Single Molecule Nanoparticles of the Conjugated Polymer MEH−PPV, Preparation and Characterization by Near-Field Scanning Optical Microscopy

Confined semiconducting polymers with boosted NIR light-triggered H2O2 production for hypoxia-tolerant persistent photodynamic therapy

Hypoxia featured in malignant tumors and the short lifespan of photo-induced reactive oxygen species (ROS) are two major issues that limit the efficiency of photodynamic therapy (PDT) in oncotherapy. Developing efficient type-I photosensitizers with long-term ˙OH generation ability provides a possible solution. Herein, a semiconducting polymer-based photosensitizer PCPDTBT was found to generate 1O2, ˙OH, and H2O2 through type-I/II PDT paths. After encapsulation within a mesoporous silica matrix, the NIR-II fluorescence and ROS generation are enhanced by 3-4 times compared with the traditional phase transfer method, which can be attributed to the excited-state lifetime being prolonged by one order of magnitude, resulting from restricted nonradiative decay channels, as confirmed by femtosecond spectroscopy. Notably, H2O2 production reaches 15.8 μM min-1 under a 730 nm laser (80 mW cm-2). Further adsorption of Fe2+ ions on mesoporous silica not only improves the loading capacity of the chemotherapy drug doxorubicin but also triggers a Fenton reaction with photo-generated H2O2 in situ to produce ˙OH continuously after the termination of laser irradiation. Thus, semiconducting polymer-based nanocomposites enables NIR-II fluorescence imaging guided persistent PDT under hypoxic conditions. This work provides a promising paradigm to fabricate persistent photodynamic therapy platforms for hypoxia-tolerant phototheranostics.

Photophysics of fluorescent nanoparticles based on organic dyes - challenges and design principles

Fluorescent nanoparticles have become attractive for bioanalysis and imaging, due to their high brightness and photostability. Many different optical materials have been applied in fluorescent nanoparticles with a broad range of properties and characteristics. One appealing approach is the incorporation of molecular organic fluorophores in nanoparticles with the intention of transferring their known attractive solution-state properties directly to the nanoparticles. However, as molecular dyes are packed closely together in the nanoparticles their interactions most often result in fluorescence quenching and change in spectral properties making this approach challenging. In this perspective we will first discuss the origins of quenching and spectral shifts observed in dye based nanoparticles. On this background, we will then describe various designs of dye based NPs and how they address the challenges of dye-dye interactions and quenching. Our aim is to provide a general framework for understanding the supramolecular mechanisms that determine the photophysics of dye based nanoparticles. This framework of molecular photophysics and its relation to the internal structure of dye based nanoparticles can hopefully serve to assist rational design and optimization of new and improved dye based nanoparticles.

Rational Design of NIR-II Emitting Conjugated Polymer Derived Nanoparticles for Image-Guided Cancer Interventions

Due to the reduced absorption, light scattering, and tissue autofluorescence in the NIR-II (1000-1700 nm) region, significant efforts are underway to explore diverse material platforms for in vivo fluorescence imaging, particularly for cancer diagnostics and image-guided interventions. Of the reported imaging agents, nanoparticles derived from conjugated polymers (CPNs) offer unique advantages to alternative materials including biocompatibility, remarkable absorption cross-sections, exceptional photostability, and tunable emission behavior independent of cell labeling functionalities. Herein, the current state of NIR-II emitting CPNs are summarized and structure-function-property relationships are highlighted that can be used to elevate the performance of next-generation CPNs. Methods for particle processing and incorporating cancer targeting modalities are discussed, as well as detailed characterization methods to improve interlaboratory comparisons of novel materials. Contemporary methods to specifically apply CPNs for cancer diagnostics and therapies are then highlighted. This review not only summarizes the current state of the field, but offers future directions and provides clarity to the advantages of CPNs over other classes of imaging agents.

Conjugated Polymer/Recombinant Escherichia coli Biohybrid Systems for Photobiocatalytic Hydrogen Production

Biohybrid photocatalysts are composite materials that combine the efficient light-absorbing properties of synthetic materials with the highly evolved metabolic pathways and self-repair mechanisms of biological systems. Here, we show the potential of conjugated polymers as photosensitizers in biohybrid systems by combining a series of polymer nanoparticles with engineered Escherichia coli cells. Under simulated solar light irradiation, the biohybrid system consisting of fluorene/dibenzo [b,d]thiophene sulfone copolymer (LP41) and recombinant E. coli (i.e., a LP41/HydA BL21 biohybrid) shows a sacrificial hydrogen evolution rate of 3.442 mmol g-1 h-1 (normalized to polymer amount). It is over 30 times higher than the polymer photocatalyst alone (0.105 mmol g-1 h-1), while no detectable hydrogen was generated from the E. coli cells alone, demonstrating the strong synergy between the polymer nanoparticles and bacterial cells. The differences in the physical interactions between synthetic materials and microorganisms, as well as redox energy level alignment, elucidate the trends in photochemical activity. Our results suggest that organic semiconductors may offer advantages, such as solution processability, low toxicity, and more tunable surface interactions with the biological components over inorganic materials.

Development of a spiropyran-assisted cellulose aerogel with switchable wettability as oil sorbent for oil spill cleanup

This research presents the successful development and optimization of a spiropyran-assisted cellulose aerogel (CNF-SP) aerogel with UV-induced switchable wettability, and the evaluation of its performance as an effective oil sorbent for oil spill cleanup. The aerogel initially exhibited strong hydrophobicity (124°) and showed UV-induced switchable wettability due to the photo-response structure of spiropyran. Upon UV irradiation, the hydrophobicity of the aerogel could be switched to hydrophilicity (31°), while visible light irradiation could restore its hydrophobicity. The three-dimensional (3D) porous structure of the CNF-SP aerogel combined with the hydrophobic properties of spiropyranol led to its great oil adsorption performance (27-30 g/g of oil adsorption ratio). The central composite design (CCD) was applied to optimize the aerogel and investigate the effects of raw material ratio (i.e., carboxymethyl cellulose, carboxyethyl spiropyran, polyvinyl alcohol, and nano zinc oxide) on the oil sorption performance of the aerogel. The optimized CNF-SP aerogel demonstrated a high oil sorption efficiency, particularly in acid and cold environments. Moreover, the switchable function indicated that the aerogel exhibited reusability and renewability, with the added benefit of UV-induced oil recovery.

Metallopolymer strategy to explore hypoxic active narrow-bandgap photosensitizers for effective cancer photodynamic therapy

Practical photodynamic therapy calls for high-performance, less O2-dependent, long-wavelength-light-activated photosensitizers to suit the hypoxic tumor microenvironment. Iridium-based photosensitizers exhibit excellent photocatalytic performance, but the in vivo applications are hindered by conventional O2-dependent Type-II photochemistry and poor absorption. Here we show a general metallopolymerization strategy for engineering iridium complexes exhibiting Type-I photochemistry and enhancing absorption intensity in the blue to near-infrared region. Reactive oxygen species generation of metallopolymer Ir-P1, where the iridium atom is covalently coupled to the polymer backbone, is over 80 times higher than that of its mother polymer without iridium under 680 nm irradiation. This strategy also works effectively when the iridium atom is directly included (Ir-P2) in the polymer backbones, exhibiting wide generality. The metallopolymer nanoparticles exhibiting efficient O2•- generation are conjugated with integrin αvβ3 binding cRGD to achieve targeted photodynamic therapy.

Detection of Per- and Polyfluoroalkyl Substances (PFAS) by Interrupted Energy Transfer

The ubiquitous presence of per- and polyfluoroalkyl substances (PFAS) in aqueous environments has aroused societal concern. Nonetheless, effective sensing technologies for continuous monitoring of PFAS within water distribution infrastructures currently do not exist. Herein, we describe a ratiometric sensing approach to selectively detect aqueous perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS) at concentrations of μg ⋅ L-1 . Our method relies on the excitonic transport in a highly fluorinated poly(p-phenylene ethynylene) to amplify a ratiometric emission signal modulated by an embedded fluorinated squaraine dye. The electronic coupling between the polymer and dye occurs through overlap of π-orbitals and is designed such that energy transfer is dominated by an electron-exchange (Dexter) mechanism. Exposure to aqueous solutions of PFAS perturbs the orbital interactions between the squaraine dye and the polymer backbone, thereby diminishing the efficiency of the energy transfer and producing a "polymer-ON/dye-OFF" response. These polymer/dye combinations were evaluated in spin-coated films and polymer nanoparticles and were able to selectively detect PFAS at concentrations of ca. 150 ppb and ca. 50 ppb, respectively. Both polymer films and nanoparticles are not affected by the type of water, and similar responses to PFAS were found in milliQ and well water.

Bone Marrow Stromal Cells Sorted by Semiconducting Polymer Nanodots for Bone Repair

The use of bone marrow stromal cells (BMSCs) for bone defect repair has shown great promise due to their differentiation potential. However, isolating the BMSCs from various cell types within the bone marrow remains challenging. To tackle this issue, we utilized semiconducting polymer dots (Pdots) as markers to select the BMSCs within a specific time frame. The therapeutic efficacy of the obtained Pdot-labeled BMSCs was assessed in a bone defect model. Initially, we evaluated the binding capacity of the Pdots with four different types of cells present in the bone marrow including BMSCs, osteoblasts, macrophages, and vascular endothelial cells, in vitro. Notably, BMSCs showed the most rapid uptake of the Pdots, being labeled within only one h of coculture, while other cells took four h to become labeled. Moreover, by colocalizing the Pdots with Prrx1, Sca-1, OSX, F480, and CD105 in the bone marrow cells of monocortical tibial defect (MTD) mice in vivo, we determined the proportions of BMSCs, macrophages, and vascular endothelial cells among all labeled cells from 1 to 8 h after the Pdots injection. It was found that BMSCs have the highest proportion (92%) among all labeled cells extracted after 1 h of Pdots injection. The therapeutic efficacy of the obtained Pdots-labeled BMSCs (1 h) was assessed in a bone defect model. Results showed that the new bone accrual was significantly increased in the treatment of Pdots-labeled BMSCs compared to the bone marrow cell-treated group. Our study revealed that BMSCs screened by the Pdots could improve bone defect repair, suggesting a promising application of the Pdots in bone healing.

Amplification of Cerenkov luminescence using semiconducting polymers for cancer theranostics

The therapeutic efficacy of photodynamic therapy is limited by the ability of light to penetrate tissues. Due to this limitation, Cerenkov luminescence (CL) from radionuclides has recently been proposed as an alternative light source in a strategy referred to as Cerenkov radiation induced therapy (CRIT). Semiconducting polymer nanoparticles (SPNs) have ideal optical properties, such as large absorption cross-sections and broad absorbance, which can be utilized to harness the relatively weak CL produced by radionuclides. SPNs can be doped with photosensitizers and have nearly 100% energy transfer efficiency by multiple energy transfer mechanisms. Herein, we investigated an optimized photosensitizer doped SPN as a nanosystem to harness and amplify CL for cancer theranostics. We found that semiconducting polymers significantly amplified CL energy transfer efficiency. Bimodal PET and optical imaging studies showed high tumor uptake and retention of the optimized SPNs when administered intravenously or intratumorally. Lastly, we found that photosensitizer doped SPNs have excellent potential as a cancer theranostics nanosystem in an in vivo tumor therapy study. Our study shows that SPNs are ideally suited to harness and amplify CL for cancer theranostics, which may provide a significant advancement for CRIT that are unabated by tissue penetration limits.

Conjugated Polymers for Aptasensing Applications

Rapid and specific assaying of molecules that report on a pathophysiological condition, environmental pollution, or drug concentration is pivotal for establishing efficient and accurate diagnostic systems. One of the main components required for the construction of these systems is the recognition element (receptor) that can identify target analytes. Oligonucleotide switching structures, or aptamers, have been widely studied as selective receptors that can precisely identify targets in different analyzed matrices with minimal interference from other components in an antibody-like recognition process. These aptasensors, especially when integrated into sensing platforms, enable a multitude of sensors that can outperform antibody-based sensors in terms of flexibility of the sensing strategy and ease of deployment to areas with limited resources. Research into compounds that efficiently enhance signal transduction and provide a suitable platform for conjugating aptamers has gained huge momentum over the past decade. The multifaceted nature of conjugated polymers (CPs), notably their versatile electrical and optical properties, endows them with a broad range of potential applications in optical, electrical, and electrochemical signal transduction. Despite the substantial body of research demonstrating the enhanced performance of sensing devices using doped or nanostructure-embedded CPs, few reviews are available that specifically describe the use of conjugated polymers in aptasensing. The purpose of this review is to bridge this gap and provide a comprehensive description of a variety of CPs, from a historical viewpoint, underpinning their specific characteristics and demonstrating the advances in biosensors associated with the use of these conjugated polymers.

Ultratrace PFAS Detection Using Amplifying Fluorescent Polymers

Per- and poly(fluoroalkyl) substances (PFAS) are environmentally persistent pollutants that are of growing concern due to their detrimental effects at ultratrace concentrations (ng·L^-1) in human and environmental health. Suitable technologies for on-site ultratrace detection of PFAS do not exist and current methods require complex and specialized equipment, making the monitoring of PFAS in distributed water infrastructures extremely challenging. Herein, we describe amplifying fluorescent polymers (AFPs) that can selectively detect perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS) at concentrations of ng·L^-1. The AFPs are highly fluorinated and have poly(p-phenylene ethynylene) and polyfluorene backbones bearing pyridine-based selectors that react with acidic PFAS via a proton-transfer reaction. The fluorinated regions within the polymers partition PFAS into polymers, whereas the protonated pyridine units create lower-energy traps for the excitons, and emission from these pyridinium sites results in red-shifting of the fluorescence spectra. The AFPs are evaluated in thin-film and nanoparticle forms and can selectively detect PFAS concentrations of ∼1 ppb and ∼100 ppt, respectively. Both polymer films and nanoparticles are not affected by the type of water, and similar responses to PFAS were found in milliQ water, DI water, and well water. These results demonstrate a promising sensing approach for on-site detection of aqueous PFAS in the ng·L^-1 range.

Semiconducting polymer dots as fluorescent probes for in vitro biosensing

Semiconducting polymer dots (Pdots) have emerged as novel fluorescent probes with excellent characteristics, such as ultrahigh molar extinction coefficient, easy tunable absorption and emission bands, high brightness, and excellent photostability. Combined with good biocompatibility properties, much effort has been devoted to Pdots for in vivo biological imaging and therapy applications, such as deep-tissue fluorescent imaging, photodynamic therapy, photothermal therapy, and nanocarriers of genes or chemical drugs. Many reviews have been presented in these fields. On the other hand, a large number of studies employing Pdots for in vitro biosensing applications have been reported during the past few years, and there are barely any relevant reports to summarize the progress in this area. Hence, it is necessary to review these studies to promote the comprehensive application of Pdots. Herein, we introduce the properties and functionalization of Pdots, and systematically summarize the progress in the in vitro applications of Pdots, including the detection of DNAs, microRNAs, proteins, enzymatic activity, and some biological small molecules and ions. Finally, we share our perspectives on the future direction of this field.

Fluorescent Nanoparticles for Super-Resolution Imaging

Super-resolution imaging techniques that overcome the diffraction limit of light have gained wide popularity for visualizing cellular structures with nanometric resolution. Following the pace of hardware developments, the availability of new fluorescent probes with superior properties is becoming ever more important. In this context, fluorescent nanoparticles (NPs) have attracted increasing attention as bright and photostable probes that address many shortcomings of traditional fluorescent probes. The use of NPs for super-resolution imaging is a recent development and this provides the focus for the current review. We give an overview of different super-resolution methods and discuss their demands on the properties of fluorescent NPs. We then review in detail the features, strengths, and weaknesses of each NP class to support these applications and provide examples from their utilization in various biological systems. Moreover, we provide an outlook on the future of the field and opportunities in material science for the development of probes for multiplexed subcellular imaging with nanometric resolution.

Preparation, characterization, evaluation and mechanistic study of organic polymer nano-photocatalysts for solar fuel production

This review provides the guidelines and knowledge gained so far on current strategies used to prepare, optimize and investigate polymer nanoparticles for fuel production, highlighting the future directions of polymer nano-photocatalyst development.

Polymer Dots with Enhanced Photostability, Quantum Yield, and Two-Photon Cross-Section using Structurally Constrained Deep-Blue Fluorophores

Semiconducting polymer dots (Pdots) have emerged as versatile probes for bioanalysis and imaging at the single-particle level. Despite their utility in multiplexed analysis, deep blue Pdots remain rare due to their need for high-energy excitation and sensitivity to photobleaching. Here, we describe the design of deep blue fluorophores using structural constraints to improve resistance to photobleaching, two-photon absorption cross sections, and fluorescence quantum yields using the hexamethylazatriangulene motif. Scanning tunneling microscopy was used to characterize the electronic structure of these chromophores on the atomic scale as well as their intrinsic stability. The most promising fluorophore was functionalized with a polymerizable acrylate handle and used to give deep-blue fluorescent acrylic polymers with M_n > 18 kDa and Đ < 1.2. Nanoprecipitation with amphiphilic polystyrene-graft-(carboxylate-terminated poly(ethylene glycol)) gave water-soluble Pdots with blue fluorescence, quantum yields of 0.81, and molar absorption coefficients of (4 ± 2) × 10⁸ M^-1 cm^-1. This high brightness facilitated single-particle visualization with dramatically improved signal-to-noise ratio and photobleaching resistance versus an unencapsulated dye. The Pdots were then conjugated with antibodies for immunolabeling of SK-BR3 human breast cancer cells, which were imaged using deep blue fluorescence in both one- and two-photon excitation modes.

All-Conjugated Polymer Core-Shell and Core-Shell-Shell Particles with Tunable Emission Profiles and White Light Emission

Future applications of conjugated polymer particles (CPP) in medicine, organic photonics, and optoelectronics greatly depend on high performance and precisely adjustable optical properties of the particles. To meet these criteria, current particle systems often combine conjugated polymers with inorganic particles in core-shell geometries, extending the possible optical characteristics of CPP. However, current conjugated polymer particles are restricted to a single polymer phase composed of a distinct polymer or a polymer blend. Here, a synthetic toolbox is presented that enables the synthesis of monodisperse core-shell and core-shell-shell particles, which consist entirely of conjugated polymers but of different types in the core and the shells. Seeded and fed-batch dispersion polymerizations based on Suzuki-Miyaura-type cross-coupling are investigated. The different approaches allow accurate control over the created interface between the conjugated polymer phases and thus also over the energy transfer phenomena between them. This approach opens up completely new synthetic freedom for fine tuning of the optical properties of CPP, enabling, for example, the synthesis of individual white light-emitting particles.

Recent Developments in Semiconducting Polymer Dots for Analytical Detection and NIR-II Fluorescence Imaging

In recent years, semiconducting polymer dots (Pdots) have attracted enormous attention in applications from fundamental analytical detection to advanced deep-tissue bioimaging due to their ultrahigh fluorescence brightness with excellent photostability and minimal cytotoxicity. Pdots have therefore been widely adopted for a variety types of molecular sensing for analytical detection. More importantly, the recent development of Pdots for use in the optical window between 1000 and 1700 nm, popularly known as the "second near-infrared window" (NIR-II), has emerged as a class of optical transparent imaging technology in the living body. The advantages of the NIR-II region over the traditional NIR-I (700-900 nm) window in fluorescence imaging originate from the reduced autofluorescence, minimal absorption and scattering of light, and improved penetration depths to yield high spatiotemporal images for biological tissues. Herein, we discuss and summarize the recent developments of Pdots employed for analytical detection and NIR-II fluorescence imaging. Starting with their preparation, the recent developments for targeting various analytes are then highlighted. After that, the importance of and latest progress in NIR-II fluorescence imaging using Pdots are reported. Finally, perspectives and challenges associated with the emergence of Pdots in different fields are given.

Physical insights into protection effect of conjugated polymers by natural antioxidants

Conjugated polymers (CPs) known as organic semiconductors have been broadly applied in photovoltaic and light emitting devices due to their easy fabrication and flexibility. However, one of the bottlenecks limiting the application of CPs is their poor photostability upon continuous excitation which is one of the crucial parameters of CPs. How to improve the photostability of CPs is always one of the key questions in this field. In this work, we found that the photostability of poly(3-hexylthiophene-2,5-diyl) (P3HT) molecules can be largely improved by addition of vitamin E (VE) in bulk solution, solid films and single molecules. In solution and films, VE can not only significantly retard the photodegradation of P3HT but also enhance the fluorescence intensity. For individual P3HT molecules, with increasing VE concentrations, the on-time duration increases and the off-time duration becomes shorter. VE as natural antioxidants can not only donate electrons to the long-lived charged species but also quench the triplet states of CPs via energy transfer accelerating the depopulation process back to the ground state. The short duration time of the charged species and the triplet states provides higher fluorescence intensity. Furthermore, VE can also directly react with singlet oxygen or other reactive oxygen species (ROS) preventing them from reacting with CPs. These results not only provide an efficient strategy for improving the photostability of conjugated polymers in solution and films, but also shed light on better understanding the photophysics of conjugated polymers at single-molecule level.

Recent advances in semiconducting polymer dots as optical probes for biosensing

This review mainly summarized the recent results that used bright polymer dots (Pdots) for the detection of different analytes such as reactive oxygen species (ROS), metal ions, pH values, and a variety of biomolecules.

Enhanced optical imaging properties of lipid nanocapsules as vehicles for fluorescent conjugated polymers

Conjugated polymer nanoparticles (CPNs) have emerged as highly photostable probes for optical and photoacoustic imaging. However, the aggregation of conjugated polymer (CP) molecules upon nanoparticle formation is associated with fluorescence quenching, poor yields and mutable particle sizes. This study investigated whether the CP encapsulation within the liquid midchain triglyceride (MCT) core of lipid nanocapsules (LNCs) may achieve reduced packing of CP chains leading to a stable system with enhanced optical features. The red- and near infrared-emitting CPs, CN-PPV and PCPDTBT, showed precipitation and aggregation-induced quenching with concentrations >~25 µg/mL in MCT alone. Despite this, CP encapsulation within LNCs abolished quenching at concentrations up to 1500 µg/mL. PCPDTBT-LNCs exhibited a quantum yield of 2.8% and a higher signal:background ratio in an optical imaging phantom compared to literature reports of PCPDTBT encapsulated in PEG-PLGA nanoparticles. In contrast, PCPDTBT-LNCs had slightly lower photoacoustic amplitudes than reported PEG-PLGA systems. CP-LNCs were also stable in size (32 ± 0.7 nm) and photoluminescence over 21 days at 4 °C, 25 °C and 37 °C. In summary, encapsulation of CP within the liquid core of lipid nanocapsules enhances the optical properties of fluorescent CP.

Conjugated polymers as nanoparticle probes for fluorescence and photoacoustic imaging

In this review, the role of conjugated polymer nanoparticles (CPNs) in emerging bioimaging techniques is described.

Application of molecularly imprinted polymers as artificial receptors for imaging

Medical diagnostics aims at specific localization of molecular targets as well as detection of abnormalities associated with numerous diseases. Molecularly imprinted polymers (MIPs) represent an approach of creating a synthetic material exhibiting selective recognition properties toward the desired template. The fabricated target-specific MIPs are usually well reproducible, economically efficient, and stable under critical conditions as compared to routinely used biorecognition elements such as fluorescent proteins, antibodies, enzymes, or aptamers and can even be created to those targets for which no antibodies are available. In this review, we summarize the methods of polymer fabrication. Further, we provide key for selection of the core material with imaging function depending on the imaging modality used. Finally, MIP-based imaging applications are highlighted and presented in a comprehensive form from different aspects. STATEMENT OF SIGNIFICANCE: In this review, we summarize the methods of polymer fabrication. Key applications of Molecularly imprinted polymers (MIPs) in imaging are highlighted and discussed with regard to the selection of the core material for imaging as well as commonly used imaging targets. MIPs represent an approach of creating a synthetic material exhibiting selective recognition properties toward the desired template. The fabricated target-specific MIPs are usually well reproducible, economically efficient, and stable under critical conditions as compared to routinely used biorecognition elements, e.g., antibodies, fluorescent proteins, enzymes, or aptamers, and can even be created to those targets for which no antibodies are available.

Fluorescent PCDTBT Nanoparticles with Tunable Size for Versatile Bioimaging

Conjugated polymer nanoparticles exhibit very interesting properties for use as bio-imaging agents. In this paper, we report the synthesis of PCDTBT (poly([9-(1'-octylnonyl)-9H-carbazole-2,7-diyl]-2,5-thiophenediyl-2,1,3-benzothiadiazole-4,7-diyl-2,5-thiophene-diyl)) nanoparticles of varying sizes using the mini-emulsion and emulsion/solvent evaporation approach. The effect of the size of the particles on the optical properties is investigated using UV-Vis absorption and fluorescence emission spectroscopy. It is shown that PCDTBT nanoparticles have a fluorescence emission maximum around 710 nm, within the biological near-infrared "optical window". The photoluminescence quantum yield shows a characteristic trend as a function of size. The particles are not cytotoxic and are taken up successfully by human lung cancer carcinoma A549 cells. Irrespective of the size, all particles show excellent fluorescent brightness for bioimaging. The fidelity of the particles as fluorescent probes to study particle dynamics in situ is shown as a proof of concept by performing raster image correlation spectroscopy. Combined, these results show that PCDTBT is an excellent candidate to serve as a fluorescent probe for near-infrared bio-imaging.

Viscoelastic Conjugated Polymer Fluids

The introduction of optoelectronic functions into viscoelastic polymers can yield highly sophisticated soft materials for biomedical devices and autonomous robotics. However, viscoelasticity and excellent optoelectronic properties are difficult to achieve because the presence of a large number of π-conjugated moieties drastically stiffens a polymer. Here, we report a variation of additive-free viscoelastic conjugated polymers (VE-CPs) at room temperature by using an intact π-conjugated backbone and bulky, yet flexible, alkyl side chains as "internal plasticizers." Some of these polymers exhibit gel- and elastomer-like rheological behaviors without cross-linking or entanglement. Furthermore, binary blends of these VE-CPs exhibit a never-seen-before dynamic miscibility with self-restorable and mechanically induced fluorescence color changes.

Thieno[3,2-b]thiophene-DPP based near-infrared nanotheranostic agent for dual imaging-guided photothermal/photodynamic synergistic therapy

Diketopyrrolopyrrole (DPP) based organic molecules have drawn significant research attention as phototheranostic agents. Herein, based on thieno[3,2-b]thienyl-DPP (TT-DPP), a near-infrared small molecule photosensitizer diethyl 3,3'-((((2,5-bis(2-decyltetradecyl)-3,6-dioxo-2,3,5,6-tetrahydropyrrolo[3,4-c]pyrrole-1,4-diyl)bis(thieno[3,2-b]thiophene-5,2-diyl))bis-(4,1-phenylene))bis(7-bromo-10H-phenothiazine-10,3-diyl))(2E,2'E)-diacrylate (PDBr), with a high singlet oxygen (¹O₂) quantum yield of 67%, was developed. After nano-precipitation, the hydrophilic PDBr NPs present an encouraging photothermal conversion efficiency of 35.7% and excellent fluorescence/infrared-thermal imaging performance. In vitro studies disclosed the high phototoxicity but low dark cytotoxicity of PDBr NPs to tumor cells. Furthermore, PDBr NPs can effectively impede the tumor growth without noticeable side effects in living mice through imaging-guided synergistic photothermal/photodynamic therapy. Therefore, PDBr NPs could be a promising nanotheranostic agent for imaging-guided synergistic photothermal and photodynamic therapy in the clinic.

Unusually Strong Electrochemiluminescence from Iridium-Based Redox Polymers Immobilized As Thin Layers or Polymer Nanoparticles

A new class of redox metallopolymer based on cyclometalated iridium(III) centers is described, with unusually intense luminescence properties in aqueous media. We report the facile synthesis, photophysical and electrochemical characterization, supported by DFT calculations and their electrochemiluminescence (ECL) properties which, under some circumstances, are significantly greater than the analogous ruthenium-based materials. The photoluminescence (PL) and ECL of these materials are further dramatically enhanced when dispersed or immobilized as polymeric nanoparticles (PNPs). This aggregation-induced emission (AIE and AIECL) operates by providing important protection for the cyclometalated iridium(III) centers against the types of quenching processes which commonly afflict iridium-based luminophores in aqueous media. The results suggest interesting new avenues of research for the application of such materials in and PL and ECL-based detection and imaging as well as light-emitting devices.

Superresolution mapping of energy landscape for single charge carriers in plastic semiconductors

The performance of conjugated polymer devices is largely dictated by charge transport processes. However, it is difficult to obtain a clear relationship between conjugated polymer structures and charge transport properties, due to the complexity of the structure and the dispersive nature of charge transport in conjugated polymers. Here, we develop a method to map the energy landscape for charge transport in conjugated polymers based on simultaneous, correlated charge carrier tracking and single-particle fluorescence spectroscopy. In nanoparticles of the conjugated polymer poly[9,9-dioctylfluorenyl-2,7-diyl)-co-1,4-benzo-{2,1′-3}-thiadiazole)], two dominant chain conformations were observed, a blue-emitting phase (λ_max = 550 nm) and a red-emitting phase (λ_max = 595 nm). Hole polarons were trapped within the red phase, only occasionally escaping into the blue phase. Polaron hopping between the red-emitting traps was observed, with transition time ranging from tens of milliseconds to several seconds. These results provide unprecedented nanoscale detail about charge transport at the single carrier level.

To understand the complex nanoscale structure-property relationships in conjugated polymers for device applications, new methods for tracking charge transport are required. Here, the authors employ superresolution mapping to study the charge carrier dynamics in conjugated polymer nanoparticles.

Photochemical Control of Exciton Superradiance in Light-Harvesting Nanotubes

Photosynthetic antennae and organic electronic materials use topological, structural, and molecular control of delocalized excitons to enhance and direct energy transfer. Interactions between the transition dipoles of individual chromophore units allow for coherent delocalization across multiple molecular sites. This delocalization, for specific geometries, greatly enhances the transition dipole moment of the lowest energy excitonic state relative to the chromophore and increases its radiative rate, a phenomenon known as superradiance. In this study, we show that ordered, self-assembled light-harvesting nanotubes (LHNs) display excitation-induced photobrightening and photodarkening. These changes in quantum yield arise due to changes in energetic disorder, which in turn increases/decreases excitonic superradiance. Through a combination of experiment and modeling, we show that intense illumination induces different types of chemical change in LHNs that reproducibly alter absorption and fluorescence properties, indicating control over excitonic delocalization. We also show that changes in spectral width and shift can be sensitive measures of system dimensionality, illustrating the mixed 1-2D nature of LHN excitons. Our results demonstrate a path forward for mastery of energetic disorder in an excitonic antenna, with implications for fundamental studies of coherent energy transport.

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

Aim: 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. Materials & methods: 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 the in vitro killing of cancer and macrophage cell lines. Results & conclusion: 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.

Hybrid AgNPs/MEH-PPV nanocomplexes with enhanced optical absorption and photoluminescence properties

Fluorescent semiconducting conjugated polymer nanoparticles (CPNs) are promising candidates for enhanced luminescent devices and bioimaging.

Conjugated Polymer Nanoparticles for Bioimaging

During the last decade, conjugated polymers have emerged as an interesting class of fluorescence imaging probes since they generally show high fluorescence brightness, high photostability, fast emission rates, non-blinking behavior and low cytotoxicity. The main concern related to most conjugated polymers is their lack of hydrophilicity and thereby poor bio-availability. This can, however, be overcome by the formulation of conjugated polymer nanoparticles in aqueous medium. This review provides an overview of the different techniques employed for the preparation of conjugated polymer nanoparticles, together with methods to improve their photoluminescence quantum yields. For selective targeting of specific cells, dedicated surface functionalization protocols have been developed, using different functional groups for ligand immobilization. Finally, conjugated polymer nanoparticles have recently also been employed for theranostic applications, wherein the particles are simultaneously used as fluorescent probes and carriers for anti-tumor drugs.

Plasmon-enhanced luminescence in novel complex conjugated polymer nanoparticles

A core-shell structure of novel complex conjugated polymer nanoparticles (CPNs) consisting of poly(2-methoxy,5-(2'-ethylhexyloxy)-1,4-phenylenevinylene), polyethyleneimine (PEI) is developed. PEI is used to construct CPN@PEI core-shell structure through electrostatic attraction, and shell thickness can be controlled by PEI. Small Au-Ag alloy nanoparticles (ANPs) are then inserted into CPN@PEI core-shell structure to plasmonically tune luminescence properties. The coupling structure with double polymer core-shell CPN@PEI and ANPs presents unique luminescent characters, and maximum luminescence enhancement is realized when shell thickness is 8.6 nm. The strategies taking polymer as shell material in construction of core-shell complex CPNs and tuning optical properties by ANPs shall have significant values in applications of CPNs as probes and fluorescent tags in biological science.

Hyperbranched Phosphorescent Conjugated Polymer Dots with Iridium(III) Complex as the Core for Hypoxia Imaging and Photodynamic Therapy

Real-time monitoring of the contents of molecular oxygen (O₂) in tumor cells is of great significance in early diagnosis of cancer. At the same time, the photodynamic therapy (PDT) could be realized by highly toxic singlet oxygen (¹O₂) generated in situ during the O₂ sensing, making it one of the most promising methods for cancer therapy. Herein, the iridium(III) complex cored hyperbranched phosphorescent conjugated polymer dots with the negative charges for hypoxia imaging and highly efficient PDT was rationally designed and synthesized. The incomplete energy transfer between the polyfluorene and the iridium(III) complexes realized the ratiometric sensing of O₂ for the accurate measurements. Furthermore, the O₂-dependent emission lifetimes are also used in photoluminescence lifetime imaging and time-gated luminescence imaging for eliminating the autofluorescence remarkably to enhance the signal-to-noise ratio of imaging. Notably, the polymer dots designed could generate the ¹O₂ effectively in aqueous solution, and the image-guided PDT of the cancer cells was successfully realized and investigated in detail by confocal laser scanning microscope. To the best of our knowledge, this represents the first example of the iridium(III) complex cored hyperbranched conjugated polymer dots with the negative charges for both hypoxia imaging and PDT of cancer cells simultaneously.

Effect of Confinement on Photophysical Properties of P3HT Chains in PMMA Matrix

The influence of arrangement of poly(3-hexylthiophene) (P3HT) chains embedded into poly(methyl methacrylate) (PMMA) matrix on photophysical properties, such as electronic absorption spectrum, band gap, and photoluminescence quantum yield, of the formed P3HT aggregates have been studied. It has been found that variation of P3HT fraction in PMMA matrix from 25 to 2 wt% is accompanied with the increasing quantum yield of photoluminescence, red shift of the band gap, and structural change of P3HT crystallites. The above changes are accompanied with disruption of the continuous network of P3HT fraction into smaller P3HT particles with size ranged from several microns to several tens of nanometers. The results are interpreted in terms of the changing intermolecular packing and reduced intramolecular torsional disorder. It is discussed that the most contribution to the above changes comes from P3HT molecules at the interface of P3HT cluster and PMMA environment.

Photoactive Donor-Acceptor Composite Nanoparticles Dispersed in Water

A major issue that inhibits the large-scale fabrication of organic solar modules is the use of chlorinated solvents considered to be toxic and hazardous. In this work, composite particles of poly[N-9'-heptadecanyl-2,7-carbazole-alt-5,5-(4,7-di-2-thienyl-2',1',3'-benzothiadiazole] (PCDTBT) and [6,6]-phenyl C71 butyric acid methyl ester (PC₇₁BM) were obtained in water from a versatile and a ready-to-market methodology based on postpolymerization miniemulsification. Depending on the experimental conditions, size-controlled particles comprising both the electron donor and the electron acceptor were obtained and characterized using transmission electron microscopy (TEM), atomic force microscopy (AFM), small-angle neutron scattering (SANS), UV-visible absorption, and fluorescence spectroscopy. Intimate mixing of the two components was definitely asserted through PCDTBT fluorescence quenching in the composite nanoparticles. The water-based inks were used for the preparation of photovoltaic active layers that were subsequently integrated into organic solar cells.

Bright conjugated polymer nanoparticles containing a biodegradable shell produced at high yields and with tuneable optical properties by a scalable microfluidic device

This study compares the performance of a microfluidic technique and a conventional bulk method to manufacture conjugated polymer nanoparticles (CPNs) embedded within a biodegradable poly(ethylene glycol) methyl ether-block-poly(lactide-co-glycolide) (PEG_5K-PLGA_55K) matrix. The influence of PEG_5K-PLGA_55K and conjugated polymers cyano-substituted poly(p-phenylene vinylene) (CN-PPV) and poly(9,9-dioctylfluorene-2,1,3-benzothiadiazole) (F8BT) on the physicochemical properties of the CPNs was also evaluated. Both techniques enabled CPN production with high end product yields (∼70-95%). However, while the bulk technique (solvent displacement) under optimal conditions generated small nanoparticles (∼70-100 nm) with similar optical properties (quantum yields ∼35%), the microfluidic approach produced larger CPNs (140-260 nm) with significantly superior quantum yields (49-55%) and tailored emission spectra. CPNs containing CN-PPV showed smaller size distributions and tuneable emission spectra compared to F8BT systems prepared under the same conditions. The presence of PEG_5K-PLGA_55K did not affect the size or optical properties of the CPNs and provided a neutral net electric charge as is often required for biomedical applications. The microfluidics flow-based device was successfully used for the continuous preparation of CPNs over a 24 hour period. On the basis of the results presented here, it can be concluded that the microfluidic device used in this study can be used to optimize the production of bright CPNs with tailored properties with good reproducibility.