Nanostructures have attracted huge interest as a rapidly growing class of materials for many applications. Several techniques have been used to characterize the size, crystal structure, elemental composition and a variety of other physical properties of nanoparticles. In several cases, there are physical properties that can be evaluated by more than one technique. Different strengths and limitations of each technique complicate the choice of the most suitable method, while often a combinatorial characterization approach is needed. In addition, given that the significance of nanoparticles in basic research and applications is constantly increasing, it is necessary that researchers from separate fields overcome the challenges in the reproducible and reliable characterization of nanomaterials, after their synthesis and further process (e.g. annealing) stages. The principal objective of this review is to summarize the present knowledge on the use, advances, advantages and weaknesses of a large number of experimental techniques that are available for the characterization of nanoparticles. Different characterization techniques are classified according to the concept/group of the technique used, the information they can provide, or the materials that they are destined for. We describe the main characteristics of the techniques and their operation principles and we give various examples of their use, presenting them in a comparative mode, when possible, in relation to the property studied in each case.

▶ NP toxicity depends on NP characteristics, administered dose and route. ▶ In vitro toxicity results do not easily translate into in vivo toxicity. ▶ Current research lacks a unifying protocol for the toxicological profiling of NPs.

Magnetic nanoparticles have great potential as mediators of localised heat as well as vehicles for drug delivery to have synergistic effect of thermo-chemotherapy for cancer treatment.

The adoption of magnetic hyperthermia as either a stand-alone or adjunct therapy for cancer is still far from being optimised due to the variable performance found in many iron oxide nanoparticle systems, including commercially available formulations. Herein, we present a reproducible and potentially scalable microwave-based method to make stable citric acid coated multi-core iron oxide nanoparticles, with exceptional magnetic heating parameters, viz. intrinsic loss parameters (ILPs) of up to 4.1 nH m² kg⁻¹, 35% better than the best commercial equivalents. We also probe the core-to-core magnetic interactions in the particles via remanence-derived Henkel and ΔM plots. These reveal a monotonic dependence of the ILP on the magnetic interaction field H_int, and show that the interactions are demagnetising in nature, and act to hinder the magnetic heating mechanism.

Gold nanorods (Au NRs) present unique optical and electronic properties that depend on their morphology. Their applications in sensing and therapeutics require easy synthesis with precise control over their dimensions. Here, we report a method for the synthesis of highly pure and monodisperse Au NRs with fine-tuneable dimensions and longitudinal localised surface plasmon resonance by addition of Hofmeister salts into the growth medium. The control of Au NR formation relies on the double interaction between salt–gold and salt–surfactant (cetyl trimethylammonium bromide, CTAB). With the addition of Hofmeister salts (i.e. NaNO₃, NaBr, NaCl and NaHSO₄) we can fine-tune the aspect ratio of Au NRs in the range of 3.3 to 4.8 with a precision of 0.1 and the longitudinal absorption band from 777 to 960 nm. In addition, we have studied the physical changes in the CTAB micelles induced by the salts using rheology, electron microscopy and light-scattering techniques. We report for the first time cryo-electron microscopy imaging of the micelles under Au NR growth conditions. With the comprehensive characterization of CTAB micelles in the growth solution, this study provides a deeper understanding of the anisotropic growth of metallic crystals.

The possibility to finely control nanostructured cubic ferrites (M^IIFe₂O₄) paves the way to design materials with the desired magnetic properties for specific applications. However, the strict and complex interrelation among the chemical composition, size, polydispersity, shape and surface coating renders their correlation with the magnetic properties not trivial to predict. In this context, this work aims to discuss the magnetic properties and the heating abilities of Zn-substituted cobalt ferrite nanoparticles with different zinc contents (Zn_xCo_1−xFe₂O₄ with 0 < x < 0.6), specifically prepared with similar particle sizes (∼7 nm) and size distributions having the crystallite size (∼6 nm) and capping agent amount of 15%. All samples have high saturation magnetisation (M_s) values at 5 K (>100 emu g⁻¹). The increase in the zinc content up to x = 0.46 in the structure has resulted in an increase of the saturation magnetisation (M_s) at 5 K. High M_s values have also been revealed at room temperature (∼90 emu g⁻¹) for both CoFe₂O₄ and Zn_0.30Co_0.70Fe₂O₄ samples and their heating ability has been tested. Despite a similar saturation magnetisation, the specific absorption rate value for the cobalt ferrite is three times higher than the Zn-substituted one. DC magnetometry results were not sufficient to justify these data, the experimental conditions of SAR and static measurements being quite different. The synergic combination of DC with AC magnetometry and ⁵⁷Fe Mössbauer spectroscopy represents a powerful tool to get new insights into the design of suitable heat mediators for magnetic fluid hyperthermia.