payload's pharmacokinetics and contributed to achieve the desired pharmacological response at the target. They are now widely exploited for therapeutic purposes, including the treatment of severe diseases such as cancer and infections. [1] A plethora of natural and synthetic materials have been engineered at a nanoscopic level and explored for drug delivery (Figure 1). Liposomes, the first nanotechnology-based drug delivery system, were discovered early in the 1960s. [2] The first Food and Drug Administration (FDA)-approved nanotechnology was the liposomal Doxil formulation designed for the treatment of Kaposi's sarcoma and since then, more than twenty liposomal and lipid-based formulations have been approved by regular authorities. [3] Many other types of drug nanocarriers have been developed, including polymeric, hybrid or metal nanoparticles (NPs), nanogels, dendrimers, quantum dots, carbon nanotubes (CNTs), and micelles (Figure 1). Several nanotechnologies containing an active molecule or a drug combination, such as Onpattro and Vyxeos, were FDA-approved in recent years, demonstrating the potential of nanomedicine and the growing interest in this field. [4,5] Moreover, the FDA-approved NP-based vaccines represent a giant step in the fight against the COVID-19 pandemic. [6] Nowadays, a large variety of materials is used to prepare drug nanocarriers: i) organic compounds (lipids, synthetic or natural polymers, biomolecules); ii) inorganic materials (silica, carbon networks, metals, or metal oxides) and iii) hybrid organic-inorganic networks combining the properties of both their organic and inorganic counterparts. Generally, drug nanocarriers have a core-shell structure: i) the cores incorporate the drugs and release them in a controlled manner and ii) the shells govern the interactions with the living media (control protein adsorption, avoid recognition by the immune system, allow targeting diseased tissues and organs, confer bio-adhesion properties). Organic compounds remain the most employed materials for drug incorporation and for engineering multifunctional shells. Additionally, the presence of metals in drug nanocarriers' composition offers new functionalities, such as antibacterial or antifungal properties, [7] radioenhancement [8] or imaging abilities for personalized therapies. [9] More recently, nanoscale hybrid metal-organic frameworks (MOFs) emerged as versatile Drug nanocarriers (NCs) with sizes usually below 200 nm are gaining increasing interest in the treatment of severe diseases such as cancer and infections. Characterization methods to investigate the morphology and physicochemical properties of multifunctional NCs are key in their optimization and in the study of their in vitro and in vivo fate. Whereas a variety of methods has been developed to characterize "bulk" NCs in suspension, the scope of this review is to describe the different approaches for the NC characterization on an individual basis, for which fewer techniques are available. The accent is put on methods devoid of labelling, whi...

Scanning transmission electron microscopy coupled with electron energy loss spectroscopy (STEM-EELS) provides spatially resolved chemical information down to the atomic scale. However, studying radiation-sensitive specimens such as organic–inorganic composites remains extremely challenging. Here, we analyzed metal–organic framework nanoparticles (nanoMOFs) at low-dose (10 e–/Å2) and liquid nitrogen temperatures, similar to cryo-TEM conditions usually employed for high-resolution imaging of biological specimens. Our results demonstrate that monochromated STEM-EELS enables damage-free analysis of nanoMOFs, providing in a single experiment, signatures of intact functional groups comparable with infrared, ultraviolet, and X-ray data, with an energy resolution down to 7 meV. The signals have been mapped at the nanoscale (<10 nm) for each of these energy spectral ranges, including the chemical features observed for high energy losses (X-ray range). By controlling beam irradiation and monitoring spectral changes, our work provides insights into the possible pathways of chemical reactions occurring under electron exposure. These results demonstrate the possibilities for characterizing at the nanoscale the chemistry of sensitive systems such as organic and biological materials.