The significance of a protein corona on nanoparticles in modulating particle properties and their biological interactions has been widely acknowledged. The protein corona is derived from proteins in biological fluids, many of which are glycosylated. To date, the glycans on the proteins have been largely overlooked in studies of nanoparticle-cell interactions. In this study, we demonstrate that glycosylation of the protein corona plays an important role in maintaining the colloidal stability of nanoparticles and influences nanoparticle-cell interactions. The removal of glycans from the protein corona enhances cell membrane adhesion and cell uptake of nanoparticles in comparison with the fully glycosylated form, resulting in the generation of a pro-inflammatory milieu by macrophages. This study highlights that the post-translational modification of proteins can significantly impact nanoparticle-cell interactions by modulating the protein corona properties.

Magnetic nanoparticles (NPs) are increasingly being considered for use in biomedical applications such as biosensors, imaging contrast agents and drug delivery vehicles. In a biological fluid, proteins associate in a preferential manner with NPs. The small sizes and high curvature angles of NPs influence the types and amounts of proteins present on their surfaces. This differential display of proteins bound to the surface of NPs can influence the tissue distribution, cellular uptake and biological effects of NPs. To date, the effects of adsorption of a protein corona (PC) on the magnetic properties of NPs have not been considered, despite the fact that some of their potential applications require their use in human blood.Here, to investigate the effects of a PC (using fetal bovine serum) on the MRI contrast efficiency of superparamagnetic iron oxide NPs (SPIONs), we have synthesized two series of SPIONs with variation in the thickness and functional groups (i.e. surface charges) of the dextran surface coating. We have observed that different physico-chemical characteristics of the dextran coatings on the SPIONs lead to the formation of PCs of different compositions. 1 H relaxometry was used to obtain the longitudinal, r 1 , and transverse, r 2 , relaxivities of the SPIONs without and with a PC, as a function of the Larmor frequency. The transverse relaxivity, which determines the efficiency of negative contrast agents (CAs), is very much dependent on the functional group and the surface charge of the SPIONs' coating. The presence of the PC did not alter the relaxivity of plain SPIONs, while it slightly increased the relaxivity of the negatively charged SPIONs and dramatically decreased the relaxivity of the positively charged ones, which was coupled with particle agglomeration in the presence of the proteins. To confirm the effect of the PC on the MRI contrast efficiency, in vitro MRI experiments at n ¼ 8.5 MHz were performed using a low-field MRI scanner. The MRI contrasts, produced by different samples, were fully in agreement with the relaxometry findings.It is well-recognized that the surface of nanoparticles (NPs) is covered by biomolecules (proteins, sugars and lipids) upon coming into contact with biological systems, resulting in the formation of a protein "corona" that is strongly associated with the NPs' surface and that denes how living organisms (e.g. cells) "see" the NPs in a biological milieu. 1-5 According to previous reports, the cell "sees" a nano-system in which the NPs are covered by a "hard" corona of slowly exchanging proteins with a surrounding "so" corona consisting of weakly interacting and rapidly exchanging proteins. 6 The composition of the protein corona (PC) is highly dependent on the physicochemical properties of the NPs such as their size, composition, and surface characteristics. 7 Superparamagnetic iron oxide nanoparticles (SPIONs) have been recognized as very promising nanosystems with good biocompatibility 8,9 and high potential to be used for diagnosis and therapy simultaneou...

Cellular barriers, such as the skin, the lung epithelium or the intestinal epithelium, constitute one of the first obstacles facing nanomedicines or other nanoparticles entering organisms. It is thus important to assess the capacity of nanoparticles to enter and transport across such barriers. In this work, Caco-2 intestinal epithelial cells were used as a well-established model for the intestinal barrier, and the uptake, trafficking and translocation of model silica nanoparticles of different sizes were investigated using a combination of imaging, flow cytometry and transport studies. Compared to typical observations in standard cell lines commonly used for in vitro studies, silica nanoparticle uptake into well-developed Caco-2 cellular barriers was found to be very low. Instead, nanoparticle association to the apical outer membrane was substantial and these particles could easily be misinterpreted as internalised in the absence of imaging. Passage of nanoparticles through the barrier was very limited, suggesting that the low amount of internalised nanoparticles was due to reduced uptake into cells, rather than a considerable transport through them.

Nanoparticles, after incubation in biological fluids, adsorb several kinds of biomolecules like lipids, sugars and mainly proteins with high affinities for the nanoparticle surface and with long residence time, forming the so-called hard corona. The biological machinery, such as cellular barriers and membrane receptors can directly engage with the protein corona while the pristine surface may remain inaccessible. Here we isolate nanoparticles associated with strongly bound biomolecules from the unbound and loosely bound ones, by different approaches: centrifugation, size exclusion chromatography and magnetic isolation. The different separation methodologies, despite requiring diverse time and operating mechanisms, gave nanoparticle-hard corona complexes which were found to be remarkably similar in both dispersion properties and protein composition thus proving to be equally valid.

Polymeric microbubbles (MBs) are gas filled particles composed of a thin stabilized polymer shell that have been recently developed as valid contrast agents for the combined use of ultrasonography (US), magnetic resonance imaging (MRI) and single photon emission computer tomography (SPECT) imaging. Due to their buoyancy, the commonly available approaches to study their behaviour in complex media are not easily applicable and their use in modern medicine requires such behaviour to be fully elucidated. Here we have used for the first time flow cytometry as a new high throughput approach that allows characterisation of the MB dispersion, prior to and after exposure in different biological media and we have additionally developed a method that allows characterisation of the strongly bound proteins adsorbed on the MBs, to fully predict their biological behaviour in biological milieu.