AVS2013 Session NL+AS+BI-ThA: Nanoparticles with Proteins and Cells: Modelling and Measurement

Nanoscale materials can interact with living organisms in a qualitatively different manner than small molecules. Crucially, biological phenomena such as immune clearance, cellular uptake and biological barrier crossing are all determined by processes on the nanometer scale. Harnessing these endogeneous biological processes (for example in creation of new nanomedicines or nanodiagnostics) will therefore require us to work on the nanoscale. This ensures that nanoscience, biology and medicine will be intimately connected for generations to come, and may well provide the best hope of tacking currently intractable diseases. These same scientific observations lead to widespread concern about the potential safety of nanomaterials in general. Early unfocussed concerns have diminished, leaving a more disciplined and balanced scientific dialogue. In particular a growing interest in understanding the fundamental principles of bionanointeractions may offer insight into potential hazard, as well as the basis for therapeutic use. Whilst nanoparticle size is important, the detailed nature of the nanoparticle interface is key to understanding interactions with living organisms. This interface may be quite complex, involving also adsorbed proteins from the biological fluid (blood, or other), leading to a ‘protein corona’ on the nanoparticle surface that determines its “biological identity.”We discuss how this corona is formed, how it is a determining feature in biological interactions, and indeed how in many cases can undermine efforts at targeting nanoparticles using simple grafting strategies. Thus, nanoparticle interactions with living organisms cannot be fully understood without explicitly accounting for the interactions with its surroundings, i.e. the nature of the corona.

·Monopoli,M. P.; Aberg,C.;Salvati, A.;Dawson,K. A. Biomolecular Coronas Provide the Biological Identity of Nanosized Materials. Nature Nanotechnology 2012,7,779-786.

Kim, J. A.;Aberg,C.; Salvati,A.;Dawson,K.A. Role of Cell Cycle on the Cellular Uptake and Dilution of Nanoparticles in a Cell Population. Nature Nanotechnology 2012,7,62-68.

·Monopoli, M. P.; Walczyk, D.;Campbell,A.; Elia,G.; Lynch, I.;Baldelli Bombelli, F.;Dawson,K. A. Physical-Chemical Aspects of Protein Corona: Relevance to in Vitro and in Vivo Biological Impacts of Nanoparticles. Journal of the American Chemical Society 2011,133,2525-2534.

·Cedervall, T.; Lynch, I.;Lindman,S.; Berggard,T.; Thulin, E.;Nilsson,H.;Dawson,K. A.;Linse,S. Understanding the Nanoparticle-Protein Corona Using Methods to Quantify Exchange Rates and Affinities of Proteins for Nanoparticles. Proceedings of the National Academy of Sciences 2007,104,2050-2055.

Products are increasingly incorporating nanomaterials because of their superior properties. It is estimated that 50,000 products will contain nanomaterials by 2015. However, we have a poor understanding of their potential adverse effects on workers, the public, and the environment. To assess risk, regulatory authorities need more experimental testing of nanoparticles. Computational models play a complementary role to experiments in allowing rapid prediction of potential toxicities of new and modified nanomaterials. We have generated quantitative, predictive models of cellular uptake and apoptosis induced by surface modified metal iron oxide nanoparticles for several cell types using sparse feature selection and optimal machine learning methods. We illustrate the potential of computational methods to make a contribution to nanosafety.

The primary analytical challenge in characterizing bacterial cells loaded with nanoparticles (NPs) is that the various methods that are traditionally used to measure cells or NPs separately are not readily applied to the mixed samples. These complex samples may contain, for example, a mixture of free NPs, NP-loaded cells, and cells without NPs, while the relative concentrations of NPs and cells or the average number of NPs loaded in one cell is not always known or readily established. Accordingly, methods for separating the different sample components have to be developed and validated before the component of interest (NP-loaded cells in most cases) can be characterized. The final challenge is determining the localization of NPs in and around the cells, as for some applications in sensing and nanomedicine NPs bound to cells externally can be the goal, whereas for exploiting physical properties of NPs, e.g., to induce hyperthermia, maximizing the internalization of NPs by cells can be advantageous.

Our approach to investigating these complex analytical challenges is based on using model systems that are amendable to quantitative characterization by complementary methods, both separately and when mixed as indicated above. Specifically, we are using Staphyloccus aureus as model bacterial cells, in part because the typical 500 nm diameter of S. aureus cells is within the size range of NP aggregates or large NPs, therefore, the same microscopy and spectroscopy methods can be applied to both components of mixed cell-NP samples. We use gold NPs as the primary model NPs because the strong plasmon peak enables their characterization in solution, while the high density and atomic number of gold can be helpful during separation and for characterization by electron microscopy and spectroscopy. Superparamagnetic iron-oxide NPs with different organic shells are used as a second type of model NPs. We will describe the use of multiple complementary microscopy and spectroscopy techniques for developing, validating, and quantifying protocols for cell-NP separation and for characterization of cell loading by NPs.