Susana Carregal-Romero

Biological applications of magnetic nanoparticles.

In this review an overview about biological applications of magnetic colloidal nanoparticles will be given, which comprises their synthesis, characterization, and in vitro and in vivo applications. The potential future role of magnetic nanoparticles compared to other functional nanoparticles will be discussed by highlighting the possibility of integration with other nanostructures and with existing biotechnology as well as by pointing out the specific properties of magnetic colloids. Current limitations in the fabrication process and issues related with the outcome of the particles in the body will be also pointed out in order to address the remaining challenges for an extended application of magnetic nanoparticles in medicine.

Multiple internalization pathways of polyelectrolyte multilayer capsules into mammalian cells.

Polyelectrolyte multilayer (PEM) capsules are carrier vehicles with great potential for biomedical applications. With the future aim of designing biocompatible, effective therapeutic delivery systems (e.g., for cancer), the pathway of internalization (uptake and fate) of PEM capsules was investigated. In particular the following experiments were performed: (i) the study of capsule co-localization with established endocytic markers, (ii) switching-off endocytotic pathways with pharmaceutical/chemical inhibitors, and (iii) characterization and quantification of capsule uptake with confocal and electron microscopy. As result, capsules co-localized with lipid rafts and with phagolysosomes, but not with other endocytic vesicles. Chemical interference of endocytosis with chemical blockers indicated that PEM capsules enter the investigated cell lines through a mechanism slightly sensitive to electrostatic interactions, independent of clathrin and caveolae, and strongly dependent on cholesterol-rich domains and organelle acidification. Microscopic characterization of cells during capsule uptake showed the formation of phagocytic cups (vesicles) to engulf the capsules, an increased number of mitochondria, and a final localization in the perinuclear cytoplasma. Combining all these indicators we conclude that PEM capsule internalization in general occurs as a combination of different sequential mechanisms. Initially, an adsorptive mechanism due to strong electrostatic interactions governs the stabilization of the capsules at the cell surface. Membrane ruffling and filopodia extensions are responsible for capsule engulfing through the formation of a phagocytic cup. Co-localization with lipid raft domains activates the cell to initiate a lipid-raft-mediated macropinocytosis. Internalization vesicles are very acidic and co-localize only with phagolysosome markers, excluding caveolin-mediated pathways and indicating that upon phagocytosis the capsules are sorted to heterophagolysosomes.

In vitro interaction of colloidal nanoparticles with mammalian cells: What have we learned thus far?

Summary The interfacing of colloidal nanoparticles with mammalian cells is now well into its second decade. In this review our goal is to highlight the more generally accepted concepts that we have gleaned from nearly twenty years of research. While details of these complex interactions strongly depend, amongst others, upon the specific properties of the nanoparticles used, the cell type, and their environmental conditions, a number of fundamental principles exist, which are outlined in this review.

NIR-light triggered delivery of macromolecules into the cytosol

Light-responsive microcapsules constructed by layer-by-layer self-assembly are used as microcarriers to deliver different macromolecules inside cells. The microcapsules carry the macromolecules as cargo in their cavity, while their walls are modified with agglomerated gold nanoparticles. Microcapsules are incorporated by living cells and are then located in lysosomal compartments. Controlled release of the encapsulated material from the interior of the capsule to the cytosol is possible upon NIR-light irradiation. This is based on local heating of the gold nanoparticles upon NIR light and disruption of the capsule wall, what results on release of encapsulated materials. We illustrate several key advances in controlled release induced by light. First, we demonstrate that capsules can be opened individually, which allows for sequentially releasing cargo from different capsules within one single cell. Second, by using a pH-indicator as cargo the claim of release from the acidic lysosomal compartments to the neutral cytosol is experimentally evident which until now has been only speculated. Third, green fluorescent protein (GFP) is released to the cytosol while retaining its functionality. This demonstrates that proteins can be released without destruction by the local heating. Fourth, GFP is also administered in biodegradable capsules, which leads to a different release mechanism compared to externally triggering for light-responsive microcapsules.

Light-Addressable Capsules as Caged Compound Matrix for Controlled Triggering of Cytosolic Reactions†

Release me: polyelectrolyte capsules with different cargo in their cavities and plasmonic and magnetic nanoparticles in their walls were synthesized. Enzymatic reactions were triggered inside cells by light-mediated opening of two individual capsules containing either an enzyme or its substrate, by using photothermal heating. Furthermore, this technique allows controlled release of mRNA from capsules, thereby resulting in synthesis of green fluorescent protein (GFP).

Colloidal Gold-Catalyzed Reduction of Ferrocyanate (III) by Borohydride Ions: A Model System for Redox Catalysis

We report results on the large catalytic effect of spherical gold nanoparticles on the rate of reduction of hexacyanoferrate (III) by sodium borohydride in aqueous solution. Because the gold nanoparticles remain stable and no aggregation takes place during the reaction, it can be monitored until completion. The presence of colloidal gold leads to a considerable increase in the observed reaction rate and to a change in the order of reaction. The reaction is first-order with respect to the hexacyanoferrate (III) concentration and gold particle concentration, but the reaction order with respect to borohydride ion is more complex. The activation energy is found to be 15 kJ/mol for 15 nm gold particles. The redox reaction is activation-controlled under most conditions, but the rate of reaction approaches the diffusion limit for higher borohydride concentrations and is over 10(4) times faster than in the absence of the gold catalyst.

Interaction of stable colloidal nanoparticles with cellular membranes

Due to their ultra-small size, inorganic nanoparticles (NPs) have distinct properties compared to the bulk form. The unique characteristics of NPs are broadly exploited in biomedical sciences in order to develop various methods of targeted drug delivery, novel biosensors and new therapeutic pathways. However, relatively little is known in the negotiation of NPs with complex biological environments. Cell membranes (CMs) in eukaryotes have dynamic structures, which is a key property for cellular responses to NPs. In this review, we discuss the current knowledge of various interactions between advanced types of NPs and CMs.

Catalytic Azide Reduction in Biological Environments

In the quest for the identification of catalytic transformations to be used in chemical biology and medicinal chemistry, we identified iron(III) meso‐tetraarylporphines as efficient catalysts for the reduction of aromatic azides to their amines. The reaction uses thiols as reducing agents and tolerates water, air, and other biological components. A caged fluorophore was employed to demonstrate that the reduction can be performed even in living mammalian cells. However, in vivo experiments in nematodes (Caenorhabditis elegans) and zebrafish (Danio rerio) revealed a limitation to this method: the metabolic reduction of aromatic azides.

Multiplexed Sensing and Imaging with Colloidal Nano- and Microparticles

Sensing and imaging with fluorescent, plasmonic, and magnetic colloidal nano- and microparticles have improved during the past decade. In this review, we describe the concepts and applications of how these techniques can be used in the multiplexed mode, that is, sensing of several analytes in parallel or imaging of several labels in parallel.

How Colloidal Nanoparticles Could Facilitate Multiplexed Measurements of Different Analytes with Analyte-Sensitive Organic Fluorophores

Multiplexed measurements of several analytes in parallel using analyte-sensitive organic fluorophores can be hampered by spectral overlap of the different fluorophores. The authors discuss how nanoparticles can help to overcome this problem. First, different organic fluorophores can be separated spatially by confining them to separate containers, each bearing a nanoparticle-based barcode. Second, by coupling different fluorophores to nanoparticles with different fluorescence lifetimes that serve as donors for excitation transfer, the effective fluorescence lifetime of the organic fluorophores as acceptors can be tuned by fluorescence resonance energy transfer (FRET). Thus, the fluorophores can be distinguished by their effective lifetimes. This is an example of how the modification of classical functional materials has already yielded improved and even new functionalities by the integration of nanoparticles with hybrid materials. We outline future opportunities in this area.