Bright Free-Radical Emission in Ionic Liquids.

It is challenging to achieve stable and efficient radical emissions under ambient conditions. Herein, we present a rational design strategy to protect photoinduced carbonyl free radical emission through electrostatic interaction and spin delocalization effects. The host-guest system is constructed from tricarbonyl-substituted benzene molecules and a series of imidazolium ionic liquids as the guest and host, respectively, whereby the carbonyl anion radical emission can be in situ generated under the light irradiation and further stabilized by electrostatic interaction. More importantly, the anion species and the alkyl chain length of imidazolium ionic liquids show a noticeable effect on luminescence efficiency, with the highest radical emission efficiency is as high as 53.3 % after optimizing the imidazole ionic liquid's structure, which is about four times higher than the polymer-protected radical system. Theoretical calculations confirm the synergistic effect of strong electrostatic interactions and that the spin delocalization effect significantly stabilizes the radical emission. Moreover, such a radical emission system also could be integrated with a fluorescent dye to induce multi-color or even white light emission with reversible temperature-responsive characteristics. The radical emission system can also be used to detect different amine compounds on the basis of the emission changes and photoactivation time.

Monomer and Excimer Emission in a Conformational and Stacking-Adaptable Molecular System.

A design strategy that combines molecular conformation, alkyl chain length, and charge-transfer effects has been developed to obtain conformational and stacking-adaptable donor-acceptor-π type molecules for precisely regulating the monomer and excimer emission in a single luminous platform under different environments. These fluorophores can exhibit bright monomer emissions when they are in the dispersed state based on their planar conformation. However, when the luminous molecules with short alkyl side chains are in the crystalline state, their molecular conformation can become distorted, further inducing strong intermolecular interactions and staggered π-π stacking for bright excimer emission. More importantly, their dispersed and aggregated states can be reversibly regulated in a phase-change fatty acid matrix, to achieve temperature-responsive fluorescence for temperature monitoring and advanced information encryption.

Tumor microenvironment-responsive polydopamine-based core/shell nanoplatform for synergetic theranostics.

Theranostic agents that integrate diagnostic and therapeutic modalities have drawn extensive attention due to their ability to deliver real-time imaging-guided tumor treatment. Herein, a novel core-shell polydopamine (PDA)-based theranostic agent (PDA@TA-Fe) was fabricated via a two-step strategy. Upon 808 nm and 1064 nm laser irradiation, this agent exhibited high photothermal conversion efficiencies of 29% and 41%, respectively. After endocytosis into tumor cells, the TA-Fe shell of PDA@TA-Fe gradually disintegrated in the weakly acidic tumor microenvironment (TME), and released the TA as an acidity-activated reductant that could reduce Fe3+ to Fe2+. Subsequently, the generated Fe2+ reacted with H2O2 to generate toxic hydroxyl radicals (˙OH) via the Fenton reaction, which induced the apoptosis of tumor cells and achieved the chemodynamic therapy (CDT). The heat produced by photothermal therapy (PTT) accelerated the ˙OH generation to achieve a synergetic effect of CDT/PTT. In vivo tumor-xenograft imaging and therapeutic assays demonstrated obvious contrast enhancement at the tumor site in the T1/T2-weighted MR imaging and efficient tumor suppression achieved after the intravenous injection of this agent because of the enhanced permeation and retention (EPR) effect. This study offered a new strategy to design an "all-in-one" nanoplatform for T1/T2 MR imaging-guided synergistic cancer treatment of CDT/PTT.

A sensitive "ON-OFF" fluorescent probe based on carbon dots for Fe2+ detection and cell imaging.

Fe2+ is a trace metal ion required by the human body, and its abnormal metabolism can cause serious diseases. Herein, we report the development of a highly efficient "ON-OFF" fluorescent probe based on carbon dots (CDs), prepared by a simple one-step hydrothermal method. The CDs exhibited exceptional water dispersibility and stability, superior luminescence performance and low cytotoxicity. The fluorescence could be efficiently quenched by Fe2+ through an electronic transfer process. And under the optimized experimental conditions, this probe shows excellent selectivity and high sensitivity towards Fe2+ with a detection limit of 51 nmol. More interestingly, this probe could realize the visual detection of Fe2+ when Fe3+ and Cu2+ ions were efficiently shielded by tartaric acid in the presence of ascorbic acid. Furthermore, the developed fluorescent probe has been successfully applied for the detection of Fe2+ in tap water and BSA solution as well as for the biosensing of Fe2+ in living cells.

Polypyrrole-based double rare earth hybrid nanoparticles for multimodal imaging and photothermal therapy.

Nanotheranostic agents that can simultaneously provide real-time tracking and accurate treatment at tumor sites are playing an increasingly important role in medicine. Herein, a novel polypyrrole (PPy)-based theranostic agent containing double rare-earth elements (PPy@BSA-Gd/Dy NPs) was successfully synthesized via an integrated strategy combining biomineralization and oxidation polymerization. The obtained PPy@BSA-Gd/Dy NPs with a diameter of approximately 59.48 ± 6.12 nm exhibited excellent solubility, long-term stability, superior biocompatibility, and negligible toxicity. Importantly, due to its intrinsic paramagnetic and strong X-ray attenuation ability, this agent demonstrated brilliant imaging performance in both T1/T2-weighted magnetic resonance imaging (MRI) and X-ray computed tomography (CT) imaging in vitro and vivo. Additionally, with an excellent photothermal conversion efficiency (26.61%) upon irradiation by an 808 nm laser, this theranostic agent showed significant photothermal cytotoxicity against HeLa cells and 4T1 cells in vitro and antitumor efficacy through intravenous injection in vivo. Meanwhile, biodistribution and blood circulation were also used to explore its fate in vivo. In summary, this study highlighted the versatility and practicability of PPy@BSA-Gd/Dy NPs and also suggested that the agent may be a promising candidate for T1/T2-weighted MRI/CT tri-modal imaging guided photothermal cancer therapy.

"ON-OFF-ON" fluorescent probes based on nitrogen-doped carbon dots for hypochlorite and bisulfite detection in living cells.

Although hypochlorite (ClO-) and bisulfite (HSO3-) play important roles in the biological immune system and the aging process of living organisms, they are also classified as a third type of carcinogens. Hence, a convenient and efficient method to monitor ClO- and HSO3- in ecological environments is highly desired. In this article, an "ON-OFF-ON" fluorescent probe based on nitrogen-doped carbon dots (N-CDs) for the detection of ClO- and HSO3- has been demonstrated successfully. Because of the destruction of the surface passivation layer, the fluorescence of the N-CDs was quenched by ClO-. Furthermore, the quenched fluorescence of the N-CDs was restored efficiently through the increase in conjugation from the attached sulfo groups, indicating the feasibility of ClO- and HSO3- detection. This fluorescent probe exhibited excellent sensitivity and selectivity to ClO- and HSO3- detection with the limits of detection (LODs) of 3.4 µM and 0.27 µM in aqueous solution, respectively. In addition, the as-prepared N-CDs were successfully applied to detect both ClO- and HSO3- in living cells due to their low toxicity and fast response speed.