A water‐soluble neutral fluorescent conjugated oligomer (FBT) is integrated with graphene oxide (GO) to form a hybrid nanoprobe with extremely low fluorescence background due to the robust quenching ...capability of GO. The contact between GO and FBT can be effectively shielded by Concanavalin A because of the strong specific protein–carbohydrate interaction, which ultimately allows for light‐up visual detection of lectin and Escherichia coli.
This Feature Article summarizes the recent advances of water‐soluble fluorescent conjugated polyelectrolytes (CPEs) in bioimaging. Apart from a brief overview of traditional linear CPEs, a special ...emphasis is placed on CPEs that can self‐assemble into or are born with three‐dimensional nano‐architectures, including grafted CPEs, hyperbranched CPEs, and polyhedral oligomeric silsesquioxanes(POSS)‐based CPE derivatives. These CPEs naturally form nanoparticles with sizes ranging from 3 to 100 nm in aqueous media, and possess reactive functional groups for bioconjugation or complexation with desired biorecognition elements. The tunable size, low cytotoxicity, good photostability, and ease of surface modification ultimately enable these CPEs with wide applications in in vitro intracellular protein sensing, cell detection, in vivo cell imaging and drug tracking. Moreover, traditional linear CPEs can be transformed into uniform nanoparticles by complexation with oppositely charged biomolecules to allow for cell detection and in situ drug release monitoring. The work featured herein not only reveals the important molecular design principles of CPEs for different imaging tasks, but also highlights the promising directions for the further development of CPE‐based imaging materials.
Conjugated polyelectrolytes with three‐dimensional size‐tunable nano‐architectures, including grafted, hyperbranched, and polyhedral oligomeric silsesquioxanes (POSS) based derivatives, can serve as bright, biocompatible and photostable fluorescent imaging materials, allowing for in vitro intracellular protein sensing, cell detection as well as in vivo cell imaging and drug tracking.
Two cationic poly(fluorene‐alt‐benzothiadiazole)s with different side chains are designed and synthesized. Both polymers show low fluorescence in aqueous solution due to the charge‐transfer character ...of the polymer's excited states. Fluorescence turn‐on biosensors for heparin detection and quantification are developed, taking advantage of complexation‐induced aggregation, which increases the polymer fluorescence in aqueous solution. It is found that good polymer water‐solubility is beneficial to the sensitivity and fluorescence contrast of the heparin turn‐on sensor as a result of the low fluorescence background. Moreover, stronger complexation between the polymer/heparin leads to a substantially larger fluorescence increase in the presence of heparin relative to that in the presence of its analog, hyaluronic acid (HA), allowing discrimination of heparin from HA. Heparin quantification with a practical calibration range covering the whole therapeutic dosing levels (0.2–8 U mL−1) is realized based on the polymer with good water‐solubility. This investigation provides a new insight for designing conjugated polymers with a light‐up signature for biomolecular sensing.
Conjugated polyelectrolytes can be used as light‐up probes for chemical and biomolecular sensing. Cationic poly(fluorene‐alt‐benzothiadiazole)s have low fluorescence in aqueous solution and exhibit aggregation‐enhanced fluorescence, which make them macromolecular probes for heparin detection and quantification.
This review summarizes recent advances in the science and applications of conjugated polyelectrolytes (CPEs), with an emphasis on direct visual sensing, cellular imaging, and the fabrication of ...optoelectronic devices. CPEs backbones that incorporate donor−acceptor units are useful for direct visual sensing, whereas CPEs with hyperbranched structures, or biocompatible long side chains, are particularly useful for cellular imaging. With specially designed counterions, CPEs also demonstrate unique function in device fabrication and operation, for example, in dye-sensitized solar cells (DSSCs), bulk heterojunction (BHJ) solar cells, polymer light-emitting diodes (PLEDs), polymer light-emitting electrochemical cells (PLECs), and organic thin film transistors (OFET). Additionally, new strategies to modify and optimize CPE properties for specific applications are provided. The work summarized herein not only illustrates relationships between molecular structures and function, but also highlights how the structural versatility of CPEs makes them a unique category of multifunctional materials with the potential for fulfilling a variety of optical and electronic applications in solution, mixed media, and in the solid state.
A red‐fluorescent conjugated polyelectrolyte (CPE, P2) is grafted with dense poly(ethylene glycol) (PEG) chains via click chemistry and subsequently modified with folic acid to form a molecular brush ...based cellular probe (P4). P4 self‐assembles into a core–shell nanostructure in aqueous medium with an average size of 130 nm measured by laser light scattering. As compared to P2, P4 possesses not only a substantially higher quantum yield (11%), but also reduced nonspecific interactions with biomolecules in aqueous medium due to the shielding effect of PEG. In conjunction with its high photostability and low cytotoxicity, utilization of P4 as a far‐red/near‐infrared cellular probe allows for effective visualization and discrimination of MCF‐7 cancer cells from NIH‐3T3 normal cells in a high contrast, selective, and nonviral manner. This study thus demonstrates a flexible molecular brush approach to overcome the intrinsic drawbacks of CPEs for advanced bioimaging applications.
A molecular brush composed of a red‐fluorescent conjugated polymer backbone and dense PEG grafting chains is synthesized via click chemistry to serve as an efficient far‐red/near infrared fluorescent probe. This molecular brush overcomes the intrinsic drawbacks of conjugated polyelectrolytes to possess high quantum yield with minimal nonspecific interactions in biological media, allowing for targeted cancer cell imaging in a high‐contrast, selective and nonviral manner.
Grain size is an important component trait of grain yield, which is frequently threatened by abiotic stress. However, little is known about how grain yield and abiotic stress tolerance are regulated. ...Here, we characterize GSA1, a quantitative trait locus (QTL) regulating grain size and abiotic stress tolerance associated with metabolic flux redirection. GSA1 encodes a UDP-glucosyltransferase, which exhibits glucosyltransferase activity toward flavonoids and monolignols. GSA1 regulates grain size by modulating cell proliferation and expansion, which are regulated by flavonoid-mediated auxin levels and related gene expression. GSA1 is required for the redirection of metabolic flux from lignin biosynthesis to flavonoid biosynthesis under abiotic stress and the accumulation of flavonoid glycosides, which protect rice against abiotic stress. GSA1 overexpression results in larger grains and enhanced abiotic stress tolerance. Our findings provide insights into the regulation of grain size and abiotic stress tolerance associated with metabolic flux redirection and a potential means to improve crops.
A facile strategy is developed to synthesize dual‐modal fluorescent‐magnetic nanoparticles (NPs) with surface folic acid by co‐encapsulation of a far‐red/near‐infrared (FR/NIR)‐emissive conjugated ...polymer (PFVBT) and lipid‐coated iron oxides (IOs) into a mixture of poly(lactic‐co‐glycolic‐acid)‐poly(ethylene glycol)‐folate (PLGA‐PEG‐FOL) and PLGA. The obtained NPs exhibit superparamagnetic properties and high fluorescence, which indicates that the lipid coated on IOs is effective at separating the conjugated polymer from IOs to minimize fluorescence quenching. These NPs are spherical in shape with an average diameter of ≈180 nm in water, as determined by laser light scattering. In vitro studies reveal that these dual‐modal NPs can serve as an effective fluorescent probe to achieve targeted imaging of MCF‐7 breast cancer cells without obvious cytotoxicity. In vivo fluorescence and magnetic resonance imaging results suggest that the NPs are able to preferentially accumulate in tumor tissues to allow dual‐modal detection of tumors in a living body. This demonstrates the potential of conjugated polymer based dual‐modal nanoprobes for versatile in vitro and in vivo applications in future.
Conjugated polymer based nanoparticles as fluorescent‐magnetic probes with targeting ability to folate‐receptor‐overexpressed cancer cells is reported. In vivo far‐red/near‐infrared fluorescence and magnetic resonance imaging studies suggest that the conjugated polymer based dual‐modal imaging probes hold great promise in advanced bioimaging applications.
A new bottom‐up strategy is used to construct water‐soluble organic/inorganic fluorescent unimolecular nanoparticles based on polyhedral oligomeric silsesquioxane (POSS) and conjugated ...oligoelectrolyte. Their high quantum yield, good cytocompatibility, and unique whole‐cell permeability could serve as a light‐harvesting energy donor to amplify the intracellular dye fluorescence for high‐quality biological imaging through fluorescence resonance energy transfer (see image).
Both kinds of solubility: An amphiphilic reduced graphene oxide (rGO) composite is synthesized by using a novel coil‐rod‐coil conjugated triblock copolymer as the π–π binding stabilizer. Such a ...graphene‐based composite can be dissolved not only in organic solvents with low polarity (such as toluene and chloroform) but also in water‐miscible solvents with high polarity (for example methanol).
A new cationic polyfluorene derivative with 20 mol % 2,1,3-benzothiadiazole (BT) content was synthesized via Suzuki cross-coupling polymerization. The high charge density and cationic oligo(ethylene ...oxide) side chains endue the polymer with a good water solubility (∼12 mg/mL), leading to a low inherent BT emission background in buffer. Addition of negatively charged heparin into the polymer solution induces polymer aggregation, giving rise to enhanced energy transfer from the fluorene segments to the BT units. With increasing heparin concentrations, the orange BT emission intensity progressively increases at the expense of the blue fluorene emission. In contrast, addition of hyaluronic acid, an analogue of heparin, results in an insignificant enhancement in BT emission. This selective optical signature not only allows distinguishing heparin from hyaluronic acid but also highlights the importance of electrostatic attraction between the polymer and the analyte in an energy transfer process. Heparin quantification is demonstrated by the linear intensity increase in the BT emission as a function of heparin concentration, providing a practical calibration scope ranging from 30 nM to 48 μM. Moreover, the distinguishable solution fluorescent color at different heparin concentrations makes naked-eye heparin detection and quantification feasible. This study hence reports a general approach to construct convenient multicolor biosensors using cationic conjugated polymers with energy donor−acceptor architecture.
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