Fluorescence bioimaging with conjugated polyelectrolytes

Illuminating the Path to Enhanced Bioimaging by Phosphole-based Fluorophores

As the research of biological systems becomes increasingly complex, there is a growing demand for fluorophores with a diverse range of wavelengths. In this study, we introduce phosphole-based fluorophores that surpass existing options like dansyl chloride. The reactive S-Cl bond in chlorosulfonylimino-5-phenylphosphole derivatives allows rapid and direct coupling to peptides making the fluorophores easily introducible to peptides. This coupling process occurs under mild conditions, demonstrated for [F7 ,P34 ]-NPY and its shorter analogues. Peptides linked with our fluorophores exhibit similar receptor activation to the control peptide, while maintaining high stability and low toxicity, making them ideal biolabeling reagents. In fluorescence microscopy experiments, they can be easily visualized even at low concentrations, without suffering from the typical issue of bleaching. These phosphole-based fluorophores represent a significant leap forward in the field. Their versatility, ease of modification, superior performance, and applicability in biological labeling make them a promising choice for researchers seeking advanced tools to unravel the details of complex biological systems.

Conjugated Polymeric Materials in Biological Imaging and Cancer Therapy

Conjugated polymers (CPs) have attracted much attention in the fields of chemistry, medicine, life science, and material science. Researchers have carried out a series of innovative researches and have made significant research progress regarding the unique photochemical and photophysical properties of CPs, expanding the application range of polymers. CPs are polymers formed by the conjugation of multiple repeating light-emitting units. Through precise control of their structure, functional molecules with different properties can be obtained. Fluorescence probes with different absorption and emission wavelengths can be obtained by changing the main chain structure. By modifying the side chain structure with water-soluble groups or selective recognition molecules, electrostatic interaction or specific binding with specific targets can be achieved; subsequently, the purpose of selective recognition can be achieved. This article reviews the research work of CPs in cell imaging, tumor diagnosis, and treatment in recent years, summarizes the latest progress in the application of CPs in imaging, tumor diagnosis, and treatment, and discusses the future development direction of CPs in cell imaging, tumor diagnosis, and treatment.

Current Progress of Interfacing Organic Semiconducting Materials with Bacteria

Microbial bioelectronics require interfacing microorganisms with electrodes. The resulting abiotic/biotic platforms provide the basis of a range of technologies, including energy conversion and diagnostic assays. Organic semiconductors (OSCs) provide a unique strategy to modulate the interfaces between microbial systems and external electrodes, thereby improving the performance of these incipient technologies. In this review, we explore recent progress in the field on how OSCs, and related materials capable of charge transport, are being used within the context of microbial systems, and more specifically bacteria. We begin by examining the electrochemical communication modes in bacteria and the biological basis for charge transport. Different types of synthetic organic materials that have been designed and synthesized for interfacing and interrogating bacteria are discussed next, followed by the most commonly used characterization techniques for evaluating transport in microbial, synthetic, and hybrid systems. A range of applications is subsequently examined, including biological sensors and energy conversion systems. The review concludes by summarizing what has been accomplished so far and suggests future design approaches for OSC bioelectronics materials and technologies that hybridize characteristic properties of microbial and OSC systems.

Formation of Multicolor Nanogels Based on Cationic Polyfluorenes and Poly(methyl vinyl ether-alt-maleic monoethyl ester): Potential Use as pH-Responsive Fluorescent Drug Carriers

In this study, we employed the copolymer poly(methyl vinyl ether-alt-maleic monoethyl ester) (PMVEMA-Es) and three fluorene-based cationic conjugated polyelectrolytes to develop fluorescent nanoparticles with emission in the blue, green and red spectral regions. The size, Zeta Potential, polydispersity, morphology, time-stability and fluorescent properties of these nanoparticles were characterized, as well as the nature of the interaction between both PMVEMA-Es and fluorescent polyelectrolytes. Because PMVEMA-Es contains a carboxylic acid group in its structure, the effects of pH and ionic strength on the nanoparticles were also evaluated, finding that the size is responsive to pH and ionic strength, largely swelling at physiological pH and returning to their initial size at acidic pHs. Thus, the developed fluorescent nanoparticles can be categorized as pH-sensitive fluorescent nanogels, since they possess the properties of both pH-responsive hydrogels and nanoparticulate systems. Doxorubicin (DOX) was used as a model drug to show the capacity of the blue-emitting nanogels to hold drugs in acidic media and release them at physiological pH, from changes in the fluorescence properties of both nanoparticles and DOX. In addition, preliminary studies by super-resolution confocal microscopy were performed, regarding their potential use as image probes.

Biological Sensing and Imaging Using Conjugated Polymers and Peptide Substrates

Peptides have been widely applied as targeting elements or enzyme-substrates in biological sensing and imaging. Conjugated Polymers (CPs) have emerged as a novel biosensing material and received considerable attention due to their excellent light absorption, strong fluorescence emission, as well as amplified quenching properties. In this review, we summarize the recent advances of using CPs and peptide substrates in biosensing and bioimaging. After a brief introduction of the advantages of CPs and peptide substrates, different sensing designs and mechanisms are discussed based on peptides' structures and functions, including targeting recognition elements, enzyme-substrates, and cell-penetrating elements. Applications of CPs and peptides in fluorescent imaging and Raman imaging in living cells are subsequently reviewed.

Hyperbranched DNA clusters

Taking advantage of the base-pairing specificity and tunability of DNA interactions, we investigate the spontaneous formation of hyperbranched clusters starting from purposely designed DNA tetravalent nanostar monomers, encoding in their four sticky ends the desired binding rules. Specifically, we combine molecular dynamics simulations and Dynamic Light Scattering experiments to follow the aggregation process of DNA nanostars at different concentrations and temperatures. At odds with the Flory-Stockmayer predictions, we find that, even when all possible bonds are formed, the system does not reach percolation due to the presence of intracluster bonds. We present an extension of the Flory-Stockmayer theory that properly describes the numerical and experimental results.

Aggregation-Enhanced Two-Photon Absorption of Anionic Conjugated Polyelectrolytes

The two-photon absorption properties of anionic poly(phenylene ethynylene)-type conjugated oligo- and polyelectrolytes are studied in molecularly dissolved and aggregated forms in aqueous solution. Several different polyvalent cations are used to induce aggregation. It is found that both materials in the aggregated form exhibit enhanced two-photon excited fluorescence (2PEF) and two-photon cross section (σ₂) compared with the molecularly dissolved structures. The 2PEF and σ₂ are unaffected by the nature of the polyvalent cation that is used to induce aggregation. The two-photon absorption cross section enhancement arises because of the increase in the difference dipole moment (Δμ) in the aggregates of the conjugated materials, an effect that is attributed to the introduction of charge transfer character into the aggregate excited state.

Polythiophenes with Cationic Phosphonium Groups as Vectors for Imaging, siRNA Delivery, and Photodynamic Therapy

In this work, we exploit the versatile function of cationic phosphonium-conjugated polythiophenes to develop multifunctional platforms for imaging and combined therapy (siRNA delivery and photodynamic therapy). The photophysical properties (absorption, emission and light-induced generation of singlet oxygen) of these cationic polythiophenes were found to be sensitive to molecular weight. Upon light irradiation, low molecular weight cationic polythiophenes were able to light-sensitize surrounding oxygen into reactive oxygen species (ROS) while the highest were not due to its aggregation in aqueous media. These polymers are also fluorescent, allowing one to visualize their intracellular location through confocal microscopy. The most promising polymers were then used as vectors for siRNA delivery. Due to their cationic and amphipathic features, these polymers were found to effectively self-assemble with siRNA targeting the luciferase gene and deliver it in MDA-MB-231 cancer cells expressing luciferase, leading to 30-50% of the gene-silencing effect. In parallel, the photodynamic therapy (PDT) activity of these cationic polymers was restored after siRNA delivery, demonstrating their potential for combined PDT and gene therapy.

Design of superior phototheranostic agents guided by Jablonski diagrams

This review summarizes how Jablonski diagrams guide the design of advanced organic optical agents and improvement of disease phototheranostic efficacies.

Red Fluorescence Conjugated Polymer with Broad Spectrum Antimicrobial Activity for Treatment of Bacterial Infections In Vivo

To address the problem of bacterial resistance, a practical strategy for broad spectrum antimicrobial based on conjugated polymers was proposed in the work. Three red fluorescence conjugated polymers (P1, P2, and P3) bearing quaternary ammonium groups with different length of side chains were designed and synthesized. By virtue of inserting capacity of the longer side chain, conjugated polymer (P3) displayed well broad spectrum antimicrobial activity toward Gram-negative and Gram-positive bacteria and fungi under a white light density of 25 mW cm^-2 and short time (15 min) by aid of dark toxicity and light toxicity, derived from the quaternary ammonium groups and reactive oxygen species produced by the backbone, respectively. Notably, for ampicillin-resistant Escherichia coli TOP10, P3 could kill the bacteria 100% at a very low concentration of 5 μM upon light irradiation. Furthermore, wound healing tests indicated that the polymer could be expediently employed for wound disinfection in vivo without any tissue damaging. The contribution of the work not only provides an efficient and broad spectrum antimicrobial material but also offers a multimodal antimicrobial strategy to fight against bacterial infections in vivo.

Synthesis of amphiphilic poly(fluorene) derivatives for selective imaging of Staphylococcus aureus

Three amphiphilic poly(fluorene-co-phenylene) derivatives with different side chains (PFP-1, PFP-2, PFP-3) were designed and synthesized for exploring their detection and imaging of pathogens. Upon incubation with six kinds of different pathogens, it was found the three polymers could selectively interact with Staphylococcus aureus (S. aureus). Their selective imaging towards S. aureus were thus realized. The selective imaging towards S. aureus was also confirmed even under the blend of microbes. PFP-3 shows stronger fluorescence imaging signal than PFP-1 and PFP-2. Zeta potential and isothermal titration microcalorimetry (ITC) tests demonstrated that both electrostatic interactions and hydrophobic interactions played important roles in the binding between PFPs and pathogens. Thus, amphiphilic PFP-3 exhibits great potential for specific imaging of S. aureus in a simple and rapid manner.

Hybridizing Carbon Nitride Colloids with a Shell of Water-Soluble Conjugated Polymers for Tunable Full-Color Emission and Synergistic Cell Imaging

We present the preparation of a new multicolor emission system constructed from two complementary conjugated materials that are highly photoluminescent, that is, phenyl-modified carbon nitride (PhCN) colloids as the core and water-soluble conjugated polymers (WSCPs) adsorbed as the shell. The fluorescence bands of the PhCN and WSCPs effectively complement each other and the overall emission can be simply adjusted to fully cover the visible light spectrum with white light emission also accessible. Photophysical insights imply that the interactions between PhCN and WSCPs preserve the binary system from emission distortion and degradation, which is essential to delicately tune the overall fluorescence bands. Notably, the continuously tunable emission color is achieved under single-wavelength excitation (365 nm). This hybrid shows a synergistic permeation performance in cell imaging, that is, PhCN nanoparticles help the WSCP to enter the cells and therefore multicolor cellular imaging achieved.

Ultrasmall Conjugated Polymer Nanoparticles with High Specificity for Targeted Cancer Cell Imaging

Fluorescent and biocompatible organic nanoparticles have attracted great interest in cancer detection and imaging, but the nonspecific cellular uptake has limited the detection specificity and sensitivity. Herein, the authors report the ultrasmall conjugated polymer nanoparticles (CPNs) with bright far-red/near-infrared emission for targeted cancer imaging with high specificity. The sizes of the ultrasmall CPNs are around 6 nm (CPN6), while large CPNs show sizes around 30 nm (CPN30). Moreover, CPN6 exhibits largely improved fluorescence quantum yield (η) of 41% than CPN30 (25%). Benefiting from the ultrasmall size, bare CPN6 shows largely suppressed nonspecific cellular uptake as compared to CPN30, while cyclic arginine-glycine-aspartic acid (cRGD) functionalized CPN6 (cRGD-CPN6) possesses excellent selectivity toward αvβ3 integrin overexpressed MDA-MB-231 cells over other cells in cell mixtures. The faster body clearance of CPN6 over CPN30 indicates its greater potentials as a noninvasive nanoprobe for in vivo and practical applications.

Recent Advances of Activatable Molecular Probes Based on Semiconducting Polymer Nanoparticles in Sensing and Imaging

Molecular probes that change their signals in response to the target of interest have a critical role in fundamental biology and medicine. Semiconducting polymer nanoparticles (SPNs) have recently emerged as a new generation of purely organic photonic nanoagents with desirable properties for biological applications. In particular, tunable optical properties of SPNs allow them to be developed into photoluminescence, chemiluminescence, and photoacoustic probes, wherein SPNs usually serve as the energy donor and internal reference for luminescence and photoacoustic probes, respectively. Moreover, facile surface modification and intraparticle engineering provide the versatility to make them responsive to various biologically and pathologically important substances and indexes including small-molecule mediators, proteins, pH and temperature. This article focuses on recent advances in the development of SPN-based activatable molecular probes for sensing and imaging. The designs and applications of these probes are discussed in details, and the present challenges to further advance them into life science are also analyzed.

Non-fused Phospholes as Fluorescent Probes for Imaging of Lipid Droplets in Living Cells

Molecular tools for fluorescent imaging of specific compartments in cells are essential for understanding the function and activity of cells. Here, we report the synthesis of a series of pyridyl- and thienyl-substituted phospholes and the evaluation of these dyes for fluorescent imaging of cells. The thienyl-substituted phospholes proved to be successful for staining of cultured normal and malignant cells due to their fluorescent properties and low toxicity. Co-staining experiments demonstrated that these probes target lipid droplets, which are, lipid-storage organelles found in the cytosol of nearly all cell types. Our findings confirm that thienyl-substituted phospholes can be utilized as fluorescent tools for vital staining of cells, and we foresee that these fluorescent dyes might be used in studies to unravel the roles that lipid droplets play in cellular physiology and in diseases.

Organic nanostructure-based probes for two-photon imaging of mitochondria and microbes with emission between 430 nm and 640 nm

Multi-photon excitation and versatile fluorescent probes are in high need for biological imaging, since one probe can satisfy many needs as a biosensor. Herein we synthesize a series of two-photon excited probes based on tetraphenylethene (TPE) structures (TPE-Acr, TPE-Py, and TPE-Quino), which can image both mammalian cells and bacteria based on aggregation-induced emission (AIE) without washing them. Because of cationic moieties, the fluorescent molecules can aggregate into nanoscale fluorescent organic nanoscale dots to image mitochondria and bacteria with tunable emissions using both one-photon and two-photon excitation. Our research demonstrates that these AIE-dots expand the functions of luminescent organic dots to construct efficient fluorescent sensors applicable to both one-photon and two-photon excitation for bio-imaging of bacteria and mammalian cells.

Light-Induced Translocation of a Conjugated Polyelectrolyte in Cells: From Fluorescent Probe to Anticancer Agent

Dual-functional probes, which not only enable visualization of diseased cells but also induce therapeutic cellular responses, are essential to biological studies. In the current work, a conjugated polyelectrolyte, PPET3-N2, was designed and synthesized as a dual-functional probe. The poly(phenylene ethynylene) terthiophene polymer backbone contributes to the polymer's light-harvesting property to ensure the strong fluorescence as well as photosensitization, whereas quantanary ammonium side chains interact with target organelle for localization. As a fluorescent probe, PPET3-N2 was endocytosed to lysosomes through clathrin-mediated endocytosis (CME) and macropinocytosis (MPC) pathways. Colocalization of the probe with commercial fluorescent lysosome labels confirmed that this probe localized on lysosomes with high specificity and photostability. Real-time monitoring of autolysosome formation in autophagic cells was also demonstrated, providing a viable platform for cell-based screening of autophagy inhibitors. Finally, as a photosensitizer, PPET3-N2 can efficiently generate singlet oxygen in living cells upon irradiation of white light, leading to the destruction of lysosome membrane and release of ROS and lysosomal enzymes in cytoplasma, causing cell death.

Relationship between Side-Chain Polarity and the Self-Assembly Characteristics of Perylene Diimide Derivatives in Aqueous Solution

Perylene-3,4,9,10-tetracarboxylic acid diimides (PDIs) have recently gained considerable interest for water-based biosensing applications. PDIs have been studied intensively in the bulk state, but their physical properties in aqueous solution in interplay with side-chain polarity are, however, poorly understood. Therefore, three perylene diimide based derivatives were synthesized to study the relationship between side-chain polarity and their self-assembly characteristics in water. The polarity of the side chains was found to dictate the size and morphology of the formed aggregates. Side-chain polarity rendered the self-assembly and photophysical properties of the PDIs-both important for imminent water-based applications-and these were revealed to be especially responsive to changes in solvent composition.

Vancomycin-conjugated polythiophene for the detection and imaging of Gram-positive bacteria

Vancomycin-conjugated polythiophene was synthesized for the discrimination and elimination of Gram-positive bacteria.

Facile synthesis of fluorescent distyrylnaphthalene derivatives for bioapplications

Synthesis of a novel type of distyrylnaphthalene derivative and their application as molecular fluorescent probes for bioimaging.

Facilely synthesized pH-responsive fluorescent polymer dots entrapping doped and coupled doxorubicin for nucleus-targeted chemotherapy

The combination of physical doping and chemical coupling can significantly enhance the drug loading/release efficiency and improve the effect of cancer treatment. Based on this strategy, PEG-Dox doped and coupled PFBT polymer dots were optimized as a nucleus-targeted drug delivery platform for tumor therapy.

Conjugated Polyelectrolyte Nanoparticles for Apoptotic Cell Imaging

Three anionic conjugated polyelectrolytes (CPEs) with poly(p-phenylene ethynylene thiophene) backbones were designed and synthesized, among which PPET3-CO2Na showed greater molar extinction coefficient with red-shifted bands in both absorption and emission spectra compared to the well-studied PPE-CO2Na polymer. PPET3-CO2Na was thus chosen to construct CPE-based nanoparticles (CPNs) with cationic octaarginine (R8) peptide through electrostatic-interaction-induced self-assembly. Due to plasma membrane permeabilization and mitochondrial outer membrane permeabilization (MOMP) in early apoptotic cells, PPET3/R8 CPNs demonstrated excellent colocalization with MitoTracker Red in apoptotic cells instead of normal cells, which had potential application in cell imaging for early apoptosis recognition.

Smart conjugated polymer nanocarrier for healthy weight loss by negative feedback regulation of lipase activity

Healthy weight loss represents a real challenge when obesity is increasing in prevalence. Herein, we report a conjugated polymer nanocarrier for smart deactivation of lipase and thus balancing calorie intake. After oral administration, the nanocarrier is sensitive to lipase in the digestive tract and releases orlistat, which deactivates the enzyme and inhibits fat digestion. It also creates negative feedback to control the release of itself. The nanocarrier smartly regulates activity of the lipase cyclically varied between high and low levels. In spite of high fat diet intervention, obese mice receiving a single dose of the nanocarrier lose weight over eight days, whereas a control group continues the tendency to gain weight. Daily intragastric administration of the nanocarrier leads to lower weight of livers or fat pads, smaller adipocyte size, and lower total cholesterol level than that of the control group. Near-infrared fluorescence of the nanocarrier reveals its biodistribution.

Selective recognition and imaging of bacterial model membranes over mammalian ones by using cationic conjugated polyelectrolytes

This work describes the use of cationic polyfluorenes as fluorescent markers to selectively recognize bacterial membranes.

Tuning cell surface charge in E. coli with conjugated oligoelectrolytes

Conjugated oligoelectrolytes intercalate into and associate with membranes, thereby changing the surface charge of microbes, as determined by zeta potential measurements.

Cationic conjugated oligoelectrolytes (COEs) varying in length and structural features are compared with respect to their association with E. coli and their effect on cell surface charge as determined by zeta potential measurements. Regardless of structural features, at high staining concentrations COEs with longer molecular dimensions associate less, but neutralize the negative surface charge of E. coli to a greater degree than shorter COEs.

An imidazole functionalized pentameric thiophene displays different staining patterns in normal and malignant cells

Molecular tools for fluorescent imaging of cells and their components are vital for understanding the function and activity of cells. Here, we report an imidazole functionalized pentameric oligothiophene, p-HTIm, that can be utilized for fluorescent imaging of cells. p-HTIm fluorescence in normal cells appeared in a peripheral punctate pattern partially co-localized with lysosomes, whereas a one-sided perinuclear Golgi associated localization of the dye was observed in malignant cells. The uptake of p-HTIm was temperature dependent and the intracellular target was reached within 1 h after staining. The ability of p-HTIm to stain cells was reduced when the imidazole side chain was chemically altered, verifying that specific imidazole side-chain functionalities are necessary for achieving the observed cellular staining. Our findings confirm that properly functionalized oligothiophenes can be utilized as fluorescent tools for vital staining of cells and that the selectivity toward distinct intracellular targets are highly dependent on the side-chain functionalities along the conjugated thiophene backbone.

Phenylenevinylene conjugated oligoelectrolytes as fluorescent dyes for mammalian cell imaging

Conjugated phenylenevinylene oligoelectrolytes, which consist of a phenylenevinylene core equipped at each end with hydrophilic pendent groups, are shown to be good candidates for mammalian cell membrane staining. When used in the micromolar concentration range, they express low to moderate cell toxicity for selected regular and cancerous cell lines as tested for adherent and suspension cells.

Benzothiadiazole Derivatives as Fluorescence Imaging Probes: Beyond Classical Scaffolds

This Account describes the origins, features, importance, and trends of the use of fluorescent small-molecule 2,1,3-benzothiadiazole (BTD) derivatives as a new class of bioprobes applied to bioimaging analyses of several (live and fixed) cell types. BTDs have been successfully used as probes for a plethora of biological analyses for only a few years, and the impressive responses obtained by using this important class of heterocycle are fostering the development of new fluorescent BTDs and expanding the biological applications of such derivatives. The first use of a fluorescent small-molecule BTD derivative as a selective cellular probe dates back to 2010, and since then impressive advances have been described by us and others. The well-known limitations of classical scaffolds urged the development of new classes of bioprobes. Although great developments have been achieved by using classical scaffolds such as coumarins, BODIPYs, fluoresceins, rhodamines, cyanines, and phenoxazines, there is still much to be done, and BTDs aim to succeed where these dyes have shown their limitations. Important organelles and cell components such as nuclear DNA, mitochondria, lipid droplets, and others have already been successfully labeled by fluorescent small-molecule BTD derivatives. New technological systems that use BTDs as the fluorophores for bioimaging experiments have been described in recent scientific literature. The successful application of BTDs as selective bioprobes has led some groups to explore their potential for use in studying membrane pores or tumor cells under hypoxic conditions. Finally, BTDs have also been used as fluorescent tags to investigate the action mechanism of some antitumor compounds. The attractive photophysical data typically observed for π-extended BTD derivatives is fostering interest in the use of this new class of bioprobes. Large Stokes shifts, large molar extinction coefficients, high quantum yields, high stability when stored in solution or as pure solids, no fading even after long periods of irradiation, bright emissions with no blinking, good signal-to-noise ratios, efficiency to transpose the cell membrane, and irradiation preferentially in the visible-light region are just some features noted by using BTDs. As the pioneering group in the use of fluorescent small-molecule BTDs for bioimaging purposes, we feel pleased to share our experience, results, advances, and personal perspectives with the readers of this Account. The readers will clearly note the huge advantages of using fluorescent BTDs over classical scaffolds, and hopefully they will be inspired and motivated to further BTD technology in the fields of molecular and cellular biology.

Narrow band gap conjugated polyelectrolytes for photothermal killing of bacteria

We report the demonstration of antimicrobial conjugated polyelectrolytes (CPEs) with high NIR absorbance for selective and efficient photothermal killing of bacteria over mammalian cells.

Conjugated polymer microparticles for selective cancer cell image-guided photothermal therapy

We report conjugated polymers (CPs) microparticles (MPs) for selective cancer cell image-guided photothermal therapy. The CPMPs without surface functionalization can target MCF-7 cancer cells over NIH-3T3 normal cells, while nanoparticles need surface decoration to possess selectivity. Benefitting from large absorption, bright fluorescence, and efficient light-to-heat conversion of CPs, the fabricated MPs can selectively kill MCF-7 cells under NIR infrared laser irradiation.

Coumarin-3-aldehyde as a scaffold for the design of tunable PET-modulated fluorescent sensors for neurotransmitters

NeuroSensor 521 (NS521) is a fluorescent sensor for primary-amine neurotransmitters based on a platform that consists of an aryl moiety appended to position C4 of the coumarin-3-aldehyde scaffold. We demonstrate that sensors based on this platform behave as a directly linked donor-acceptor system that operates through an intramolecular acceptor-excited photoinduced electron transfer (a-PET) mechanism. To evaluate the PET process, a series of benzene- and thiophene-substituted derivatives were prepared and the photophysical properties, binding affinities, and fluorescence responses toward glutamate, norepinephrine, and dopamine were determined. The calculated energy of the highest occupied molecular orbital (EHOMO ) of the pendant aryl substituents, along with oxidation and reduction potential values derived from the calculated molecular orbital energy values of the platform components, allowed for calculation of the fluorescence properties of the benzene sensor series. Interestingly, the thiophene derivatives did not fit the typical PET model, highlighting the limitations of the method. A new sensor, NeuroSensor 539, displayed enhanced photophysical properties aptly suited for biological imaging. NeuroSensor 539 was validated by selectively labeling and imaging norepinephrine in secretory vesicles of live chromaffin cells.

Self-assembled nanoparticles based on PEGylated conjugated polyelectrolyte and drug molecules for image-guided drug delivery and photodynamic therapy

A drug delivery system based on poly(ethylene glycol) (PEG) grafted conjugated polyelectrolyte (CPE) has been developed to serve as a polymeric photosensitizer and drug carrier for combined photodynamic and chemotherapy. The amphiphilic brush copolymer can self-assemble into micellar nanopaticles (NPs) in aqueous media with hydrophobic conjugated polyelectrolyte backbone as the core and hydrophilic PEG as the shell. The NPs have an average diameter of about 100 nm, with the absorption and emission maxima at 502 and 598 nm, respectively, making them suitable for bioimaging applications. Moreover, the CPE itself can serve as a photosensitizer, which makes the NPs not only a carrier for drug but also a photosensitizing unit for photodynamic therapy, resulting in the combination of chemo- and photodynamic therapy for cancer. The half-maximal inhibitory concentration (IC50) value for the combination therapy to U87-MG cells is 12.7 μg mL(-1), which is much lower than that for the solely photodynamic therapy (25.5 μg mL(-1)) or chemotherapy (132.8 μg mL(-1)). To improve the tumor specificity of the system, cyclic arginine-glycine-aspartic acid (cRGD) tripeptide as the receptor to integrin αvβ3 overexpressed cancer cells was further incorporated to the surface of the NPs. The delivery system based on PEGylated CPE is easy to fabricate, which integrates the merits of targeted cancer cell image, chemotherapeutic drug delivery, and photodynamic therapy, making it promising for cancer treatment.

Sonication-induced formation of size-controlled self-assemblies of amphiphilic Janus-type polymers as optical tumor-imaging agents

In this study, amphiphilic Janus-type polymers were synthesized via ring-opening metathesis polymerization (ROMP), multiple vicinal diol formation, and grafting of poly(ethylene glycol) monomethyl ether (mPEG). These amphiphilic polymers formed self-assemblies, which were a mixture of micelles and multimicellar aggregates, in water. By choosing suitable Janus-type polymers and irradiating an aqueous solution of polymers using a sonicator, either small micelles or large multimicellar aggregates were obtained selectively. Hydrophobic substituents controlled the aggregation-disaggregation behavior, leading to the formation of metastable self-assemblies by sonication. The formation of self-assemblies with a uniform size was affected by ultrasonic frequency, rather than power. In vivo optical tumor imaging revealed that the large-size multimicellar aggregates persisting for a long time in blood circulation slowly accumulated in tumor tissues. In contrast, the tumor site was rapidly, clearly visualized using the small-size micelles.

QM/MM-MD simulations of conjugated polyelectrolytes: a study of luminescent conjugated oligothiophenes for use as biophysical probes

A methodological development is reported for the study of luminescence properties of conjugated polyelectrolytes, encompassing systems in which dihedral rotational barriers are easily overcome at room temperature. The components of the model include (i) a molecular mechanics (MM) force field description of the solvent in its electronic ground state as well as the chromophore in its electronic ground and excited states, (ii) a conformational sampling by means of classical molecular dynamics (MD) in the respective electronic states, and (iii) spectral response calculations by means of the quantum mechanics/molecular mechanics QM/MM approach. A detailed analysis of the combined polarization effects of the ionic moiety and the polar water solvent is presented. At an increased computational cost of 30% compared to a calculation excluding the solvent, the error in the transition wavelength of the dominant absorption band is kept as small as 1 nm as compared to the high-quality benchmark result, based largely on a QM description of the solvent. At a reduced computational cost the error of the same quantity is kept as small as 6 nm, with the cost reduction being the result of an effective description of the effects of the solvent by means of replacing the carboxylate ions with neutral hydrogens. In absorption spectroscopy, the obtained best theoretical results are in excellent agreement with the experimental benchmark measurement, regarding excitation energies as well as band intensities and profiles. In fluorescence spectroscopy, the experimental spectrum shows a vibrational progression that is not addressed by theory, but the theoretical band position is in excellent agreement with experiment, with a highly accurate description of the Stokes shift as a result.

Increased ion conductance across mammalian membranes modified with conjugated oligoelectrolytes

Variation in conjugated oligoelectrolyte (COE) repeat units is shown to affect the rate of COE insertion into mammalian membrane patches and membrane patch stabilities. These findings suggest that it is possible to find COE structures that do not destroy membranes while at the same time allow for more facile transmembrane movement of ions/substrates.

Bright single-chain conjugated polymer dots embedded nanoparticles for long-term cell tracing and imaging

Single-chain conjugated polymer (CP) dots embedded nanoparticles (NPs) bearing cell penetration peptide (TAT) as surface ligands are synthesized for long term cancer cell tracing applications. The CPNPs are fabricated by matrix-encapsulation method and the embedded CPs can be modulated into spherical dots with different size upon alteration of feed concentrations. Single-chain CP dots are formed upon decreasing feed concentration to 0.2 mg/mL, where CPNPs exhibit highest fluorescence quantum yield of 32%. Maleimide is introduced as the new NP surface functional group, which favors easy conjugation with cell penetration peptide via click chemistry to preserve its biofunctions. The obtained CPNPs show high brightness and good biocompatibility, which allow cell tracing for over 9 generations, superior to commercial cell tracker Qtracker 585.