Fluorophore molecules can be monitored by fluorescence spectroscopy and microscopy, which are highly useful and widely used techniques in cell biology, biochemistry, and medicine (e.g., biomarker analysis, immunoassays, cancer diagnosis). Several fluorescent micro-and nanoparticle systems based on block copolymer micelles and cross-linked polymer networks, quantum dots, π-conjugated polymers, and dendrimers have been evaluated as optical imaging systems. In this review, we highlight recent

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... ces in the construction of fluorescent single-chain nanoparticles (SCNPs), which are valuable artificial soft nano-objects with a small tunable size (as small as 3 nm). In particular, the main methods currently available to endow SCNPs with fluorescent properties are discussed in detail, showing illustrative examples. green, and blue photoluminescent (PL) emission via crystallization-driven self-assembly, allowing even white light PL emission [7] . Fluorescent cross-linked polymer networks have been typically prepared through direct free radical cross-linking oil-in-water emulsion polymerization [8] . QDs which are inorganic nanocrystals with excellent fluorescence properties (extinction coefficients ×10 to ×100 of those of organic fluorophobe dyes) have been fabricated by a variety of methods [9] . Different fluorescent π-conjugated polymers [10] and dendrimers [11] have also been synthesized and evaluated as optical imaging systems. A nice example of the current fluorescent toolbox available for assessing protein location and function in cell biology is depicted in Figure 1 , in which a variety of targeting methods and fluorophores (organic dyes, QDs, green fluorescent protein) were combined to visualize different cell structures of HeLa cancer cells [12] .