A BODIPY‐Based Donor/Donor–Acceptor System: Towards Highly Efficient Long‐Wavelength‐Excitable Near‐IR Polymer Dots with Narrow and Strong Absorption Features

Bright long‐wavelength‐excitable semiconducting polymer dots (LWE‐Pdots) are highly desirable for in vivo imaging and multiplexed in vitro bioassays. LWE‐Pdots have been obtained by incorporating a near‐infrared (NIR) emitter into the backbone of a polymer host to develop a binary donor–acceptor (D–A) system. However, they usually suffer from severe concentration quenching and a trade‐off between fluorescence quantum yield (Φ_f) and absorption cross‐section (σ). Herein, we describe a ternary component (D₁/D₂–A) strategy to achieve ultrabright, green laser‐excitable Pdots with narrow‐band NIR emission by introducing a BODIPY‐based assistant polymer donor as D₁. The D₁/D₂–A Pdots possess improved Φ_f and σ compared to corresponding binary D₂–A Pdots. Their Φ_f is as high as 40.2 %, one of the most efficient NIR Pdots reported. The D₁/D₂–A Pdots show ultrahigh single‐particle brightness, 83‐fold brighter than Qdot 705 when excited by a 532 nm laser. When injected into mice, higher contrast in vivo tumor imaging was achieved using the ternary Pdots versus the binary D–A Pdots.     

Polymer Dots Compartmentalized in Liposomes as a Photocatalyst for In Situ Hydrogen Therapy

Semiconducting polymer dots (Pdots) have recently attracted considerable attention because of their photocatalytic activity as well as tunable optical band gap. In this contribution, we describe the therapeutic application of Pdots through in situ photocatalytic hydrogen generation. Liposomes were employed as nanoreactors to confine the Pdot photocatalyst, reactants, intermediates, and by‐products. Upon photon absorption by the Pdots, the catalytic cycle is initiated and repeated within the aqueous interior, while the H₂ product diffuses across the lipid bilayer to counteract reactive oxygen species (ROS) overexpressed in diseased tissues. Ensemble and single‐particle Förster resonance energy transfer microscopy confirmed the proposed nanoreactor model. We demonstrate that a liposomal nanoreactor containing Pdots and a sacrificial electron donor is a potential photocatalytic nanoreactor for in situ hydrogen therapy.     

Dual Intramolecular Electron Transfer for In Situ Coreactant‐Embedded Electrochemiluminescence Microimaging of Membrane Protein

The demand for transporting coreactant to emitter and short lifetime of the radicals in electrochemiluminescence (ECL) emission inhibit greatly its application in cytosensing and microscopic imaging. Herein we designed a dual intramolecular electron transfer strategy and tertiary amine conjugated polymer dots (TEA‐Pdots) to develop a coreactant‐embedded ECL mechanism and microimaging system. The TEA‐Pdots could produce ECL emission at +1.2 V without need of coreactant in test solution. The superstructure and intramolecular electron transfer led to unprecedented ECL strength, which was 132 and 45 times stronger than those from the mixture of Pdots with TEA at equivalent and 62.5 times higher amounts, respectively. The ECL efficiency was even higher than that of typical [Ru(bpy)₃]²⁺ system. Therefore, this strategy and coreactant‐embedded ECL system could be used for in situ ECL microimaging of membrane protein on single living cells without additional permeable treatment for transporting coreactant. The feasibility and validity were demonstrated by evaluating the specific protein expression on cell surface. This work opens new avenues for ECL applications in single cell analysis and dynamic study of biological events.     

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.     

Semiconducting polymer dots with photosensitizer loading and peptide modification for enhanced cell penetration and photodynamic effect

We utilized semiconducting polymer do-PFDTBT, photosensitizer ZnPc and functional polymer PSMA to prepare carboxyl Pdots. The carboxyl Pdots were modified with cell penetrating peptides (R8) to prepare peptide coated-Pdots, which could enhance the cell penetration and photodynamic effect.     

Polymer Dots as Effective Phototheranostic Agents

Conjugated polymer dots (Pdots, also named polymer nanoparticles, PNPs), which consist of π‐conjugated organic polymers, are novel organic nanomaterials with size in the range of 1–100 nm. Compared with traditional organic small molecules, semiconductor quantum dots and inorganic nanomaterials, the Pdots exhibit significant potential applications in biological imaging, sensing and detection, drug delivery and theranostics, due to their advantages of special optical properties, diverse structure, easy surface modification and good biocompatibility. In this short review, we present a brief summary of the current development in Pdots as phototheranostic agents, including fluorescence imaging, photoacoustic imaging, photodynamic therapy and photothermal therapy. Current challenges in Pdot research and future directions in the field are proposed.     

Ratiometric temperature sensing with semiconducting polymer dots

This communication describes ultrabright single-nanoparticle ratiometric temperature sensors based on semiconducting polymer dots (Pdots). We attached the temperature sensitive dye-Rhodamine B (RhB), whose emission intensity decreases with increasing temperature-within the matrix of Pdots. The as-prepared Pdot-RhB nanoparticle showed excellent temperature sensitivity and high brightness because it took advantage of the light harvesting and amplified energy transfer capability of Pdots. More importantly, the Pdot-RhB nanoparticle showed ratiometric temperature sensing under a single wavelength excitation and has a linear temperature sensing range that matches well with the physiologically relevant temperatures. We employed Pdot-RhB for measuring intracellular temperatures in a live-cell imaging mode. The exceptional brightness of Pdot-RhB allows this nanoscale temperature sensor to be used also as a fluorescent probe for cellular imaging.     

Organic Polymer Dots Photocatalyze CO2 Reduction in Aqueous Solution

Developing low-cost and efficient photocatalysts to convert CO₂ into valuable fuels is desirable to realize a carbon-neutral society. In this work, we report that polymer dots (Pdots) of poly[(9,9′-dioctylfluorenyl-2,7-diyl)-co-(1,4-benzo-thiadiazole)] (PFBT), without adding any extra co-catalyst, can photocatalyze reduction of CO₂ into CO in aqueous solution, rendering a CO production rate of 57 μmol g⁻¹ h⁻¹ with a detectable selectivity of up to 100 %. After 5 cycles of CO₂ re-purging experiments, no distinct decline in CO amount and reaction rate was observed, indicating the promising photocatalytic stability of PFBT Pdots in the photocatalytic CO₂ reduction reaction. A mechanistic study reveals that photoexcited PFBT Pdots are reduced by sacrificial donor first, then the reduced PFBT Pdots can bind CO₂ and reduce it into CO via their intrinsic active sites. This work highlights the application of organic Pdots for CO₂ reduction in aqueous solution, which therefore provides a strategy to develop highly efficient and environmentally friendly nanoparticulate photocatalysts for CO₂ reduction.     

Light-induced crosslinkable semiconducting polymer dots

This paper describes a synthetic approach for photocrosslinkable polyfluorene (pc-PFO) semiconducting polymer dots, and demonstrates their superior ability to crosslink and form 3-D intermolecular polymer networks. The crosslinked pc-PFO Pdots are equipped with excellent encapsulating ability of functional small molecules. Optimum conditions of light irradiation on pc-PFO Pdots were investigated and clarified by using polymer thin films as a model. By employing the optimal light irradiation conditions, we successfully crosslinked pc-PFO Pdots and studied their particle sizes, photophysical, and colloidal properties. Single-particle imaging and dynamic-light-scattering measurements were conducted to understand the behaviors of photocrosslinked Pdots. Our results indicate pc-PFO Pdots can be easily photocrosslinked and the crosslinked species have excellent colloidal stability, physical and chemical stability, fluorescence brightness, and specific binding properties for cellular labeling. Considering that optical stimulus can work remotely, cleanly, and non-invasively, this study should pave the way for a promising approach to further develop stimuli-responsive ultrabright and versatile Pdot probes for biomedical imaging.     

Organic Polymer Dots as Photocatalysts for Visible Light‐Driven Hydrogen Generation

For the first time, organic semiconducting polymer dots (Pdots) based on poly[(9,9′‐dioctylfluorenyl‐2,7‐diyl)‐co‐(1,4‐benzo‐{2,1′,3} thiadiazole)] (PFBT) and polystyrene grafting with carboxyl‐group‐functionalized ethylene oxide (PS‐PEG‐COOH) are introduced as a photocatalyst towards visible‐light‐driven hydrogen generation in a completely organic solvent‐free system. With these organic Pdots as the photocatalyst, an impressive initial rate constant of 8.3 mmol h^?1 g^?1 was obtained for visible‐light‐driven hydrogen production, which is 5‐orders of magnitude higher than that of pristine PFBT polymer under the same catalytic conditions. Detailed kinetics studies suggest that the productive electron transfer quench of the excited state of Pdots by an electron donor is about 40 %. More importantly, we also found that the Pdots can tolerate oxygen during catalysis, which is crucial for further application of this material for light‐driven water splitting.     

Spectral imaging of single molecules by transmission grating-based epi-fluorescence microscopy

A spectral imaging method of single protein molecules labeled with a single fluorophore is presented. The method is based on a transmission grating and a routine fluorescence microscope. The bovine serum alubmin (BSA) and antiBSA molecules labeled with Alexa Fluor 488 and Alexa Fluor 594, respectively, are used as the model proteins. The fluorescence of single molecules is dispersed into zeroth-order spectrum and first-order spectrum by the transmission grating. Results show that the fluorescence emission spectrum of single molecule converted from the first-order spectral imaging is in good agreement with the bulk fluorescence spectrum. The spectral resolution of 2.4 nm/pixel is obtained, which is sufficient for identifying the molecular species in a multicomponent system.     

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.     

Understanding the Origin of Highly Selective CO2 Electroreduction to CO on Ni,N-doped Carbon Catalysts

Ni,N-doped carbon catalysts have shown promising catalytic performance for CO₂ electroreduction (CO₂R) to CO; this activity has often been attributed to the presence of nitrogen-coordinated, single Ni atom active sites. However, experimentally confirming Ni−N bonding and correlating CO₂ reduction (CO₂R) activity to these species has remained a fundamental challenge. We synthesized polyacrylonitrile-derived Ni,N-doped carbon electrocatalysts (Ni-PACN) with a range of pyrolysis temperatures and Ni loadings and correlated their electrochemical activity with extensive physiochemical characterization to rigorously address the origin of activity in these materials. We found that the CO₂R to CO partial current density increased with increased Ni content before plateauing at 2 wt % which suggests a dispersed Ni active site. These dispersed active sites were investigated by hard and soft X-ray spectroscopy, which revealed that pyrrolic nitrogen ligands selectively bind Ni atoms in a distorted square-planar geometry that strongly resembles the active sites of molecular metal–porphyrin catalysts.     

Fluorination Enhances NIR-II Fluorescence of Polymer Dots for Quantitative Brain Tumor Imaging

Here, we describe a fluorination strategy for semiconducting polymers for the development of highly bright second near-infrared region (NIR-II) probes. Tetrafluorination yielded a fluorescence QY of 3.2 % for the polymer dots (Pdots), over a 3-fold enhancement compared to non-fluorinated counterparts. The fluorescence enhancement was attributable to a nanoscale fluorous effect in the Pdots that maintained the molecular planarity and minimized the structure distortion between the excited state and ground state, thus reducing the nonradiative relaxations. By performing through-skull and through-scalp imaging of the brain vasculature of live mice, we quantitatively analyzed the vascular morphology of transgenic brain tumors in terms of the vessel lengths, vessel branches, and vessel symmetry, which showed statistically significant differences from the wild type animals. The bright NIR-II Pdots obtained through fluorination chemistry provide insightful information for precise diagnosis of the malignancy of the brain tumor.     

Single chromophore spectroscopy of MEH-PPV: homing-in on the elementary emissive species in conjugated polymers.

Low-temperature, single-molecule spectroscopy can provide unparalleled access to the primary emissive species of conjugated polymers. We demonstrate this with the example of one of the most commonly studied polymers, poly(2-methoxy-5-(2'-ethylhexoxy)-1,4-phenylenevinylene), MEH-PPV, which is shown to exhibit sharp fluorescence signatures over one hundred times narrower than the ensemble. These unprecedented narrow emission features can be assigned to single chromophores on the polymer chain, which are selectively addressed by the narrow band excitation. As with organic dye systems, the emission from single chromophores is not static with time, but shows a substantial spectral fluctuation. We find that, for single chromophores, this spectral fluctuation always follows a universal Gaussian statistical distribution. High-resolution spectroscopy provides unique insight into low-energy vibrational modes in the polymer emission, which are generally inaccessible with conventional spectroscopic methods such as site-selective fluorescence or Raman spectroscopy. Interchromophoric coupling can also occur owing to the flexible nature of the polymer backbone. This leads to substantial spectral broadening and a loss of resolution in the vibronic progression. We observe reversible switching within one single molecule between narrow and broad emission, which directly correlates with a discrete switching in emission intensity. We conclude that one and the same single molecule can support aggregated and nonaggregated emission, that is, emission from isolated and aggregated chromophores in one single molecule, rather than the tendency for aggregate emission being intrinsic to the molecule.     

Understanding the Origin of Highly Selective CO2 Electroreduction to CO on Ni,N‐doped Carbon Catalysts

Ni,N‐doped carbon catalysts have shown promising catalytic performance for CO₂ electroreduction (CO₂R) to CO; this activity has often been attributed to the presence of nitrogen‐coordinated, single Ni atom active sites. However, experimentally confirming Ni?N bonding and correlating CO₂ reduction (CO₂R) activity to these species has remained a fundamental challenge. We synthesized polyacrylonitrile‐derived Ni,N‐doped carbon electrocatalysts (Ni‐PACN) with a range of pyrolysis temperatures and Ni loadings and correlated their electrochemical activity with extensive physiochemical characterization to rigorously address the origin of activity in these materials. We found that the CO₂R to CO partial current density increased with increased Ni content before plateauing at 2 wt % which suggests a dispersed Ni active site. These dispersed active sites were investigated by hard and soft X‐ray spectroscopy, which revealed that pyrrolic nitrogen ligands selectively bind Ni atoms in a distorted square‐planar geometry that strongly resembles the active sites of molecular metal–porphyrin catalysts.     

Near-Infrared-II Semiconducting Polymer Dots for Deep-tissue Fluorescence Imaging

Fluorescence imaging, particularly in the NIR-II region (1000–1700 nm), has become an unprecedented tool for deep-tissue in vivo imaging. Among the fluorescent nanoprobes, semiconducting polymer nanoparticles (Pdots) appear to be a promising agent because of their tunable optical and photophysical properties, ultrahigh brightness, minimal autofluorescence, narrow-size distribution, and low cytotoxicity. This review elucidates the recent advances in Pdots for deep-tissue fluorescence imaging and the facing future translation to clinical use.     

Fine Tuning of Chlorophyll Spectra by Protein‐Induced Ring Deformation

The ability to tune the light‐absorption properties of chlorophylls by their protein environment is the key to the robustness and high efficiency of photosynthetic light‐harvesting proteins. Unfortunately, the intricacy of the natural complexes makes it very difficult to identify and isolate specific protein–pigment interactions that underlie the spectral‐tuning mechanisms. Herein we identify and demonstrate the tuning mechanism of chlorophyll spectra in type II water‐soluble chlorophyll binding proteins from Brassicaceae (WSCPs). By comparing the molecular structures of two natural WSCPs we correlate a shift in the chlorophyll red absorption band with deformation of its tetrapyrrole macrocycle that is induced by changing the position of a nearby tryptophan residue. We show by a set of reciprocal point mutations that this change accounts for up to 2/3 of the observed spectral shift between the two natural variants.     

Impact of silica nanoparticles dispersion on the dielectric and electro-optical properties and absorption spectra of host ferroelectric liquid crystal

The present work concerns with the investigation of the effect of dispersion of Silica (SiO₂) nanoparticles (NPs) in host ferroelectric liquid crystal (FLC) KCFLC10S on the dielectric and electro-optical properties and ultraviolet-visible (UV-VIS) absorption spectra of the pristine and dispersed systems. We have found that the dispersion of SiO₂ NPs in the host FLC strongly influences the various properties of dispersed systems. No evidence of aggregates and clumps in the dispersed system has been observed. Due to SiO₂ NPs dispersion, a rapid decrease in dielectric permittivity ε’, increase in conductivity σ with frequency, increase in spontaneous polarisation P_s and decrease in switching time with bias voltage have been observed. Based on the absorption spectra, we have also made an attempt to link the electro-optical and dielectric response with the mechanism of FLC–NPs interactions.     

Bioconjugation of ultrabright semiconducting polymer dots for specific cellular targeting

Semiconducting polymer dots (Pdots) represent a new class of ultrabright fluorescent probes for biological imaging. They exhibit several important characteristics for experimentally demanding in vitro and in vivo fluorescence studies, such as their high brightness, fast emission rate, excellent photostability, nonblinking, and nontoxic feature. However, controlling the surface chemistry and bioconjugation of Pdots has been a challenging problem that prevented their widespread applications in biological studies. Here, we report a facile yet powerful conjugation method that overcomes this challenge. Our strategy for Pdot functionalization is based on entrapping heterogeneous polymer chains into a single dot, driven by hydrophobic interactions during nanoparticle formation. A small amount of amphiphilic polymer bearing functional groups is co-condensed with the majority of semiconducting polymers to modify and functionalize the nanoparticle surface for subsequent covalent conjugation to biomolecules, such as streptavidin and immunoglobulin G (IgG). The Pdot bioconjugates can effectively and specifically label cellular targets, such as cell surface marker in human breast cancer cells, without any detectable nonspecific binding. Single-particle imaging, cellular imaging, and flow cytometry experiments indicate a much higher fluorescence brightness of Pdots compared to those of Alexa dye and quantum dot probes. The successful bioconjugation of these ultrabright nanoparticles presents a novel opportunity to apply versatile semiconducting polymers to various fluorescence measurements in modern biology and biomedicine.