Chemical defects in the highly fluorescent conjugated polymer dots

Biodistribution and Biotoxicity Assessment of Fluorescent Conjugated Polymer Dots

Conjugated polymer dots (Pdots) have shown potential in the biomedical fields due to their optical properties and customizable design. However, the limited research on the biotoxicity of Pdots hinders their further application and translation. Lipophilic Pdots are prone to adsorbing specific proteins, leading to targeted tissue accumulation. Therefore, lipophilic fluorescent Pdots (Bare-Pdots) are synthesized using the conjugated polymer poly[2-methoxy-5-(2'-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) to systematically evaluate their biodistribution and biotoxicity in stem cells, zebrafish embryos, and mice. It is observed that Bare-Pdots are readily internalized by cells and adhered to the embryonic chorion. Additionally, Bare-Pdots exhibit a distinct distribution in brown adipose tissue and heart, closely associated with phagocytosis of capillary endothelial cells involved in lipid metabolism. Notably, injection of Bare-Pdots at 5 mg kg-1 results in dysfunction of brown adipose tissue and an increased risk of obesity 90 days post-injection. Furthermore, hydrophilic COOH-Pdots and NH2-Pdots with reduced lipophilicity are synthesized using amphiphilic ligands. NH2-Pdots show similar distribution but lower biotoxicity compared to Bare-Pdots. Nevertheless, injection of COOH-Pdots at 5 mg kg-1 causes a decrease in white blood cells and renal tubular damage. These findings provide valuable insights for optimizing dosage to ensure the safe use of Pdots in preclinical applications.

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.

Aggregation-Induced Stimulated Emission of 100% Dye Microspheres

Dyes with aggregation-induced emission (AIE) properties have gained interests due to their bright luminescence in solid-state aggregates. While fluorescence from AIE dyes have been widely exploited, relatively little is known about aggregation-induced stimulated emission. Here, we investigated stimulated emission of tetraphenylethene (TPE)-based organoboron AIE dyes, TPEQBN, in thin films and in microcavity lasers. Using femtosecond pump-probe spectroscopy, gain coefficients up to 230 cm-1 at 500 nm were measured. Using rate equations, we analyzed concentration- and pump-dependent gain dynamics as well as laser build up dynamics. During laser oscillation, radiative stimulated emission allows high instantaneous quantum yield greater than 90% to be achieved. We fabricated solid-state microspheres made of 100% AIE dyes via microfluidic emulsion and solvent evaporation method. Coupled with high gain and high refractive index of 1.76, microspheres as small as 2 μm in diameter showed lasing by nanosecond pumping with a threshold of ~10 pJ μm-2. Polymer coated, but not bare, microspheres were internalized by live cells and generated narrowband cavity mode emission from within the cytoplasm. Our work shows the potential of AIE dyes as laser materials.

Ratiometric and visual determination of copper ions with fluorescent nanohybrids of semiconducting polymer nanoparticles and carbon dots

Developing nanohybrid composition based fluorescent carbon dots (CDs) for ratiometric detection of copper ions is highly appealing. Herein, a ratiometric sensing platform (GCDs@RSPN) for copper ions detection has been developed by loaded green fluorescence carbon dots (GCDs) on the surface of red emission semiconducting polymer nanoparticles (RSPN) through electrostatic adsorption. The GCDs, featuring abundant amino groups, can selectively bind copper ions to induce the photoinduced electron transfer, leading to fluorescence quenching. A good linearity within the range of 0-100 μM is obtained, and the limit of detection (LOD) is 0.577 μM by using obtained GCDs@RSPN as ratiometric probe to detect copper ion. Moreover, the paper-based sensor derived from GCDs@RSPN was successfully applied for the visual detection of Cu²⁺.

Two-photon ratiometric fluorescent probe based on NBD-amine functionalized semiconducting polymer nanoparticles for real-time imaging of hydrogen sulfide in living cells and zebrafish

The thiolysis of 7-nitro-1,2,3-benzoxadiazole amine (NBD-A) paves the way for specific sensing of H₂S over biothiols and real-time imaging in living organisms. Rational fabrication of NBD-A-based probe with ratiometric mode and two-photon excitation is highly appealing to achieve high quality bioimaging. In this work, the NBD-A molecules are assembled with poly(9,9-dioctylfluorenyl-2,7-diyl) polymer nanoparticles, defined as NBD@PFO, to construct two-photon ratiometric probes for H₂S detection through the fluorescence resonance energy transfer (FRET). For the construction of NBD@PFO nanohybrids, polymer nanoparticles are employed as the NBD-A molecular vehicle, energy donor and two-photon absorber, while NBD-A is served as the response unit and energy acceptor. Taking advantages of NBD-A and polymer nanoparticles, the obtained NBD@PFO probes exhibit high selectivity, fast response (<5 s), ratiometric detection and two-photon excitation. Our results indicate that NBD@PFO nanohybrids are successfully applied for monitoring of H₂S concentration in living cells and zebrafish, exhibiting great potential of polymer nanoparticles to improve the imaging capability of an organic small molecular probe.

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.

Engineering fluorescent semiconducting polymer nanoparticles for biological applications and beyond

We summarize the recent advances in engineering approaches to obtain functionalized semiconducting polymer nanoparticles (SPNs) for biological applications. The challenges and outlook of fabricating functionalized SPNs are also provided.

Ultrastable and Biofunctionalizable Conjugated Polymer Nanoparticles with Encapsulated Iron for Ferroptosis Assisted Chemodynamic Therapy

We report the development of novel tumor-targeted conjugated polymer nanoparticles (CPNPs) carrying iron for chemodynamic therapy (CDT). Tumor cell killing proceeds through ferroptosis, a reactive oxygen species (ROS) mechanism that is not dependent on external activation by, for example, light, as is the case in photodynamic therapy (PDT). The ferroptosis mechanism is also not heavily reliant on oxygen availability and is, therefore, promising for the treatment of hypoxic tumors. In this work, we apply this development to the case study of melanoma, a difficult to treat cancer in advanced stages due to resistance to chemotherapy. The iron-carrying CPNPs reported here are targeted to endothelin-B receptors (EDNRB) through endothelin-3 surface moieties (EDN3-CPNPs). Our results show excellent targeting to tumor cells that overexpress EDNRB, specifically for melanoma and bladder tumor cells. In these cases, efficient cell killing, over 80% at higher doses, was found. Conversely, tumor cells not targeted by the EDN3-CPNPs show little effects of CDT, with tumor cell death under 20% in most cases. The outcomes of our work demonstrate that EDN3-CPNPs enable ferroptosis-assisted CDT and present a new therapeutic avenue for tumor treatment.

Ratiometric Sensing for Alkaline Phosphatase Based on Two Independent Signals from in Situ Formed Nanohybrids of Semiconducting Polymer Nanoparticles and MnO2 Nanosheets

Ratiometric sensing systems transduced through independent analyte-sensitive response signals, which are simultaneously obtained from a single material, are highly desired to improve sensing reliability and sensitivity. In this study, a dual-model ratiometric sensing system with fluorescence and second-order light scattering (SOS) as transducing signals has been designed for the ratiometric detection of alkaline phosphatase (ALP). Semiconducting polymer nanoparticles (SPNs) made of poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-(1,4-benzo-{2,1',3}-thiadiazole)] are prepared and used as reducing and stabilizing agents to prepare MnO₂ nanosheets in situ through the reduction of KMnO₄. The formed SPNs@MnO₂ nanohybrids exhibit independent fluorescence and SOS response to ALP by using l-ascorbic acid 2-phosphate trisodium salt as the enzyme substrate. Benefiting from the simultaneous availability of fluorescence and SOS signals under the same excitation, a ratiometric probe has been constructed successfully for ALP sensing. Under optimal conditions, the SPNs@MnO₂ nanohybrids for ALP detection show a good linear detection range from 0.1 to 9.0 U L^-1 with a detection limit of 0.034 U L^-1. Additionally, a visual and portable sensing device for ALP detection is also constructed based on the fluorescent performances of the SPNs@MnO₂ nanohybrids. We believe the proposed method with the in situ preparation of SPN-based hybrid probes via the reducing ability of SPNs will pave a new way for the construction of multifunctional sensing materials in chemo-/biosensing applications.

Highly Stable and Luminescent Oxygen Nanosensor Based on Ruthenium-Containing Metallopolymer for Real-Time Imaging of Intracellular Oxygenation

Metal complex-based luminescent oxygen nanosensors have been intensively studied for biomedical applications. In terms of monitoring dynamics of intracellular oxygen, however, high-quality nanosensors are still badly needed, because of stringent requirements on stability, biocompatibility and luminescence intensity, aside from oxygen sensitivity. In this paper, we reported a type of highly luminescent and stable oxygen nanosensors prepared from metallopolymer. First, a novel ruthenium(II)-containing metallopolymer was synthesized by chelating the oxygen probe [Ru(bpy)₃]²⁺ with a bipyridine-branched hydrophobic copolymer, which was then doped into polymeric nanoparticles (NPs) by a reprecipitation method, followed by further conjugation to selectively target mitochondria (Mito-NPs). The resultant Mtio-NPs possessed a small hydrodynamic size of ∼85 nm, good biocompatibility and high stability resulting from PEGylation and stable nature of Ru-complex. Because the complexed [Ru(bpy)₃]²⁺ homogeneously resided on particle surface, Mito-NPs exhibited strong luminescence at 608 nm that was free of aggregation-caused-quenching, the utmost oxygen sensitivity of free [Ru(bpy)₃]²⁺ probe ( Q = 75%), and linear Stern-Volmer oxygen luminescence quenching plots. Taking advantage of the mitochondria-specific nanosensors, intracellular oxygenation and deoxygenation processes were real-time monitored for 10 min by confocal luminescence imaging, visualized by the gradual weakening (by more than 90%) and enhancing (by 50%) of the red emission, respectively.

Robot-Based High-Throughput Engineering of Alcoholic Polymer: Fullerene Nanoparticle Inks for an Eco-Friendly Processing of Organic Solar Cells

Development of high-quality organic nanoparticle inks is a significant scientific challenge for the industrial production of solution-processed organic photovoltaics (OPVs) with eco-friendly processing methods. In this work, we demonstrate a novel, robot-based, high-throughput procedure performing automatic poly(3-hexylthio-phene-2,5-diyl) and indene-C₆₀ bisadduct nanoparticle ink synthesis in nontoxic alcohols. A novel methodology to prepare particle dispersions for fully functional OPVs by manipulating the particle size and solvent system was studied in detail. The ethanol dispersion with a particle diameter of around 80-100 nm exhibits reduced degradation, yielding a power conversion efficiency of 4.52%, which is the highest performance reported so far for water/alcohol-processed OPV devices. By successfully deploying the high-throughput robot-based approach for an organic nanoparticle ink preparation, we believe that the findings demonstrated in this work will trigger more research interest and effort on eco-friendly industrial production of OPVs.

Highly Stable Conjugated Polymer Dots as Multifunctional Agents for Photoacoustic Imaging-Guided Photothermal Therapy

Theranostic nanomedicines involved in photothermal therapy (PTT) have received constant attention as promising alternatives to traditional therapies in clinic. However, most photothermal agents are limited by their instability and low photothermal conversion efficiency. In this study, we report new conjugated polymer dots (Pdots) as multifunctional agents for photoacoustic (PA) imaging-guided PTT. The novel 4,8-bis[5-(2-ethylhexyl)thiophen-2-yl]-2,6-bis(trimethylstannyl)benzo[1,2-b:4,5-b']dithiophene-6,6'-dibromo-N,N'-(2-ethylhexyl)isoindigo (BDT-IID) Pdots are readily fabricated though nanoreprecipitation and can absorb strongly in the 650-700 nm region. Furthermore, the BDT-IID Pdots possess a stable nanostructure and an extremely low biotoxicity. In particular, its photothermal conversion efficiency can be up to 45%. More importantly, our in vivo results exhibit that the BDT-IID Pdots are able to offer concurrently enhanced PA contrast and sufficient photothermal effect. Consequently, the BDT-IID Pdots can be exploited as a unique theranostic nanoplatform for PA imaging-guided PTT of tumors, holding great promise for their clinical translational development.

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.

Functionalized dye encapsulated polymer nanoparticles attached with a BSA scaffold as efficient antenna materials for artificial light harvesting

A potential strategy for a new generation light harvesting system is multi-chromophoric donor-acceptor pairs where light energy is absorbed by an antenna complex and subsequently transfers its energy to the acceptor via energy transfer. Here, we design a system of a functionalized polymer nanoparticle-protein scaffold for efficient light harvesting and white light generation where a dye doped polymer nanoparticle acts as a donor and a dye encapsulated BSA protein acts as an acceptor. Analysis reveals that 91.3% energy transfer occurs from the dye doped polymer nanoparticle to the dye encapsulated BSA protein. The antenna effect of this light harvesting system is found to be 31 at a donor to acceptor ratio of 0.82 : 1 which is unprecedented. The enhanced effective molar extinction coefficient of the acceptor dye is potential for the light harvesting system. Bright white light emission with a quantum yield of 14% under single wavelength excitation is obtained by changing the ratio of donor to acceptor. Analysis reveals that the efficient energy transfer in this polymer-protein assembly may open up new possibilities in designing artificial light harvesting systems for future applications.

Functionalization of emissive conjugated polymer nanoparticles by coprecipitation: consequences for particle photophysics and colloidal properties

The functionalization of polyfluorene (PFO) nanoparticles by coprecipitation of the conjugated polymer with an amphiphilic comb polymer, consisting of a hydrophobic polystyrene backbone with hydrophilic, carboxylic acid-terminated polyethylene oxide side-chains (PS-PEG-COOH), is investigated. The comb polymer affects the properties of the formed hybrid nanoparticles. Non-functionalized particles are typically larger (28 nm) than functionalized ones (20 nm); peak molar extinction coefficients are found to differ in a similar trend. Zeta potentials are negative, consistent with negative surface charge on PFO particles due to chemical defect formation, with additional charge on functionalized particles due to the pendant carboxylic acid groups. Emission quantum yields of functionalized particles are typically larger, consistent with lower efficiency of energy transfer to quenchers in smaller particles and weaker PFO interchain interactions due to chain dilution. The trend in per-particle fluorescence brightness values, as confirmed by single particle fluorescence imaging, reflects the nanoparticle extinction coefficients. Photostability studies on aqueous dispersions of hybrid particles indicate mild photobrightening under continuous illumination while PFO particles exhibit slow exponential emission decay. Functionalized particles are also resistant to aggregation during exposure to adenocarcinoma cells. Generally, the hybrid particles exhibit more favorable time-, pH- and medium-dependent stabilities, likely due to steric and electrostatic stabilization by PEG-carboxylic acid functionalities. Overall, the functionalized particles exhibit attractive properties: Reasonably small size, tight size distribution, high absorption cross section, radiative rate and emission quantum yield, excellent brightness and photostability, and good colloidal stability.

Anodic electrogenerated chemiluminescence behavior and the choline biosensing application of blue emitting conjugated polymer dots

The anodic electrochemiluminescence (ECL) behavior of poly(9,9-dioctylfluorenyl-2,7-diyl) (PFO) dots was studied and applied in oxidoreductase-based ECL biosensing using Chox as the model enzyme.

Semiconductor polymer dots induce proliferation in human gastric mucosal and adenocarcinoma cells

We investigated the cellular uptake behavior and cell viability of semiconducting polymer dots (Pdots) on human gastric adenocarcinoma (SGC-7901) cells and human gastric mucosal (GES-1) cells. MTT studies indicate the Pdot treatment induces obvious cell proliferation in both types of cell lines. We performed further investigations such as reactive oxygen species (ROS) generation and mitochondrial membrane potential (MMP) change, which indicate that the cell proliferation is in good agreement with the increase in the ROS and MMP levels. Moreover, expression of protein kinase B (Akt) decreased as the Pdot concentration increases, but the expression of protein dual-phosphorylated Erk (p-Erk) and phosphorylated c-Jun N-terminal kinases (p-JNK) were increased. These effects indicated that the Pdots could promote the growth of SGC-7901 cells and GES-1 cells by appropriately regulating the expressions of protein Akt, p-Erk, and p-JNK.

Functionalization of conjugated polymer nanoparticles for fluorescence photomodulation

The emission of conjugated polymer nanoparticles (CPNs or Pdots) is often tailored for specific uses by functionalizing CPNs with dyes that act as fluorescence resonance energy transfer (FRET) acceptors. A number of dye functionalization methods for CPNs have been developed, ranging from simple noncovalent doping to covalent attachment. We seek to develop guidelines for when noncovalent doping is acceptable and when covalent attachment is necessary to achieve the desired result. We present results of CPNs functionalized with photochromic spirooxazines by four different methods: simple doping, doping with an amphiphilic coating polymer, covalent functionalization prior to CPN formation, and covalent functionalization after CPN formation. The different CPNs are evaluated in terms of their fluorescence photomodulation properties to determine how the preparation method affects the CPN-dye photophysical interactions. Doping preparations yield the most efficient quenching of CPN emission due to shorter donor-acceptor distances in these CPNs compared to those with covalently tethered dyes. Aging studies reveal that the photochromic dyes in doped samples degrade over time to a far greater extent than those in covalently functionalized samples. These results suggest that dye-doped CPNs are appropriate for short-term experiments where highly efficient FRET is desired while covalent dye functionalization is a better choice for experiments executed over an extended time frame.

Conjugated polymer dots for ultra-stable full-color fluorescence patterning

Stable full-color fluorescence patterning are achieved by multicolor polymer-dot inks. The fluorescent patterns show extraordinary stability upon various treatments, offering a superior combination of bright fluorescence, excellent photostability, chemical resistance, and eco-friendship.

Fluorescent π-conjugated polymer dots versus self-assembled small-molecule nanoparticles: what's the difference?

Fluorescent nanoparticles based on π-conjugated small molecules and polymers are two different classes of π-conjugated systems that have attracted much interest. To date, both emerging classes have only been studied separately and showed no clear differences in their properties. Herein these nanoparticles are compared on the basis of a fluorene co-polymer and its corresponding small molecule. Both systems formed nanoparticles with the same diameter, whereas the fluorescence properties clearly differed. In case of the polymer the fluorescence diminished, whereas for the small molecules the fluorescence increased. In addition, the capability of encapsulation and release of a hydrophobic dye from the fluorescent nanoparticles was studied. For the polymer system, encapsulation was highly efficient and no release was observed, whereas for the small molecule system encapsulation was less efficient and release of the dye was observed. These studies show a clear difference between small molecules and polymers which has important implications for the design of fluorescent nanoparticles.

Highly fluorescent semiconducting polymer dots for biology and medicine

In recent years, semiconducting polymer nanoparticles have attracted considerable attention because of their outstanding characteristics as fluorescent probes. These nanoparticles, which primarily consist of π-conjugated polymers and are called polymer dots (Pdots) when they exhibit small particle size and high brightness, have demonstrated utility in a wide range of applications such as fluorescence imaging and biosensing. In this review, we summarize recent findings of the photophysical properties of Pdots which speak to the merits of these entities as fluorescent labels. This review also highlights the surface functionalization and biomolecular conjugation of Pdots, and their applications in cellular labeling, in vivo imaging, single-particle tracking, biosensing, and drug delivery. We discuss the relationship between the physical properties and performance, and evaluate the merits and limitations of the Pdot probes for certain imaging tasks and fluorescence assays. We also tackle the current challenges of Pdots and share our perspective on the future directions of the field.

The relative brightness of PEG lipid-conjugated polymer nanoparticles as fluid-phase markers in live cells

While conjugated polymer nanoparticles (CPNs) have been widely touted as ultra-bright labels for biological imaging, no direct comparative measurements of their intracellular brightness have been reported. Simple in vitro comparisons are not definitive since fluorophore brightness in vitro may not correspond with intracellular brightness. We have compared the fluorescence brightness of J774A.1 cells loaded with 24 nm methoxy-capped 2,000 M(r) polyethylene glycol lipid PFBT nanoparticles (PEG lipid-PFBT CPNs) to cells loaded with carboxy-functionalized quantum dots (Qdots) or a dextran-linked small molecule organic dye, Alexa Fluor 488 dextran (AF488-dex). Under conditions likely to be used for biological imaging or flow cytometry, these CPNs are 175× brighter than Qdots and 1,400× brighter than AF488-dex in cells. Evaluation of the minimum incubation concentration required for detection of nanoparticle fluorescence with a commercial flow cytometer indicated that the limit of detection for PEG lipid-PFBT CPNs was 19 pM (86 ppb), substantially lower than values obtained for Qdots (980 pM) or AF488-dex (11.2 nM). Investigation of the mechanism of cellular uptake of the three fluid-phase labels indicates that these particles are passively taken into macrophage cells via macropinocytosis without interaction with cell surface receptors, and ultimately localize in lysosomes. In addition, no cytotoxicity could be observed at any of the CPN concentrations tested. Together, these data suggest that these CPNs are appropriate and attractive candidates as fluid-phase markers with significantly greater fluorescence brightness than existing dyes or nanoparticles. We expect that these CPNs will find application in both imaging and flow cytometry.

Reversible photoswitching of spiropyran-conjugated semiconducting polymer dots

Semiconducting polymer dots (Pdots) recently have emerged as a new class of ultrabright fluorescent probes with promising applications in biological detection and imaging. We developed photoswitchable Pdots by conjugating photochromic spiropyran molecules onto poly[9,9-dioctylfluorenyl-2,7-diyl)-co-1,4-benzo-{2,1'-3}-thiadiazole)] (PFBT). The modulation of fluorescence was achieved by ultraviolet irradiation, which converted spiropyran into its visible-absorbing merocyanine form. The merocyanine efficiently quenched the fluorescence of PFBT via Förster resonance energy transfer (FRET). We then reversed the quenching by subsequent irradiation with visible light to get back the fluorescence of PFBT. This FRET-based photomodulation of Pdot fluorescence could be repeated multiple times. We next conjugated biomolecules onto the surface of these photoswitchable Pdots and demonstrated their specific cellular and subcellular labeling to different types of cells without any noticeable nonspecific binding. We anticipate these photoswitchable and biocompatible Pdots will be useful in developing bioimaging techniques in the future.

Importance of having low-density functional groups for generating high-performance semiconducting polymer dots

Semiconducting polymers with low-density side-chain carboxylic acid groups were synthesized to form stable, functionalized, and highly fluorescent polymer dots (Pdots). The influence of the molar fraction of hydrophilic side-chains on Pdot properties and performance was systematically investigated. Our results show that the density of side-chain carboxylic acid groups significantly affects Pdot stability, internal structure, fluorescence brightness, and nonspecific binding in cellular labeling. Fluorescence spectroscopy, single-particle imaging, and a dye-doping method were employed to investigate the fluorescence brightness and the internal structure of the Pdots. The results of these experiments indicate that semiconducting polymers with low density of side-chain functional groups can form stable, compact, and highly bright Pdots as compared to those with high density of hydrophilic side-chains. The functionalized polymer dots were conjugated to streptavidin (SA) by carbodiimide-catalyzed coupling and the Pdot-SA probes effectively and specifically labeled the cancer cell-surface marker Her2 in human breast cancer cells. The carboxylate-functionalized polymer could also be covalently modified with small functional molecules to generate Pdot probes for click chemistry-based bio-orthogonal labeling. This study presents a promising approach for further developing functional Pdot probes for biological applications.

Generation of functionalized and robust semiconducting polymer dots with polyelectrolytes

We describe a facile method to functionalize semiconducting polymer dots (Pdots) with polyelectrolytes. The polyelectrolyte coating dramatically improves the colloidal stability of the Pdots in solutions which are either of high ionic strength or contain bivalent metal ions: this feature allows Pdots to be used under physiologically relevant environments without losing their functionality. We conjugated the polyelectrolyte-coated Pdots with streptavidin to demonstrate their application in specific cell labeling.

Ratiometric fluorescence detection of mercury ions in water by conjugated polymer nanoparticles

We present dye-doped polymer nanoparticles that are able to detect mercury in aqueous solution at parts per billion levels via fluorescence resonance energy transfer (FRET). The nanoparticles are prepared by reprecipitation of highly fluorescent conjugated polymers in water and are stable in aqueous suspension. They are doped with rhodamine spirolactam dyes that are nonfluorescent until they encounter mercury ions, which promote an irreversible reaction that converts the dyes to fluorescent rhodamines. The rhodamine dyes act as FRET acceptors for the fluorescent nanoparticles, and the ratio of nanoparticle-to-rhodamine fluorescence intensities functions as a ratiometric fluorescence chemodosimeter for mercury. The light harvesting capability of the conjugated polymer nanoparticles enhances the fluorescence intensity of the rhodamine dyes by a factor of 10, enabling sensitive detection of mercury ions in water at levels as low as 0.7 parts per billion.

Coarse-Grained Simulations of the Effects of Chain Length, Solvent Quality, and Chemical Defects on the Solution-Phase Morphology of MEH-PPV Conjugated Polymers

A mesoscale coarse-grained model of the conjugated polymer poly(2-methoxy-5-(2′-ethylhexyloxy)-1,4-phenylenevinylene) (MEH-PPV) in implicit solvent is developed. The model is parametrized to reproduce the local structure and dynamics of an atomistic simulation model and accounts for the effects of solvent quality and saturation chemical defects on the polymer structure. Polymers with defect concentrations of 0 to 10 % are simulated using Langevin dynamics in tetrahydrofuran (THF) and in a model poor solvent for chain lengths and solution concentrations used experimentally. The polymer chains are extended in THF and collapse into compact structures in the poor solvent. The radius of gyration decreases with defect content in THF and agrees quantitatively with experiment. The structures formed in poor solvent by chains with 300 monomer units change from toroidal to cylindrical with increasing defect content, while chains containing 1000 monomers form cylinders regardless of defect content. These results have implications for energy transfer in MEH-PPV.