Protein-Sized Bright Fluorogenic Nanoparticles Based on Cross-Linked Calixarene Micelles with Cyanine Corona

The key challenge in the field of fluorescent nanoparticles (NPs) for biological applications is to achieve superior brightness for sizes equivalent to single proteins (3-7 nm). We propose a concept of shell-cross-linked fluorescent micelles, in which PEGylated cyanine 3 and 5 bis-azides form a covalently attached corona on micelles of amphiphilic calixarene bearing four alkyne groups. The fluorescence quantum yield of the obtained monodisperse NPs, with a size of 7 nm, is a function of viscosity and reached up to 15 % in glycerol. In the on-state they are circa 2-fold brighter than quantum dots (QD-585), which makes them the smallest PEGylated organic NPs of this high brightness. FRET between cyanine 3 and 5 cross-linkers at the surface of NPs suggests their integrity in physiological media, organic solvents, and living cells, in which the NPs rapidly internalize, showing excellent imaging contrast. Calixarene micelles with a cyanine corona constitute a new platform for the development of protein-sized ultrabright fluorescent NPs.

Fluorescent Polymer Nanoparticles Based on Dyes: Seeking Brighter Tools for Bioimaging

Speed, resolution and sensitivity of today's fluorescence bioimaging can be drastically improved by fluorescent nanoparticles (NPs) that are many-fold brighter than organic dyes and fluorescent proteins. While the field is currently dominated by inorganic NPs, notably quantum dots (QDs), fluorescent polymer NPs encapsulating large quantities of dyes (dye-loaded NPs) have emerged recently as an attractive alternative. These new nanomaterials, inspired from the fields of polymeric drug delivery vehicles and advanced fluorophores, can combine superior brightness with biodegradability and low toxicity. Here, we describe the strategies for synthesis of dye-loaded polymer NPs by emulsion polymerization and assembly of pre-formed polymers. Superior brightness requires strong dye loading without aggregation-caused quenching (ACQ). Only recently several strategies of dye design were proposed to overcome ACQ in polymer NPs: aggregation induced emission (AIE), dye modification with bulky side groups and use of bulky hydrophobic counterions. The resulting NPs now surpass the brightness of QDs by ≈10-fold for a comparable size, and have started reaching the level of the brightest conjugated polymer NPs. Other properties, notably photostability, color, blinking, as well as particle size and surface chemistry are also systematically analyzed. Finally, major and emerging applications of dye-loaded NPs for in vitro and in vivo imaging are reviewed.

A new biomimetic route to engineer enzymatically active mechano-responsive materials

Using modified β-galactosidase covalently linked to cross-linked polyelectrolyte multilayers (PEM), catalytically active materials have been designed. Their enzymatic activity can be modulated, partially in a reversible way, simply by stretching. This strategy, based on enzyme conformational changes, constitutes a new tool for the development of biocatalytic mechano-responsive materials.

Neuronal Uptake and Neuroprotective Properties of Curcumin-Loaded Nanoparticles on SK-N-SH Cell Line: Role of Poly(lactide-co-glycolide) Polymeric Matrix Composition

Curcumin, a neuroprotective agent with promising therapeutic approach has poor brain bioavailability. Herein, we demonstrate that curcumin-encapsulated poly(lactide-co-glycolide) (PLGA) 50:50 nanoparticles (NPs-Cur 50:50) are able to prevent the phosphorylation of Akt and Tau proteins in SK-N-SH cells induced by H2O2 and display higher anti-inflammatory and antioxidant activities than free curcumin. PLGA can display various physicochemical and degradation characteristics for controlled drug release applications according to the matrix used. We demonstrate that the release of curcumin entrapped into a PLGA 50:50 matrix (NPs-Cur 50:50) is faster than into PLGA 65:35. We have studied the effects of the PLGA matrix on the expression of some key antioxidant- and neuroprotective-related genes such as APOE, APOJ, TRX, GLRX, and REST. NPs-Cur induced the elevation of GLRX and TRX while decreasing APOJ mRNA levels and had no effect on APOE and REST expressions. In the presence of H2O2, both NPs-Cur matrices are more efficient than free curcumin to prevent the induction of these genes. Higher uptake was found with NPs-Cur 50:50 than NPs-Cur 65:35 or free curcumin. By using PLGA nanoparticles loaded with the fluorescent dye Lumogen Red, we demonstrated that PLGA nanoparticles are indeed taken up by neuronal cells. These data highlight the importance of polymer composition in the therapeutic properties of the nanodrug delivery systems. Our study demonstrated that NPs-Cur enhance the action of curcumin on several pathways implicated in the pathophysiology of Alzheimer's disease (AD). Overall, these results suggest that PLGA nanoparticles are a promising strategy for the brain delivery of drugs for the treatment of AD.

Fluorinated counterion-enhanced emission of rhodamine aggregates: ultrabright nanoparticles for bioimaging and light-harvesting

The key to ultrabright fluorescent nanomaterials is the control of dye emission in the aggregated state. Here, lipophilic rhodamine B derivatives are assembled into nanoparticles (NPs) using tetraphenylborate counterions with varied fluorination levels that should tune the short-range dye ordering. Counterion fluorination is found to drastically enhance the emission characteristics of these NPs. Highly fluorinated counterions produce 10-20 nm NPs containing >300 rhodamine dyes with a fluorescence quantum yield of 40-60% and a remarkably narrow emission band (34 nm), whereas, for other counterions, aggregation caused quenching with a weak broad-band emission is observed. NPs with the most fluorinated counterion (48 fluorines) are ∼40-fold brighter than quantum dots (QD585 at 532 nm excitation) in single-molecule microscopy, showing improved photostability and suppressed blinking. Due to exciton diffusion, revealed by fluorescence anisotropy, these NPs are efficient FRET donors to single cyanine-5 acceptors with a light-harvesting antenna effect reaching 200. Finally, NPs with the most fluorinated counterion are rather stable after entry into living cells, in contrast to their less fluorinated analogue. Thus, the present work shows the crucial role of counterion fluorination in achieving high fluorescence brightness and photostability, narrow-band emission, efficient energy transfer and high intracellular stability of nanomaterials for light harvesting and bioimaging applications.

Exploiting Fast Exciton Diffusion in Dye-Doped Polymer Nanoparticles to Engineer Efficient Photoswitching

Photoswitching of bright fluorescent nanoparticles opens new possibilities for bioimaging with superior temporal and spatial resolution. However, efficient photoswitching of nanoparticles is hard to achieve using Förster resonance energy transfer (FRET) to a photochromic dye, because the particle size is usually larger than the Förster radius. Here, we propose to exploit the exciton diffusion within the FRET donor dyes to boost photoswitching efficiency in dye-doped polymer nanoparticles. To this end, we utilized bulky hydrophobic counterions that prevent self-quenching and favor communication of octadecyl rhodamine B dyes inside a polymer matrix of poly(D,L-lactide-co-glycolide). Among tested counterions, only perfluorinated tetraphenylborate that favors the exciton diffusion enables high photoswitching efficiency (on/off ratio ∼20). The switching improves with donor dye loading and requires only 0.1-0.3 wt % of a diphenylethene photochromic dye. Our nanoparticles were validated both in solution and at the single-particle level. The proposed concept paves the way to new efficient photoswitchable nanomaterials.

Charge-controlled nanoprecipitation as a modular approach to ultrasmall polymer nanocarriers: making bright and stable nanoparticles

Ultrasmall polymer nanoparticles are rapidly gaining importance as nanocarriers for drugs and contrast agents. Here, a straightforward modular approach to efficiently loaded and stable sub-20-nm polymer particles is developed. In order to obtain ultrasmall polymer nanoparticles, we investigated the influence of one to two charged groups per polymer chain on the size of particles obtained by nanoprecipitation. Negatively charged carboxylate and sulfonate or positively charged trimethylammonium groups were introduced into the polymers poly(d,l-lactide-co-glycolide) (PLGA), polycaprolactone (PCL), and poly(methyl methacrylate) (PMMA). According to dynamic light scattering, atomic force and electron microscopy, the presence of one to two charged groups per polymer chain can strongly reduce the size of polymer nanoparticles made by nanoprecipitation. The particle size can be further decreased to less than 15 nm by decreasing the concentration of polymer in the solvent used for nanoprecipitation. We then show that even very small nanocarriers of 15 nm size preserve the capacity to encapsulate large amounts of ionic dyes with bulky counterions at efficiencies >90%, which generates polymer nanoparticles 10-fold brighter than quantum dots of the same size. Postmodification of their surface with the PEG containing amphiphiles Tween 80 and pluronic F-127 led to particles that were stable under physiological conditions and in the presence of 10% fetal bovine serum. This modular route could become a general method for the preparation of ultrasmall polymer nanoparticles as nanocarriers of contrast agents and drugs.

Tuning the color and photostability of perylene diimides inside polymer nanoparticles: towards biodegradable substitutes of quantum dots

Fluorescent organic nanoparticles (NPs) are attractive alternatives to quantum dots due to their potential biodegradability. However, preparation of fluorescent organic NPs is challenging due to the problem of self-quenching of the encapsulated dyes. Moreover, the photostability of organic dyes is much lower than that of quantum dots. To address both problems, we studied encapsulation into biodegradable polymer PLGA NPs of perylene diimide (PDI) derivatives, which are among the most photostable dyes reported to date. Two PDIs were tested, one bearing bulky hydrophobic groups at the imides, while the other was substituted in both imide and bay regions (Lumogen Red). Encapsulation of the former resulted in aggregation, which was accompanied by the emission color change from green to red, some decrease in the fluorescence quantum yield and a significant drop in the photostability, unexpected for PDI dyes. In contrast, Lumogen Red showed nearly no aggregation inside polymer NPs and maintained high quantum yield and photostability. According to wide-field fluorescence microscopy with a 532 nm excitation laser, our 40 nm PLGA NPs loaded with 1 wt% Lumogen Red were >10-fold brighter than quantum dots (QD-585). These NPs were stable in biological media, including serum, and entered spontaneously into HeLa cells by endocytosis showing no sign of cytotoxicity. Due to excellent photostability, these nanoparticles could be considered as biodegradable substitutes of quantum dots in bioimaging.

On the benefits of rubbing salt in the cut: self-healing of saloplastic PAA/PAH compact polyelectrolyte complexes

The inherent room temperature mending and self-healing properties of saloplastic PAA/PAH CoPECs are studied. After ultracentrifugation of PAA/PAH polyelectrolyte complexes, tough, elastic materials are obtained that undergo self-healing facilitated by salt. At intermediate salt concentrations the CoPECs remain elastic enough to recover their original shape while the chains are mobile enough to repair the cut, thus leading to actual self-healing behavior.

Electrochemically addressed cross-links in polyelectrolyte multilayers: cyclic duravoltammetry

In situ nanoindentation was performed on a multilayer of poly(acrylic acid) and a high molecular weight, pendant chain polyviologen under controlled electrochemical potential. The modulus of the thin film of polyelectrolyte complex was reversibly modulated, by about an order of magnitude, upon changing the state of charge within the material using the electrochemically active and addressable viologen repeat units. The applied potential, under aqueous conditions, is believed to control the extent of cross-link formation. Simultaneous quartz crystal microbalance measurements revealed the flux of ions into or out of the multilayer during redox cycling. Apparent film modulus also depends on the identity of the last layer.

Exploring the heteroatom effect on polyelectrolyte multilayer assembly: the neglected polyoniums

Different positive polyelectrolytes having the same charge density, molecular weight, and molecular weight distribution were employed for polyelectrolyte multilayer (PEMU) assembly. The polycations differed only in the heteroatom on which the positive charge resided: poly(vinyl benzyl trimethyl ammonium) chloride, poly(vinyl benzyl trimethyl phosphonium) chloride, and poly(vinyl benzyl dimethyl sulfonium) chloride. While the ammonium repeat unit has been employed on numerous occasions for PEMU assembly, the phosphonium and sulfonium units are relatively neglected. The polyanions, poly(styrene sulfonate), PSS, or poly(acrylic acid), PAA, were typical pH-independent or pH-dependent polymers, respectively. All three polyoniums were quite similar in showing linear layer-by-layer buildup with PSS and exponential growth with PAA, under the conditions employed. Hydration and wettability were also similar between polyoniums.

Polyelectrolyte multilayers capped with polyelectrolytes bearing phosphorylcholine and triethylene glycol groups: parameters influencing antifouling properties

In this paper, we investigate the design of antifouling surfaces by the deposition of polyelectrolytes modified by grafting of antifouling groups onto a (PSS/PAH)n precursor multilayer film [PSS, poly(styrenesulfonate); PAH, poly(allylamine)]. Different polyelectrolytes and different antifouling moieties are investigated, in particular, (EO)3 and (EO)3PC moieties (EO, ethylene oxide; PC, phosphorylcholine group). We find that protein adsorption can strongly be reduced and even practically suppressed through the deposition of only one layer of polyelectrolyte modified with PC and/or (EO)3 groups. We discuss the influence of various parameters such as the nature of the polyelectrolyte backbone, the nature of the antifouling moiety, and the grafting ratio on the reduction of protein adsorption. We find in particular that (EO)3 and (EO)3PC moieties grafted on poly(acrylic acid) (PAA) totally prevent protein adsorption for grafting ratios of 25% or more, at least within the detection limits of the used quartz crystal microbalance and optical waveguide light mode spectroscopy devices. The mechanism that leads to the antifouling property is discussed and compared to that leading to the antifouling properties of ethylene oxide self-assembled monolayers. Finally, by incorporating biotin on top of the precursor film, we show that one layer of PAA-(EO)3PC is not sufficient to prevent interaction with streptavidin but a PAA-(EO)3PC/PAH/PAA-(EO)3PC multilayer largely protects the biotin from interacting with streptavidin.

[Video capsule endoscopy in a group of networked users: effective and cost saving]

BACKGROUND

At present extensive application of video capsule endoscopy (VCE) as the most innovative diagnostic tool for small bowel diseases is limited by its high costs. The present study describes the first experience in the mobile use of VCE in a cooperation of associated gastroenterology departments in different hospitals.

METHODS

The VCE device was bought by a centrally located hospital. In the case of a need for VCE elsewhere the mobile equipment was brought to the respective hospital. The examination was done on site by local physicians, who additionally were responsible for the procedure itself. The evaluation of the VCE pictures was carried out exclusively by the Ophysicians of the central hospital.

RESULTS

Within 15 months VCE was performed in 40 patients (19 male, 21 female; age 61 +/- 14 years). Ten examinations were performed in the central hospital, 30 in the associated gastroenterology departments of other hospitals. Indications for VCE were obscure GI bleeding (65 %), chronic diarrhea and Crohn's disease (17.5 %) or suspected small bowel neoplasms (17.5 %). Clinically relevant pathological abnormalities were detected in 62.5 % of the patients, mainly ulcerations and erosions. Complications were non-spontaneous capsule passage in one patient. Compared to a single hospital, the multicenter use of VCE increased the frequency of investigations four times and reduced expenses to almost 30 %.

CONCLUSIONS

The mobile use of VCE makes this innovative technique available for every patient while remaining in his local gastroenterology department. Additionally, this concept accelerates amortization and improves the quality of evaluation by focusing experience.