Beatriz Pelaz

Protein corona formation around nanoparticles – from the past to the future

The protein adsorption layer (a.k.a. the “protein corona”) that forms on the surface of colloidal nanoparticles plays an important role in their interaction with living matter. Thus, characterization of the protein corona is of utmost importance for understanding how exposure to nanoparticles affects the biological responses of cells and organisms. Although a lot of experimental studies have been reported in this direction, a comprehensive picture is still missing, in particular due to the multitude of different scenarios under which experiments have been performed. In this review an analysis of existing experimental data about the protein corona, and an outline for required future work will be given. In particular we review how existing simple analytical models such as the adopted Hill model may help to extract quantitative data from such experiments such as equilibrium dissociation and kinetic coefficients. Careful quantitative assessment of equilibrium and kinetic properties would allow for a comparison of protein binding data from the vast array of engineered nanoparticles, so that basic principles could be revealed. This review outlines that the field is in dire need of more quantitative studies to further our understanding of protein corona formation and its biological consequences.

Surface Functionalization of Nanoparticles with Polyethylene Glycol: Effects on Protein Adsorption and Cellular Uptake

Here we have investigated the effect of enshrouding polymer-coated nanoparticles (NPs) with polyethylene glycol (PEG) on the adsorption of proteins and uptake by cultured cells. PEG was covalently linked to the polymer surface to the maximal grafting density achievable under our experimental conditions. Changes in the effective hydrodynamic radius of the NPs upon adsorption of human serum albumin (HSA) and fibrinogen (FIB) were measured in situ using fluorescence correlation spectroscopy. For NPs without a PEG shell, a thickness increase of around 3 nm, corresponding to HSA monolayer adsorption, was measured at high HSA concentration. Only 50% of this value was found for NPs with PEGylated surfaces. While the size increase clearly reveals formation of a protein corona also for PEGylated NPs, fluorescence lifetime measurements and quenching experiments suggest that the adsorbed HSA molecules are buried within the PEG shell. For FIB adsorption onto PEGylated NPs, even less change in NP diameter was observed. In vitro uptake of the NPs by 3T3 fibroblasts was reduced to around 10% upon PEGylation with PEG chains of 10 kDa. Thus, even though the PEG coatings did not completely prevent protein adsorption, the PEGylated NPs still displayed a pronounced reduction of cellular uptake with respect to bare NPs, which is to be expected if the adsorbed proteins are not exposed on the NP surface.

CuTe Nanocrystals: Shape and Size Control, Plasmonic Properties, and Use as SERS Probes and Photothermal Agents

We report a procedure to prepare highly monodisperse copper telluride nanocubes, nanoplates, and nanorods. The procedure is based on the reaction of a copper salt with trioctylphosphine telluride in the presence of lithium bis(trimethylsilyl)amide and oleylamine. CuTe nanocrystals display a strong near-infrared optical absorption associated with localized surface plasmon resonances. We exploit this plasmon resonance for the design of surface-enhanced Raman scattering sensors for unconventional optical probes. Furthermore, we also report here our preliminary analysis of the use of CuTe nanocrystals as cytotoxic and photothermal agents.

The State of Nanoparticle-Based Nanoscience and Biotechnology: Progress, Promises, and Challenges

Colloidal nanoparticles (NPs) have become versatile building blocks in a wide variety of fields. Here, we discuss the state-of-the-art, current hot topics, and future directions based on the following aspects: narrow size-distribution NPs can exhibit protein-like properties; monodispersity of NPs is not always required; assembled NPs can exhibit collective behavior; NPs can be assembled one by one; there is more to be connected with NPs; NPs can be designed to be smart; surface-modified NPs can directly reach the cytosols of living cells.

Tumour homing and therapeutic effect of colloidal nanoparticles depend on the number of attached antibodies

Active targeting of nanoparticles to tumours can be achieved by conjugation with specific antibodies. Specific active targeting of the HER2 receptor is demonstrated in vitro and in vivo with a subcutaneous MCF-7 breast cancer mouse model with trastuzumab-functionalized gold nanoparticles. The number of attached antibodies per nanoparticle was precisely controlled in a way that each nanoparticle was conjugated with either exactly one or exactly two antibodies. As expected, in vitro we found a moderate increase in targeting efficiency of nanoparticles with two instead of just one antibody attached per nanoparticle. However, the in vivo data demonstrate that best effect is obtained for nanoparticles with only exactly one antibody. There is indication that this is based on a size-related effect. These results highlight the importance of precisely controlling the ligand density on the nanoparticle surface for optimizing active targeting, and that less antibodies can exhibit more effect.

Interfacing engineered nanoparticles with biological systems: anticipating adverse nano-bio interactions.

The innovative use of engineered nanomaterials in medicine, be it in therapy or diagnosis, is growing dramatically. This is motivated by the current extraordinary control over the synthesis of complex nanomaterials with a variety of biological functions (e.g. contrast agents, drug-delivery systems, transducers, amplifiers, etc.). Engineered nanomaterials are found in the bio-context with a variety of applications in fields such as sensing, imaging, therapy or diagnosis. As the degree of control to fabricate customized novel and/or enhanced nanomaterials evolves, often new applications, devices with enhanced performance or unprecedented sensing limits can be achieved. Of course, interfacing any novel material with biological systems has to be critically analyzed as many undesirable adverse effects can be triggered (e.g. toxicity, allergy, genotoxicity, etc.) and/or the performance of the nanomaterial can be compromised due to the unexpected phenomena in physiological environments (e.g. corrosion, aggregation, unspecific absorption of biomolecules, etc.). Despite the need for standard protocols for assessing the toxicity and bio-performance of each new functional nanomaterial, these are still scarce or currently under development. Nonetheless, nanotoxicology and relating adverse effects to the physico-chemical properties of nanomaterials are emerging areas of the utmost importance which have to be continuously revisited as any new material emerges. This review highlights recent progress concerning the interaction of nanomaterials with biological systems and following adverse effects.

Gold nanoprisms as optoacoustic signal nanoamplifiers for in vivo bioimaging of gastrointestinal cancers.

Early detection of cancer greatly increases the chances of a simpler and more effective treatment. Traditional imaging techniques are often limited by shallow penetration, low sensitivity, low specificity, poor spatial resolution or the use of ionizing radiation. Hybrid modalities, like optoacoustic imaging, an emerging molecular imaging modality, contribute to improving most of these limitations. However, this imaging method is hindered by relatively low signal contrast. Here, gold nanoprisms (AuNPrs) are used as signal amplifiers in multispectral optoacoustic tomography (MSOT) to visualize gastrointestinal cancer. PEGylated AuNPrs are successfully internalized by HT-29 gastrointestinal cancer cells in vitro. Moreover, the particles show good biocompatibility and exhibit a surface plasmon band centered at 830 nm, a suitable wavelength for optoacoustic imaging purposes. These findings extend well to an in vivo setting, in which mice are injected with PEGylated AuNPrs in order to visualize tumor angiogenesis in gastrointestinal cancer cells. Overall, both our in vitro and in vivo results show that PEGylated AuNPrs have the capacity to penetrate tumors and provide a high-resolution signal amplifier for optoacoustic imaging. The combination of PEGylated AuNPrs and MSOT represents a significant advance for the in vivo imaging of cancers.

Tailoring the synthesis and heating ability of gold nanoprisms for bioapplications.

The paper describes a novel and straightforward wet-chemical synthetic route to produce biocompatible single-crystalline gold tabular nanoparticles, herein called nanoprisms (NPRs) due to their characteristic shape. Besides the novelty of the method to produce NPRs with an unprecedented high yield, the synthesis avoids the use of highly toxic cetyltrimethylammonium bromide (CTAB), the most widely used surfactant for the synthesis of gold anisotropic nanoparticles such as nanorods or nanoprisms. The method presented here allows for tuning the edge length of NPRs in the range of 100-170 nm by adjusting the final concentration/molar ratio of gold salt and reducing agent (thiosulfate), while the thickness of NPRs remained constant (9 nm). Thus, the surface plasmon band of NPRs can be set along the near-infrared (NIR) range. The resulting NPRs were derivatized with heterobifunctional polyethylene glycol (PEG) and 4-aminophenyl β-D-glucopyranoside (glucose) chains to improve their stability and cellular uptake, respectively. The heating properties of colloidal solutions of NPRs upon 1064 nm light illumination were evaluated. As a proof of concept, the biocompatibility and suitability of functional NPRs as photothermal agents were studied in cell cultures. Due to their biocompatibility (avoiding CTAB), ease of production, ease of functionalization, and remarkable heating features, the NPRs discussed herein represent a significant advance in the biocompatibility of nanoparticles and serve as an attractive alternative to those currently in use as plasmonic photothermal agents.

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.

The effect of static magnetic fields and tat peptides on cellular and nuclear uptake of magnetic nanoparticles.

Magnetic nanoparticles are widely used in bioapplications such as imaging (MRI), targeted delivery (drugs/genes) and cell transfection (magnetofection). Historically, the impermeable nature of both the plasma and nuclear membranes hinder potential. Researchers combat this by developing techniques to enhance cellular and nuclear uptake. Two current popular methods are using external magnetic fields to remotely control particle direction or functionalising the nanoparticles with a cell penetrating peptide (e.g. tat); both of which facilitate cell entry. This paper compares the success of both methods in terms of nanoparticle uptake, analysing the type of magnetic forces the particles experience, and determines gross cell response in terms of morphology and structure and changes at the gene level via microarray analysis. Results indicated that both methods enhanced uptake via a caveolin dependent manner, with tat peptide being the more efficient and achieving nuclear uptake. On comparison to control cells, many groups of gene changes were observed in response to the particles. Importantly, the magnetic field also caused many change in gene expression, regardless of the nanoparticles, and appeared to cause F-actin alignment in the cells. Results suggest that static fields should be modelled and analysed prior to application in culture as cells clearly respond appropriately. Furthermore, the use of cell penetrating peptides may prove more beneficial in terms of enhancing uptake and maintaining cell homeostasis than a magnetic field.