The chelating gadolinium-complex is routinely used as magnetic resonance imaging (MRI) -contrast enhancer. However, several safety issues have recently been reported by FDA and PRAC. There is an urgent need for the next generation of safer MRI-contrast enhancers, with improved local contrast and targeting capabilities. Cerium oxide nanoparticles (CeNPs) are designed with fractions of up to 50% gadolinium to utilize the superior MRI-contrast properties of gadolinium. CeNPs are well-tolerated in vivo and have redox properties making them suitable for biomedical applications, for example scavenging purposes on the tissue- and cellular level and during tumor treatment to reduce in vivo inflammatory processes. Our near edge X-ray absorption fine structure (NEXAFS) studies show that implementation of gadolinium changes the initial co-existence of oxidation states Ce³⁺ and Ce⁴⁺ of cerium, thereby affecting the scavenging properties of the nanoparticles. Based on ab initio electronic structure calculations, we describe the most prominent spectral features for the respective oxidation states. The as-prepared gadolinium-implemented CeNPs are 3–5 nm in size, have r₁-relaxivities between 7–13 mM⁻¹ s⁻¹ and show clear antioxidative properties, all of which means they are promising theranostic agents for use in future biomedical applications.

Intracellular lipid metabolism occurs in lipid droplets (LDs), which is critical to the survival of cells. Imaging LDs is an intuitive way to understand their physiology in live cells. However, this is limited by the availability of specific probes that can properly visualize LDs in vivo. Here, an LDs-specific red-emitting probe is proposed to address this need, which is not merely with an ultrahigh signal-to-noise (S/N) ratio and a large Stokes shift (up to 214 nm), but also with superior resistance to photobleaching. The probe has been successfully applied to real-time tracking of intracellular LDs behaviors, including fusion, migration and lipophagy processes in live cells. We deem that the proposed probe here offers a new possibility to deeply understanding of LDs-associated behaviors, elucidate their roles and mechanisms in cellular metabolism, and determine the transition between adaptive lipid storage and lipotoxicity as well.

Uniform, highly water-dispersible and ultra-small Fe₃O₄ nanoparticles were synthesized via a modified one-step coprecipitation approach. The prepared Fe₃O₄ nanoparticles not only show good magnetic properties, long-term stability in a biological environment, but also exhibit good biocompatibility in cell viability and hemolysis assay. Due to the ultra-small sized and highly water-dispersibility, they exhibit excellent relaxivity properties, the 1.7 nm sized Fe₃O₄ nanoparticles reveal a low r₂/r₁ ratio of 2.03 (r₁ = 8.20 mM⁻¹ s⁻¹, r₂ = 16.67 mM⁻¹ s⁻¹); and the 2.2 nm sized Fe₃O₄ nanoparticles also appear to have a low r₂/r₁ ratio of 4.65 (r₁ = 6.15 mM⁻¹ s⁻¹, r₂ = 28.62 mM⁻¹ s⁻¹). This demonstrates that the proposed ultra-small Fe₃O₄ nanoparticles have great potential as a new type of T₁ magnetic resonance imaging contrast agents. Especially, the 2.2 nm sized Fe₃O₄ nanoparticles, have a competitive r₁ value and r₂ value compared to commercial contrasting agents such as Gd-DTPA (r₁ = 4.8 mM⁻¹ s ⁻¹), and SHU-555C (r₂ = 69 mM⁻¹ s⁻¹). In vitro and in vivo imaging experiments, show that the 2.2 nm sized Fe₃O₄ nanoparticles exhibit great contrast enhancement, long-term circulation, and low toxicity, which enable these ultra-small sized Fe₃O₄ nanoparticles to be promising as T₁ and T₂ dual contrast agents in clinical settings.

Near-IR (NIR) emitting semiconducting polymer dots (Pdots) with ultrabright fluorescence have been prepared for specific cellular targeting. A series of π-conjugated polymers were synthesized to form water dispersible multicomponent Pdots by an ultrasonication-assisted co-precipitation method. By optimizing cascade energy transfer in Pdots, high-intensity NIR fluorescence (Φ = 0.32) with tunable excitations, large absorption–emission separation (up to 330 nm), and narrow emission bands (FWHM = 44 nm) have been achieved. Single-particle fluorescence imaging show that the as-prepared NIR Pdots were more than three times brighter than the commercially available Qdot705 with comparable sizes under identical conditions of excitation and detection. Because of the covalent introduction of carboxylic acid groups into polymer side chains, the bioconjugation between NIR-emitting Pdots and streptavidins can be readily completed via these functional groups on the surface of Pdots. Furthermore, through flow cytometry and confocal fluorescence microscopy the NIR-emitting Pdot–streptavidin conjugates proved that they could effectively label EpCAM receptors on the surface of MCF-7 cells, via specific binding between streptavidin and biotin.