Erythrocyte Incubation as a Method for Free-Dye Presence Determination in Fluorescently Labeled Nanoparticles

New Analytical Approaches for Effective Quantification and Identification of Nanoplastics in Environmental Samples

Nanoplastics (NPs) are a rapidly developing subject that is relevant in environmental and food research, as well as in human toxicity, among other fields. NPs have recently been recognized as one of the least studied types of marine litter, but potentially one of the most hazardous. Several studies are now being reported on NPs in the environment including surface water and coast, snow, soil and in personal care products. However, the extent of contamination remains largely unknown due to fundamental challenges associated with isolation and analysis, and therefore, a methodological gap exists. This article summarizes the progress in environmental NPs analysis and makes a critical assessment of whether methods from nanoparticles analysis could be adopted to bridge the methodological gap. This review discussed the sample preparation and preconcentration protocol for NPs analysis and also examines the most appropriate approaches available at the moment, ranging from physical to chemical. This study also discusses the difficulties associated with improving existing methods and developing new ones. Although microscopical techniques are one of the most often used ways for imaging and thus quantification, they have the drawback of producing partial findings as they can be easily mixed up as biomolecules. At the moment, the combination of chemical analysis (i.e., spectroscopy) and newly developed alternative methods overcomes this limitation. In general, multiple analytical methods used in combination are likely to be needed to correctly detect and fully quantify NPs in environmental samples.

Fluorescently Labeled PLGA Nanoparticles for Visualization In Vitro and In Vivo: The Importance of Dye Properties

Fluorescently labeled nanoparticles are widely used for evaluating their distribution in the biological environment. However, dye leakage can lead to misinterpretations of the nanoparticles' biodistribution. To better understand the interactions of dyes and nanoparticles and their biological environment, we explored PLGA nanoparticles labeled with four widely used dyes encapsulated (coumarin 6, rhodamine 123, DiI) or bound covalently to the polymer (Cy5.5.). The DiI label was stable in both aqueous and lipophilic environments, whereas the quick release of coumarin 6 was observed in model media containing albumin (42%) or liposomes (62%), which could be explained by the different affinity of these dyes to the polymer and lipophilic structures and which we also confirmed by computational modeling (log PDPPC/PLGA: DiI-2.3, Cou6-0.7). The importance of these factors was demonstrated by in vivo neuroimaging (ICON) of the rat retina using double-labeled Cy5.5/Cou6-nanoparticles: encapsulated Cou6 quickly leaked into the tissue, whereas the stably bound Cy.5.5 label remained associated with the vessels. This observation is a good example of the possible misinterpretation of imaging results because the coumarin 6 distribution creates the impression that nanoparticles effectively crossed the blood-retina barrier, whereas in fact no signal from the core material was found beyond the blood vessels.

Micro and Nanoplastics Identification: Classic Methods and Innovative Detection Techniques

Micro and nanoplastics are fragments with dimensions less than a millimeter invading all terrestrial and marine environments. They have become a major global environmental issue in recent decades and, indeed, recent scientific studies have highlighted the presence of these fragments all over the world even in environments that were thought to be unspoiled. Analysis of micro/nanoplastics in isolated samples from abiotic and biotic environmental matrices has become increasingly common. Hence, the need to find valid techniques to identify these micro and nano-sized particles. In this review, we discuss the current and potential identification methods used in microplastic analyses along with their advantages and limitations. We discuss the most suitable techniques currently available, from physical to chemical ones, as well as the challenges to enhance the existing methods and develop new ones. Microscopical techniques (i.e., dissect, polarized, fluorescence, scanning electron, and atomic force microscopy) are one of the most used identification methods for micro/nanoplastics, but they have the limitation to produce incomplete results in analyses of small particles. At present, the combination with chemical analysis (i.e., spectroscopy) overcome this limit together with recently introduced alternative approaches. For example, holographic imaging in microscope configuration images microplastics directly in unfiltered water, thus discriminating microplastics from diatoms and differentiates different sizes, shapes, and plastic types. The development of new analytical instruments coupled with each other or with conventional and innovative microscopy could solve the current problems in the identification of micro/nanoplastics.

Multiscale Live Imaging Using Förster Resonance Energy Transfer (FRET) for Evaluating the Biological Behavior of Nanoparticles as Drug Carriers

To develop targeted drug delivery systems using nanoparticles for treating various diseases, the evaluation of nanoparticle behavior in biological environments is necessary. In the present study, the biological behavior of polymeric nanoparticles was directly traced in living mice and cells. The dissociation of nanoparticles was detected by Förster resonance energy transfer (FRET) imaging. DiR and DiD were encapsulated in the nanoparticles for near-infrared FRET imaging, and they were traced using in vivo FRET imaging and intravital FRET imaging at the whole-body and tissue scales, respectively. In vivo FRET imaging revealed that the nanoparticles dissociated over time following intravenous administration. Intravital FRET imaging revealed that the nanoparticles dissociated in the liver and blood vessels following intravenous administration. DiI and DiO were encapsulated in nanoparticles for FRET imaging using confocal microscopy, and they were traced using in vitro FRET imaging in HepG2 cells. In vitro FRET imaging revealed that the nanoparticles dissociated and released fluorescent dyes that distributed in the cell membrane. Finally, live imaging was performed using FRET at the whole-body, tissue, and cellular scales. This method is suitable for obtaining information regarding the biological kinetic properties of nanoparticles and their use in targeted drug delivery.

Use of fluorescent-labelled nanoplastics (NPs) to demonstrate NP absorption is inconclusive without adequate controls

Whether nanoplastics (NPs) are able to be absorbed across epithelial membranes and accumulate within internal tissues of organisms is an important determinant of their potential toxicity. Evidence of absorption and accumulation requires detection of NPs within internal tissues, and investigations with fluorescently labelled NPs have attempted to provide this information. We hypothesize that studies that do not control for the fluorescent dye leachate and/or cellular autofluorescence are inconclusive and can be misinterpreted. Our goal was to analyse previous investigations critically and conduct further research to determine if fluorescent-labelled polystyrene NPs (nanoPS) can provide conclusive evidence of absorption and internal accumulation of NPs. We exposed zebrafish embryos and larvae to NPs (500 and 1000 nm) labelled with a green or an orange fluorescent dye, to solutions resulting from nanoPS dialysis, and to Nile-Red (a fluorescent dye used as a positive control). Previous studies have claimed that NPs cross epithelia without accounting for dye leachates and/or cellular autofluorescence. Our results demonstrate that commercial fluorescent-labelled nanoPS can leach their fluorophores, and the fluorophore alone can accumulate within internal tissues of zebrafish larvae. We further observed green autofluorescence in fish larvae not exposed to any particles. Previous claims of NP absorption based on observations of fluorescence in zebrafish tissues should thus be considered inconclusive. Although the addition of purification steps and inclusion of controls for leaching of dyes are methodological improvements, the use of fluorescent nanoPS should not be considered to provide absolute conclusive evidence of particle absorption.

Human serum albumin nanoparticles loaded with phthalocyanine dyes for potential use in photodynamic therapy for atherosclerotic plaques

Diseases caused by obstruction or rupture of vulnerable plaques in the arterial walls such as cardiovascular infarction or stroke are the leading cause of death in the world. In the present work, we developed human serum albumin nanoparticles loaded by physisorption with zinc phthalocyanine, TT1, mainly used for industrial application as near-infrared photosensitizer and compared these to HSA NPs loaded with the well-known silicone phthalocyanine (Pc4). The use of NIR light allows for better tissue penetration, while the use of nanoparticles permits high local concentrations. The particles were characterized and tested for toxicity and stability as well as for their potential use as a contrast agent and NIR photosensitizer for photodynamic therapy in cardiovascular disease. We focused on the distribution of the nanoparticles in RAW264.7 macrophage cells and atherosclerotic mice. The nanoparticles had an average size of 120 nm according to dynamic light scattering, good loading capacity for zinc phthalocyanine, and satisfying stability in 50% (v/v) fetal bovine serum for 8 hours and in an aqueous environment at 4°C for 4–6 weeks. Under light irradiation we found a high production of singlet oxygen and the products showed no dark toxicity in vitro with macrophages (the target cells in vulnerable plaques), but at a low g/mL nanoparticle concentration killed efficiently the macrophages upon LED illumination. Injection of the contrast agent in atherosclerotic mice led to a visible fluorescence signal of zinc phthalocyanine in the atherosclerotic plaque at 30 minutes and in the lungs with a fast clearance of the nanoparticles. Zinc phthalocyanine loaded human serum albumin nanoparticles present an interesting candidate for the visualization and potentially photodynamic treatment of macrophages in atherosclerotic plaques.

Distribution of superparamagnetic Au/Fe nanoparticles in an isolated guinea pig brain with an intact blood brain barrier

Diagnosis and treatment of brain disorders, such as epilepsy, neurodegenerative diseases and tumors, would benefit from innovative approaches to deliver therapeutic or diagnostic compounds into the brain parenchyma, with either a homogeneous or a targeted localized distribution pattern. To assess the mechanistic aspect of penetration of nanoparticles (NPs) into the brain parenchyma, a complex, yet controlled and facilitated environment was used: the isolated guinea pig brain maintained in vitro by arterial perfusion. In this unique preparation the blood-brain barrier and the interactions between vascular and neuronal compartments are morphologically and functionally preserved. In this study, superparamagnetic Au/Fe nanoparticles (MUS:OT Au/Fe NPs), recently studied as a promising magnetic resonance T2 contrast agent with high cellular penetration, were arterially perfused into the in vitro isolated brain and showed high and homogeneous penetration through transcytosis into the brain parenchyma. Ultramicroscopy investigation of the in vitro isolated brain sections by TEM analysis of the electron-dense core of the MUS:OT Au/Fe NPs was conducted to understand NPs' brain penetration through the BBB after in vitro arterial perfusion and their distribution in the parenchyma. Our data suggest that MUS:OT Au/Fe NPs enter the brain utilizing a physiological route and therefore can be exploited as brain penetrating nanomaterials with potential contrast agent and theranostics capabilities.

Amphiphilic nanoparticle delivery enhances the anticancer efficacy of a TLR7 ligand via local immune activation

Although immunotherapy shows great promise for the long-term control of cancer, many tumors still fail to respond to treatment. To improve the outcome, the delivery of immunostimulants to the lymph nodes draining the tumor, where the antitumor immune response is initiated, is key. Efforts to use nanoparticles as carriers for cancer immunotherapy have generally required targeting agents and chemical modification of the drug, and have unfortunately resulted in low delivery and therapeutic efficiency. Here, we report on the efficacy of gold nanoparticles with approximately 5 nm hydrodynamic diameter coated with a mixture of 1-octanethiol and 11-mercaptoundecanesulfonic acid for the delivery of an immunostimulatory TLR7 ligand to tumor-draining lymph nodes. The drug was loaded without modification through nonspecific adsorption into the ligand shell of the nanoparticles, taking advantage of their amphiphilic nature. After loading, nanoparticles retained their stability in solution without significant premature release of the drug, and the drug cargo was immunologically active. Upon subcutaneous injection into tumor-bearing mice, the drug-loaded particles were rapidly transported to the tumor-draining lymph nodes. There, they induced a local immune activation and fostered a cytotoxic T-cell response that was specific for the tumor. Importantly, the particle-delivered TLR7 ligand blocked the growth of large established tumors and significantly prolonged survival compared to the free form of the drug. Thus, we demonstrate for the first time that nanoparticle delivery of a TLR7 immunostimulant to the tumor-draining lymph nodes enhances antitumor immunity and improves the outcome of cancer immunotherapy.

Photosensitizer Decorated Red Blood Cells as an Ultrasensitive Light-Responsive Drug Delivery System

Red blood cells (RBCs) have been widely explored as a natural drug delivery system (DDS) owing to their inherent biocompatibility and large internal cavities to load various types of functional molecules. Herein, we uncover that a photosensitizer, chlorin e6 (Ce6), could be decorated into the membrane of RBCs upon simple mixing, without affecting the membrane integrity and stability in dark. Upon light irradiation with a rather low power density, the singlet oxygen generated by Ce6 would lead to rather efficient disruption of RBC membrane. With doxorubicin (DOX), a typical chemotherapy drug, as the model, we engineer a unique type of light-responsive RBC-based DDS by decorating Ce6 on the cell membrane and loading DOX inside cells. The light triggered cell membrane breakdown would thus trigger instant release of DOX, enabling light-controlled chemotherapy with great specificity. Beyond that our RBC system could also be utilized for loading of larger biomolecules such as enzymes, whose release as well as catalytic function is also controlled by light. Our work thus presents a unique type of biocompatible cell-based DDS that can be precisely controlled by mild external stimuli, promising not only for cancer therapy but also for other potential applications in biotechnologies.

Advances of blood cell-based drug delivery systems

Blood cells, including erythrocytes, leukocytes and platelets are used as drug carriers in a wide range of applications. They have many unique advantages such as long life-span in circulation (especially erythrocytes), target release capacities (especially platelets), and natural adhesive properties (leukocytes and platelets). These properties make blood cell based delivery systems, as well as their membrane-derived carriers, far superior to other drug delivery systems. Despite the advantages, the further development of blood cell-based delivery systems was hindered by limitations in the source, storage, and mass production. To overcome these problems, synthetic biomaterials that mimic blood cell and nanocrystallization of blood cells have been developed and may represent the future direction for blood cell membrane-based delivery systems. In this paper, we review recent progress of the rising blood cell-based drug delivery systems, and also discuss their challenges and future tendency of development.

Two-Color Single Hybrid Plasmonic Nanoemitters with Real Time Switchable Dominant Emission Wavelength

We demonstrate two-color nanoemitters that enable the selection of the dominant emitting wavelength by varying the polarization of excitation light. The nanoemitters were fabricated via surface plasmon-triggered two-photon polymerization. By using two polymerizable solutions with different quantum dots, emitters of different colors can be positioned selectively in different orientations in the close vicinity of the metal nanoparticles. The dominant emission wavelength of the metal/polymer anisotropic hybrid nanoemitter thus can be selected by altering the incident polarization.

Influence of the glycocalyx and plasma membrane composition on amphiphilic gold nanoparticle association with erythrocytes

Erythrocytes are attractive as potential cell-based drug carriers because of their abundance and long lifespan in vivo. Existing methods for loading drug cargos into erythrocytes include hypotonic treatments, electroporation, and covalent attachment onto the membrane, all of which require ex vivo manipulation. Here, we characterized the properties of amphiphilic gold nanoparticles (amph-AuNPs), comprised of a ∼2.3 nm gold core and an amphiphilic ligand shell, which are able to embed spontaneously within erythrocyte membranes and might provide a means to load drugs into red blood cells (RBCs) directly in vivo. Particle interaction with RBC membranes occurred rapidly at physiological temperature. We further show that amph-AuNP uptake by RBCs was limited by the glycocalyx and was particularly influenced by sialic acids on cell surface proteoglycans. Using a reductionist model membrane system with synthetic lipid vesicles, we confirmed the importance of membrane fluidity and the glycocalyx in regulating amph-AuNP/membrane interactions. These results thus provide evidence for the interaction of amph-AuNPs with erythrocyte membranes and identify key membrane components that govern this interaction, providing a framework for the development of amph-AuNP-carrying erythrocyte 'pharmacytes' in vivo.

Effect of particle diameter and surface composition on the spontaneous fusion of monolayer-protected gold nanoparticles with lipid bilayers

Anionic, monolayer-protected gold nanoparticles (AuNPs) have been shown to nondisruptively penetrate cellular membranes. Here, we show that a critical first step in the penetration process is potentially the fusion of such AuNPs with lipid bilayers. Free energy calculations, experiments on unilamellar and multilamellar vesicles, and cell studies all support this hypothesis. Furthermore, we show that fusion is only favorable for AuNPs with core diameters below a critical size that depends on the monolayer composition.