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Extracellular matrix (ECM) undergoes dynamic inflation that dynamically changes ligand nanospacing but has not been explored. Here we utilize ECM-mimicking photocontrolled supramolecular ligand-tunable Azo+self-assembly composed of azobenzene derivatives (Azo+) stacked via cation-π interactions and stabilized with RGD ligand-bearing poly(acrylic acid). Near-infrared-upconverted-ultraviolet light induces cis-Azo+-mediated inflation that suppresses cation-π interactions, thereby inflating liganded self-assembly. This inflation increases nanospacing of “closely nanospaced” ligands from 1.8 nm to 2.6 nm and the surface area of liganded self-assembly that facilitate stem cell adhesion, mechanosensing, and differentiation both in vitroand in vivo, including the release of loaded molecules by destabilizing water bridges and hydrogen bonds between the Azo+molecules and loaded molecules. Conversely, visible light induces trans-Azo+formation that facilitates cation-π interactions, thereby deflating self-assembly with “closely nanospaced” ligands that inhibits stem cell adhesion, mechanosensing, and differentiation. In stark contrast, when ligand nanospacing increases from 8.7 nm to 12.2 nm via the inflation of self-assembly, the surface area of “distantly nanospaced” ligands increases, thereby suppressing stem cell adhesion, mechanosensing, and differentiation. Long-term in vivostability of self-assembly via real-time tracking and upconversion are verified. This tuning of ligand nanospacing can unravel dynamic ligand-cell interactions for stem cell-regulated tissue regeneration.

Hybrid nanostructures are promising for ultrasound-triggered drug delivery and treatment, called sonotheranostics. Structures based on plasmonic nanoparticles for photothermal-induced microbubble inflation for ultrasound imaging exist. However, they have limited therapeutic applications because of short microbubble lifetimes and limited contrast. Photochemistry-based sonotheranostics is an attractive alternative, but building near-infrared (NIR)-responsive echogenic nanostructures for deep tissue applications is challenging because photolysis requires high-energy (UV–visible) photons. Here, we report a photochemistry-based echogenic nanoparticle for in situNIR-controlled ultrasound imaging and ultrasound-mediated drug delivery. Our nanoparticle has an upconversion nanoparticle core and an organic shell carrying gas generator molecules and drugs. The core converts low-energy NIR photons into ultraviolet emission for photolysis of the gas generator. Carbon dioxide gases generated in the tumor-penetrated nanoparticle inflate into microbubbles for sonotheranostics. Using different NIR laser power allows dual-modal upconversion luminescence planar imaging and cross-sectional ultrasonography. Low-frequency (10 MHz) ultrasound stimulated microbubble collapse, releasing drugs deep inside the tumor through cavitation-induced transport. We believe that the photoechogenic inflatable hierarchical nanostructure approach introduced here can have broad applications for image-guided multimodal theranostics.

With increasing ozone depletion, ultraviolet (UV) exposure from sunlight has become a significant health risk. Although commercially available sun protectants provide reasonable protection, they have limitations in terms of safety and aesthetics. Here, we have developed biocompatible and biodegradable sunscreens by facile synthesis of organosilica nanoparticles (o-SNPs) with self-encapsulated phenyl motifs using phenylsilane precursors. The physical structure of o-SNPs is elaborately controlled such that they are large enough to reflect UVA but small enough to be imperceptible when applied on the skin. The chemically attached phenyl motifs to o-SNPs facilitate filtering UVB via their delocalized π-orbitals. The o-SNPs generate a negligible amount of reactive oxygen species under UV exposure. Ex vivo two-photon microscopy reveals that the o-SNPs tend to adhere to the outer layers of skin without further intradermal penetration, resulting in less skin irritation. In vivo UV protection tests confirmed the excellent sunscreen effect of o-SNPs compared with conventional organic and inorganic UV filters.

In this article, we demonstrate that TiO2@carbon core/shell (TiO2@C) nanocomposite photocatalysts prepared by carbonizing a single molecular layer of aromatic compounds adsorbed on the surface of TiO2nanoparticles selectively enhance the generation of hydrogen peroxide (H2O2). Atomically thin carbon shells have been formed directly on the surface of TiO2nanoparticles through pyrolytic decarboxylation of the adsorbed aromatic compounds, benzoic acid (BA), and 1-naphthoic acid (NA), which yields two types of TiO2@C nanocomposites, TiO2@C(BA) and TiO2@C(NA). Raman spectroscopy shows that the as-obtained nanocomposites have similar degrees of graphitization (D/G band ratio), regardless of the type of aromatic precursors, but TiO2@C(NA) contains more oxygenic species than TiO2@C(BA) (D*/G band ratio). Such oxygenic species predominantly exist in the form of epoxide groups, as determined by attenuated total reflection infrared spectroscopy. The sp2carbon atoms near the epoxide groups in the carbon shell can act as active sites for the two-electron reduction of O2. Therefore, TiO2@C(NA) can generate H2O2more efficiently than TiO2@C(BA). Furthermore, the carbon shells retard the reconsumption of the generated H2O2by inhibiting the adsorption of H2O2on the surface of TiO2nanoparticles, thereby improving the photocatalytic efficiency of H2O2generation. Finally, we have shown the durability and reproducibility of our TiO2@C-based photocatalytic systems. We believe that our research may offer a potentially improved strategy for H2O2generation and other photocatalytic applications.

Challenges exist in taking advantage of dye molecules for reliable and reproducible molecular probes in biomedical applications. In this study, we show how to utilize the dye molecules for bioimaging within protective carriers of nanocrystalline metal–organic frameworks (nMOFs) particles. Specifically, Resorufin and Rhodamine-6G having different molecular sizes were encapsulated within close-fitting pores of nMOF-801 and nUiO-67 particles, respectively. The resulting nanocrystalline particles have high crystallinity, uniform size, and morphology and preserve enhanced photoluminescence properties with exceptional stabilities in biomedical environment. The samples are further functionalized with a targeting agent and successfully work for fluorescence imaging of FL83B (human hepatocyte cell) and HepG2 (human hepatocellular carcinoma) without cytotoxicity.

With biocompatibility, biodegradability, and high functionality, silica nanoparticles (SNPs) have been widely investigated for various biomedical applications. However, lack of optical fluorescence has limited the application of SNPs as a degradable imaging agent. Here, we hydrothermally synthesized fluorescent SNPs by artificially generating optically active defect centers using tetraethyl orthosilicate and (3-aminopropyl)trimethoxysilane. The synthesized SNPs demonstrated strong blue photoluminescence originating from the dioxasilyrane (=Si(O2)) and silylene (=Si:) defect centers with the aid of aminopropyl groups. Furthermore, phosphorescence was observed at 459 nm, indicating the presence of silylene in SNPs. Finally, these SNPs have been successfully utilized as a fluorescent probe for bioimaging of normal, cancer, and macrophage cells.