Conjugated Polymer Nanoparticles Research Articles

Perspective of dye-encapsulated conjugated polymer nanoparticles for potential applications

Design of highly luminescent nanomaterials is an emerging area of research for photonic and bio-photonic applications. Nowadays, dye-encapsulated polymer nanoparticles (PNPs) are found to be very promising alternative next-generation luminescent nanomaterials because of extraordinary brightness, easy synthesis, higher photo-stability and nontoxic behaviour. Herein, we have highlighted the dynamics of the fluorophore molecules inside PNPs. Furthermore, we discuss the fundamental correlation of particle brightness with the size of the PNPs as well as population of the dye molecules inside the PNPs. Considering the resonance energy transfer process, generation of white light by varying the dye concentration and singlet oxygen generation using photosensitizer dye have been described. Finally, we discuss the importance of hybrids of conjugated PNPs for potential light harvesting systems such as photovoltaic and optoelectronic applications.

Controlling Photoswitching via pcFRET in Conjugated Polymer Nanoparticles

Nanoparticles prepared from conjugated polymers (CPNs or Pdots) are powerful fluorophores for sensing and imaging applications, including those that require fluorescence photoswitching. We and others have developed CPNs doped with photochromic dyes that act as acceptors in only one of their two forms via fluorescence resonance energy transfer (pcFRET). We recently developed visible-light-responsive CPNs doped with a reverse photochromic spirooxazine dye that has a thermally stable merocyanine form. Off-to-on fluorescence switching occurs when the merocyanine is switched to its nonquenching spirooxazine form. The on-state fluorescence intensity is more than 100 times greater when photoswitching occurs via FRET from the CPNs than when the dyes are excited directly. Temporal control of fluorescence intensity is achieved using a single-color input of variable intensity for fluorescence excitation (read-only mode) and photoswitching (read–write mode). Here, we present photokinetic measurements and simulations ...

Ultrafast Energy Transfer Followed by Electron Transfer in a Polymeric Nanoantenna-Based Light Harvesting System

A polymeric nanoantenna-based light harvesting system is prospective because of it captures more number of photons by a multichromophoric donor and subsequently transfers its energy to the acceptor. Here, we have designed an aqueous solution-based polymeric nanoantenna, where conjugated polymer nanoparticles (donor) are attached with Au nanoparticle-capped porphyrin (acceptor)-encapsulated bovine serum albumin protein for both energy transfer and electron transfer processes. Ultrafast fluorescence upconversion and transient absorption spectroscopic studies reveal that the ultrafast energy transfer occurs from the conjugated polymer nanoparticle to porphyrin in 130 fs, followed by the electron transfer from porphyrin to Au nanoparticles in 70 ps after photoexcitation. Furthermore, the antenna effect of this light harvesting system is found to be 79 at the donor to acceptor ratio of 16:1. Analysis reveals that this polymeric nanoantenna opens up a new avenue for designing a highly efficient aqueous solution...

Highly Sensitive Detection of Melamine Based on the Fluorescence Resonance Energy Transfer between Conjugated Polymer Nanoparticles and Gold Nanoparticles.

Adding melamine as additives in food products will lead to many diseases and even death. However, the present techniques of melamine detection require time-consuming steps, complicated procedures and expensive analytical apparatus. The fluorescent assay method was facile and highly sensitive. In this work, a fluorescence resonance energy transfer (FRET) system for melamine detection was constructed based on conjugated polymer nanoparticles (CPNs) and gold nanoparticles (AuNPs). The energy transfer efficiency is up to 82.1%, and the system is highly selective and sensitive to melamine detection with a lower detection limit of 1.7 nmol/L. Moreover, the interaction mechanism was explored. The results showed that the fluorescence of CPNs were firstly quenched by AuNPs, and then restored after adding melamine because of reducing FRET between CPNs and AuNPs. Lastly, the proposed method was carried out for melamine detection in powdered infant formula with satisfactory results.

Through Scalp and Skull NIR‐II Photothermal Therapy of Deep Orthotopic Brain Tumors with Precise Photoacoustic Imaging Guidance

Brain tumor is one of the most lethal cancers owing to the existence of blood-brain barrier and blood-brain tumor barrier as well as the lack of highly effective brain tumor treatment paradigms. Herein, cyclo(Arg-Gly-Asp-D-Phe-Lys(mpa)) decorated biocompatible and photostable conjugated polymer nanoparticles with strong absorption in the second near-infrared (NIR-II) window are developed for precise photoacoustic imaging and spatiotemporal photothermal therapy of brain tumor through scalp and skull. Evidenced by the higher efficiency to penetrate scalp and skull for 1064 nm laser as compared to common 808 nm laser, NIR-II brain-tumor photothermal therapy is highly effective. In addition, via a real-time photoacoustic imaging system, the nanoparticles assist clear pinpointing of glioma at a depth of almost 3 mm through scalp and skull with an ultrahigh signal-to-background ratio of 90. After spatiotemporal photothermal treatment, the tumor progression is effectively inhibited and the survival spans of mice are significantly extended. This study demonstrates that NIR-II conjugated polymer nanoparticles are promising for precise imaging and treatment of brain tumors.

Crosslinked fluorescent conjugated polymer nanoparticles for high performance explosive sensing in aqueous media

In this work, water dispersible crosslinked fluorescent poly(triphenylamine-co-benzothiadiazole)s (PTPABT) nanoparticles have been synthesized via Suzuki-type coupling (A3 + B2) in a toluene/water miniemulsion. Dialysis method was used to purify the PTPABT nanoparticles with a diameter range of 40–70 nm. The good dispersion property of the polymer in water could be attributed to the small sizes of the PTPABT nanoparticles. The obtained PTPABT nanoparticles possess microporous characteristic and display bright red emission in aqueous solution, which makes them possible to detect the nitro-aromatic explosive in aqueous media by monitoring the photoluminescence. The sensing property of the polymer nanoparticles towards 1,3,5-trinitrobenzene (TNB) in aqueous media has been researched, resulting a Stern-Volmer quenching constant Ksv of 1.22 × 104 M−1. The most attractive character of the conjugated polymer nanoparticles is the combination of both physical stability and solution-processability, thus making them good candidates for sensors and optoelectronic applications.

Magnetic conjugated polymer nanoparticles doped with a europium complex for biomedical imaging.

Self-assembling conjugated polymer nanoparticles containing PVK and PLGA-PEG as a matrix polymer were doped with both a luminescent rare-earth complex and magnetic nanoparticles (SPIONs), giving rise to materials that are both luminescent and magnetic. Nanoparticle sizes ranged from 80-110 nm without SPIONs and showed an increase in size (200-1000 nm) with additional SPION content (11-54%). Quantum yields (QYs) of 24% and 18% were measured for systems without and with 11% SPIONs, respectively. Optical properties were stable and suitable for biological imaging applications.

Photothermal-Responsive Conjugated Polymer Nanoparticles for the Rapid and Effective Killing of Bacteria

The emergence of drug-resistant bacterial strains makes antimicrobial treatment a big challenge. Thus, more novel and effective antimicrobial agents and treatments are urgently desired. Herein, we developed a facile and rapid photothermal antimicrobial nanoplatform based on near-infrared (NIR)-active and photothermal-responsive conjugated polymer nanoparticles (CPNs) functionalized with cell-penetrating peptide (CPNs-Tat). With a positively charged Tat peptide, CPNs-Tat could enhance the interaction with bacteria cells with the formation of CPNs-Tat/bacteria aggregation. Under NIR irradiation, CPNs-Tat could convert the light into heat efficiently and produce local hyperthermia to kill bacteria within a few minutes. This photothermal-responsive strategy offers a rapid and effective modality for combating bacterial infections.

Size-dependent properties of functional PPV-based conjugated polymer nanoparticles for bioimaging.

Conjugated polymer nanoparticle systems have gained significant momentum in the bioimaging field on account of their biocompatibility and outstanding spectroscopic properties. Recently, new control procedures have spawned custom-built functional poly(p-phenylene vinylene) (PPV). These facilitate the one-pot synthesis of semiconducting polymer NPs with incorporated surface functional groups, an essential feature for advanced biomedical applications. In this work, nanoparticles (NPs) of different sizes are synthesized consisting of the statistical copolymer CPM-co-MDMO-PPV with monomer units 2-(5'-methoxycarbonylpentyloxy)-5-methoxy-1,4-phenylenevinylene (CPM-PPV) and poly(2-methoxy-5-(3',7'-dimethoxyoctyloxy)-1,4-phenylenevinylene) (MDMO-PPV). To monitor potential implications of switching from a commonly used homopolymer to copolymer system, MDMO-PPV NPs were prepared as a control. The versatile combination of the miniemulsion and solvent evaporation method allowed for an easy adaptation of the NP size. Decreasing the diameter of functional PPV-based NPs up to 20 nm did not significantly affect their optical properties nor the biocompatibility of the bioimaging probe, as cell viability never dropped below 90%. The quantum yield and molar extinction coefficient remained stable at values of 1-2% and 106 M-1 cm-1 respectively, indicating an excellent fluorescence brightness. However, a threshold was observed to which the size could be lowered without causing irreversible changes to the system. Cell uptake varied drastically depended on size and material choice, as switching from homo- to copolymer system and lowering the size significantly increased NP uptake. These results clearly demonstrate that adjusting the size of functional PPV-based NPs can be achieved easily to a lower limit of 20 nm without adversely affecting their performance in bioimaging applications.

Fluorescence development of fingerprints by combining conjugated polymer nanoparticles with cyanoacrylate fuming

Selecting appropriate developing methods/reagents or their combination to enhance the effect for fingerprint development is of great significance for practical forensic investigation. Ethyl-2-cyanoacrylate ester (superglue) fuming is a popular method for “in-situ” developing fingerprints in forensic science, followed by fluorescence staining to enhance the contrast of the fingerprint image in some occasion. In this study, a series of fluorescent poly(p-phenylene vinylene) (PPV) nanoparticles (NPs) in colloidal solution were successfully prepared and the emission color was tuned via a simple way. The fuming process was carried out using a home-made device. The staining was accomplished by immersing a piece of absorbent cotton into the solution of NPs, and then gently applied on the fumed fingerprints for several times. The PPV NPs were found to have a better developing effect than Rhodamine 6G when excited by 365 nm UV lamp. Different emission colors of NPs are advantageous in developing fingerprints on various substrates. Mechanism study suggested that the NPs were embedded in the porous structure of the superglue resin. In all, the combination of fuming method with the staining by conjugated polymer NPs has been demonstrated to be successful for fluorescent fingerprint development and be promising for more practical forensic applications.

Tuning the Key Properties of Singlet Oxygen‐Responsive Acene‐Doped Conjugated Polymer Nanoparticles

AbstractThis paper describes the effects of nanoparticle composition on energy transfer and ratiometric fluorescent response to singlet oxygen (1O2) of a series of acene‐doped conjugated polymer nanoparticles (CPNs). These CPNs are comprised of the conjugated polymer poly [(9,9‐dioctylfluorenyl‐2,7‐diyl)‐alt‐co‐(1,4‐benzo‐(2,1′,3)‐thiadiazole) (F8BT) as the polymer donor matrix and one of four different 1O2‐sensitive acene acceptor dopants. In the dense chromophore matrix of the CPN, the quantum yield of fluorescence of each acene‐doped CPN matches or exceeds that of the undoped F8BT CPN. Reactivity with 1O2 of the acenes follows the same trend in the solid matrix of CPNs as previously found in dilute solution. The doping levels of acenes in the CP matrix have important implications for both the extent of energy transfer and the subsequent rates of ratiometric response. This study therefore lends important insight into the rational design of luminescent, stimuli‐responsive CPNs and the reactivity of singlet oxygen in heterogeneous material systems.

Photodynamic Therapy with Conjugated Polymer Nanoparticles: Recent Advances and Therapeutic Considerations

Many types of cancers require elevated levels of Reactive Oxygen Species (ROS) for uncontrolled proliferation. However, this also makes tumor cells more susceptible to ROS induced cell death by additional oxidative stress caused by external stimuli. By selectively targeting cancer cells and tumors that exhibit high levels of ROS with nanotechnology-based materials to trigger further elevation of ROS therapeutic possibilities become available. Specifically, light-activated treatment through Photodynamic Therapy (PDT) has been demonstrated as a feasible approach with Photophryn as the leading FDA approved sensitizer. However, such small molecule sensitizers do still have significant hurdles to overcome, including poor solubility, non-targeted delivery, and low absorption of light. In this mini review, recent advances in the development of Conjugated Polymer Nanoparticles (CP-NPs) solving these issues are discussed, including amplified ROS generation, tumor targeting, theranostic capabilities, and multimodal CP-NPs. We also give an outlook towards further needs in CP-NP development for clinical application.

Conjugated Polymer Nanoparticle–Graphene Oxide Charge‐Transfer Complexes

AbstractThe game‐changing role of graphene oxide (GO) in tuning the excitonic behavior of conjugated polymer nanoparticles is described for the first time. This is demonstrated by using poly(3‐hexylthiophene) (P3HT) as a benchmark conjugated polymer and employing an in situ reprecipitation approach resulting in P3HT nanoparticles (P3HTNPs) with sizes of 50–100 nm in intimate contact with GO. During the self‐assembly process, GO changes the crystalline packing of P3HT chains in the forming P3HTNPs from H to H/J aggregates exhibiting exciton coupling constants as low as 2 meV, indicating favorable charge separation along the P3HT chains. Concomitantly, π–π interface interactions between the P3HTNPs and GO sheets are established resulting in the creation of P3HTNPs–GO charge‐transfer complexes whose energy bandgaps are lowered by up to 0.5 eV. Moreover, their optoelectronic properties, preestablished in the liquid phase, are retained when processed into thin films from the stable aqueous dispersions, thus eliminating the critical dependency on external processing parameters. These results can be transferred to other types of conjugated polymers. Combined with the possibility of employing water based “green” processing technologies, charge‐transfer complexes of conjugated polymer nanoparticles and GO open new pathways for the fabrication of improved optoelectronic thin film devices.

Hydrogen Evolution at Conjugated Polymer Nanoparticle Electrodes

Currently, there is a global effort being made to reduce greenhouse gas emissions through the implementation of renewable energies. An attractive alternative to fossil fuels is hydrogen, as it can be stored, transported and used as on demand as a liquid fuel while producing only water vapor as a by-product. The production of hydrogen can be attained through the photoelectrochemical splitting of water into hydrogen and oxygen, representing a sustainable, carbon neutral method of hydrogen generation. Our research focuses on the use of conjugated polymers, namely poly(3-hexylthiophene) (P3HT), as photocathode materials to convert solar energy into hydrogen. Using phenyl-C61-butryic acid methyl ester (PCBM) as an electron acceptor to effectively separate the photogenerated electron-hole pair within the semiconducting polymer, we can take advantage of these separated charges to perform electrochemical reactions at the polymer/electrolyte interface. This work investigates the preparation of nanostructured organic thin films from P3HT:PCBM nanoparticles and their characterization as photoelectrodes for photoelectrochemical hydrogen evolution. The morphology and optoelectronic properties of the nanostructured photocathodes are compared with conventional, solution-cast thin films of P3HT:PCBM. The nanostructured photoelectrodes provide increased surface area compared with solution-cast films, as well as greater control of the nanoscale morphology within each nanoparticle, leading to enhanced P3HT:PCBM phase segregation. The photo-assisted deposition of platinum nanoparticles as hydrogen evolution reaction (HER) catalysts onto the nanostructured P3HT:PCBM photocathodes facilitates the photoreduction of protons to H2.

Conjugated Polymer Nanoparticles Based Fluorescent Electronic Nose for the Identification of Volatile Compounds.

A fluorescence sensing array (or fluorescent electronic nose) is designed on a disposable paper card using 36 sets of soluble conjugated polymeric nanoparticles (SCPNs) as sensors to easily identify wide ranges of volatile analytes, including explosives and toxic industrial chemicals (amines and pungent acids). A 108-dimensional vector obtained from the fluorescent color change in the sensing array is defined and directly treated as an index in a standard chemical library (30 kinds of volatile analytes and a control group). Hierarchical clustering analysis (HCA) and principal component analysis (PCA) indicated the diversity in electronic structures; saturated vapor pressure and miscibility of analytes are keys in differentiating the analytes, with electron-rich arenes and alkylamines enhancing fluorescence and electron-deficient analytes attenuating fluorescence. A support vector machine (SVM) works well to predict an unknown sample, reaching 99.5% accuracy. The excellent fluorescence stability (no fluorescence quenching after being exposed in air for one month) and high sensitivity (emission color changes within minutes when exposed to analytes) suggest that the fluorescent polymer-based electronic nose will play an important role in field detection and identification of a wide spreading of hazardous substances.

Conjugated Polymer Nanotherapeutics for Next Generation Photodynamic Therapy

First and second-generation photosensitizers for Photodynamic Therapy (PDT) are in clinical trials, with a few approved for clinical application. While effective, several drawbacks have remained unaddressed that could increase the impact of PDT as an efficient therapy, including lack of selectivity to diseased tissue, toxicity, low to moderate light absorption, and poor solubility of the sensitizers that results in low bioavailability. It’s likely that a new generation of PDT sensitizers must be developed to improve on these shortcomings. In this review, we summarize our progress in the development of Conjugated Polymer Nanoparticles as a next generation nanotherapeutic for Photodynamic Therapy (PDT). We show that their unprecedented light absorption, efficient ROS generation, high level of targeted delivery and selective uptake, absence of dark toxicity and high percentage of PDT induced cell mortality observed indicate a promising next generation PDT sensitizer. The simple design and ease of fabrication of the Conjugated Polymer Nanoparticles holds promise for broad applicability.

Second Near-Infrared Conjugated Polymer Nanoparticles for Photoacoustic Imaging and Photothermal Therapy.

Photothermal conversion in the second near-infrared (NIR-II) window allows deeper penetration and higher exposure to lasers, but examples of NIR-II photothermal agents are mainly formulated by inorganic compounds. In view of the underlying influence of inorganic materials, a novel NIR-II photothermal nanoagent based on a narrow band gap D-A conjugated polymer (TBDOPV-DT) with 2,2-bithiophene as the donor and thiophene-fused benzodifurandione-based oligo( p-phenylenevinylene) as the acceptor has been developed. More importantly, TBDOPV-DT nanoparticles (TBDOPV-DT NPs) are demonstrated to combine excellent photoacoustic imaging (PAI) and photothermal therapy (PTT) ability. TBDOPV-DT NPs exhibit dramatic photostability and heating reproducibility with a photothermal conversion efficiency of 50%. Especially, the NPs possess a remarkable PTT effect toward cancer cells in vitro and can eliminate tumor cells completely in vivo under 1064 nm laser irradiation, while no appreciable side effects have been observed. This study achieves PAI-guided cancer therapy and sheds light on the future of using organic polymer NPs for the NIR-II PTT of cancer.

Molecular Engineering of Photoacoustic Performance by Chalcogenide Variation in Conjugated Polymer Nanoparticles for Brain Vascular Imaging.

As conjugated polymer nanoparticles (CPNs) have attracted growing interest as photoacoustic (PA) imaging contrast agents, revelation of the relationship between the molecular structure of conjugated polymers and PA property is highly in demand. Here, three donor-acceptor-structured conjugated polymer analogs are designed, where only a single heteroatom of acceptor units changes from oxygen to sulfur to selenium, allowing for systematic investigation of the molecular structure-PA property relationship. The absorption and PA spectra of these CPNs can be facilely tuned by changing the heteroatoms of the acceptor units. Moreover, the absorption coefficient, and in turn the PA signal intensity, decreases when the heteroatom changes from oxygen to sulfur to selenium. As these CPNs exhibit weak fluorescence and similar photothermal conversion efficiency (≈70%), their PA intensities are approximately proportional to their absorption coefficients. The in vivo brain vasculature imaging in this study also demonstrates this trend. This study provides a simple but efficient strategy to manipulate the PA properties of CPNs through changing the heteroatom at key positions.

Metallated porphyrin-doped conjugated polymer nanoparticles for efficient photodynamic therapy of brain and colorectal tumor cells.

Assess biocompatibility, uptake and photodynamic therapy (PDT) mechanism of metallated porphyrin doped conjugated polymer nanoparticles (CPNs) in human brain and colorectal tumor cells and macrophages. CPNs were developed employing 9,9-dioctylfluorene-alt-benzothiadiazole, an amphiphilic polymer (PS-PEG-COOH), and platinum octaethylporphyrin. T98G, SW480 and RAW 264.7 cell lines were exposed to CPNs to assess uptake and intracellular localization. Additionally, a PDT protocol using CPNs was employed for thein vitro killing of cancer and macrophage cell lines. CPNs were well incorporated into glioblastoma and macrophage cells with localization in lysosomes. SW480 cells were less efficient incorporating CPNs with localization in the plasma membrane. In all cell lines PDT treatment was efficient inducing oxidative stress that triggered apoptosis.

Conjugated polymer nanoparticles-based fluorescent biosensor for ultrasensitive detection of hydroquinone

This work describes a simple and sensitive fluorescent method for detection of hydroquinone utilizing conjugated polymer nanoparticles (CPNs). The CPNs serve both as a catalyst to accelerate the conversion of hydroquinone to benzoquinone and a fluorescent probe. In the presence of hydroquinone, the fluorescence of CPNs can be effectively quenched by benzoquinone. The detection limit of hydroquinone was down to 5 nM and excellent selectivity toward possible interferences was obtained. This method was successfully applied for hydroquinone detection in lake water and satisfactory results were achieved.