Oxidative stress-dependent inflammatory diseases represent a major concern for the population's health worldwide. Biocompatible nanomaterials with enzymatic properties could play a crucial role in the treatment of such pathologies. In this respect, platinum nanoparticles (PtNPs) are promising candidates, showing remarkable catalytic activity, able to reduce the intracellular reactive oxygen species (ROS) levels and impair the downstream pathways leading to inflammation. This review reports a critical overview of the growing evidence revealing the anti-inflammatory ability of PtNPs and their potential applications in nanomedicine. It provides a detailed description of the wide variety of synthetic methods recently developed, with particular attention to the aspects influencing biocompatibility. Special attention has been paid to the studies describing the toxicological profile of PtNPs with an attempt to draw critical conclusions. The emerging picture suggests that the material per se is not causing cytotoxicity, while other physicochemical features related to the synthesis and surface functionalization may play a crucial role in determining the observed impairment of cellular functions. The enzymatic activity of PtNPs is also summarized, analyzing their action against ROS produced by pathological conditions within the cells. In particular, we extensively discuss the potential of these properties in nanomedicine to down-regulate inflammatory pathways or to be employed as diagnostic tools with colorimetric readout. A brief overview of other biomedical applications of nanoplatinum is also presented.

In recent years, the use of nanomaterials as biomimetic enzymes has attracted great interest. In this work, we show the potential of biocompatible platinum nanoparticles (Pt NPs) as antioxidant nanozymes, which combine abundant cellular internalization and efficient scavenging activity of cellular reactive oxygen species (ROS), thus simultaneously integrating the functions of nanocarriers and antioxidant drugs. Careful toxicity assessment and intracellular tracking of Pt NPs proved their cytocompatibility and high cellular uptake, with compartmentalization within the endo/lysosomal vesicles. We have demonstrated that Pt NPs possess strong and broad antioxidant properties, acting as superoxide dismutase, catalase, and peroxidase enzymes, with similar or even superior performance than natural enzymes, along with higher adaptability to the changes in environmental conditions. We then exploited their potent activity as radical scavenging materials in a cellular model of an oxidative stress-related disorder, namely human Cerebral Cavernous Malformation (CCM) disease, which is associated with a significant increase in intracellular ROS levels. Noteworthily, we found that Pt nanozymes can efficiently reduce ROS levels, completely restoring the cellular physiological homeostasis.

The fundamental interactions underlying citrate-mediated chemical stability of metal nanoparticles, and their surface characteristics dictating particle dispersion/aggregation in aqueous solutions, are largely unclear. Here, we developed a theoretical model to estimate the stoichiometry of small, charged ligands (like citrate) chemisorbed onto spherical metallic nanoparticles and coupled it with atomistic molecular dynamics simulations to define the uncovered solvent-accessible surface area of the nanoparticle. Then, we integrated coarse-grained molecular dynamics simulations and two-body free energy calculations to define dispersion state phase diagrams for charged metal nanoparticles in a range of medium’s ionic strength, a known trigger for aggregation. Ultraviolet-visible spectroscopy experiments of citrate-capped nanocolloids validated our predictions and extended our results to nanoparticles up to 35 nm. Altogether, our results disclose a complex interplay between the particle size, its surface charge density, and the ionic strength of the medium, which ultimately clarifies how these variables impact colloidal stability.

Size-tunable platinum nanoparticles (PtNPs) prepared by a facile method in an aqueous environment without the use of catalyst-poisoning reagents are used here in the electrocatalytic detection of hydrogen peroxide. Spherical nanoparticles with sizes as small as 4 and 20 nm are obtained as shown by transmission electron microscopy (TEM) analysis only using small easy-to-remove molecules such as sodium citrate. PtNPs are freed from the citrate capping agent at the surface by changing the pH to basic values and then deposited on a glassy carbon electrode by a very simple and rapid drop-casting method, achieving high cleanliness of the nanoparticle surface without the need for further treatments. The superior quality of nanoparticles on the glassy carbon is further investigated by scanning electron microscopy (SEM) analysis, which shows a highly homogeneous distribution of well-dispersed nanoparticles on the electrode surface, as well as by X-ray photoelectron spectroscopy (XPS) analysis, which confirms a drastic decrease of the citrate content, providing useful information about the citrate–platinum interaction, and evidences a related remarkable increase of conductivity of capping-free washed nanoparticles. Due to such key features, PtNPs possess excellent electrocatalytic properties, which have been tested in hydrogen peroxide electroreduction, a well-known catalytic reaction of nanostructured platinum materials. The size effect on PtNPs electrocatalytic properties is demonstrated, achieving higher performances with smaller NPs in the amperometric detection of hydrogen peroxide at −0.1 V in the concentration range of 25–750 μM, with a detection limit of 10 μM. Good sensing results toward hydrogen peroxide have also been obtained in terms of sensitivity, selectivity, repeatability, stability, and in tests performed in tap water samples. In addition, the strong adhesion of nanoparticles to the electrode surface has been verified and ascribed to their coating-free surface.