Due to their small size, nanoparticles have distinct properties compared with the bulk form of the same materials. These properties are rapidly revolutionizing many areas of medicine and technology. Despite the remarkable speed of development of nanoscience, relatively little is known about the interaction of nanoscale objects with living systems. In a biological fluid, proteins associate with nanoparticles, and the amount and presentation of the proteins on the surface of the particles leads to an in vivo response. Proteins compete for the nanoparticle "surface," leading to a protein "corona" that largely defines the biological identity of the particle. Thus, knowledge of rates, affinities, and stoichiometries of protein association with, and dissociation from, nanoparticles is important for understanding the nature of the particle surface seen by the functional machinery of cells. Here we develop approaches to study these parameters and apply them to plasma and simple model systems, albumin and fibrinogen. A series of copolymer nanoparticles are used with variation of size and composition (hydrophobicity). We show that isothermal titration calorimetry is suitable for studying the affinity and stoichiometry of protein binding to nanoparticles. We determine the rates of protein association and dissociation using surface plasmon resonance technology with nanoparticles that are thiol-linked to gold, and through size exclusion chromatography of protein-nanoparticle mixtures. This method is less perturbing than centrifugation, and is developed into a systematic methodology to isolate nanoparticle-associated proteins. The kinetic and equilibrium binding properties depend on protein identity as well as particle surface characteristics and size.

https://www.pnas.org/content/pnas/104/7/2050.full.pdf

Understanding the nanoparticle-protein corona using methods to quantify exchange rates and affinities of proteins for nanoparticles.

Nanoparticles in a biological fluid (plasma, or otherwise) associate with a range of biopolymers, especially proteins, organized into the "protein corona" that is associated with the nanoparticle and continuously exchanging with the proteins in the environment. Methodologies to determine the corona and to understand its dependence on nanomaterial properties are likely to become important in bionanoscience. Here, we study the long-lived ("hard") protein corona formed from human plasma for a range of nanoparticles that differ in surface properties and size. Six different polystyrene nanoparticles were studied: three different surface chemistries (plain PS, carboxyl-modified, and amine-modified) and two sizes of each (50 and 100 nm), enabling us to perform systematic studies of the effect of surface properties and size on the detailed protein coronas. Proteins in the corona that are conserved and unique across the nanoparticle types were identified and classified according to the protein functional properties. Remarkably, both size and surface properties were found to play a very significant role in determining the nanoparticle coronas on the different particles of identical materials. We comment on the future need for scientific understanding, characterization, and possibly some additional emphasis on standards for the surfaces of nanoparticles.

https://www.pnas.org/content/pnas/105/38/14265.full.pdf

Nanoparticle size and surface properties determine the protein corona with possible implications for biological impacts

Superparamagnetic nanoparticles for biomedical applications: Possibilities and limitations of a new drug delivery system

In medicine, nanotechnology has sparked a rapidly growing interest as it promises to solve a number of issues associated with conventional therapeutic agents, including their poor water solubility (at least, for most anticancer drugs), lack of targeting capability, nonspecific distribution, systemic toxicity, and low therapeutic index. Over the past several decades, remarkable progress has been made in the development and application of engineered nanoparticles to treat cancer more effectively. For example, therapeutic agents have been integrated with nanoparticles engineered with optimal sizes, shapes, and surface properties to increase their solubility, prolong their circulation half-life, improve their biodistribution, and reduce their immunogenicity. Nanoparticles and their payloads have also been favorably delivered into tumors by taking advantage of the pathophysiological conditions, such as the enhanced permeability and retention effect, and the spatial variations in the pH value. Additionally, targeting ligands (e.g., small organic molecules, peptides, antibodies, and nucleic acids) have been added to the surface of nanoparticles to specifically target cancerous cells through selective binding to the receptors overexpressed on their surface. Furthermore, it has been demonstrated that multiple types of therapeutic drugs and/or diagnostic agents (e.g., contrast agents) could be delivered through the same carrier to enable combination therapy with a potential to overcome multidrug resistance, and real-time readout on the treatment efficacy. It is anticipated that precisely engineered nanoparticles will emerge as the next-generation platform for cancer therapy and many other biomedical applications.

Engineered Nanoparticles for Drug Delivery in Cancer Therapy

Most research on the toxicology of nanomaterials has focused on the effects of nanoparticles that enter the body accidentally. There has been much less research on the toxicology of nanoparticles that are used for biomedical applications, such as drug delivery or imaging, in which the nanoparticles are deliberately placed in the body. Moreover, there are no harmonized standards for assessing the toxicity of nanoparticles to the immune system (immunotoxicity). Here we review recent research on immunotoxicity, along with data on a range of nanotechnology-based drugs that are at different stages in the approval process. Research shows that nanoparticles can stimulate and/or suppress the immune responses, and that their compatibility with the immune system is largely determined by their surface chemistry. Modifying these factors can significantly reduce the immunotoxicity of nanoparticles and make them useful platforms for drug delivery.

Immunological properties of engineered nanomaterials.

Influence of surface charge density on protein adsorption on polymeric nanoparticles: analysis by two-dimensional electrophoresis

Electron microscopic analysis of nanoparticles delivering thioflavin-T after intrahippocampal injection in mouse: implications for targeting β-amyloid in Alzheimer's disease

The magnetic guidance of antiplastic and antibacterial agents as well as x-ray and MRI contrast substances in vivo by means of magnetic particles has been attempted repeatedly during the last 2 decades with more or less success. When using microparticles, the circulation time in the blood, the biodistribution, and to a greater or lesser extent, the specific targeting are determined by the uniformity of size, chemical composition, surface modification, and the electric surface charge. The electrophoretic mobility is an important parameter for the prediction of the usefulness of the prepared particle, modified by chemical and biological molecules. For its success, radionuclide therapy depends on the critical relationship between the amount of radioactive isotopes in the target tissue and in critical normal tissue. Because the implementation of radioimmunotherapy for the treatment of cancer has proven to be considerably more difficult than initially anticipated, we propose the use of magnetic nanospheres for the well directed delivery of radionuclides to a tumor after the intravenous administration of the biodegradable colloidal suspension.

Biocompatible Magnetic Polymer Carriers for In Vivo Radionuclide Delivery

99mTc labelled model drug carriers - labeling, stability and organ distribution in rats

The applicability of magnetic particles is strongly dependent on the electric surface charge and the magnetic susceptibility of the individual particles. Particle electrophoresis is a common method to control the production process and to assess the final colloidal solution. Particles within a wide size range are used and different measuring principles must therefore be applied. Laser based techniques using the Doppler or image transduction effect are very useful for the estimation of the mean electrophoretic mobility of particles within the size range below 500 nm. Automated techniques with image analysis are preferred for the analysis of mixtures of particles with sizes larger than 500 nm and with a broad variation of the surface charge. Electrophoretic fingerprints representing the mean electrophoretic mobility of a given particle suspension versus pH and ionic strength of the media are a helpful method for the assessment of the production and modification procedure of particles.

Bernd R Paulke

Papers

Influence of surface charge density on protein adsorption on polymeric nanoparticles: analysis by two-dimensional electrophoresis

Electron microscopic analysis of nanoparticles delivering thioflavin-T after intrahippocampal injection in mouse: implications for targeting β-amyloid in Alzheimer's disease

Biocompatible Magnetic Polymer Carriers for In Vivo Radionuclide Delivery

99mTc labelled model drug carriers - labeling, stability and organ distribution in rats

Techniques for Electro- and Magnetokinetic Particle Characterization