Self-assembled multicolor fluorescent nanoparticles derived from dopamine analogues: A versatile platform for biomedical applications

Fluorescent polydopamine (PDA) nanoparticles (FPNPs) have gained recognition as invaluable resources for a wide range of biomedical applications. Typically, these FPNPs are synthesized solely from dopamine (DA). In this study, our focus lies in the design of PDA-based multicolor fluorescent nanoparticles (m-FNPs) utilizing DA and its analogues, including levodopa (LVD), norepinephrine (NPP), 6-hydroxydopamine (HDA), and epinephrine (EPP) monomers, thereby paving the way for the next generation of FPNPs. The m-FNPs, respectively labeled as L-FNPs, N-FNPs, H-FNPs, E-FNPs, and D-FNPs, exhibit distinct band gaps influenced by the monomer's structure, allowing versatile multicolor fluorescence bioimaging across a broad fluorescence emission spectrum ranging from 410 to 680 nm. Significantly, the catechol groups present on the surfaces of m-FNPs enable chelation with various theranostic metal ions and subsequent release under endo/lysosome pH conditions in cancer cells, thereby eliciting a cancer-specific "OFF-ON" fluorescence signal in vivo. Furthermore, integrating m-FNPs into poly(dimethylsiloxane) (PDMS) produces a tissue-adhesive fluorescence sheet that permits fluorescence monitoring of internal tissue surfaces within living organisms for 15 days. These m-FNPs-incorporated PDMS (m-FNPs-PDMS) sheets, enriched with catechol, carboxyl, and amine groups on their surfaces, exhibit significantly enhanced adhesion to biological tissues compared to conventional PDMS sheets containing PDA. Our findings suggest that m-FNPs pave the way for advancing PDA-based fluorescent nanoparticles with diverse applications in the biomedical field, supported by comprehensive in vitro and in vivo evaluations.