RESUMEN
Self-reporting fluorescence methods for monitoring folding and aggregation of proteins have a long history in biochemistry. Placing orthogonal luminophores within individual synthetic polymer chains for self-reporting both folding (i.e., its intramolecular compaction to isolated single-chain nanoparticles, SCNPs) and unbidden aggregation (i.e., the intermolecular association of SCNPs) remains a great challenge. Herein, a simple and efficient platform to identify both single-chain compaction and intermolecular aggregation phenomena via photoluminescence is presented based on simultaneous synthesis through Hantzsch ester formation of orthogonal luminophores within the same polymer chain. Starting from non-luminescent ß-ketoester-decorated chains, intramolecular compaction is visually detected through fluorescence arising from Hantzsch fluorophores generated as intra-chain connectors during folding. Complementary, intermolecular association is identified via aggregation-induced emission (AIE) from orthogonal luminophores displaying intense photoluminescence at redshifted wavelengths after formation of multi-SCNPs assemblies.
RESUMEN
Single-chain nanoparticles (SCNPs) are ultrasmall soft nanomaterials constructed via intrachain cross-linking of individual precursor polymer chains, with promising prospects for nanomedicine, catalysis, and sensing, among other different fields. SCNPs are versatile building blocks for the construction of new fluorescent probes with ultrasmall size, higher brightness, and better photostability than previous particle-based systems. Herein, we report on a new, fast, and efficient method to produce SCNPs with intense fluorescence emission in solution which is based on the photoactivation of appropriate aggregation-induced emission (AIE) cross-linking molecules containing azide functional groups. Remarkably, the presence of the azide moiety-that can be transformed to highly reactive nitrene species upon UV irradiation-was found to be essential for the SCNPs to display intense fluorescence emission. We attribute the fluorescence properties of the SCNPs to the immobilization of the initially nonfluorescent AIE molecules via intrachain cross-linking upon photoactivation. Such cross-linking-induced immobilization process activates the AIE mechanism and, hence, leads to fluorescent SCNPs in both solution and solid state.
RESUMEN
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 advances 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.