Tunable Fluorescence, Morphology, and Antibacterial Behaviors of Conjugated Oligomers via Host-Guest Supramolecular Self-Assembly.

Host-guest supramolecular self-assembly has become one facile but efficient way to regulate the optical properties of conjugated oligomers and construct promising photofunctional materials. Herein, we design two linear conjugated oligomers terminated with two or four pyridinium moieties, which show different 1:1 'head-to-tail' binding patterns with cucurbit[8]uril (CB[8]) to form host-guest supramolecules. After being encapsulated in the hydrophobic cavity of the CB[8] host, the fluorescence emission of the conjugated oligomers undergoes significant changes, resulting in tunable fluorescence color with enhanced quantum yields. Triggered by the aggregation of supramolecules, the regular or rigid binding modes lead to the formation of cuboids and spheroids in nanoscale, respectively. Due to the macrocyclic-confinement effect, the light-driven reactive oxygen species (ROS) production of the host-guest complex is increased significantly, thereby improving the photodynamic antibacterial performance toward Staphylococcus aureus (S. aureus).

Covalent Organic Frameworks as Efficient Photoinitiators and Cross-Linkers To Fabricate Highly Stretchable Hydrogels.

In this work, two kinds of imine-type covalent organic framework (COF) nanoparticles are demonstrated as efficient photocatalytic initiators to trigger the free-radical polymerization of acrylamide (AM) to prepare polyacrylamide (PAM) hydrogels under visible light irradiation, without any assistance from the co-initiator. Simultaneously, the COF nanoparticles bearing vinyl side groups (COF-V) promote covalent cross-linking of the polymer chains, which significantly reinforces the mechanical properties of the nanocomposite hydrogel. The obtained PAM/COF-V hydrogel is highly stretchable with an extraordinary elongation up to 3300% strain. On the other hand, the COF nanoparticles modified with methoxy moieties (COF-OMe) endow the resulting PAM/COF-OMe hydrogel with a promising fluorescence feature. In addition, this strategy provides a visible-light-regulated photocatalytic polymerization approach with a simplified recipe to fabricate COF-based nanocomposite hydrogels or resins with diverse functions.

In Situ Synthesis of Gold Nanoclusters in Covalent Organic Frameworks with Enhanced Photodynamic Properties and Antibacterial Performance.

In this work, ultrasmall gold nanoclusters (AuNCs) have been in situ synthesized in nanopores of covalent organic framework (COF) nanoparticles, which exhibited enhanced fluorescence, improved photosensitizing capabilities, and promising antibacterial performance. A small organic molecule, 1-vinylimidazole (Vim), was diffused into the nanopores of imine-based COFs and served as a reducing agent and capping ligand for the in situ synthesis of ultrasmall AuNCs. The as-obtained AuNCs were homogeneously distributed throughout the COF nanoparticles whose fluorescence intensity was enhanced remarkably. Due to the efficient electron transfer between AuNCs and COFs and increased separation of photogenerated electron-hole pairs, the light-triggered reactive oxygen species (ROS) production of COFs was prominently enhanced by AuNCs. Moreover, the obtained nanocomposites exhibited an efficient photodynamic killing behavior on Escherichia coli under visible light exposure. Thus, we provide a facile strategy to prepare COF/AuNC nanocomposites for ROS-related applications.

Internal Chemiluminescence Light-Driven Photocatalysis.

Photocatalysis is a promising strategy to tackle the problem of energy and pollution. To date, it is driven by external physical light sources, which are not always applicable in some practical applications. In this research, we explore the possibility of chemiluminescence as internal light to drive the photocatalysis reaction using graphitic carbon nitride as the catalyst. A biphasic reaction is employed where the light-generating reaction occurs in the oil phase, and the photocatalysis mainly takes place in the aqueous phase. This system exhibits efficient catalytic activity in degradation of rhodamine B, methyl orange, and methylene blue. The proof-of-concept design of chemiluminescence-driven photocatalysis provides an alternative strategy to address environmental issues and other photochemistry reactions.

Antibacterial Activity of Porous Gold Nanocomposites via NIR Light-Triggered Photothermal and Photodynamic Effects.

Phototherapeutic approaches, including photothermal therapy (PTT) and photodynamic therapy (PDT), have become a promising strategy to combat microbial pathogens and tackle the crisis brought about by antibiotic-resistant strains. Herein, porous gold nanoparticles (AuPNs) were synthesized as photothermal agents and loaded with indocyanine green (ICG), a common photosensitizer for PDT, to fabricate a nanosystem presenting near-infrared (NIR) light-triggered synchronous PTT and PDT effects. The AuPNs can not only convert NIR light into heat with a high photothermal conversion efficiency (50.6-68.5%), but also provide a porous structure to facilely load ICG molecules. The adsorption of ICG onto AuPNs was mainly driven by electrostatic and hydrophobic interactions with the surfactant layer of AuPNs, and the aggregate state of ICG significantly enhanced its generation of reactive oxygen species. Moreover, taking advantage of its synergistic PTT and PDT effect, the hybrid nanocomposites displayed a remarkable antibacterial effect to the gram-positive pathogen Staphylococcus aureus (S. aureus) upon 808 nm laser irradiation.

Intramolecular Charge Transfer-Based Conjugated Oligomer with Fluorescence, Efficient Photodynamics, and Photothermal Activities.

To develop efficient photoactive agents with satisfactory fluorescence, photodynamic, and photothermal effects is crucial for a phototherapeutic strategy to combat cancer diseases and pathogenic microbes. Herein, a water-soluble donor-acceptor-donor (D-A-D) structured conjugated oligomer was designed and synthesized, consisting of two cyclopenta-dithiophene (CDT) units as the electron donor and boron dipyrromethene (BODIPY) as the electron acceptor. Upon excitation, dual emission was observed for CDT-BODIPY with blue and red fluorescence peaks at 463 nm and at 730 nm, respectively, which was ascribed to intramolecular charge transfer (ICT). Due to the ICT effect, the singlet-to-triplet intersystem crossing rate of CDT-BODIPY was also enhanced, leading to an outstanding photodynamic behavior to produce reactive oxygen species (ROS). Meanwhile, its low bandgap also enabled it a moderate photothermal capability with a conversion efficiency of 33.1%. Taking advantage of its phototriggered activities, this conjugated oligomer exhibited an effective inhibition behavior on the pathogenic growth of Escherichia coli (E. coli), Staphylococcus aureus (S. aureus), and Candida albicans (C. albicans), which can be guided by dual-wavelength fluorescence imaging. This D-A-D type conjugated oligomer with balanced photophysical characteristics provides a promising strategy to imaging-guided photoactive therapy.

Near-Infrared Conjugated Oligomer for Effective Killing of Bacterial through Combination of Photodynamic and Photothermal Treatment.

In recent years, phototherapeutic strategies including photodynamic therapy (PDT) and photothermal treatment (PTT) have attracted extensive interest in biological and medical applications. To achieve high efficiency in therapy, it is crucial to develop promising agents possessing synergistic PDT and PTT effects, especially those triggered by single-wavelength near-infrared (NIR) light. Herein, a low-bandgap fluorene-based conjugated oligomer OF-Green-N with a donor-acceptor-donor (D-A-D) structure was synthesized, which had a broad absorption in both the visible and NIR range. Upon irradiation by 808 nm laser, the oligomer displayed a good photothermal capacity with a conversion efficiency of 37.7%, together with simultaneous photodynamic behavior which produced reactive oxygen species. By incubation with Escherichia coli, OF-Green-N was demonstrated to possess outstanding antibacterial activity owing to the synergistic effects of PDT/PTT. Moreover, its green fluorescence excited by 420 nm light also provides an opportunity for imaging-guided treatment.

Fluorescent Nanoparticles Synthesized by Carbon-Nitride-Stabilized Pickering Emulsion Polymerization for Targeted Cancer Cell Imaging.

Graphitic carbon nitride (CN) has been found to possess amphiphilic properties, enabling it to act as a solid emulsifier to stabilize the Pickering emulsion and subsequent polymerization. Herein, we used CN-stabilized Pickering emulsion polymerization to prepare molecularly imprinted polymer nanoparticles, which showed selective binding toward cancer cells. Taking advantage of its intrinsic amphiphilicity and emission properties, CN served as both the emulsifier in the polymerization process and emissive probe for cellular imaging application. Sialic acid (SA), as an important indicator of some certain cancers, was introduced into the polymer nanoparticles by forming reversible bonds with 4-vinylphenylboronic acid comonomer and removed by adjusting the pH value. The obtained SA-imprinted polymer nanoparticles exhibited good biocompatibility and excellent targeted imaging of DU 145 cells, which are prostate cancer cells having an SA-overexpressed surface. This work provides an easy, low-cost, low-toxicity, and large-scale strategy to prepare various functional polymer nanoparticles.

A Diarylethene-Based Photoswitch and its Photomodulation of the Fluorescence of Conjugated Polymers.

Photochromic diarylethene derivatives, which can reversibly switch the fluorescence of adjacent fluorophores between the ON and OFF states under light irradiation, have been widely used to construct photoswitchable materials. Herein, eight dithienylethene (DTE) groups are integrated onto one polyhedral oligomeric silsesquioxane (POSS) core, obtaining a novel super molecular photoswitch. After being doped into conjugated polymer nanoparticles, the POSS-DTE8 molecules show a higher contrast on/off photoswitching performance and a quicker responsive speed than free DTE molecules at same molar concentration of photochromic units. This enhanced photoswitching efficiency is attributed to the increased molecular interaction of the ring-open form and lowered energy of the ring-closed form of the DTE units on the POSS core, which is beneficial for the ring-closing reaction and subsequent energy transfer between photoswitch and fluorophores. In addition, POSS-DTE8 also exhibits good photomodulation behavior in the conjugated polymer film, giving it potential applications in optical devices.

Direct Observation of Carbon Nitride-Stabilized Pickering Emulsions.

Pickering emulsions are emulsions stabilized by solid particles located at surfaces/interfaces of liquid droplets that have promising applications for drug delivery and in nanomaterials synthesis. Direct observation of Pickering emulsions can be challenging. Normally, cryoelectron microscopy needs to be used to better understand these types of emulsion systems, but cryofreezing these emulsions may cause them to lose their original morphologies. In this work, we demonstrate that graphitic carbon nitride (g-C3N4) can stabilize oil-in-water (o/w) emulsions, with hexane illustrated as a typical oil phase. The g-C3N4-stabilized emulsions can act as an excellent platform for in situ study of emulsifying behavior from the mechanical point of view. Owing to its large lateral size and blue, stable fluorescence, the locations and motions of the g-C3N4 stabilizer can be finely in situ monitored by light microscopy, fluorescence microscopy, and confocal microscopy. Accordingly, we illustrate two stabilizing configurations of the g-C3N4 particles with respect to the emulsion droplets under static conditions. Further, we demonstrate the capability to manipulate emulsion droplets and investigate their response to external forces. We perform real-time observations of the g-C3N4 particles and the emulsion droplets that move in the continuous phase and study their adsorption kinetics toward each other. Finally, the π-π interaction between the stabilizer and aromatic liquid phase (e.g., toluene) is considered and studied as an influencing factor on emulsifying behavior.

Graphitic Carbon Nitride as a Distinct Solid Stabilizer for Emulsion Polymerization.

g-C3 N4 has been found to be highly functional in many fields, such as photocatalysis, electrocatalysis, and chemical analysis. Pickering emulsion polymerization is a fascinating strategy to fabricate a range of nanomaterials, in which the emulsion is stabilized by solid particles, rather than molecular surfactants. Herein, we demonstrate that g-C3 N4 can act as a remarkable stabilizer for Pickering emulsion polymerization. Contrary to normal Pickering systems, monodisperse polystyrene microspheres with tunable size, surface charge, and morphology were achieved using this approach. Importantly, the g-C3 N4 hybridized latex is highly processable and has exhibited multiple functions: manufacture of photonic crystals via self-organization, stabilizing Pickering emulsion owing to proper wettability, and acting as bioimaging agents with enriched fluorescent colors. Considering the easy synthesis and low cost of g-C3 N4 , our approach has a high potential for scale-up synthesis and practical translation.

Tunable fluorescence behaviors of a supramolecular system based on a fluorene derivative and cucurbit[8]uril and its application for ATP sensing.

In this work, we developed a supramolecular fluorescent system based on host-guest interactions between a fluorene derivative carrying two bispyridinium units (FPy) and cucurbit[8]uril (CB[8]). In aqueous solution, the system showed outstanding tunable emission properties. After being encapsulated into the rigid hydrophobic cavity of the CB[8] host, the fluorescence emission of fluorene had an obvious red-shift with enhanced quantum yield. Interestingly, the emission behavior of the FPy/CB[8] complex showed a two-step self-assembly process when the molar ratio of FPy to CB[8] changed from 1 : 1 to 1 : 2. Besides, the influence of several factors on the emission properties of the FPy/CB[8] complex was also investigated, like pH value, salt concentration, and temperature. Finally, the fluorescent FPy/CB[8] complexes displayed a good performance for detection of adenosine-5'-triphosphate (ATP), which can cause aggregation-induced quenching of the complexes via electrostatic attraction.

Hybridizing Carbon Nitride Colloids with a Shell of Water-Soluble Conjugated Polymers for Tunable Full-Color Emission and Synergistic Cell Imaging.

We present the preparation of a new multicolor emission system constructed from two complementary conjugated materials that are highly photoluminescent, that is, phenyl-modified carbon nitride (PhCN) colloids as the core and water-soluble conjugated polymers (WSCPs) adsorbed as the shell. The fluorescence bands of the PhCN and WSCPs effectively complement each other and the overall emission can be simply adjusted to fully cover the visible light spectrum with white light emission also accessible. Photophysical insights imply that the interactions between PhCN and WSCPs preserve the binary system from emission distortion and degradation, which is essential to delicately tune the overall fluorescence bands. Notably, the continuously tunable emission color is achieved under single-wavelength excitation (365 nm). This hybrid shows a synergistic permeation performance in cell imaging, that is, PhCN nanoparticles help the WSCP to enter the cells and therefore multicolor cellular imaging achieved.

Ultrabright Fluorescent Silica Nanoparticles Embedded with Conjugated Oligomers and Their Application in Latent Fingerprint Detection.

Fluorescent micro- and nanosized particles have a broad range of applications in biology, medicine, and engineering. For these uses, the materials should have high emission efficiency and good photostability. However, many organic fluorophores suffer from aggregation-induced quenching effects and photobleaching. Here, we used a simple method based on covalently blending a fluorescent conjugated oligomer with silica nanoparticles to achieve emission quantum yields as high as 97%. The resulting system also showed excellent stability under continuous light illumination, in a range of pH values and temperatures, and in common solvents. This fluorescent material showed outstanding properties, including highly efficient blue emission, low cost, low toxicity, and easy synthesis. Furthermore, its effectiveness for latent fingerprint detection was demonstrated as a proof of concept on various substrates. The obtained emissive fingerprint powder gave good optical/fluorescent images with high contrast and resolution between the ridges and spaces.

Preparation of Sialic Acid-Imprinted Fluorescent Conjugated Nanoparticles and Their Application for Targeted Cancer Cell Imaging.

Fluorescent conjugated polymer nanoparticles have attracted great interest for applications in biological imaging owing to their excellent optical properties and low cytotoxicity; however, a lack of effective targeting limits their use. In this work, we design and synthesize a fluorescent conjugated polymer modified with a phenylboronic acid group, which can covalently bind with cis-diol-containing compounds, such as sialic acid (SA), by forming a cyclic ester. However, the obtained conjugated polymer nanoparticles failed to discriminate between cancer cells, with or without SA overexpressed surfaces (such as DU 145 and HeLa cells, respectively). To address this problem, we introduced SA template molecules into the polymer nanoparticles during the reprecipitation process and then removed the template by adjusting the solution pH. The SA-imprinted nanoparticles showed a uniform size around 30 nm and enhanced fluorescence intensity compared with unmodified polymer nanoparticles. The SA-imprinted nanoparticles exhibited selective staining for DU 145 cancer cells and did not enter HeLa cells even after long incubation times. Thus, we present a facile method to prepare fluorescent nanoparticles for applications in targeted cancer cell imaging.

Aggregation-Induced Energy Transfer of Conjugated Polymer Materials for ATP Sensing.

Water-soluble conjugated polymers are attractive fluorescent materials for applications in chemical and biological sensing. The molecular wire effect of such polymers amplifies changes in the fluorescence signal, which can be used for detecting various analytes with high sensitivity. In this work, we report an efficient ratiometric fluorescent probe based on a water-soluble conjugated polymer that showed high sensitivity and selectivity toward adenosine 5'-triphosphate (ATP). The macromolecular probe consisted of a polyfluorene backbone doped with 5 mol % 1,4-dithienylbenzothiadiazole (DBT) modified by bis-imidazolium and oligo(ethylene glycol) moieties. Solutions of the polymer emitted purple fluorescence, which changed to red upon addition of ATP molecules. The addition of ATP caused the polymer to aggregate, which enhanced fluorescence resonance energy transfer efficiency from the fluorene segments to DBT units, leading to an increase in red emission. The ratio of the fluorescence at these different wavelengths (I655/I423) showed a strong dependence on the ATP concentration. PF-DBT-BIMEG also exhibited high selectivity for ATP sensing over other representative anions and discriminated it from adenosine 5'-diphosphate (ADP) and adenosine 5'-monophosphate (AMP). This can be explained by the much stronger electrostatic interactions between the polymer and ATP than the interactions between the polymer and ADP or AMP, as confirmed through molecular dynamics simulations.

Preparation of Hybrid Gold/Polymer Nanocomposites and Their Application in a Controlled Antibacterial Assay.

In this work, we report a photosensitizer-loaded hybrid nanostructure that shows high antibacterial efficiency after surface interaction with a lectin protein. Gold nanoparticles were generated on the polymer nanoparticle surface through an in situ reduction method and behaved as a plasmonic amplifier. After conjugation of the photosensitizer rose bengal onto the hybrid nanoparticles, higher phosphorescence intensity and generation of reactive oxygen species (ROS) were observed. The nanocomposites showed high antibacterial efficiency toward Gram-negative Escherichia coli treated with a lectin protein concanavalin A, which caused self-assembly of the bacteria and nanoparticles. Therefore, the as-prepared nanostructure considerably improved the effectiveness of ROS toward bacteria and provides an alternative strategy for controlled antibacterial assays.

Self-Assembly of Fluorescent Organic Nanoparticles for Iron(III) Sensing and Cellular Imaging.

Fluorescent organic nanoparticles have attracted increasing attentions for chemical or biological sensing and imaging due to their low-toxicity, facile fabrication and surface functionalization. In this work, we report novel fluorescent organic nanoparticles via facile self-assembly method in aqueous solution. First, the designed water-soluble fluorophore shows a weak and negligible intrinsic fluorescence in water. Upon binding with adenosine-5'-triphosphate (ATP), fluorescent nanoparticles were formed immediately with strongly enhanced fluorescence. These fluorescent nanoparticles exhibit high sensitivity and selectivity toward Fe(3+) sensing with detection limit of 0.1 nM. In addition, after incubation with HeLa cells, the fluorophore shows excellent imaging performance by interaction with entogenous ATP in cells. Finally, this fluorescent system is also demonstrated to be capable of Fe(3+) sensing via fluorescence quenching in cellular environment.

Phenyl-Modified Carbon Nitride Quantum Dots with Distinct Photoluminescence Behavior.

A novel type of quantum dot (Ph-CN) is manufactured from graphitic carbon nitride by "lining" the carbon nitride structure with phenyl groups through supramolecular preorganization. This approach requires no chemical etching or hydrothermal treatments like other competing nanoparticle syntheses and is easy and safe to use. The Ph-CN nanoparticles exhibit bright, tunable fluorescence, with a high quantum yield of 48.4 % in aqueous colloidal suspensions. Interestingly, the observed Stokes shift of approximately 200 nm is higher than the maximum values reported for carbon nitride based fluorophores. The high quantum yield and the large Stokes shift are related to the structural surface organization of the phenyl groups, which affects the π-electron delocalization in the conjugated carbon nitride networks and induces colloidal stability. The remarkable performance of the Ph-CN nanoparticles in imaging is demonstrated by a simple incubation study with HeLa cells.

Fabrication of Au@Pt multibranched nanoparticles and their application to in situ SERS monitoring.

Here, we present an Au@Pt core-shell multibranched nanoparticle as a new substrate capable of in situ surface-enhanced Raman scattering (SERS), thereby enabling monitoring of the catalytic reaction on the active surface. By careful control of the amount of Pt deposited bimetallic Au@Pt, nanoparticles with moderate performance both for SERS and catalytic activity were obtained. The Pt-catalyzed reduction of 4-nitrothiophenol by borohydride was chosen as the model reaction. The intermediate during the reaction was captured and clearly identified via SERS spectroscopy. We established in situ SERS spectroscopy as a promising and powerful technique to investigate in situ reactions taking place in heterogeneous catalysis.