Redox-switchable multicolor luminescent polymers for theragnosis of osteoarthritis

Nonaromatic and nonconjugated fluorescent materials have garnered increasing attention in recent years. However, most non-classical chromophores are derived from electro-rich nitrogen and oxygen atoms, which suffer from short emission wavelengths, low efficiency, limited responsiveness, and obscure luminescence mechanisms. Here we present an emission mechanism in bioactive polycysteine, an aliphatic polymer that displays polymerization- and aggregation-induced emission, high quantum yield, and multicolor emission properties. We show that the hydrogen atoms bonded to the sulfur atoms play a crucial role in luminescence. This enables reversible modulation of polymer fluorescence under reducing and oxidizing conditions, facilitating specific imaging and quantitative detection of redox species in cells and in vivo. Furthermore, the polymer exhibits better anti-inflammatory and antioxidative activities compared to first-line clinical antioxidants, offering a promising platform for in vivo theragnosis of diseases such as osteoarthritis. Nonaromatic and nonconjugated fluorescent materials are promising for in vivo uses, but usually have low fluorescence quantum yields and limited responsiveness. Here, the authors report a polycysteine derived from natural amino acids that displays intrinsic fluorescence, color switching properties and applicability as a drug-free and self-reporting system for the theragnosis of osteoarthritis.