Quatsomes Loaded with Squaraine Dye as an Effective Photosensitizer for Photodynamic Therapy.

Photodynamic therapy is a non-invasive therapeutic strategy that combines external light with a photosensitizer (PS) to destroy abnormal cells. Despite the great progress in the development of new photosensitizers with improved efficacy, the PS's photosensitivity, high hydrophobicity, and tumor target avidity still represent the main challenges. Herein, newly synthesized brominated squaraine, exhibiting intense absorption in the red/near-infrared region, has been successfully incorporated into Quatsome (QS) nanovesicles at different loadings. The formulations under study have been characterized and interrogated in vitro for cytotoxicity, cellular uptake, and PDT efficiency in a breast cancer cell line. The nanoencapsulation of brominated squaraine into QS overcomes the non-water solubility limitation of the brominated squaraine without compromising its ability to generate ROS rapidly. In addition, PDT effectiveness is maximized due to the highly localized PS loadings in the QS. This strategy allows using a therapeutic squaraine concentration that is 100 times lower than the concentration of free squaraine usually employed in PDT. Taken together, our results reveal the benefits of the incorporation of brominated squaraine into QS to optimize their photoactive properties and support their applicability as photosensitizer agents for PDT.

Stable nanovesicles formed by intrinsically planar bilayers.

HYPOTHESIS: Quatsome nanovesicles, formed through the self-assembly of cholesterol (CHOL) and cetyltrimethylammonium bromide (CTAB) in water, have shown long-term stability in terms of size and morphology, while at the same time exhibiting high CHOL-CTAB intermolecular binding energies. We hypothesize that CHOL/CTAB quatsomes are indeed thermodynamically stable nanovesicles, and investigate the mechanism underlying their formation. EXPERIMENTS: A systematic study was performed to determine whether CHOL/CTAB quatsomes satisfy the experimental requisites of thermodynamically stable vesicles. Coarse-grain molecular dynamics simulations were used to investigate the molecular organization in the vesicle membrane, and the characteristics of the simulated vesicle were corroborated with experimental data obtained by cryo-electron microscopy, small- and wide-angle X-ray scattering, and multi-angle static light scattering. FINDINGS: CHOL/CTAB quatsomes fulfill the requisites of thermodynamically stable nanovesicles, but they do not exhibit the classical membrane curvature induced by a composition asymmetry between the bilayer leaflets, like catanionic nanovesicles. Instead, CHOL/CTAB quatsomes are formed through the association of intrinsically planar bilayers in a faceted vesicle with defects, indicating that distortions in the organization and orientation of molecules can play a major role in the formation of thermodynamically stable nanovesicles.

Fluorescent Multifunctional Organic Nanoparticles for Drug Delivery and Bioimaging: A Tutorial Review.

Fluorescent organic nanoparticles (FONs) are a large family of nanostructures constituted by organic components that emit light in different spectral regions upon excitation, due to the presence of organic fluorophores. FONs are of great interest for numerous biological and medical applications, due to their high tunability in terms of composition, morphology, surface functionalization, and optical properties. Multifunctional FONs combine several functionalities in a single nanostructure (emission of light, carriers for drug-delivery, functionalization with targeting ligands, etc.), opening the possibility of using the same nanoparticle for diagnosis and therapy. The preparation, characterization, and application of these multifunctional FONs require a multidisciplinary approach. In this review, we present FONs following a tutorial approach, with the aim of providing a general overview of the different aspects of the design, preparation, and characterization of FONs. The review encompasses the most common FONs developed to date, the description of the most important features of fluorophores that determine the optical properties of FONs, an overview of the preparation methods and of the optical characterization techniques, and the description of the theoretical approaches that are currently adopted for modeling FONs. The last part of the review is devoted to a non-exhaustive selection of some recent biomedical applications of FONs.

Ultrabright Föster Resonance Energy Transfer Nanovesicles: The Role of Dye Diffusion.

The development of contrast agents based on fluorescent nanoparticles with high brightness and stability is a key factor to improve the resolution and signal-to-noise ratio of current fluorescence imaging techniques. However, the design of bright fluorescent nanoparticles remains challenging due to fluorescence self-quenching at high concentrations. Developing bright nanoparticles showing FRET emission adds several advantages to the system, including an amplified Stokes shift, the possibility of ratiometric measurements, and of verifying the nanoparticle stability. Herein, we have developed Förster resonance energy transfer (FRET)-based nanovesicles at different dye loadings and investigated them through complementary experimental techniques, including conventional fluorescence spectroscopy and super-resolution microscopy supported by molecular dynamics calculations. We show that the optical properties can be modulated by dye loading at the nanoscopic level due to the dye's molecular diffusion in fluid-like membranes. This work shows the first proof of a FRET pair dye's dynamism in liquid-like membranes, resulting in optimized nanoprobes that are 120-fold brighter than QDot 605 and exhibit >80% FRET efficiency with vesicle-to-vesicle variations that are mostly below 10%.

Hierarchical Quatsome-RGD Nanoarchitectonic Surfaces for Enhanced Integrin-Mediated Cell Adhesion.

The synthesis and study of the tripeptide Arg-Gly-Asp (RGD), the binding site of different extracellular matrix proteins, e.g., fibronectin and vitronectin, has allowed the production of a wide range of cell adhesive surfaces. Although the surface density and spacing of the RGD peptide at the nanoscale have already shown a significant influence on cell adhesion, the impact of its hierarchical nanostructure is still rather unexplored. Accordingly, a versatile colloidal system named quatsomes, based on fluid nanovesicles formed by the self-assembling of cholesterol and surfactant molecules, has been devised as a novel template to achieve hierarchical nanostructures of the RGD peptide. To this end, RGD was anchored on the vesicle's fluid membrane of quatsomes, and the RGD-functionalized nanovesicles were covalently anchored to planar gold surfaces, forming a state of quasi-suspension, through a long poly(ethylene glycol) (PEG) chain with a thiol termination. An underlying self-assembled monolayer (SAM) of a shorter PEG was introduced for vesicle stabilization and to avoid unspecific cell adhesion. In comparison with substrates featuring a homogeneous distribution of RGD peptides, the resulting hierarchical nanoarchitectonic dramatically enhanced cell adhesion, despite lower overall RGD molecules on the surface. The new versatile platform was thoroughly characterized using a multitechnique approach, proving its enhanced performance. These findings open new methods for the hierarchical immobilization of biomolecules on surfaces using quatsomes as a robust and novel tissue engineering strategy.

Quatsomes Formulated with l-Prolinol-Derived Surfactants as Antibacterial Nanocarriers of (+)-Usnic Acid with Antioxidant Activity.

The efficacy of the treatment of bacterial infection is seriously reduced because of antibiotic resistance; thus, therapeutic solutions against drug-resistant microbes are necessary. Nanoparticle-based solutions are particularly promising for meeting this challenge because they can offer intrinsic antimicrobial activity and sustained drug release at the target site. Herein, we present a newly developed nanovesicle system of the quatsome family, composed of l-prolinol-derived surfactants and cholesterol, which has noticeable antibacterial activity even on Gram-negative strains, demonstrating great potential for the treatment of bacterial infections. We optimized the vesicle stability and antibacterial activity by tuning the surfactant chain length and headgroup charge (cationic or zwitterionic) and show that these quatsomes can furthermore serve as nanocarriers of pharmaceutical actives, demonstrated here by the encapsulation of (+)-usnic acid, a natural substance with many pharmacological properties.

Methods for the Characterization of Protein Aggregates.

The physicochemical characterization of protein aggregates yields an important contribution to further our understanding on many diseases for which the formation of protein aggregates is one of the pathological hallmarks. On the other hand, bacterial inclusion bodies (IBs) have recently been shown to be highly pure proteinaceous aggregates of a few hundred nanometers, produced by recombinant bacteria supporting the biological activities of the embedded polypeptides. Despite the wide spectrum of uses of IBs as functional and biocompatible materials upon convenient engineering, very few is known about their physicochemical properties.In this chapter we present methods for the characterization of protein aggregates as particulate materials relevant to their physicochemical and nanoscale properties.Specifically, we describe the use of dynamic light scattering (DLS) for sizing, nanoparticle tracking analysis for sizing and counting, and zeta potential measurements for the determination of colloidal stability. To study the morphology of protein aggregates we present the use of atomic force microscopy (AFM) and scanning electron microscopy (SEM). Cryo-transmission electron microscopy (cryo-TEM) will be used for the determination of the internal structuration. Moreover, wettability and nanomechanical characterization can be performed using contact angle (CA) and force spectroscopic AFM (FS-AFM) measurements of the proteinaceous nanoparticles, respectively. Finally, the 4'4-dithiodipyridine (DTDP) method is presented as a way of relatively quantifying accessible sulfhydryl groups in the structure of the nanoparticle .The physical principles of the methods are briefly described and examples are given to help clarify capabilities of each technique.

Methods for Processing Protein Aggregates into Surfaces.

The processing of inclusion bodies (IBs) into surfaces is of great interest for cell culture applications due to the combined physical and biological cues these particles provide. The arrangement of these IBs into defined and tunable micropatterns can be useful for basic research purposes regarding the mechanical properties needed for cell adhesion and migration, among other responses. There are several approaches that can be used when functionalizing a substrate with IBs, regarding both the strategy used and also the kind of surface-particle interaction. The interaction between surface and IB can be mainly of three types: physisorption, electrostatic or covalent. This interaction can be controlled by depositing an appropriate self-assembled monolayer (SAM) on top of a substrate as an interface. Furthermore, several strategies can be used to immobilize IBs on surfaces in various configurations, like random deposition, micrometric printed geometries or gradient patterns.

Engineering pH-Sensitive Stable Nanovesicles for Delivery of MicroRNA Therapeutics.

MicroRNAs (miRNAs) are small non-coding endogenous RNAs, which are attracting a growing interest as therapeutic molecules due to their central role in major diseases. However, the transformation of these biomolecules into drugs is limited due to their unstability in the bloodstream, caused by nucleases abundantly present in the blood, and poor capacity to enter cells. The conjugation of miRNAs to nanoparticles (NPs) could be an effective strategy for their clinical delivery. Herein, the engineering of non-liposomal lipid nanovesicles, named quatsomes (QS), for the delivery of miRNAs and other small RNAs into the cytosol of tumor cells, triggering a tumor-suppressive response is reported. The engineered pH-sensitive nanovesicles have controlled structure (unilamellar), size (<150 nm) and composition. These nanovesicles are colloidal stable (>24 weeks), and are prepared by a green, GMP compliant, and scalable one-step procedure, which are all unavoidable requirements for the arrival to the clinical practice of NP based miRNA therapeutics. Furthermore, QS protect miRNAs from RNAses and when injected intravenously, deliver them into liver, lung, and neuroblastoma xenografts tumors. These stable nanovesicles with tunable pH sensitiveness constitute an attractive platform for the efficient delivery of miRNAs and other small RNAs with therapeutic activity and their exploitation in the clinics.

Dye-Loaded Quatsomes Exhibiting FRET as Nanoprobes for Bioimaging.

Fluorescent organic nanoparticles (FONs) are emerging as an attractive alternative to the well-established fluorescent inorganic nanoparticles or small organic dyes. Their proper design allows one to obtain biocompatible probes with superior brightness and high photostability, although usually affected by low colloidal stability. Herein, we present a type of FONs with outstanding photophysical and physicochemical properties in-line with the stringent requirements for biomedical applications. These FONs are based on quatsome (QS) nanovesicles containing a pair of fluorescent carbocyanine molecules that give rise to Förster resonance energy transfer (FRET). Structural homogeneity, high brightness, photostability, and high FRET efficiency make these FONs a promising class of optical bioprobes. Loaded QSs have been used for in vitro bioimaging, demonstrating the nanovesicle membrane integrity after cell internalization, and the possibility to monitor the intracellular vesicle fate. Taken together, the proposed QSs loaded with a FRET pair constitute a promising platform for bioimaging and theranostics.

MKC-Quatsomes: a stable nanovesicle platform for bio-imaging and drug-delivery applications.

Quatsomes are outstanding new lipid-based nanovesicles that are highly homogeneous and stable in different media for years, but the composition must be carefully chosen to avoid any potentially toxic side effects in in vivo applications. To this end, we have developed and studied a novel type of Quatsomes composed of cholesterol and myristalkonium chloride (MKC), the latter being extensively used as antimicrobial preservative in many ophthalmic and parenteral formulations on the EU and USA market. We have synthesized these novel MKC-Quatsomes in different media that are suitable for parenteral administration, and confirmed their stability in these media for 18 months, as well as the stability in human serum for 24 hours. Biodistribution assays were performed after intravenous injection of fluorescently labeled MKC-Quatsomes in live mice bearing xenografted colorectal tumors, showing nanovesicle accumulation in tumors, liver, spleen, and kidneys. No histological alteration or toxicity was observed in any of these organs.

Publisher's Note: Biological Magnetometry: Torque on Superparamagnetic Beads in Magnetic Fields [Phys. Rev. Lett. 114, 218301 (2015)].

This corrects the article DOI: 10.1103/PhysRevLett.114.218301.

High-throughput, high-force probing of DNA-protein interactions with magnetic tweezers.

Recent advances in high-throughput single-molecule magnetic tweezers have paved the way for obtaining information on individual molecules as well as ensemble-averaged behavior in a single assay. Here we describe how to design robust high-throughput magnetic tweezers assays that specifically require application of high forces (>20pN) for prolonged periods of time (>1000s). We elaborate on the strengths and limitations of the typical construct types that can be used and provide a step-by-step guide towards a high tether yield assay based on two examples. Firstly, we discuss a DNA hairpin assay where force-induced strand separation triggers a tight interaction between DNA-binding protein Tus and its binding site Ter, where forces up to 90pN for hundreds of seconds were required to dissociate Tus from Ter. Secondly, we show how the LTag helicase of Simian virus 40 unwinds dsDNA, where a load of 36pN optimizes the assay readout. The approaches detailed here provide guidelines for the high-throughput, quantitative study of a wide range of DNA-protein interactions.

Biological magnetometry: torque on superparamagnetic beads in magnetic fields.

Superparamagnetic beads are widely used in biochemistry and single-molecule biophysics, but the nature of the anisotropy that enables the application of torques remains controversial. To quantitatively investigate the torques experienced by superparamagnetic particles, we use a biological motor to rotate beads in a magnetic field and demonstrate that the underlying potential is π periodic. In addition, we tether a bead to a single DNA molecule and show that the angular trap stiffness increases nonlinearly with magnetic field strength. Our results indicate that the superparamagnetic beads' anisotropy derives from a nonuniform intrabead distribution of superparamagnetic nanoparticles.

Nanoparticle-mediated monitoring of carbohydrate-lectin interactions using Transient Magnetic Birefringence.

The development of sensitive and easy-to-use biosensors that allow an adequate characterization of specific weak biological interactions like carbohydrate-lectin interactions still remains challenging today. Nanoparticles functionalized with carbohydrates are one of the most powerful systems for studying carbohydrate-lectin interactions, because they mimic the multivalent presentation of carbohydrates encountered in nature, for example when viruses and bacteria bind to cells. On the basis of the model system glucose-Concanavalin A (ConA), we explore the application of Transient Magnetic Birefringence (TMB) to study these weak interactions, using glucose-functionalized colloidal magnetite nanoparticles (NPs) as probes. We demonstrate that the binding dynamics can be monitored and derive a model to obtain the apparent cooperativity. For our studies, we use nanoparticles of 6 and 8 nm in diameter. The ConA-generated response shows apparent cooperativity, due to the cross-linking of nanoparticles by the ConA tetramer which has four binding sites. Cooperativity is higher for 6 nm NPs, possibly due to a better accessibility of all four ConA binding sites on smaller NPs, enhancing cross-linking. For this system, we find a detection limit of 3-23 nM.

Double-stranded RNA under force and torque: similarities to and striking differences from double-stranded DNA.

RNA plays myriad roles in the transmission and regulation of genetic information that are fundamentally constrained by its mechanical properties, including the elasticity and conformational transitions of the double-stranded (dsRNA) form. Although double-stranded DNA (dsDNA) mechanics have been dissected with exquisite precision, much less is known about dsRNA. Here we present a comprehensive characterization of dsRNA under external forces and torques using magnetic tweezers. We find that dsRNA has a force-torque phase diagram similar to that of dsDNA, including plectoneme formation, melting of the double helix induced by torque, a highly overwound state termed "P-RNA," and a highly underwound, left-handed state denoted "L-RNA." Beyond these similarities, our experiments reveal two unexpected behaviors of dsRNA: Unlike dsDNA, dsRNA shortens upon overwinding, and its characteristic transition rate at the plectonemic buckling transition is two orders of magnitude slower than for dsDNA. Our results challenge current models of nucleic acid mechanics, provide a baseline for modeling RNAs in biological contexts, and pave the way for new classes of magnetic tweezers experiments to dissect the role of twist and torque for RNA-protein interactions at the single-molecule level.

A force calibration standard for magnetic tweezers.

To study the behavior of biological macromolecules and enzymatic reactions under force, advances in single-molecule force spectroscopy have proven instrumental. Magnetic tweezers form one of the most powerful of these techniques, due to their overall simplicity, non-invasive character, potential for high throughput measurements, and large force range. Drawbacks of magnetic tweezers, however, are that accurate determination of the applied forces can be challenging for short biomolecules at high forces and very time-consuming for long tethers at low forces below ∼1 piconewton. Here, we address these drawbacks by presenting a calibration standard for magnetic tweezers consisting of measured forces for four magnet configurations. Each such configuration is calibrated for two commonly employed commercially available magnetic microspheres. We calculate forces in both time and spectral domains by analyzing bead fluctuations. The resulting calibration curves, validated through the use of different algorithms that yield close agreement in their determination of the applied forces, span a range from 100 piconewtons down to tens of femtonewtons. These generalized force calibrations will serve as a convenient resource for magnetic tweezers users and diminish variations between different experimental configurations or laboratories.

Ammonia induces aquaporin-4 rearrangement in the plasma membrane of cultured astrocytes.

Aquaporin-4 (AQP4) is a water channel protein mainly located in the astroglial plasma membrane, the precise function of which in the brain edema that accompanies hepatic encephalopathy (HE) is unclear. Since ammonia is the main pathogenic agent in HE, its effect on AQP4 expression and distribution in confluent primary astroglial cultures was examined via their exposure to ammonium chloride (1, 3 and 5 mM) for 5 and 10 days. Ammonia induced the general inhibition of AQP4 mRNA synthesis except in the 1 mM/5 day treatment. However, the AQP4 protein content measured was dependent on the method of analysis; an apparent increase was recorded in treated cells in in-cell Western assays, while an apparent reduction was seen with the classic Western blot method, perhaps due to differences in AQP4 aggregation. Ammonia might therefore induce the formation of insoluble AQP4 aggregates in the astroglial plasma membrane. The finding of AQP4 in the pellet of classic Western blot samples, plus data obtained via confocal microscopy, atomic force microscopy (using immunolabeled cells with gold nanoparticles) and scanning electron microscopy, all corroborate this hypothesis. The effect of ammonia on AQP4 seems not to be due to any osmotic effect; identical osmotic stress induced by glutamine and salt had no significant effect on the AQP4 content. AQP4 functional analysis (subjecting astrocytes to a hypo-osmotic medium and using flow cytometry to measure cell size) demonstrated a smaller water influx in ammonia-treated astrocytes suggesting that AQP4 aggregates are representative of an inactive status; however, more confirmatory studies are required to fully understand the functional status of AQP4 aggregates. The present results suggest that ammonia affects AQP4 expression and distribution, and that astrocytes change their expression of AQP4 mRNA as well as the aggregation status of the ensuing protein depending on the ammonia concentration and duration of exposure.

Transient magnetic birefringence for determining magnetic nanoparticle diameters in dense, highly light scattering media.

The increasing use of biofunctionalized magnetic nanoparticles in biomedical applications calls for further development of characterization tools that allow for determining the interactions of the nanoparticles with the biological medium in situ. In cell-incubating conditions, for example, nanoparticles may aggregate and serum proteins adsorb on the particles, altering the nanoparticles' performance and their interaction with cell membranes. In this work we show that the aggregation of spherical magnetite nanoparticles can be detected with high sensitivity in dense, highly light scattering media by making use of magnetically induced birefringence. Moreover, the hydrodynamic particle diameter distribution of anisometric nanoparticle aggregates can be determined directly in these media by monitoring the relaxation time of the magnetically induced birefringence. As a proof of concept, we performed measurements on nanoparticles included in an agarose gel, which scatters light in a similar way as a more complex biological medium but where particle-matrix interactions are weak. Magnetite nanoparticles were separated by agarose gel electrophoresis and the hydrodynamic diameter distribution was determined in situ. For the different particle functionalizations and agarose concentrations tested, we could show that gel electrophoresis did not yield a complete separation of monomers and small aggregates, and that the electrophoretic mobility of the aggregates decreased linearly with the hydrodynamic diameter. Furthermore, the rotational particle diffusion was not clearly affected by nanoparticle-gel interactions. The possibility to detect nanoparticle aggregates and their hydrodynamic diameters in complex scattering media like cell tissue makes transient magnetic birefringence an interesting technique for biological applications.

Nanogeometry matters: unexpected decrease of capillary adhesion forces with increasing relative humidity.

The sticking effect between hydrophilic surfaces occurring at increasing relative humidity (RH) is an everyday phenomenon with uncountable implications. Here experimental evidence is presented for a counterintuitive monotonous decrease of the capillary adhesion forces between hydrophilic surfaces with increasing RH for the whole humidity range. It is shown that this unexpected result is related to the actual shape of the asperity at the nanometer scale: a model based on macroscopic thermodynamics predicts this decrease in the adhesion force for a sharp object ending in an almost flat nanometer-sized apex, in full agreement with experiments. This anomalous decrease is due to the fact that a significant growth of the liquid meniscus formed at the contact region with increasing humidity is hindered for this geometry. These results are relevant in the analysis of the dynamical behavior of nanomenisci. They could also have an outstanding value in technological applications, since the undesirable sticking effect between surfaces occurring at increasing RH could be avoided by controlling the shape of the surface asperities at the nanometric scale.