probe interference. So-called ACQ probes emit fluorescence when dispersed molecularly within the carrier matrix but quench immediately and absolutely once they are released into the ambient aqueous environment upon the degradation of the nanocarriers. Therefore, the fluorescence observed represents integral nanocarriers. Based on this rationale, the in vivo fates of various nanocarriers have been explored using live imaging equipment, with very interesting findings revealing the role of the particles. The current applications are however restricted to nanocarriers with highly hydrophobic matrices (lipid or polyester nanoparticles) or with a hydrophobic core-hydrophilic shell structure (micelles). The ACQ-based bioimaging strategy is emerging as a promising tool to achieve more accurate bioimaging of drug nanocarriers. This review article provides an overview of the ACQ phenomenon and the rationale for and examples of applications, as well as the limitations of the ACQ-based strategy, with a focus on improving the accuracy of bioimaging of nanoparticles.

Preparation of Tin Oxide Quantum Dots in Aqueous Solution and Applications in Semiconductor Gas Sensors

Tin oxide quantum dots (QDs) were prepared in aqueous solution from the precursor of tin dichloride via a simple process of hydrolysis and oxidation. The average grain size of QDs was 1.9 nm. The hydrothermal treatment was used to control the average grain size, which increased to 2.7 and 4.0 nm when the operating temperatures of 125 and 225 °C were employed, respectively. The X-ray photoelectron spectroscopy (XPS) spectrum and X-ray diffraction analysis (XRD) pattern confirmed a rutile SnO₂ system for the QDs. A band gap of 3.66 eV was evaluated from the UV-VIS absorption spectrum. A fluorescence emission peak was observed at a wavelength of 300 nm, and the response was quenched by the high concentration of QDs in the aqueous solution. The current-voltage (I-V) correlation inferred that grain boundaries had the electrical characteristics of the Schottky barrier. The response of the QD thin film to H₂ gas revealed its potential application in semiconductor gas sensors.

Coordination-Driven Self-Assembled Metallacycles Incorporating Pyrene: Fluorescence Mutability, Tunability, and Aromatic Amine Sensing

Constructing polycyclic aromatics-based, highly emissive fluorophores with good solubility and tunable aggregated structures and properties is of great importance for film fabrication, solution processing, and relevant functionality studies. Herein, we describe a general strategy to endow conventional organic fluorophores with enhanced solubility and modulated fluorescent properties via their incorporation into coordination-driven self-assembled metallacycles. A widely used fluorophore, pyrene, was decorated with two pyridyl groups to yield functionalized pyrene 4. Mixing 4 with three aromatic dicarboxylates with different lengths and a 90° Pt(II) metal acceptor in a 2:2:4 stoichiometric ratio resulted in the formation of three metallacycles, 1, 2, and 3. The metallacycles display good solubility in polar organic solvents, highly aggregation-dependent fluorescence, and size-dependent emissions at higher concentrations. Moreover, metallacycle 2-based, silica-gel-supported film as fabricated not only is more emissive than the ligand 4-based one but also displays much improved sensing properties for amines in the vapor state, as demonstrated by significantly increased response speed and decreased recovery time. The enhanced solubility, unique fluorescence behavior, and multi-factor modulation character show that coordination-driven self-assembly can be utilized for the development of new fluorophores through simple modification of conventional fluorophores. The fluorophores synthesized this way possess not only complex topological structures but also good modularity and tunability in fluorescence behavior, which are important for grafting multi-stage energy-transfer systems necessary for the development of high-performance sensing materials.

Visualizing biofilm by targeting eDNA with long wavelength probe CDr15

We developed a small molecule CDr15, which has eDNA selectivity of bacterial biofilm.

Bimodal detection of carbon dioxide using fluorescent molecular aggregates

Fluorescent aggregates of a cyano-substituted phenylenevinylene derivative (R-1) have been used as a bimodal probe for the easy and fast detection of CO₂.

Mechanism for Copper(II)-Mediated Disaggregation of a Porphyrin J-Aggregate

J-aggregates of anionic meso-tetrakis(4-sulfonatophenyl)porphyrin form at intermediate pH (2.3-3.1) in the presence of NiSO₄ or ZnSO₄ (ionic strength, I.S. = 3.2 M). These aggregates convert to monomeric porphyrin units via metallation with copper(II) ions. The kinetics for the disassembly process, as monitored by UV/vis spectroscopy, exhibits zeroth-order behavior. The observed zeroth-order rate constants show a two-term dependence on copper(II) ion concentrations: linear and second order. Also observed is an inverse dependence on hydrogen ion concentration. Activation parameters have been determined for the disassembly process leading to ΔH ^≠ = (+163 ± 15) kJ·mol^-1 and ΔS ^≠ = (+136 ± 11) J·K^-1. A mechanism is proposed in which copper(II) cation is in pre-equilibrium with a reactive site at the rim of the J-aggregate. An intermediate copper species is thus formed that eventually leads to the final metallated porphyrin either through an assisted attack of a second metal ion or through a direct insertion of the metal cation into the macrocycle core.

A DIE responsive NIR-fluorescent cell membrane probe

It is challenging to achieve selective off to on modulation of the emissive state of a fluorophore within a complex and heterogeneous cellular environment. Herein we show that the dis-assembly of a non-fluorescent aggregate to produce individual fluorescent molecules, termed disaggregation induced emission (DIE), can be utilised to achieve this goal with an amphiphilic BF₂-azadipyrromethene (NIR-AZA) probe. Optical near-infrared properties of the NIR-AZA probe used in this study include absorption and emission maxima at 700 and 726 nm respectively when in the emissive non-aggregated state. Key to the success of the probe is the bis-sulfonic acid substitution of the NIR-AZA fluorophore, which is atypical for membrane probes as it does not contain zwitterionic lipid substituents. The aggregation/disaggregation properties of the NIR-fluorophore have been investigated in model surfactant and synthetic liposomal systems and shown to be emissive responsive to both. Real-time live cell imaging experiments in HeLa Kyoto and MC3T3 cells showed a rapid switch on of emission specific to the plasma membrane of viable and apoptotic cells attributable to a disaggregation-induced emission of the probe. Image analysis software confirmed localisation of fluorescence to the plasma membrane. Cell membrane staining was also effective for formaldehyde fixed cells, with staining possible either before or after fixation. This study adds new and important findings to recent developments of DIE responsive probes and further applications of this controllable emission-switching event are anticipated.

Reassessment of long circulation via monitoring of integral polymeric nanoparticles justifies a more accurate understanding

Monitoring of payloads results in a biased perception of long circulation of nanoparticles. Instead, herein, the long-circulation effect was re-confirmed by monitoring integral nanoparticles, but circulation was not found to be as long as generally perceived. In contrast, disparate pharmacokinetics were obtained by monitoring a model drug, paclitaxel, highlighting the bias of the conventional protocol.

Visual validation of the measurement of entrapment efficiency of drug nanocarriers

Entrapment efficiency (EE) is a crucial parameter for the evaluation of nanocarriers. The accurate measurement of EE demands clear separation of nanocarriers from free drugs, which so far has not been clearly validated due to a lack of functional tools to identify nanocarriers. Herein, an environment-responsive water-quenching fluorophore was employed to label and identify model nanocarriers, polycaprolactone nanoparticles (PN), methoxy polyethylene glycol-poly(d,l-lactic acid) polymeric micelles (PM) and solid lipid nanoparticles (SLN). The separation process of three commonly used methods (centrifugation, ultrafiltration and gel permeation chromatography) was visualized by live imaging. The separation efficiency of the centrifugation method is very poor, especially for PM (40 nm), SLN (100 nm) and PN (100 nm); only PN (200 nm) can be efficiently separated but at a consumption of enormous energy. The ultrafiltration method shows the best separation efficiency with only 0.32-0.93% of leakage of the nanocarriers. Gel permeation chromatography exhibits good separation as well but suffers from low recovery, a potential factor that might compromise the accuracy of EE measurement. In conclusion, the ultrafiltration method is the method of choice for efficient separation and accurate measurement of EE.

Twisted-Intramolecular-Charge-Transfer-Based Turn-On Fluorogenic Nanoprobe for Real-Time Detection of Serum Albumin in Physiological Conditions

Two cyanine-based fluorescent probes, ( E)-2-(4-(diethylamino)-2-hydroxystyryl)-3-ethyl-1,1-dimethyl-1 H-benzo[ e]indol-3-ium iodide (L) and ( E)-3-ethyl-1,1-dimethyl-2-(4-nitrostyryl)-1 H-benzo[ e]indol-3-ium iodide (L₁), have been designed and synthesized. Of these two probes, the twisted-intramolecular-charge-transfer (TICT)-based probe, L, can preferentially self-assemble to form nanoaggregates. L displayed a selective turn-on fluorescence response toward human and bovine serum albumin (HSA and BSA) in ∼100% aqueous PBS medium, which is noticeable with the naked eye, whereas L₁ failed to sense these albumin proteins. The selective turn-on fluorescence response of L toward HSA and BSA can be attributed to the selective binding of probe L with HSA and BSA without its interfering with known drug-binding sites. The specific binding of L with HSA led to the disassembly of the self-assembled nanoaggregates of L, which was corroborated by dynamic-light-scattering (DLS) and transmission-electron-microscopy (TEM) analysis. Probe L has a limit of detection as low as ∼6.5 nM. The sensing aptitude of probe L to detect HSA in body fluid and an artificial-urine sample has been demonstrated.

Enhancing the Anti-Solvatochromic Two-Photon Fluorescence for Cirrhosis Imaging by Forming a Hydrogen-Bond Network

Two-photon imaging is an emerging tool for biomedical research and clinical diagnostics. Electron donor-acceptor (D-A) type molecules are the most widely employed two-photon scaffolds. However, current D-A type fluorophores suffer from solvatochromic quenching in aqueous biological samples. To address this issue, we devised a novel class of D-A type green fluorescent protein (GFP) chromophore analogues that form a hydrogen-bond network in water to improve the two-photon efficiency. Our design results in two-photon chalcone (TPC) dyes with 0.80 quantum yield and large two-photon action cross section (210 GM) in water. This strategy to form hydrogen bonds can be generalized to design two-photon materials with anti-solvatochromic fluorescence. To demonstrate the improved in vivo imaging, we designed a sulfide probe based on TPC dyes and monitored endogenous H₂ S generation and scavenging in the cirrhotic rat liver for the first time.

Aggregation-induced phosphorescence enhancement of Mn-doped ZnS quantum dots: the role of dot-to-dot distance

Assembled nanoparticles promote many applications in optics due to their instinct properties. The aggregation-induced phosphorescence enhancement (AIPE) of Mn-doped ZnS quantum dots (QDs) is widely used in biosensing, but the mechanism of such an enhancement is still unproven. This study explores the mechanism of the interesting finding of AIPE of Mn-doped ZnS QDs. To induce the aggregation of QDs, the method of electrostatic assembly was explored herein: negatively charged QDs were aggregated with protamine and positively charged QDs were aggregated with heparin. Using several ligands with hierarchical molecular weights for capping Mn-doped ZnS QDs, it was found that the AIPE of Mn-doped ZnS QDs was exponentially dependent on the dot-to-dot distance in aggregates. Together with detailed analysis of both the steady- and transient-state luminescence behaviors of Mn-doped ZnS QDs before and after aggregation, charge transfer from one dot (surface traps) to another (dopant bands) was identified as the driving factor for AIPE. Moreover, the d-band of the Mn2+ dopants was essential for the AIPE since it acts as the acceptor for the transferred charge from neighboring QDs. These conclusions can significantly contribute for better understanding of this interesting luminescence mechanism and future designing of the most suitable sensing systems.

Novel intramolecular π-π-interaction in a BODIPY system by oxidation of a single selenium center: geometrical stamping and spectroscopic and spectrometric distinctions

A new BODIPY system displaying an intramolecular π-π-interaction was synthesized and studied. When the selenium center was oxidized, the substituted phenyl group undergoes π-π stacking with one side of the BODIPY core. The oxidized form showed, not only a down-field shift in the NMR peak, but also splitting due to geometrical changes that arise when going from C_s to C₁. The compound was characterized by X-ray diffraction; DFT methods helped elucidate the influence of the unexpected π-π stack and its connection to the photophysical properties imparted by the Se oxidation.

Facile one-step synthesis of highly luminescent N-doped carbon dots as an efficient fluorescent probe for chromium(vi) detection based on the inner filter effect

Label-free fluorescence assay system is designed for Cr(iv) detection.

Advances in the design of cell-permeable fluorescent probes for applications in live cell imaging

Advances in the design strategy of cell-permeable small fluorescent probes are discussed. Their applications in imaging specific cell types and intracellular bioanalytes, as well as the cellular environment in live conditions, are presented.

Photothermal Möbius aromatic metallapentalenofuran and its NIR-responsive copolymer

A novel thermally and NIR-light responsive metallopolymer was copolymerized from a photothermal aromatic metallapentalenofuran and a glycol methyl ether methacrylate.

Epithelia transmembrane transport of orally administered ultrafine drug particles evidenced by environment sensitive fluorophores in cellular and animal studies

Little is known about the in vivo fate of drug particles taken orally, in particular, the drug release kinetics and interaction with the gastrointestinal (GI) membrane. Lacking is analytical means that can reliably identify the integrity of drug particles under the complexity of biological environment. Herein, we explored fluorescent probes whose signals become quenched upon being released from drug carriers. Taking advantage of so-called the aggregation caused quenching (ACQ), particles may be identified by the integrated fluorophores, which are "turned off" when the particles become destructed and dyes are released. In the current study, ultrafine amorphous particles (UAPs) of cyclosporin A (CsA) were prepared with synthesized ACQ dyes physically entrapped. The fluorescence intensity of suspension of these UAPs was found correlated well with the dissolution of the particles. When given to rats orally, it was found that some of the administered UAPs could survive the animal's GI tracts for as long as 18h. Whole-body fluorescence imaging detected fluorescent signals in the liver and lungs. Particularly noticed in sections of jejunum and ileum, the detection suggested the possibility of direct absorption of UAPs through epithelial membranes. Moreover, 250nm particles were absorbed faster via transepithelia than larger ones (550nm), while the latter were preferably taken up by M cells in the follicle-associated epithelium (FAE) region of Peyer's patches. In vitro permeation studies with Caco-2 cells confirmed the transmembrane transport of the dye-integrated UAPs. Our study supports the idea of using ACQ fluorophores for imaging and characterizing the fate of intact particles in a biological environment.

Bulk Aggregation Based Fluorescence Turn-On Sensors for Selective Detection of Progesterone in Aqueous Solution

Steroids are polycyclic compounds that share tetracyclic ring as core scaffold, and selective detection of a steroid is challenging owing to their structural similarities. The discovery of chemosensors that recognize progesterone by alteration of self-aggregation state is described, and these show significant fluorescence turn-on. A self-aggregated 48-membered dansyl library was screened against a series of metabolites in aqueous buffer and discovered two compounds (PG-1, PG-2) exhibited exceptional selectivity for progesterone. Following studies of aggregation properties of probes using dynamic light scattering and transmission electron microscopy supports progesterone recognition lead to the generation of bulk aggregates that induce fluorescence enhancement. Though many fluorescence sensing mechanisms have been proposed, a sensing mode based on the bulk aggregate formation of fluorophore has never been reported, and this may open a new avenue of chemosensor design.

The aggregation induced emission quenching of graphene quantum dots for visualizing the dynamic invasions of cobalt(ii) into living cells

A highly sensitive and selective approach for cobalt(ii) detection based on the aggregation induced emission quenching strategy, which is opposite to aggregation induced emission enhancement, was developed using graphene quantum dots (GQDs). The detection could be achieved in the range of 10 nM-5 μM and the limit of detection was 2 nM. Importantly, the as-prepared GQDs showed a specific response to cobalt(ii) with excellent stability in A549 cells owing to their good biocompatibility and long-time anti-photobleaching. Thus, these environmentally and bio-friendly carbon nanomaterials were employed to visualize and monitor significant physiological changes of living cells induced by cobalt(ii). This shows great potential for in vitro analysis of cobalt(ii).

PyrrolylBODIPYs: Syntheses, Properties, and Application as Environment-Sensitive Fluorescence Probes

Four pyrrole B-ring-functionalized pyrrolylBODIPYs and their B-ring unsubstituted analogues were synthesized from easily accessible starting 5-halo-2-formylpyrroles and were characterized by nuclear magnetic resonance, high-resolution mass spectrometry, X-ray analysis, and optical/electronic properties. In great contrast to the substitution(s) at the other two pyrrolic units, electron-donating substituent(s) at pyrrole B-ring bring significant blue shift of the absorption and emission bands. Cyclic voltammetry and density functional theory calculations indicate that this blue shift may be attributed to the increased highest occupied molecular orbital and the lowest unoccupied molecular orbital energy levels and the overall increase in the energy band gaps. These pyrrolylBODIPYs generally show intense absorption (centered at 570-624 nm) and fluorescence emission (582-654 nm) in nonpolar solvents. A gradual decrease in the fluorescence intensity was observed for these dyes with the increase in solvent dipolar moment, which combines with the red to far-red absorption/emission, rendering these pyrrolylBODIPYs potential applications as environment-sensitive fluorescence probes as demonstrated in this work for bovine serum albumin.

Amplified fluorescence emission of bolaamphiphilic perylene-azacrown ether derivatives directed towards molecular recognition events

Long-term creative approaches have been considered in the design of molecular probes to overcome the quenching effect of important dyes in an aqueous medium. Using the rational donor-acceptor based design principle, we demonstrate herein the different fluorescence states of a non-conjugated symmetrical perylene-azacrown ether system in a solution, from the molecular to the aggregated states. The ethylene-spacer is exceptionally capable of fluorescence enhancement, even in the aggregated state (organic nanoparticle, ONPs, 44 nm), overcoming the quenching effect on changing the solvent from tetrahydrofuran to water. The ONPs with crown ether receptors at the surface show colloidal stability in an aqueous solution. Furthermore, an improved fluorescent state is developed via ONPs-polymer (protamine, Pro) hybridization. Supramolecular interactions between the crown ring and the guanidinium group in Pro play an important role in the ONPs-Pro hybrid formation. The decorated fluorescent hybrid state is finally used as a nano-probe for sensing heparin via the turn-OFF mechanism. The decoration method is further generalized by recognition of the nucleotides. Herein, we detail the bottom-up approach to the molecular design and development of the different fluorescent states of a useful probe. Most excitingly, this new approach is very general and adaptive to facile detection.

Aggregation-Switching Strategy for Promoting Fluorescent Sensing of Biologically Relevant Species: A Simple Near-Infrared Cyanine Dye Highly Sensitive and Selective for ATP

We report a strategy for enhanced performance of fluorescent sensing of biologically relevant species that often bind with natural receptors via multiple interactions. We propose making a fluorescent sensory molecule to form H-aggregates such that its emission is quenched leaving a low background, and upon binding to a biologically relevant species, the aggregate switches to another form in which the fluorescent species is better protected to afford a stronger emission signal. Meanwhile, the aggregated fluorescent dyes afford multiple interactions with the sensing species that require multiple binding sites. The lower background, stronger binding, and stronger signal would therefore lead to a much higher sensing performance, as improved selectivity would also result in along with the signal amplification. We thus designed a near-IR cyanine dye bearing two boronic acid groups (Cy-BA) for fluorescent sensing of ATP such that the boronic acid groups in the dye molecule bind to the cis-diol moiety in ATP. Introduction of the cationic surfactant dodecyltrimethylammonium bromide (DTAB) below its critical aggregation concentration is key because Cy-BA molecules made into H-aggregates were practically nonfluorescent. Upon mixing with ATP, a dramatic enhancement in the fluorescence occurred because of the formation of ATP/Cy-BA/DTAB vesicles in which the fluorescent dye is well dispersed and protected. This sensing scheme, despite the dynamic nature of the boronic acid/cis-diol interaction, weakness of the electrostatic interactions among ATP/Cy-BA/DTAB, and poor selectivity of these interactions, allows for highly sensitive and selective detection of ATP in aqueous solution.

Graphene quantum dot based "switch-on" nanosensors for intracellular cytokine monitoring

The detection of cytokines in body fluids, cells, tissues and organisms continues to attract considerable attention due to the importance of these key cell signalling molecules in biology and medicine. We report a graphene quantum dot (GQD) based aptasensor able to specifically detect ultra-small amounts of cytokine molecules intracellularly. Graphene quantum dots modified with cytokine aptamers (Ap-GQDs) and epitope modified GQDs (Ep-GQDs) were prepared; both are normally fluorescent at sufficient dilution. However, the fluorescence of the conjugates of Ap-GQDs and Ep-GQDs is quenched due to aggregation between Ap-GQDs and Ep-GQDs. After incubation of the cytokine-secreting cells with the conjugates of Ap-GQDs and Ep-GQDs, the cytokines secreted in cells compete for binding with the epitope which is then displaced. The ensuing binding of cytokines with the aptamers results in the disaggregation of Ap-GQDs and Ep-GQDs, and the recovery of fluorescence. The conjugates of Ap-GQDs and Ep-GQDs were used as nanosensors for monitoring intracellular cytokine IFN-γ secretion with very high sensitivity (2 pg mL^-1). The disaggregation based sensing strategy in this nanosensor design is simple and universal; similar nanosensors can be used for the detection of a broad spectrum of cell-secreted molecules. Such nanosensors will serve as potential biomaterials for in vivo devices to monitor a variety of biological phenomena, in particular to understand cytokine secretion pathways in live cells.

Activatable fluorescence: From small molecule to nanoparticle

Molecular imaging has emerged as an indispensable technology in the development and application of drug delivery systems. Targeted imaging agents report the presence of biomolecules, including therapeutic targets and disease biomarkers, while the biological behaviour of labelled delivery systems can be non-invasively assessed in real time. As an imaging modality, fluorescence offers additional signal specificity and dynamic information due to the inherent responsivity of fluorescence agents to interactions with other optical species and with their environment. Harnessing this responsivity is the basis of activatable fluorescence imaging, where interactions between an engineered fluorescence agent and its biological target induce a fluorogenic response. Small molecule activatable agents are frequently derivatives of common fluorophores designed to chemically react with their target. Macromolecular scale agents are useful for imaging proteins and nucleic acids, although their biological delivery can be difficult. Nanoscale activatable agents combine the responsivity of fluorophores with the unique optical and physical properties of nanomaterials. The molecular imaging application and overall complexity of biological target dictate the most advantageous fluorescence agent size scale and activation strategy.

Adaptive Self-Assembly Behavior Restrained by Supramolecular Crystallization and Molecular Recognition

The control over supramolecular interactions and obtaining information beyond the molecular scale is an extended challenge. The intriguing self-assembly of a perylene-3,4,9,10-tetracarboxylic acid diimide (PDI)-based novel bolaamphiphilic probe is experienced within an artificial environment that is restrained by using supramolecular crystallization and molecular recognition. The bolaamphiphile with a hydrophilic [18]-azacrown ether ring produced nanoaggregates due to differing solubilities in organic and aqueous media. A structural evolution was observed in the presence of alkali metal ions as guests. The metal complexes form a pseudo-cationic structure, which is further involved in an ionic self-assembly with biomolecules, thus resulting new spectroscopic information on the dye self-assembly. The overarching aim of this study is to emphasize the importance of the concept of supramolecular adaptability, which has been used to establish an environment-friendly behavior based on noncovalent forces, thus leading to the evolution of new assembly structures and photophysical properties.

Photophysical properties of quinoxalin-2(1H)-ones: application in the preparation of an azide-based fluorogenic probe for the detection of hydrogen sulfide

Fluorescent quinoxalinones with good quantum yields were obtained and used in the preparation of a probe for the detection of H₂S.

Motion-induced change in emission (MICE) for developing fluorescent probes

A new concept of motion-induced change in emission (MICE) in a single molecule for developing fluorescent probes is presented and summarized.

A New Tetraphenylethylene-Derived Fluorescent Probe for Nitroreductase Detection and Hypoxic-Tumor-Cell Imaging

The fluorescence detection of nitroreductase (NTR) and evaluation of the hypoxia status of tumor cells are vital, not only for clinical diagnoses and therapy, but also for biomedical research. Herein, we report the synthesis and application of a new fluorometric "turn-on" probe for the detection of NTR (TPE-NO₂ ) that takes advantage of the aggregation-induced emission of tetraphenylethylene. TPE-NO₂ can detect NTR at concentrations as low as 5 ng mL^-1 in aqueous solution. The detection mechanism relied on the aggregation and deaggregation of tetraphenylethylene molecules. Moreover, this fluorescent probe can be used to monitor the hypoxia status of tumor cells through the detection of endogenous NTR.

Interaction of BODIPY dyes with bovine serum albumin: a case study on the aggregation of a click-BODIPY dye

The fluorescence of BODIPY and click-BODIPY dyes was found to substantially increase in the presence of bovine serum albumin (BSA). BSA acted as a solubilizer for dye aggregates, in addition to being a conventional binding scaffold for the click-BODIPY dyes, indicating that disaggregation of fluorophores should be considered when evaluating dye-protein interactions.

Development of a disaggregation-induced emission probe for the detection of RecA inteins from Mycobacterium tuberculosis

A novel fluorescent sensor with disaggregation-induced emission characteristics has been developed for the detection of RecA inteins from Mycobacterium tuberculosis.

Construction of a novel INHIBIT logic gate through a fine-tuned assembly of anthryl fluorophores via selective anion recognition and host–guest interactions

A novel ligand containing of anthryl fluorophore was achieved. The assembly and disassembly of anthryl fluorophore by Pi and β-CD as chemical inputs and emission around 500 nm as output resulted in the construction of novel INHIBIT gate.