Electrochromic materials (EMs) are widely used color-switchable materials, but their applications as stimuli-responsive biomaterials to monitor and control biological processes remain unexplored. This study reports the engineering of an organic π-electron structure-based EM (dicationic 1,1,4,4-tetra­aryl­buta­diene, 1 2+) as a unique hydrogen sulfide (H2S)-responsive chromophore amenable to build H2S-activatable fluorescent probes (1 2+-semiconducting polymer nanoparticles, 1 2+-SNPs) for in vivo H2S detection. We demonstrate that EM 1 2+, with a strong absorption (500–850 nm), efficiently quenches the fluorescence (580, 700, or 830 nm) of different fluorophores within 1 2+-SNPs, while the selective conversion into colorless diene 2 via H2S-mediated two-electron reduction significantly recovers fluorescence, allowing for non-invasive imaging of hepatic and tumor H2S in mice in real time. Strikingly, EM 1 2+ is further applied to design a near-infrared photosensitizer with tumor-targeting and H2S-activatable ability for effective photodynamic therapy (PDT) of H2S-related tumors in mice. This study demonstrates promise for applying EMs to build activatable probes for molecular imaging of H2S and selective PDT of tumors, which may lead to the development of new EMs capable of detecting and regulating essential biological processes in vivo.

Afterglow luminescent probes with high signal-to-background ratio show promise for in vivo imaging; however, such probes that can be selectively delivered into target sites and switch on afterglow luminescence remain limited. We optimize an organic electrochromic material and integrate it into near-infrared (NIR) photosensitizer (silicon 2,3-naphthalocyanine bis(trihexylsilyloxide) and (poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene]) containing nanoparticles, developing an H 2 S-activatable NIR afterglow probe (F1 2+-ANP). F1 2+-ANP displays a fast reaction rate (1563 ± 141 M −1 s −1) and large afterglow turn-on ratio (~122-fold) toward H 2 S, enabling high-sensitivity and-specificity measurement of H 2 S concentration in bloods from healthy persons, hepatic or colorectal cancer patients. We further construct a hepatic-tumor-targeting and H 2 Sactivatable afterglow probe (F1 2+-ANP-Gal) for noninvasive, real-time imaging of tiny subcutaneous HepG2 tumors (<3 mm in diameter) and orthotopic liver tumors in mice. Strikingly, F1 2+-ANP-Gal accurately delineates tumor margins in excised hepatic cancer specimens, which may facilitate intraoperative guidance of hepatic cancer surgery.

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Effective photosensitizers are of particular importance for the widespread clinical utilization of phototherapy. However, conventional photosensitizers are usually plagued by short-wavelength absorption, inadequate photostability, low reactive oxygen species (ROS) quantum yields, and aggregation-caused ROS quenching. Here, we report a near-infrared (NIR)-supramolecular photosensitizer (RuDA) via self-assembly of an organometallic Ru(II)-arene complex in aqueous solution. RuDA can generate singlet oxygen (1O2) only in aggregate state, showing distinct aggregation-induced 1O2 generation behavior due to the greatly increased singlet-triplet intersystem crossing process. Upon 808 nm laser irradiation, RuDA with excellent photostability displays efficient 1O2 and heat generation in a 1O2 quantum yield of 16.4% (FDA-approved indocyanine green: ΦΔ = 0.2%) together with high photothermal conversion efficiency of 24.2% (commercial gold nanorods: 21.0%, gold nanoshells: 13.0%). In addition, RuDA-NPs with good biocompatibility can be preferably accumulated at tumor sites, inducing significant tumor regression with a 95.2% tumor volume reduction in vivo during photodynamic therapy. This aggregation enhanced photodynamic therapy provides a strategy for the design of photosensitizers with promising photophysical and photochemical characteristics.

Tumor response to radiotherapy or ferroptosis is closely related to hydroxyl radical (•OH) production. Noninvasive imaging of •OH fluctuation in tumors can allow early monitoring of response to therapy, but is challenging. Here, we report the optimization of a diene electrochromic material (1-Br-Et) as a •OH-responsive chromophore, and use it to develop a near-infrared ratiometric fluorescent and photoacoustic (FL/PA) bimodal probe for in vivo imaging of •OH. The probe displays a large FL ratio between 780 and 1113 nm (FL780/FL1113), but a small PA ratio between 755 and 905 nm (PA755/PA905). Oxidation of 1-Br-Et by •OH decreases the FL780/FL1113 while concurrently increasing the PA755/PA905, allowing the reliable monitoring of •OH production in tumors undergoing erastin-induced ferroptosis or radiotherapy.