A dendritic single-molecule fluorescent probe that is monovalent, photostable and minimally blinking

Steric protection of near-infrared fluorescent dyes for enhanced bioimaging

Near-fluorescent (NIR) dyes that absorb and emit light in the wavelength range of 650-1700 nm are well-suited for bioimaging due to the improved image contrast and increased penetration of the long-wavelength light through biological tissue. However, the imaging performance of NIR fluorescent dyes is limited by several inherent photophysical and physicochemical properties including, low fluorescence quantum yield, high chemical and photochemical reactivity, propensity to self-aggregate in water, non-specific association with off-target biological sites, and non-optimal pharmacokinetic profiles in living subjects. In principle, all these drawbacks can be alleviated by steric protection which is a structural process that surrounds the fluorophore with bulky groups that block undesired intermolecular interactions. The literature methods to sterically protect a long-wavelength dye can be separated into two general strategies, non-covalent dye encapsulation and covalent steric appendage. Illustrative examples of each method show how steric protection improves bioimaging performance by providing: (a) increased fluorescence brightness, (b) higher fluorophore ground state stability, (c) decreased photobleaching, and (d) superior pharmacokinetic profile. Some sterically protected dyes are commercially available and further success with future systems will require experts in chemistry, microscopy, cell biology, medical imaging, and clinical medicine to work closely as interdisciplinary teams.

Blinking characteristics of organic fluorophores for blink-based multiplexing

Single-molecule fluorescence experiments have transformed our understanding of complex materials and biological systems. Whether single molecules are used to report on their nano-environment or provide for localization, understanding their blinking dynamics (i.e., stochastic fluctuations in emission intensity under continuous illumination) is paramount. We recently demonstrated another use for blinking dynamics called blink-based multiplexing (BBM), where individual emitters are classified using a single excitation laser based on blinking dynamics, rather than color. This study elucidates the structure-activity relationships governing BBM performance in a series of model rhodamine, BODIPY, and anthraquinone fluorophores that undergo different photo-physical and-chemical processes during blinking. Change point detection and multinomial logistic regression analyses show that BBM can leverage spectral fluctuations, electron and proton transfer kinetics, as well as photostability for molecular classification-even within the context of a shared blinking mechanism. In doing so, we demonstrate two- and three-color BBM with ≥ 93% accuracy using spectrally-overlapped fluorophores.

Coordination-Induced Conformational Control Enables Highly Luminescent Metallo-Cages

In recent years, luminescent materials have received a great deal of attention due to their wide range of applications. However, exploring a simple solution to overcome the fluorescence quenching resulting from the aggregation of conventional organic fluorophores remains a valuable area of investigation. In this study, we successfully constructed two metallo-cages, namely, SA and SB, through coordination-driven self-assemblies of the triphenylamine (TPA)-based donor L with different diplatinum(II) acceptors LA and LB, respectively. These metallo-cages take advantage of their steric nature and curved conformation to more effectively limit the free rotation of the benzene ring and hinder π-π stacking in the solid state, which successfully inhibited fluorescence quenching and realizing highly efficient luminescent properties. Therefore, this work offers a new design strategy for preparing materials with excellent luminescent properties.

Bodipy-Based Metal-Organic Frameworks Transformed in Solid States from 1D Chains to 2D Layer Structures as Efficient Visible Light Heterogeneous Photocatalysts for Forging C-B and C-C Bonds

Boron dipyrromethene (also known as bodipy), as a class of versatile and robust fluorophores and a structural analogue of porphyrins, has received a great deal of interests in the field of light-harvesting and energy-transfer processes. However, the fabrication of bodipy monomers into metal-organic frameworks (MOFs) and the exploitation of their potential still lags behind the porphyrin MOFs. In this work, two bodipy-based MOFs, BMOF 1D with 1D chain structure and BMOF 2D with 2D layer structure, were assembled by using dicarboxyl-functionalized bodipy ligands. BMOF 1D can also be converted to BMOF 2D by inserting additional ligands into BMOF 1D to cross-link the adjacent chains into the rhombic grid layer. During this process, spontaneous exfoliation occurred simultaneously and resulted in the formation of several hundred nanometer thickness BMOF 2D (nBMOF 2D), which can be further exfoliated into one-layer MOF nanosheets (BMON 2D) by using the ultrasonic liquid exfoliation method in a high yield. Featuring the distinct bodipy scaffolds in the porous frameworks, both BMOF 2D and BMON 2D displayed high reactivity and recyclability in the photocatalytic inverse hydroboration and cross-dehydrogenative coupling reactions to afford α-amino organoborons and α-amino amides in moderate to high yields. This work not only highlights the cascade utilization of ligand installation and ultrasonic liquid exfoliation methods to provide the single-layer MOF sheets in high yields but also advances the bodipy-based MOFs as a new type of heterogeneous photocatalysts in the forging of C-B and C-C bonds driven by visible light.

Dendrimer: An update on recent developments and future opportunities for the brain tumors diagnosis and treatment

A brain tumor is an uncontrolled cell proliferation, a mass of tissue composed of cells that grow and divide abnormally and appear to be uncontrollable by the processes that normally control normal cells. Approximately 25,690 primary malignant brain tumors are discovered each year, 70% of which originate in glial cells. It has been observed that the blood-brain barrier (BBB) limits the distribution of drugs into the tumour environment, which complicates the oncological therapy of malignant brain tumours. Numerous studies have found that nanocarriers have demonstrated significant therapeutic efficacy in brain diseases. This review, based on a non-systematic search of the existing literature, provides an update on the existing knowledge of the types of dendrimers, synthesis methods, and mechanisms of action in relation to brain tumours. It also discusses the use of dendrimers in the diagnosis and treatment of brain tumours and the future possibilities of dendrimers. Dendrimers are of particular interest in the diagnosis and treatment of brain tumours because they can transport biochemical agents across the BBB to the tumour and into the brain after systemic administration. Dendrimers are being used to develop novel therapeutics such as prolonged release of drugs, immunotherapy, and antineoplastic effects. The use of PAMAM, PPI, PLL and surface engineered dendrimers has proven revolutionary in the effective diagnosis and treatment of brain tumours.

Single-molecule characterization of a bright and photostable deep-red fluorescent squaraine-figure-eight (SF8) dye

Squaraine Figure Eight (SF8) dyes are a unique class of deep-red fluorescent dyes with self-threaded molecular architecture that provides structural rigidity while simultaneously encapsulating and protecting the emissive fluorochrome. Previous cell microscopy and bulk phase studies of SF8 dyes indicated order of magnitude enhancements in photostability over conventional pentamethine cyanine dyes such as Cy5. Studies conducted at the single molecule level now reveal that these ensemble level enhancements carry over to the single molecule level in terms of enhanced emission quantum yields, longer times to photobleaching, and enhanced total photon yields. When compared to Cy5, the SF8-based dye SF8(D4)2 possesses a three-fold larger single molecule emission quantum yield, exhibits order of magnitude longer average times before photobleaching, and exhibits twenty times larger photon yields. Additional features such as water solubility, fluorochrome encapsulation to protect it against nucleophilic attack, and selective biomarker targeting capability make SF8-based dyes promising candidates for biological labeling and microscopy applications and single molecule tracking.

Controllable self-assembly of thiophene-based π-conjugated molecule and further construction of pillar[5]arene-based host-guest white-light emission system

Photoluminescence materials have been widely applied in biological imaging and sensing, anti-counterfeiting, light-emitting diodes, logic gates et al. The fabrication of luminescent materials with adjustable emission color by self-assembly of π-conjugated molecules has attracted particular attention. In this study, we designed and synthesized a thiophene-based α-cyanostyrene-derivative (TPPA), then investigate its self-assembly morphology and fluorescence emission under different organic solvents, different proportions of H2O/THF (DMSO) mixture and different pH conditions by UV, FL and SEM images. It was found that TPPA formed nanoparticles by self-assembly in organic solvent (THF or DMSO), accompanied by strong fluorescence emission. However, with the increase of water ratio, the fluorescence intensity decreased accompany with red shift, and the self-assembly morphology changed from nanoparticles to fibers. More interestingly, when pillar[5]arene (P5) was added to form host-guest complex with TPPA, white light emission could be successfully constructed when the ratio of TPPA to P5 was 1:20 and THF to water was 19:1.

Ultra-photostable DNA FluoroCubes: Mechanism of Photostability and Compatibility with FRET and Dark Quenching

DNA-based FluoroCubes were recently developed as a solution to photobleaching, a ubiquitous limitation of fluorescence microscopy (Niekamp; ; Stuurman; ; Vale Nature Methods, 2020). FluoroCubes, that is, compact ∼4 × 4 × 5.4 nm3 four-helix bundles coupled to ≤6 fluorescent dyes, remain fluorescent up to ∼50× longer than single dyes and emit up to ∼40× as many photons. The current work answers two important questions about the FluoroCubes. First, what is the mechanism by which photostability is enhanced? Second, are FluoroCubes compatible with Förster resonance energy transfer (FRET) and similar techniques? We use single particle photobleaching studies to show that photostability arises through interactions between the fluorophores and the four-helix DNA bundle. Supporting this, we discover that smaller ∼4 × 4 × 2.7 nm3 FluoroCubes also confer ultraphotostability. However, we find that certain dye-dye interactions negatively impact FluoroCube performance. Accordingly, 4-dye FluoroCubes lacking these interactions perform better than 6-dye FluoroCubes. We also demonstrate that FluoroCubes are compatible with FRET and dark quenching applications.

Stable, Bright, and Long-Fluorescence-Lifetime Dyes for Deep-Near-Infrared Bioimaging

Near-infrared (NIR) fluorophores absorbing maximally in the region beyond 800 nm, i.e., deep-NIR spectral region, are actively sought for biomedical applications. Ideal dyes are bright, nontoxic, photostable, biocompatible, and easily derivatized to introduce functionalities (e.g., for bioconjugation or aqueous solubility). The rational design of such fluorophores remains a major challenge. Silicon-substituted rhodamines have been successful for bioimaging applications in the red spectral region. The longer-wavelength silicon-substituted congeners for the deep-NIR spectral region are unknown to date. We successfully prepared four silicon-substituted bis-benzannulated rhodamine dyes (ESi5a-ESi5d), with an efficient five-step cascade on a gram-scale. Because of the extensive overlapping of their HOMO-LUMO orbitals, ESi5a-ESi5d are highly absorbing (λ_abs ≈ 865 nm and ε > 10⁵ cm^-1 M^-1). By restraining both the rotational freedom via annulation and the vibrational freedom via silicon-imparted strain, the fluorochromic scaffold of ESi5 is highly rigid, resulting in an unusually long fluorescence lifetime (τ > 700 ps in CH₂Cl₂) and a high fluorescence quantum yield (ϕ = 0.14 in CH₂Cl₂). Their half-lives toward photobleaching are 2 orders of magnitude longer than the current standard (ICG in serum). They are stable in the presence of biorelevant concentration of nucleophiles or reactive oxygen species. They are minimally toxic and readily metabolized. Upon tail vein injection of ESi5a (as an example), the vasculature of a nude mouse was imaged with a high signal-to-background ratio. ESi5 dyes have broad potentials for bioimaging in the deep-NIR spectral region.

Distinguishing cancer cells from normal cells with an organelle-targeted fluorescent marker

In this paper we report a hemicyanine dye that is used to distinguish cancer cells from normal cells with its ability to target different organelles. Probe 1, a red emission hemicyanine functional dye, was connected to oxazolo[4,5-b]pyridine and diethylaminobenzene with a double bond. The maximum absorption peaks of probe 1 were located in the 509-552 nm range in organic solvents. Meanwhile, the probe possessed a high molar extinction coefficient (5.50 × 10⁴ M^-1 cm^-1 in DMSO) with high photostability. The maximum emission wavelength of the probe ranged from 572 nm to 644 nm, and it also had a large Stokes shift (126 nm in DMSO). In particular, the probe showed weak fluorescence in water (Φ = 0.016), whereas it displayed strong fluorescence at 595 nm in β-cyclodextrin (β-CD) solution (Φ = 0.13). In addition, cell colocalization experiments showed that probe 1 (3 μM) was located in the endoplasmic reticulum in cancer cells, while it could target lysosomes in normal cells. What's more, further cell imaging experiments demonstrated that the average fluorescence intensity of probe 1 (0.3 μM) in cancer cells increased with the addition of β-CD, but it did not occur in normal cells. The study provides a convenient way to distinguish cancer cells from normal ones, which has potential for application in the early detection of cancer.

Linker Molecules Convert Commercial Fluorophores into Tailored Functional Probes during Biolabelling

Many life‐science techniques and assays rely on selective labeling of biological target structures with commercial fluorophores that have specific yet invariant properties. Consequently, a fluorophore (or dye) is only useful for a limited range of applications, e.g., as a label for cellular compartments, super‐resolution imaging, DNA sequencing or for a specific biomedical assay. Modifications of fluorophores with the goal to alter their bioconjugation chemistry, photophysical or functional properties typically require complex synthesis schemes. We here introduce a general strategy that allows to customize these properties during biolabelling with the goal to introduce the fluorophore in the last step of biolabelling. For this, we present the design and synthesis of ‘linker’ compounds, that bridge biotarget, fluorophore and a functional moiety via well‐established labeling protocols. Linker molecules were synthesized via the Ugi four‐component reaction (Ugi‐4CR) which facilitates a modular design of linkers with diverse functional properties and bioconjugation‐ and fluorophore attachment moieties. To demonstrate the possibilities of different linkers experimentally, we characterized the ability of commercial fluorophores from the classes of cyanines, rhodamines, carbopyronines and silicon‐rhodamines to become functional labels on different biological targets in vitro and in vivo via thiol‐maleimide chemistry. With our strategy, we showed that the same commercial dye can become a photostable self‐healing dye or a sensor for bivalent ions subject to the linker used. Finally, we quantified the photophysical performance of different self‐healing linker–fluorophore conjugates and demonstrated their applications in super‐resolution imaging and single‐molecule spectroscopy.

Bleaching-Resistant Super-Resolution Fluorescence Microscopy

Photobleaching is the permanent loss of fluorescence after extended exposure to light and is a major limiting factor in super-resolution microscopy (SRM) that restricts spatiotemporal resolution and observation time. Strategies for preventing or overcoming photobleaching in SRM are reviewed developing new probes and chemical environments. Photostabilization strategies are introduced first, which are borrowed from conventional fluorescence microscopy, that are employed in SRM. SRM-specific strategies are then highlighted that exploit the on-off transitions of fluorescence, which is the key mechanism for achieving super-resolution, which are becoming new routes to address photobleaching in SRM. Off states can serve as a shelter from excitation by light or an exit to release a damaged probe and replace it with a fresh one. Such efforts in overcoming the photobleaching limits are anticipated to enhance resolution to molecular scales and to extend the observation time to physiological lifespans.

Benzyl-rich ligand engineering of the photostability of atomically precise gold nanoclusters

A series of [core+exo]-type Au8 nanoclusters (NCs) bearing two benzyl-rich ligands on the exo gold atoms were synthesized, which exhibit significant photostability and chemical stability. Furthermore, the benzyl-rich ligands enhance...

Dynamic Polymer Free Volume Monitored by Single-Molecule Spectroscopy of a Dual Fluorescent Flapping Dopant

Single-molecule spectroscopy (SMS) of a dual fluorescent flapping molecular probe (N-FLAP) enabled real-time nanoscale monitoring of local free volume dynamics in polystyrenes. The SMS study was realized by structural improvement of a previously reported flapping molecule by nitrogen substitution, leading to increased brightness (22 times) of the probe. In a polystyrene thin film at the temperature of 5 K above the glass transition, the spectra of a single N-FLAP molecule undergo frequent jumps between short- and long-wavelength forms, the latter one indicating planarization of the molecule in the excited state. The observed spectral jumps were statistically analyzed to reveal the dynamics of the molecular environment. The analysis together with MD and QM/MM calculations show that the excited-state planarization of the flapping probe occurs only when sufficiently large polymer free volume of more than, at least, 280 ų is available close to the molecule, and that such free volume lasts for an average of 1.2 s.

Dendronized Arm Snowflake Polymer as a Highly Branched Scaffold for Cellular Imaging and Delivery

Incorporation of branched structures is a major pathway to build macromolecules with desired three-dimensional (3D) structures, which are of high importance in the rational design of functional polymeric scaffolds. Dendrimers and hyperbranched polymers have been extensively studied for this purpose, but proper gain-of-function for these structures usually requires large enough molecular weights and a highly branched interior so that a spherical 3D core-shell architecture can be obtained, yet it is generally challenging to achieve precise control over the structure, high molecular weight, and high degree of branching (DoB) simultaneously. In this article, we present a set of snowflake-shaped star polymers with functional cores and dendronized arms, which ensure a high DoB and an overall globular conformation, thus facilitating the introduction of functional moieties onto the easily achieved scaffold without the need for high-generation dendrons. Using a polyglycerol dendron (PGD) as a proof of concept, we propose that this dendronized arm snowflake polymer (DASP) structure can serve as a better performing alternative to high-generation PGDs. DASPs with molecular weights of 750, 1220, 2120, and 3740 kDa were prepared with >85% yields in all cases, and we show that these DASPs have high encapsulating efficiency of Nile Red due to their high DoB and high biocompatibility due to their hydroxyl-rich nature after ketal removal, as well as high cell permeability that is molecular-weight-dependent. Introduced fluorophores such as fluorescein and difluoroboron 1,3-diphenylaminophenyl β-diketonate with suitable excitation wavelengths may turn the DASPs into stable, endosome-staining fluorophores with ultra-large Stokes shifts, narrowed emission bands, and suitability for long-term cellular tracing. Moreover, the scaffold can encapsulate antibiotic molecules and deliver them into phagolysosomes for efficient elimination of intracellular Staphylococcus aureus, which is insensitive toward many antibiotics but is a key target for the clinical success of methicillin-resistant Staphylococcus aureus infection treatment. Elimination of Staphylococcus aureus could be improved to >99.9% for chloramphenicol at 32 μg/mL with 450 μg/mL DASP.

Substituent screening effect on single-molecule photostability: comparison of three differently substituted porphycenes

Photobleaching of single molecules has been studied using confocal fluorescence microscopy for porphycene, a porphyrin isomer, and its two derivatives. Fourfold substitution of porphycene with bulkytert-butyl groups leads to the enhancement of photostability, even though the spectral, photophysical, and redox parameters remain similar. We attribute this effect to the increase of the efficiency of physical quenching of the chromophore triplet state by oxygen, compared with the yield of chemical reaction that leads to photobleaching. Analysis of the observed photon fluxes from single emitters embedded in a polymer film shows that the experiment based on fluorescence is biased towards detection of molecules which have oxygen-the triplet quencher-in their vicinity. The distribution of the measured photodegradation quantum yields is very heterogeneous, suggesting that physical and chemical quenching rates exhibit different distance and orientation dependences.

Substituent Effects on the Solubility and Electronic Properties of the Cyanine Dye Cy5: Density Functional and Time-Dependent Density Functional Theory Calculations

The aggregation ability and exciton dynamics of dyes are largely affected by properties of the dye monomers. To facilitate aggregation and improve excitonic function, dyes can be engineered with substituents to exhibit optimal key properties, such as hydrophobicity, static dipole moment differences, and transition dipole moments. To determine how electron donating (D) and electron withdrawing (W) substituents impact the solvation, static dipole moments, and transition dipole moments of the pentamethine indocyanine dye Cy5, density functional theory (DFT) and time-dependent (TD-) DFT calculations were performed. The inclusion of substituents had large effects on the solvation energy of Cy5, with pairs of withdrawing substituents (W-W pairs) exhibiting the most negative solvation energies, suggesting dyes with W-W pairs are more soluble than others. With respect to pristine Cy5, the transition dipole moment was relatively unaffected upon substitution while numerous W-W pairs and pairs of donating and withdrawing substituents (D-W pairs) enhanced the static dipole difference. The increase in static dipole difference was correlated with an increase in the magnitude of the sum of the Hammett constants of the substituents on the dye. The results of this study provide insight into how specific substituents affect Cy5 monomers and which pairs can be used to engineer dyes with desired properties.

Photo-switchable Fluorescence in Hydrogen-Bonded Liquid Crystals

A series of hydrogen-bonded liquid crystals showing switchable fluorescence is reported. The fluorescence behavior results from the unique combination of hydrogen bonding, liquid crystallinity, and photobasicity. Thus, the molecular mobility in the mesophase is essential for the reversible photo-initiated proton transfer switching on the fluorescence of the assemblies. The application potential of the materials for photo-patterning was demonstrated.

Dendrimers as Modulators of Brain Cells

Nanostructured hyperbranched macromolecules have been extensively studied at the chemical, physical and morphological levels. The cellular structural and functional complexity of neural cells and their cross-talk have made it rather difficult to evaluate dendrimer effects in a mixed population of glial cells and neurons. Thus, we are at a relatively early stage of bench-to-bedside translation, and this is due mainly to the lack of data valuable for clinical investigations. It is only recently that techniques have become available that allow for analyses of biological processes inside the living cells, at the nanoscale, in real time. This review summarizes the essential properties of neural cells and dendrimers, and provides a cross-section of biological, pre-clinical and early clinical studies, where dendrimers were used as nanocarriers. It also highlights some examples of biological studies employing dendritic polyglycerol sulfates and their effects on glia and neurons. It is the aim of this review to encourage young scientists to advance mechanistic and technological approaches in dendrimer research so that these extremely versatile and attractive nanostructures gain even greater recognition in translational medicine.

Self-Healing Dyes-Keeping the Promise?

Self-healing dyes have emerged as a new promising class of fluorescent labels. They consist of two units, a fluorescent dye and a photostabilizer. The latter heals whenever the fluorescent dye is in danger of taking a reaction pathway toward photobleaching. We describe the underlying concepts and summarize the developmental history and state-of-the-art, including latest applications in high-resolution microscopy, live-cell, and single-molecule imaging. We further discuss remaining limitations, which are (i) lower photostabilization of most self-healing dyes when compared to solution additives, (ii) limited mechanistic understanding on the influence of the biochemical environment and molecular oxygen on self-healing, and (iii) the lack of cheap and facile bioconjugation strategies. Finally, we provide ideas on how to further advance self-healing dyes, show new data on redox blinking caused by double-stranded DNA, and highlight forthcoming work on intramolecular photostabilization of fluorescent proteins.

Tuning the Brightness and Photostability of Organic Dots for Multivalent Targeted Cancer Imaging and Surgery

Specific labeling of biomarkers with bright and high photostable fluorophores is vital in fluorescent imaging applications. Here, we report a general strategy to develop single-molecule dendritic nanodots with finely tunable optical properties for in vivo fluorescent imaging. The well-defined nanodots are based on the divergent growth of biodegradable polylysine dendrimers with a fluorophore as the core. By tuning the size and surface chemistry, we obtained fluorescent nanodots with excellent brightness and photostability, favorable pharmacokinetics, and multivalent tumor-targeting capability. The nanodots provided robust, stable, long-lasting, and specific fluorescence enhancement in tumor tissue with an in situ tumor-to-normal ratio (TNR) of ∼3 and lasting over 5 days and an ex vivo TNR up to ∼17, holding considerable promise for cancer imaging and image-guided surgery. This strategy significantly improves the in vivo performance of fluorophores and can be applied to other modality imaging probes.

Photobleaching of organic fluorophores: quantitative characterization, mechanisms, protection

Photochemical stability is one of the most important parameters that determine the usefulness of organic dyes in different applications. This Review addresses key factors that determine the dye photostability. It is shown that photodegradation can follow different oxygen-dependent and oxygen-independent mechanisms and may involve both ¹S₁-³T₁ and higher-energy ¹S_n-³T_n excited states. Their involvement and contribution depends on dye structure, medium conditions, irradiation power. Fluorescein, rhodamine, BODIPY and cyanine dyes, as well as conjugated polymers are discussed as selected examples illustrating photobleaching mechanisms. The strategies for modulating and improving the photostability are overviewed. They include the improvement of fluorophore design, particularly by attaching protective and anti-fading groups, creating proper medium conditions in liquid, solid and nanoscale environments. The special conditions for biological labeling, sensing and imaging are outlined.

Tunable multi-color luminescence from a self-assembled cyanostilbene and cucurbit[7]uril in aqueous media

A tunable multicolor luminescent supramolecular system was designed in aqueous media employing the self-assembly of a cationic amphiphilic cyanostilbene and the host–guest chemistry of cucurbit[7]uril.

Water-soluble polyglycerol-dendronized poly(norbornene)s with functional side-chains

High molecular weight polyglycerol-dendronized poly(norbornene)s (PGD-PNBs) were prepared via ring-opening metathesis polymerization of norbornene monomers containing amine functional groups on the side-chains followed by dendron growth from the olefins of PNB backbones using iterative dihydroxylation and allylation. The fourth-generation PGD-PNB with a degree of polymerization of ca. 500 is thus functionalized with 16 peripheral hydroxyl groups as well as a single amine on each repeat unit of the PNB backbone. Furthermore, the amine functionality could be used to install hydrophobic fluorophores such as coumarin and pyrene, thereby obtaining the final PGD-PNB structures which are highly water-soluble and fluorescent.

Molecular Engineering of Near-Infrared Light-Responsive BODIPY-Based Nanoparticles with Enhanced Photothermal and Photoacoustic Efficiencies for Cancer Theranostics

Background: Engineering a single organic-molecule-based nanoparticle integrating precise diagnosis and effective therapy is of great significance for cancer treatment and future clinical applications but remains a great challenge. The goal of this study is to explore small organic molecule-based nanoparticles with high photothermal conversion efficiency for photoacoustic imaging-guided therapy. Methods: Heptacyclic B, O-chelated BODIPY structure (namely Boca-BODIPY) with strong near-infrared (NIR) absorption was designed as a theranostic agent through simply molecular engineering, in which heavy atoms and alkyl chains were introduced to promote its application for tumor theranostics. The Boca-BODIPY molecules are further encapsulated in reduced bovine serum albumin (BSA) through self-assembly. Results: The BSA-Boca-BODIPY exhibited excellent biocompatibility, extraordinary stability and high photothermal conversion efficiency up to 58.7%. The nanoparticles could dramatically enhance photoacoustic contrast of the tumor region, and the signal-to-noise ratio was increased about 14 times at 10 h post intravenous injection in 4T1 tumor-bearing mice. In addition, the nanoassemblies can efficiently convert laser energy (808 nm, 0.75 w cm-2, 5min) into hyperthermia for tumor ablation. Under the photoacoustic imaging-guided photothermal therapy (PTT), the 4T1 cancer cells were efficiently killed, no tumor recurrence and PTT-induced toxicity is observed. Conclusions: Molecular engineering is a promising way to design organic-molecule-based nanoparticles for cancer theranostics. Other organic-molecule-based nanoparticles which show great promise for imaging-guided cancer precision therapy can be engineered through this method.

Synthesis, Characterization, and Properties of Tetraphenylethylene-Based Tetrakis-NHC Ligands and Their Metal Complexes

The development of highly emissive dinuclear Ag^I or Au^I complexes [M₂ L](PF₆ )₂ (L=2 a, 2 b; M=Ag, Au) derived from tetraphenylethylene (TPE)-based tetrabenzimidazolin-2-ylidene ligands is reported. The new complexes exhibit a remarkable fluorescence enhancement compared to their parent benzimidazolium salts. The quantum yield (Φ_F ) value for salt H₄ -2 a(PF₆ )₄ in dilute solution (c=10^-5  m) was found to be less than 1 %, whereas its metal complexes show Φ_F values up to 55 % at similar solution concentration. This observation can be attributed to the rigidification of the TPE skeleton upon metalation resulting in a restriction of the intramolecular rotation of the phenyl groups. Functionalization of the complexes [M₂ 2 b](PF₆ )₂ (M=Ag, Au) with terminal coumarin groups and subsequent photoirradiation yielded the complexes [M₂ 3 b](PF₆ )₂ (M=Ag, Au) bearing a new type of ligand with an unaffected TPE moiety.

Synthesis of near-infrared absorbing and fluorescing thiophene-fused BODIPY dyes with strong electron-donating groups and their application in dye-sensitised solar cells

Thiophene-fused BODIPY dyes with two diethylaminophenyl groups as strong donors demonstrated near-infrared (NIR) absorption (λ_max: 783–812 nm, ε: 119 500–145 900) and fluorescence (F_max: 862–916 nm, Φ_f: 0.02–0.12) in dichloromethane.

Linkage induced enhancement of fluorescence in metal-carbene bond directed metallacycles and metallacages

Two new 1,4-dihydropyrrolo[3,2-b]pyrrole based aggregation induced emission (AIE)-inactive di- and tetra-imidazolium salts were employed with Ag(i) for the synthesis of a Ag-carbene bond directed metallacycle (1) and metallacage (2), respectively. Transmetalation of these complexes allowed their facile conversion to their respective Au(i)-metallacycle (3) and metallacage (4). The final assemblies exhibit linkage induced enhancement of fluorescence (LIEF). The free ligands are almost non-fluorescent (ΦF = 3.2, 3.4) in comparison to their metal-carbene counterparts (ΦF up to 32.0). Thus, without using any AIEgen, obtaining high emission efficiencies in complexes AgI-CNHC (1, 2) via linkage is a nice approach towards turn-on fluorescence.

In vitro and in vivo studies of a chlorin-based carbon nanocarrier with photodynamic therapy features

Carbonaceous materials have long been developed to utilize "nano-spaces" and numerous guest species could be encapsulated. A remarkable fluorescence difference has been observed after newly designed pyropheophorbide-a-appended carbon nanohorns were incorporated in a cellular medium and confocal microscopy was employed for the determination of the intracellular localization. Our study supported the role of carbon nanohorns as carriers of photodynamic therapy (PDT) agents and their heating behavior was discussed. We have developed a theranostic platform based on photosensitizer-conjugated carbon nanostructures and this system has been applied in an animal model. In addition, a negligible toxicity of CNH-Pyro was found in body weight experiments and histopathological examination of the major organs.

Synthesis, oligonucleotide incorporation and fluorescence properties in DNA of a bicyclic thymine analogue

Fluorescent base analogues (FBAs) have emerged as a powerful class of molecular reporters of location and environment for nucleic acids. In our overall mission to develop bright and useful FBAs for all natural nucleobases, herein we describe the synthesis and thorough characterization of bicyclic thymidine (bT), both as a monomer and when incorporated into DNA. We have developed a robust synthetic route for the preparation of the bT DNA monomer and the corresponding protected phosphoramidite for solid-phase DNA synthesis. The bT deoxyribonucleoside has a brightness value of 790 M⁻¹cm⁻¹ in water, which is comparable or higher than most fluorescent thymine analogues reported. When incorporated into DNA, bT pairs selectively with adenine without perturbing the B-form structure, keeping the melting thermodynamics of the B-form duplex DNA virtually unchanged. As for most fluorescent base analogues, the emission of bT is reduced inside DNA (4.5- and 13-fold in single- and double-stranded DNA, respectively). Overall, these properties make bT an interesting thymine analogue for studying DNA and an excellent starting point for the development of brighter bT derivatives.

High Singlet Oxygen Yield Photosensitizer Based Polypeptide Nanoparticles for Low-Power Near-Infrared Light Imaging-Guided Photodynamic Therapy

NIR photosensitizer is attractive for photodynamic therapy (PDT). Low-power light irradiation and imaging-guided PDT makes it possible to increase tissue penetration depth. The pyrrole-substituted iodinated BODIPY (BDPI) molecule was designed and synthesized, and it possesses an intense NIR absorption and emission band, and exhibits a high singlet oxygen quantum yield (Φ_Δ = 0.80) which leads remarkable cytotoxicity upon low power illumination (IC50 = 0.60 μg/mL, 6.1 mW/cm²). After being encapsulated with biocompatibility polypeptide PEG-PLys, polymeric micelles nanoparticles (PBDPI NPs) was obtained that are water-dispersed and passively tumor-targetable. Such enhanced accumulation in tumor area makes it easily traced in vivo due to its NIR fluorescence. In addition, such nanoparticles offer an unprecedented photodynamic therapeutic effect by using a low-power irradiation light, which makes it possible to kill cancer cells in deep tissue efficiently.

A Simple Mannose-Coated Poly (p-Phenylene Ethynylene) for Qualitative Bacterial Capturing

A mannose-functionalized poly (p-phenylene ethynylene) was rationally designed to achieve selective detection of bacteria. The polymer was constructed as a signaling unit and was modified by attaching aminoethyl mannose using the carboxylic acid group at the end of the linker. Incubation of Escherichia coli with the polymer yielded fluorescent bacteria aggregates through polyvalent interactions. The utility of the mannose functionalized polymer to detect E. coli expressing functional FimH mannose-specific lectin on their surface was also demonstrated. The sugar units displayed on the surface of the polymer retained their functional ability to interact with mannose-binding lectin. To determine the optimum binding time, we measured the fluorescence intensity of the polymer-bacteria suspension at intervals. Our results showed that binding in this system will reach an optimum level within 30 min of incubation. The polymer’s affinity for bacteria has been demonstrated and bacteria with a concentration of 10³ CFU mL⁻¹ can be detected by this system.

Reduction-sensitive polypeptide nanogel conjugated BODIPY-Br for NIR imaging-guided chem/photodynamic therapy at low light and drug dose

A heavy atoms modified reaction-active photosensitizer NHS-BODIPY-Br possessing efficient near infrared (NIR) fluorescence emission and singlet oxygen generation properties has been synthesized, which can be used for synchronous NIR imaging and photodynamic therapy (PDT). A reduction-sensitive PEGylated polypeptide nanogel was prepared by ring-opening polymerization (ROP) of l-cystine-N-carboxy anhydride. Poly (ethylene glycol) methyl ether was used as initiator and hydrophilic segment, the as-prepared nanogel was conjugated with the NHS-BODIPY-Br molecule by chemical linkage, and it can be directly used as a macrophotosentizer for NIR imaging-guided PDT. In addition, the nanogel also showed good encapsulating ability for doxorubicin (DOX). In the presence of glutathione (10 mM), the obtained NIR nanogel showed obvious reduction-induced drug release behavior. In vitro tests on internalization of the NIR nanogel by HepG2 cells indicated its efficiency in detecting cancer cells. Meanwhile, MTT assays performed on HepG2 cells confirmed that the cancer cells growth could be obviously suppressed (almost all cells) when exposed to an extremely low energy light (25 mW/cm², 10-15 J/cm²) and low dose of DOX (3-5 μg/ml), indicates an efficient NIR image-guided chem/photodynamic therapy.

Fluorescent analysis of bioactive molecules in single cells based on microfluidic chips

Single-cell analysis of bioactive molecules is an essential strategy for a better understanding of cell biology, exploring cell heterogeneity, and improvement of the ability to detect early diseases. In single-cell analysis, highly efficient single-cell manipulation techniques and high-sensitive detection schemes are in urgent need. The rapid development of fluorescent analysis techniques combined with microfluidic chips have offered a widely applicable solution. Thus, in this review, we mainly focus on the application of fluorescence methods in components analysis on microchips at a single-cell level. By targeting different types of biological molecules in cells such as nucleic acids, proteins, and active small molecules, we specially introduce and comment on their corresponding fluorescent probes, fluorescence labelling and sensing strategies, and different fluorescence detection instruments used in single-cell analysis on a microfluidic chip. We hope that through this review, readers will have a better understanding of single-cell fluorescence analysis, especially for single-cell component fluorescence analysis based on microfluidic chips.

Linear dendronized polyols as a multifunctional platform for a versatile and efficient fluorophore design

Linear dendronized polyols (LDPs)as a modular platform for bright, stable, and biocompatible polymeric fluorophores applicable for fluorescent bioimaging studies.