Physicochemical characterization of nanoparticles and their behavior in the biological environment.

Whilst the physical and chemical properties of nanoparticles in the gas or idealized solvent phase can nowadays be characterized with sufficient accuracy, this is no longer the case for particles in the presence of a complex biological environment. Interactions between nanoparticles and biomolecules are highly complex on a molecular scale. The detailed characterization of nanoparticles under these conditions and the mechanistic knowledge of their molecular interactions with the biological world is, however, needed for any solid conclusions with regards to the relationship between the biological behavior of such particles and their physicochemical properties. In the present article we discuss some of the challenges with characterization and behavior of nanoparticles that are associated with their presence in chemically complex biological environments. Our focus is on the stability of colloids as well as on the formation and characteristics of protein coronae that have recently been shown to significantly modify the properties of pristine particles. Finally, we discuss the perspectives that may be expected from an improved understanding of nanoparticles in biological media.

Influence of individual ionic components on the agglomeration kinetics of silver nanoparticles.

The precise characteristic of the agglomeration behavior of colloidal suspensions is of paramount interest to many current studies in nanoscience. This work seeks to elucidate the influence that differently charged salts have on the agglomeration state of a Lee-Meisel-type silver colloid. Moreover, we investigate the influence of the chemical nature of individual ions on their potential to induce agglomeration. Raman spectroscopy and surface-enhanced Raman spectroscopy are used to give insights into mechanistic aspects of the agglomeration process and to assess the differences in the influence of different salts on the agglomeration behavior. Finally, we demonstrate the potential of the measurement procedure used in this work to determine the elementary charge on colloidal NPs.

Deliquescence behaviour and crystallisation of ternary ammonium sulfate/dicarboxylic acid/water aerosols.

The deliquescence behaviour of ternary aerosols composed of ammonium sulfate (AS) and water, internally mixed with malonic acid (MOA), maleic acid (MEA) and glutaric acid (GAA), has been studied using a new surface aerosol microscope setup (SAM) as well as an electrodynamic balance (EDB). In each of the systems studied the addition of the organic acids to ammonium sulfate leads to a decrease of the deliquescence relative humidities (DRH). However, the observed behaviour of the DRH values over a large range of acid concentrations is complex and indicates a eutectic behaviour. Moreover, the ternary AS/MOA/water aerosols show a two step deliquescence process whose magnitude and concentration dependence have been quantitatively investigated for the first time. The results suggest that previous DRH interpretations underestimate the strength and the atmospheric implications of the MOA influence. In addition to the deliquescence behaviour, effloresced ternary aerosols were studied with respect to their morphology and crystal behaviour using environmental scanning electron microscopy (ESEM) and Raman microscopy (RM), respectively. It is found that in each case crystalline mixtures consisting of the pure AS and pure organic acid are formed. However, the crystalline appearances of the solids formed are different from those of the effloresced pure acids. Moreover, a maximum size of the single crystallites formed during the efflorescence of these complex ternary aerosols has been assigned.

Deliquescence behaviour of single levitated ternary salt/carboxylic acid/water microdroplets.

The deliquescence relative humidities (DRH) of ammonium sulfate as well as ammonium sulfate/dicarboxylic acid (glutaric, maleic and tartaric) mixtures as a function of temperature and relative composition have been studied using an electrodynamic balance (EDB) in connection with optical microscopy and Mie scattering. The absolute DRH values for pure ammonium sulfate as well as their temperature dependence are consistent with literature data and with the AIM model of Clegg et al. The addition of either glutaric or maleic acid to ammonium sulfate leads to a decrease of the DRH value, with the temperature dependence either remaining constant (glutaric acid) or increasing (maleic acid) with increasing acid concentration. This difference is attributed to the higher acidity of maleic acid, which generates stronger ionic interactions with the ammonium sulfate system. In the case of tartaric acid, the deliquescence behaviour of ammonium sulfate is substantially influenced by the formation of insoluble ammonium tartrate.