Fluorescent nanoparticles (NPs), owing to their superior brightness, are an attractive alternative to organic dyes. However, their cellular applications remain limited because of their large size, poor homogeneity and non-specific interactions in biological media. Herein, we propose a concept of monomolecular fluorescent organic nanoparticle of high brightness and very small size (10-14 nm) built of a single amphiphilic polymer bearing specially designed fluorescent dyes. We found that high PEGylation of poly(maleic anhydride-alt-1-octadecene (PMAO) favors a single-chain polymer folding into monomolecular stealth NPs with highly reduced non-specific interactions with live cells. To ensure high stability of our NPs, the fluorophores (BODIPYs) are covalently linked to the polymer through an optimized linker. Among tested linkers of different lengths and polarity, short medium-polar linker favoring location of the dyes at NPs interface ensures good 2 fluorescence quantum yield and small particle size. The fluorescence brightness of these NPs has been dramatically enhanced by increasing the bulkiness of the BODIPY dyes that prevents their H-aggregation, reaching 2,500,000 M -1 cm -1 (extinction coefficient × quantum yield).Fluorescence microscopy revealed that the single-particle brightness of these NPs is ~5-fold higher than that of QDot-585 using the same excitation wavelength (532 nm). Finally, when microinjected inside cells, these small and stealth NPs (10-nm diameter) distribute more evenly than 20-nm QDots inside the cytosol, showing similar spreading as a fluorescent protein. Thus, the developed monomolecular NPs, owing to small size and stealth properties, are artificial analogues of fluorescent proteins, surpassing the latter >50-fold in terms of brightness.

Integration of efficient platinum group metal (PGM)-free catalysts to fuel cells and electrolysers is a prerequisite to their large-scale deployment. Here, we describe the development of a molecular based anode for hydrogen oxidation reaction (HOR) through non-covalent integration of a DuBois type Ni bio-inspired molecular catalyst at the surface of a carbon nanotubes modified gas diffusion layer. This mild immobilization strategy enabled to gain high control over the loading in catalytic sites. Additionally, through the adjustment of the hydration level of the active layer, new record current densities of 214 ± 20 mA cm -2 could be reached at 0.4 V vs RHE with a PGM-free anode, at 25°C. Near-industrially relevant current densities were obtained at 55°C with 150 ± 20 and 395 ± 30 mA cm -2 at 0.1 and 0.4 V overpotential, respectively. These results further demonstrate the relevance of such molecular approaches for the development of electrocatalytic platforms for energy conversion.